Air space (mm) 30 40 50 60 80-100 150 200Added sound reduction (dB) 6 8 9 10 12 10 6

If the wall contains a door, the equivalent resistance is anintermediate value between those for the wall and door, depen-dent upon the relative decibel values and areas. For a brick wallof say 46 dB and door of 20 dB and the wall 10 times the area ofthe door, the equivalent sound reduction values (obtained fromcharts, e.g. Neufert7) is 3OdB. The full insulation value isobtained only if all holes, e.g. for services, are sealed; even verysmall openings such as keyholes and open joints representserious sound leaks and must be taken into account in the designif good insulation is to be achieved.

21.11 Water supply, drainage andpublic health

21.11.1 Water supply

Potable water supplies are generally supplied from the localwater undertaking's mains, the local water companies beingrequired under the Water Act, 1945 and EEC directives tosupply consumers with a potable supply. The conditions arebased on the Model Water Byelaws of 1982, the purpose ofwhich is to prevent waste, undue consumption, misuse andcontamination. Water charges may be based on rateable value,assessed annual consumption or on metered consumption.

In the UK, storage provision for cold water for purposesother than drinking is normal and is provided for convenience inthe event of mains failure. British Standard Code of Practice 310schedules the amount of water storage required based uponoccupancy (or number of fittings) and building type. Waterstorage is ideally located at roof level and below the availablemains head to minimize operating and maintenance costs and toavoid pumping. A major revision to the various existing waterservices codes of practice is BS 6700.

It is increasingly found that water mains have insufficienthead to deliver water to the upper levels of buildings without theaid of supplementary boosting. The method of boosting shouldtake into account the location of storage, the possible need forany intermediate storage, pressure limitations or requirementsin the distribution system, routing, quantities and usage ofwater. The two most common methods are direct centrifugalpumps serving high-level storage tanks or pneumatic pressurecylinders to boost the available mains pressure; the latter avoidsthe need for, but does not preclude, the use of high-level storagetanks. Break-cisterns are often required at ground level tocushion demand and very high buildings require break-pressurecisterns restricting gravity drops to about 30 m.

The distribution pipework generally separates cold- and hot-water service feeds and is preferably arranged to provide hotand cold water to the fitments at equal pressures. The routingshould take into consideration maintenance, the requirementsfor draining down, protection against back siphonage andinsulation against freezing and condensation.

Most large buildings have extended hot-water distributionsystems served by a central heating plant which generally alsoprovides the space heating. A central plant offers economies ofscale and uses less fuel than a system of dispersed boilers. Theboiler water is kept separate, the hot-water supply being heatedby means of heat-exchange coils in calorifiers located in proxi-mity to the outlets being served. Deadlegs need to be avoidedwherever possible. Intermediate calorifiers can be located to actas break-pressure cisterns.

21.11.2 Fire installations

Water for fire-fighting purposes in buildings is separated from

general water usage and is required for the hose reels, wet risersand sprinklers.

Consultations with the local fire authorities are required toensure that storage and system duties are met. A number ofpackaged pumping units are available on the market for hy-draulic hose reel installations. Wet risers are a fire authorityrequirement in tall and large-volume buildings. Sprinklers maybe a requirement of the local fire authority or the buildingowner's insurance company. In the UK, most installations arerequired to comply with the 29th edition of the Fire Officers'Committee Rules* which have very specific water flow/pressurerequirements and can involve large bulk water-storage require-ments, dependent upon the fire risk hazard category. Specialistadvice should be sought on these installations.

21.11.3 Water treatment

The growth of the electronics and pharmaceutical industries hasexpanded the need for water-quality levels far in excess of thosesupplied by the statutory authorities and special advice shouldbe sought. In hospitals, additional chemical treatment may berequired to reduce the rise of disease transmission through thewater system.

21.11.4 Drainage

The aim of a well-designed building drainage, sanitation andrainwater installation is to convey foul waste and rainwaterefficiently to the sewer or outfall without nuisance or risk tohealth and self-cleansing. The layout should be as simple anddirect as possible and in accordance with the requirements of BSCode of Practice 8301:1985 'Building drainage', BS 572:1978Sanitary pipework, and BS Code of Practice 6367:1985 'Drain-age of roofs and paved areas'.

21.11.4.1 Design considerations

The practice of combining soil and rainwater pipes within abuilding is extremely unwise and the connection of the twosystems, even with a combined sewer system, should be locatedexternally, preferably at the last manhole before discharging tothe sewer. Soil and waste stacks should be as vertical as possiblewith the minimum number of offsets. Particular care should betaken with discharges from kitchens, laboratories and disposalunits. Separate systems should be provided for activities involv-ing chemical and radioactive effluents. Ventilation pipes arerequired to maintain a balanced air pressure throughout thesoils and waste system. All access locations for rodding shouldbe reviewed in design and located to enable easy maintenance.Ground-floor fittings should be discharged direct to drains andseparate from upper-floor fittings. Consideration should begiven to draining basement levels via pumps to reduce the risk offlooding in the event of sewer back-up. In selecting pipeworkmaterials, consideration should be given to such items as noise,fixings, condensation and material damage in addition to thegeneral material performance criteria.

All sanitary appliances need to be trapped to prevent sewerand drain smells entering the building. Precautions are requiredto prevent the seals being broken by siphonic action or plugpressure generated within an adjoining stack. Traps can beprotected against these dangers by design or by the incorpora-tion of secondary venting immediately behind the trap. Gener-ally, the provision of sanitary appliances should accord with BS6465:1984, Part 1.

21.11.5 Public health

The importance of providing a wholesome drinking water

supply and an efficient system of sanitation within buildingscannot be stressed strongly enough and improvements in thestandards of installation and design must continually be soughtto avoid the risk of infection and the creation of health hazards.The inter-relationship of these aspects with the other buildingservices, particularly air-conditioning, is of growing importanceas more is understood of the nature and transmission of diseasessuch as legionnaires. Specialist advice is available from theDepartment of Health and others on the precautions required.

21.12 Lifts, escalators and passengerconveyors

Many modern buildings are dependent upon lifts and thusdemand high standards of performance and reliability from thedrive and control systems. The advent of microprocessor con-trols has meant greater flexibility and quicker response tochanging traffic conditions since a wide variety of inputs, such ascar positions and car loading, even system failures or thenumber of people waiting at each landing, can be scanned manytimes a second. This continuous updating is used to secure theoptimum lift performance. Equally, lift-drive systems are bene-fiting from the use of electronic speed-control techniques whichwill enable the robust and simple a.c. motor to replace the d.c.motor with its higher maintenance costs. Bulky worm gearinghas been used traditionally to reduce the rotational speed of thetraction motor but helical gearing with its superior mechanicalefficiency and compact dimensions is now being considered.

With the issue of the various parts of BS 5655 for lifts andBS 5656 for escalators, the UK lift industry is now closelyaligned with European standards. Only small national differ-ences remain. Although not mandatory, these British Standardsdefine standards of safe and practicable transport for buildings.

High-rise buildings may call for special solutions to thetransport needs. One approach is the provision of 'shuttle' liftswhere there are common liftshafts shared by two cars. One carcovers the zone from ground level to an interchange floor or 'skylobby', rising nonstop. The second car covers the zone from thesky lobby to the top floor served. A variation is where theshuttle cars are built as double-deckers, serving two levels at atime. Here, of course, two sky lobbies are required.

Undoubtedly, the type of lift attracting the most interest atpresent is the 'wallclimber' and its close relative, the panoramalift. The wallclimber lifts move on guides attached to the exteriorelevation of a building and generally are found only in congenialclimates. Panorama lifts resemble more closely a conventionallift but with the car projected through the shaft wall opposite thelift entrance. In both cases there is an emphasis on concealingmechanism and providing the largest practicable area of glass inthe car construction. The current popularity of the atrium hasadded further impetus to the use of such lifts.

A lift pit is required at the bottom of every lift well of depthdetermined by lift speed; no occupied space is permitted beneathunless special provisions are incorporated to strengthen the pitbottom and lift safety gear. Lift motor rooms should berestricted to lift machinery and associated equipment. The liftwell enclosure, pit and motor room form part of the buildingconstruction and may require particular construction as a'protected shaft' passing between fire compartments.

Escalators have a much greater carrying capacity, but canonly be used between two floors. Their use is mainly in high-flow areas with a limited number of floors. Capacity is varied bywidth and speed and can exceed 10000 persons per hour.

Passenger conveyors are used basically for horizontal move-ment but increasing use is being made of them on shallowinclines to replace pedestrian ramps. They are used in transportterminals and interchanges.

21.13 Energy

The ready availability of cheap energy and the technology tocontrol the internal environment meant that, for a long time,energy aspects were not a primary consideration in the design ofbuildings. Generally more effort was put into saving initial costthan into saving energy. All this changed radically when energycosts escalated in the mid 1970s. Today, energy aspects are afundamental consideration in the design of buildings.

In the UK, analysis showed that buildings use half thenation's energy and that potentially 30% of this could be saved.In new building the potential saving is even greater. Forexample, a study of the energy used in hospitals9 showed thatsavings of 50% and more could be achieved without any majorchange in hospital standards or building techniques.

Given a reasonable payback period, investment to reduceenergy is sound economics. The problem is deciding what is anappropriate payback period. Various energy accounting meth-ods exist. One approach is to compare the primary energy savedwith the added primary energy needed to effect the saving.Alternative methods use a traditional financial approach, butthese were sensitive to future fuel prices, inflation and interestrates. In the end, economic analysis is seen as a tool to sharpenjudgement, particularly when comparing options within theresources available for investment. Other things being equal,priority should be given to those options which would be moredifficult to introduce when the building is in occupation. Figure21.7 is an interesting way of illustrating the combined impact ofan energy-saving measure on cost of construction and cost inuse. The most attractive measures reduce both initial andrunning costs of the building as a whole.

Heat loss considerations are important components of build-ing regulations in most countries. In some cases these rely onspecific thermal properties for the building fabric. More ad-vanced regulations call for examination of the thermal perform-ance of the building as a whole, thus encouraging the innovativeskills of architects and engineers.

Existing buildings are being adapted to the new energysituation by energy conservation through insulation, the intro-duction of more sophisticated control systems or by the intro-duction of new plant.

In new construction, energy-conscious design is now thenorm through building form and fabric and through the instal-lations and controls provided. It is not enough simply to providemore thermal insulation; a whole set of measures is required toobtain the optimum solution.

The principal steps in producing an energy-efficient design areas follows:

(1) Computer analysis of local daily and seasonal weatherconditions to optimize peak and long-term energy require-ments.

(2) Analysis of building orientation, shape, height and con-struction to control heat gain or loss and the use of internalthermal capacity to reduce peak and total energy demands.

(3) Incorporation of heat conservation and recovery by transferfrom points of surplus to points of need and reclamation ofwaste heat.

(4) Incorporating sophisticated control systems sensitive tovariable building use and external weather conditions, toensure that energy is injected only when needed.

(5) Where applicable using combined heat and power plants sothat waste heat may be put to good use.

To save energy buildings are designed so that air-conditioning isunnecessary unless some special factor predominates such aswind, noise or fumes, or client requirement. Walls and roofs areused as the primary climatic modifiers with the environmental

Differential ofrunning cost(million yen/yr)

(1) Architectural planning:(a) optimum building direction;(b) partial underground;(c) twin core;(d) reduction in floor height;(e) cubical structure;(f) 6 other methods.

(2) Reduction in power for plumbing facilities:(a) water-saving toilet;(b) local domestic hot water supply;(c) 7 other methods.

(3) Reduction in ventilation:(a) local ventilation;(b) double-staged use of conditioned air;(c) 2 other methods.

(4) Reduction in thermal load:(a) use of thermal wheel exchanger;(b) control on natural free cooling;(c) volume control on minimum outside air intake;(d) adoption of outside-air intake through underground pipes;(e) use of non-leaky damper;(f) 7 other methods.

(5) Insulation, shading device, and ventilation of building:(a) reduction in glazing areas;(b) use of insulated window shutters;(c) use of external louvre blinds;(d) adoption of double skin;(e) tilting outer glass of double skin;(f) 10 other methods.

Figure 21.7 Economics of energy-saving devices in Ohbayashi'senergy conservation building. (Courtesy. IABSE PERIODICA,IABSE, CH-8093, Zurich)

*Amount of primary energy consumed

(6) Reduction in power for fans and pumps:(a) adoption of VAV system;(b) adoption of large temperature differential system;(c) control on number of operating pumps;(d) 7 other methods.

(7) Reduction in lighting power:(a) task/ambient lighting;(b) dimming control on lighting in perimeter zone;(c) turning off light during lunch hour;(d) 8 other methods.

(8) Upgrade of efficiency:(a) adoption of heat reclaim system;(b) adoption of thermally-stratified heat storage tank;(c) optimal control on starting operation;(d) upgraded insulation around mechanical system;(e) 9 other methods.

(9) Active solar:(a) direct utilization of solar energy for air-conditioning

and heating;(b) earth heat storage of solar energy;(c) 3 other methods.

(10) Reduction in electric power:(a) improvement of power factor;(b) control on number of operating transformers;(c) solar photovolatic power generation system without

battery unit;(d) 5 other methods.

Vector diagram for thermal economics Differential ofinitial cost (million yen)

Calculation of depreciationand conditions assumedInterest of loan 8.80%Energy price increase 13.18%

*378Mcal/m2/yr

*300Mcal/m2/yr

Number of depreciation yearsT= 12yr

*200Mcal/m2/yr

T= 10yr

*100Mcal/m2/yr

engineering systems providing fine-tuning to match local need.Elevational treatment is directed to the beneficial control ofsolar gain, the windows being set back to provide shading fromthe high Sun in summer, but permitting warmth to enter fromthe low Sun in winter. Glass remains an attractive material butis now less ^extensively used and is double- or triple-glazed.Passive solar heating can be an integral part of the heating inmajor buildings. There is now less general lighting and morelocal or task lighting with automatic systems of control sensitiveto external daylight conditions and programmed for plannedinternal use. There is greater emphasis on variable air systemswhich use less energy and are more tailored to provide localventilation needs. Heat reclamation techniques are now widelyapplied, particularly those based on the use of heat pumps andexhaust-air-inlet heat exchange. Heat from lights and officeequipment is reclaimed, and 'run-around' systems are used totransfer heat from the hot, to the cool, side of a building.Energy-consciousness has extended from individual buildings togroups of buildings incorporating complementary energy re-quirements.

The impact on the structure arises mainly from changes inbuilding form which result from the above considerations,coupled with the possible use of the thermal inertia of thestructure to stabilize temperatures or as a heat store. Figure 21.8illustrates the range of energy-saving measures adopted for theTokyo Electrical Power Company (TEPCO), Ohtsuka Branch,Tokyo, while Figure 21.9 compares the achieved savings againstthose estimated.

12.14 Building Regulations

Building control in England and Wales is governed by theBuilding Act 1984 and the Building Regulations 1985. Scotlandand Northern Ireland have separate systems of control.

Building work is defined as: (1) the erection or extension of abuilding; (2) the material alteration of a building; (3) theprovision, extension or material alteration of a controlledservice or fitting; and (4) work required on a material change inuse. Certain small buildings and extensions and buildings forcertain purposes are exempt from the regulations.

The regulations are silent on when repair work becomessubject to control. However, there comes a point in some caseswhen so much has to be done to repair or replace that the localauthority could reasonably require the regulations to be ap-plied.

21.14.1 Procedures

The new regulations contain an important innovation in thatthe proposed building work may be supervised either by thelocal authority or by an 'approved inspector'. Under localauthority supervision, a further choice is available of depositingeither full plans or a 'building notice' which contains much lessinformation.

Full plans may be accompanied by a certificate of compliancewith regulation requirements relating to structural stability and/or energy conservation. Such certificates can be given only by an'approved person' and must be accompanied by a declarationthat an approved insurance scheme applies. The details of whowill qualify as an 'approved person' have yet to be resolved butit is expected that the relevant professional institutions willbecome the approving bodies for individuals wishing to under-take this work. When full plans are deposited, the local auth-ority must pass or reject them within 5 weeks, or 2 months if thedeveloper agrees. The 'building notice' option is simpler but isnot applicable to shops or offices or any building work subjectto the requirement for means of escape in the event of fire. The

'building notice' contains a short description of the work, ablock plan and proposals for drainage. The local authority doesnot issue any approval but may wish to check work in progress.

The Building (Approved Inspectors) Regulations 1985 set outdetailed procedures for private certification by approved inspec-tors as an alternative to local authority supervision. Underprivate certification, the developer and approved inspectorjointly serve an 'initial notice' on the local authority. Thisdescribes the proposed works and can be rejected by the localauthority only on certain prescribed grounds specified in theApproved Inspectors Regulations. The 'initial notice' must beaccompanied by a declaration that an approved scheme ofinsurance applies to the work. If the local authority does notreject the notice within 10 days it is presumed to have accepted itwithout conditions. On acceptance, the local authority's powersto enforce the regulations are suspended and the approvedinspector becomes responsible for inspecting the plans andbuilding work and, on completion, issuing a final certificate ofcompliance.

21.14.2 Appeals procedure

When building work is alleged to contravene the regulations, thelocal authority can require its removal or alteration by serving aSection 36 notice on the building owner who has a right ofappeal to a magistrates' court. The building owner may elect toobtain an expert's report from a 'suitably qualified person'. Ifaccepted by the local authority, the Section 36 notice would bewithdrawn and the building owner reimbursed his costs. Ifrejected, the report may be produced to the court and if theappeal is successful the building owner will recover his costs.

21.14.3 Approved Documents and mandatoryrequirements

The new regulations are much shorter and simpler since thetechnical details are now contained in a set of nonstatutoryApproved Documents which give practical guidance on ways ofmeeting the regulation requirements. The obligation is to meetthe requirement. The Approved Document may be used inwhole or in part, or some other arrangement may be adoptedprovided the basic requirement is met. Use of the ApprovedDocument would tend to be regarded as evidence of compliancewith the regulations. If some other method is used, the reversewould apply and demonstration of compliance will be required.

Means of escape from fire, however, are covered by manda-tory requirements although the local authority may agree torelax them in particular circumstances. The requirements arecovered by the Rules.I0 A fire certificate is required for certainuses of building. Such buildings, in addition to means of escape,must include provision for fire alarms and fire-fighting equip-ment. Currently included are certain factories, offices, shops,railway premises, hotels and boarding houses. The Health andSafety Executive have similar responsibilities for special riskpremises such as nuclear installations, buildings at the surfacesof mines and large chemical or petrochemical plants where theprocesses carried out affect general fire precautions.

Heat losses from certain classes of building are subject tominimum mandatory requirements. Four procedures for meet-ing the requirements are allowed:

(1) Specified insulation thickness.(2) Specified U values to take account of full construction

features.(3) Calculated trade-off within glazed and solid areas and in the

case of dwellings between solid areas and windows.(4) Calculated energy use in buildings other than dwellings,

allowing heat gains to be set off against heat losses.

(Mcal/m2.a)Figure 21.9 Energy consumption in the Tokyo Electrical PowerCo., Ohtsuka Branch, Tokyo. (Courtesy IABSE PERIODICA,IABSE, CH-8093 Zurich)

Estimated (Total 217)

Consumed in 1980 (Total 241)

(Total 450)

Others

TEPCOOhtsukabranch

Ordinaryoffice building

Heat source TransportLighting andwall-receptacles

Figure 21.8 Outline of energy-saving techniques. (Courtesy.IABSE PERIODICA, IABSE, CH-8093 Zurich)

Solar energy utilizationSolar collectors installed on

the roof of the building supplyall domestic hot waterrequirements

Sun-control eaves and blindsOverall heating and cooling

load is reduced by eaves andautomatically-adjusted blindsto control interior insulationaccording to the season

Reduction of outsideair infiltration

Outside air infiltrationis reduced by usingdouble doors atentrances, air-tightwindow sashes, andmaintaining positiveair pressure in the interior

Ground level

Monitoring and control ofenergy use

Changing external and internalconditions are constantlymonitored by computer, andall systems and equipment areprecisely controlled tomaintain optimal energy-saving operation

Water savingsWater-saving fixturesReclamation of waste water

for nondrinking purposesUtilization of rain waterWaste water from washstands,

kitchenettes, showers andbathtubs is reclaimed andfiltered in a reclamationplant, and used along withrain water for toiletflushing needs

Intake air volume controlAutomatic control of intake

air volume according to room-use demands

Automatic shutoff of intakeair during preheating andprecooling periods

Climate control by intake aironly in appropriate seasons

Energy savings in fansand blowers

Variable air volumecontrol system

Power is saved bycontrolling airdistribution volumein accordance withclimate control needsin the various zones

Thermal storagesystem

Utilization ofnew storagematerials

Waste heatstorage

Shifting heatpump andchilleroperationsto period oflow energydemand

Heat recoverysystem

Total-heat exchangerExhaust air heat is

recovered and used topreheat intake air duringwinter months. Thesystem is reversed torecover cooled air duringthe summer

Reduction of conductiveheat loss or gain through theroof

Insulating materials are usedto reduce the conduction ofheat through the roof

Reduction of heat loss or gainthrough perimeter walls andwindows

Improved insulationIncreased heat capacitySun-control eaves and blindsAirtight sashesHeat-reflecting glazingDouble glazingOverall heating and cooling

loads are reduced by insulatingall perimeter surfaces to curtailboth in and out heatconduction. Similarly,temperature differenceswithin rooms are minimizedin order to maintain comfortableenvironments with less energy

Interior lighting systemsLowered illumination levelsDirect lighting methodsGrouping of lighting circuitsCombined use of spot lightingAutomatic on-off controlMaximum utilization of

natural lightingUse of energy-saving fluorescent

fixtures incorporatingelectronic ballasts

Contrary to conventionalbuildings which rely almostexclusively on artificiallighting, the model buildingincorporates a series ofautomatic controls to maximizethe use of natural lighting

Electric supply distribution andtransforming systems

Control of the number of transformer-banksImprovement of the power factor by

condensersMonitoring and control of power demand

Energy saving in pumpsVariable flow rate controlConventional heating and cooling systems

maintain climate control by changing thetemperature of chilled or hot water whilekeeping the rate of water flow constant.However, the systems in the model build-ing achieve greater efficiency by keepingwater temperature constant, insteadvarying the flow rate and operating thepumps only as required by actualdemands in various zones

Heat source systemHeat recovery systemUtilization of heat pumpsCareful monitoring and control for

operational efficiencyWaste heat generated by occupants,

lighting, office machinery,equipment and other sources isrecovered by a heat pump systemand stored in thermal tanks tosupplement heat-source equipment

21.14.4 Structure

There are three requirements: Al concerned with loading; A2with ground movement; and A3 with disproportionate collapse.

Al: Loading.

(1) The building shall be so constructed that the combineddead, imposed and wind loads are sustained and transmittedto the ground:(a) safely; and(b) without causing such deflection or deformation of any

part of the building, or such movement of the ground, aswill impair the stability of any part of another building.

(2) In assessing whether a building complies with (1) regardshall be had to the imposed and wind loads to which it islikely to be subjected in the ordinary course of its use for thepurpose for which it is intended.

A2: Ground movement

The building shall be so constructed that movements of thesubsoil caused by swelling, shrinkage or freezing will not impairthe stability of any part of the building.

A3: Disproportionate collapse.

The building shall be so constructed that in the event of anaccident the structure will not be damaged to an extent dispro-portionate to the cause of the damage. This requirement appliesonly to:

(1) A building having five or more storeys (each basementlevel being counted as one storey).

(2) A public building the structure of which incorporates aclear span exceeding 9 m between supports.

The Approved Document's guidance is in three sections: (1)Section 1 gives sizes for certain structural elements for housesand other small buildings, covering walls, floors, roofs, chim-neys and strip foundations: (2) Section 2 lists codes and stan-dards which are appropriate for all buildings and which may beused to satisfy the requirements of regulations Al and A2; and(3) the final part deals with disproportionate collapse andquotes codes and standards which may be used in designing tomeet the requirement of A3 for a building having five or morestoreys, provided the recommendations on ties, and the effect ofmisuse or accident, are followed. Structural work of concrete iscovered by BS 8110:1985, Parts 1 and 2. For steel it is BS5950:1985, Part 1, and the accident loading referred to in clause2.4.5.5 should be chosen having particular regard to the import-ance of the key element and the consequences of its failure; thekey element should always be capable of withstanding a load ofat least 34 kN/m2 applied from any direction. British Standard5628:1978 is quoted as the relevant standard for structural workof masonry.

By way of'additional information', the Approved Documentstates that the structural failure of any member not designed as aprotected key element or member, in any one storey, should notresult in failure of the structure beyond the immediately adjac-ent storeys or beyond an area within those storeys of: (1) 70 m2;or (2) 15% of the area of the storey, whichever is less.

Protected key elements or members are single structuralelements on which large parts of the structure rely, i.e. support-ing a floor or roof area of more than 70 m2 or 15% of the area ofthe storey, whichever is less, and their design should take theirimportance into account. The least loadings they have towithstand are described in the codes and standards listed.

The Approved Document offers no specific guidance on wide-span public buildings of less than five storeys. Clearly, suchbuildings do require special care in design and construction toreduce risks to human safety and the designer should considercarefully structural behaviour and consequence in the event ofan unforeseen hazard or accident.

Structural matters are referred to additionally in otherApproved Documents, e.g. in AD7 ('Materials and workman-ship') and AD B2/3/4 ('Fire spread').

21.14.5 Fire spread

The requirements cover internal fire spread (surfaces) in B2,internal fire spread (structure) in B3, and external fire spread inB4. Approved Document B/2/3/4 describes how the require-ments can be met by controlling aspects of the construction andmaterials used in the building, e.g. fire resistance and surfacespread of flame characteristics.

21.14.5.1 Internal fire spread (surfaces)

The spread of fire over a surface is restricted by provisions forthe surface material to have low rates of surface spread of flame,and in some cases to restrict the rate of heat produced.

The provisions are made for walls and ceilings and varyaccording to the use of the building or compartment, thelocation of the room or space concerned, and in some caseswhether the surface is a wall or ceiling.

21.14.5.2 Internal fire spread (structure)

Premature failure of the structure is prevented and the spread offire within a building restricted by specifying minimum periodsof fire resistance for the elements of structure. Fire resistanceincludes requirements for one or more of the following:

(1) Resistance to collapse (stability - applicable to load-bearingelements).

(2) Resistance to fire penetration (integrity - applicable to fire-separating elements).

(3) Resistance to the transfer of excess heat (insulation -applicable to fire-separating elements).

Structural stability under fire conditions necessitates consider-ation of the following aspects of design:

(1) The coincident effects of dead, imposed and wind loads.(2) The effect of heat on the structural elements.(3) The provision of structural integrity to resist the effect of

fire-induced movements.

The minimum period of fire resistance is set out relevant to thebuilding use and depends upon the height of the building and onthe size of the building or compartment. In basements, theprovisions are generally more onerous in view of the greaterdifficulty of dealing with a fire.

21.14.5.3 Compartmentation

The spread of fire can also be restricted by subdividing thebuilding into compartments of restricted floor area and cubiccapacity, by means of compartment walls and compartmentfloors. The degree of subdivision depends upon the use of thebuilding and in some cases its height. In single-storey buildings,the life risk from fire involving the whole building is generallyless than that for a multistorey building. Thus, compartmen-tation in single-storey buildings applies only to those with asignificant sleeping risk. There are, however, provisions for

compartmentation of most multistorey buildings. Other formsof compartmentation apply between adjoining buildings andbetween a small garage and a house to which it is attached orforms part. As the minimum period of fire resistance increaseswith size of building or compartment it may be advantageous toprovide compartments of smaller size than specified. Similarly,where a building is used for more than one purpose, it may bedesirable to separate by compartmentation the use which hasthe more onerous fire-resistance requirement.

In order for compartments to be effective, junctions betweenthe different elements enclosing the compartment must beprotected. Similarly, any openings connecting one compartmentwith another should not present a weakness. Any spaces con-necting the compartments need to be protected to restrict firespread. These are termed 'protected shafts'.

21.14.5.4 Concealed spaces and fire stoppingHidden voids provide a ready route for smoke and flame spread,e.g. above a suspended ceiling or in a roof space. As any spreadis concealed, it presents a greater danger than would a moreobvious fire weakness in the construction. Provision is thereforemade to restrict the hidden spread of fire in concealed spaces byclosing the edges of cavities, interrupting cavities which couldform a pathway around a fire barrier and subdividing extensivecavities. Similarly, pipe or cable penetrations through a fireprotection building element should be sealed appropriately.

21.14.5.5 External fire spread

The construction of external walls and the separation betweenbuildings to prevent external fire spread are closely related, andmany of the provisions specified are related to the distance ofthe wall from the boundary.

Whether a fire will spread across an open space betweenbuildings, and the consequences if it does depend on: (1) the sizeof the fire; (2) the risk it presents to people in the other buildings;(3) the distance between the buildings; and (4) the fire protectiongiven by their facing sides.

There are provisions limiting the extent of openings inexternal walls to reduce the risk of fire spread by radiation. Lessonerous provisions for separation apply where compartmen-tation exists. Provisions for roof construction and coveringsvary with the size and use of the building and the proximity ofthe roof to the site boundary.

2Ll4.5.6 Structural integrity of the building as a whole

The required level of performance will be met if the guidance inAD Al and AD A2 and the Guidelines" are followed.

21.14.5.7 Varying the provisions

Where the fire provisions are thought to be unduly restrictive,the fire safety of the building as a whole may be considered andguidance is given about varying the provisions. Factors to betaken into account include: (1) whether the building is new orexisting; (2) the construction and fire properties of the materials;(3) fire hazard and fire load; (4) space separation from boundar-ies and other buildings; (5) means of escape; (6) ease of accessfor fire-fighting; and (7) the provision of any compensatoryfeatures such as sprinklers or other automatic fire-detectionsystems. For example, the maximum compartment size in shopsmay be doubled when a sprinkler installation is fitted.

Shopping centres pose special problems and alternativemeasures and additional compensatory features to those set outin the Approved Document may be appropriate. These include:

(1) Unified ownership and control of fire prevention measures.

(2) Adequate means of escape and smoke control.(3) Sprinkler protection of all areas of fire load.(4) Automatic fire alarm system.(5) Good access for fire fighting.(6) Materials of limited combustibility and fire spread.(7) Generally 2 h fire resistance of structure (4 h in basement).(8) Floors generally of compartment construction.(9) Walls between shop units of compartment construction.

(10) Compartmentation between large shop units (over370Om2) and a mall, and between opposing shop units(over 2000 m2) and a mall. Fire shutters may be used forthis purpose.

The above items are not exhaustive but draw attention to theneed to consider proposals as a comprehensive fire-safety pack-age.

21.14.6 Other Approved Documents

Other Approved Documents are as follows.C1/2/3 'Site preparation and contaminants'.C4/ 'Resistance to weather and ground moisture'.Dl- 'Cavity insulation'.E1/2/3 'Airborne and impact sound'.Fl 'Means of ventilation'.F2 'Condensation'.H1/2/3/4 'Drainage and waste disposal'.J1/2/3 'Heat-producing appliances'.K1/2/3 'Stairways, ramps and guards'.L2/3/4/5 'Conservation of fuel and power'.Part 7 'Materials and workmanship'.

21.15 Building security and control

With the increased size and complexity of buildings, systemsdesigned to monitor and control the mechanical and electricalinstallation, fire protection and escape, burglary, assault andemergency communication have become very important.

In tall buildings, and other major complexes, the mostimportant security requirement is the fire-safety system. Inaddition to the structural precautions of fire protection andcompartmentation, special systems are required to monitor andcontrol: (1) fire detection and suppression; (2) movement andprotection of people; (3) smoke control including pressurizationand barriers; (4) safe places of refuge; and (5) emergencyarrangements and communication.

In major buildings, these arrangements are integrated withthose required to monitor and control the heating, ventilationand air-conditioning systems and other aspects of securitywithin a single electronic system. The computer monitors allsignificant local conditions and appropriate action is taken.Such measures for security and control could, for example,bring in the use of: (1) heating, ventilation and air-conditioningplant and equipment to suit internal and external conditions orprogrammed requirements; (2) data collection for maintenanceand resource management, particularly energy use and analysis,programmed responses to suit anticipated emergencies, e.g.defining smoke-free zones and escape routes in the event of fire;and (3) security interlocks, surveillance and access control.

The terms energy management system (EMS), building auto-mation system (BAS) and building management system (BMS)are used to describe these systems. The EMS controls theenvironmental functions, the BAS the technical automatic con-trols, and the BMS includes such matters as status reports onenvironmental conditions, lifts and the location of people forsecurity purposes. All these aspects influence and are influencedby the overall building designs.

The problems of security are by no means limited to majorbuilding complexes. Studies of housing estates with very dif-ferent crime rates but with comparable density, size and tenantincome, demonstrate clear relationships with specific buildingdesign characteristics, the nature of the surrounding areas andwhether these are under the ready surveillance of the inhabi-tants. This has given rise to the design concept of 'defensiblespace' whereby tenants can act as their own 'policemen' simplybecause they identify with a particular space and easily monitorwhat is going on.

21.16 Materials

The principal materials used in buildings are concrete, steel,brick and masonry, and timber: each has its own developingtechnology. Other materials include aluminium, various alloys,glass, plastics and rubber. When used structurally, the essentialproperties concern strength, rigidity, durability and fire resis-tance. Relevant general properties concern hardness, thermalcharacteristics of insulation and expansion, weight, uniformity,appearance and workability. All these may be affected bychanging temperature, humidity and weather. The choice ofmaterial for a particular building element will be determined bysuitability for the intended purpose, cost and availability andcompatibility with other materials.

21.16.1 ConcreteAs a building and structural material, concrete is durable andrelatively impermeable. It is readily available, and with the useof different cements, aggregates, forms and surface treatments itcan provide a wide range of strengths, densities and finishes. Itsmass automatically provides good airborne sound insulationand high thermal capacity, and with appropriate constituents itis resistant to chemical attack.

Lightweight concrete, in both structural and nonstructuralelements, is used when weight is at a premium or when its betterfire and thermal resistance is required. Precast applicationsinclude building blocks, fire casings, and floor, roof and clad-ding units. It is used in situ for floor slabs, screeds and generallyfor reinforced or prestressed structures. Its reduced stiffnessshould be allowed for in design.

Specially dense concrete is used as kentledge or for radiationshielding.

Normal-weight concrete is used unreinforced in mass founda-tions, gravity retaining walls, screeds and blinding, and precastas paving flags, kerbs and building blocks. For structural workit is normally reinforced with bars of high-tensile or mild steel,fibre-reinforced (with steel, glass or plastic), or prestressed.Fibre reinforcement gives improved impact resistance and canallow thinner sections; current applications are precast cladding,pipes and pile shells. Prestressing is used in precast floor unitsand in long-span beams as a means of controlling deflection orreducing member depth, and has special application in hangingand transfer structures.

Concrete cladding to buildings is generally precast, and maybe nonstructural or structural. Panels may incorporate windowsor doors, and may be of sandwich construction with a layer ofthermal insulation. Many surface finishes are available includ-ing exposed aggregate, mosaic or tiles, and profiles may be plainor sculptured. Great care is required in detailing the profile andsurface finish to control staining and to ensure satisfactoryweathering.

The choice between precast and in situ construction willdepend on cost, speed, access and availability of labour. Precast-ing minimizes the on-site work, but requires good accuracy andsuitable lifting equipment. In situ work requires more on-site

labour, but can be speeded by using prefabricated formworksystems and concrete pumps.

Where reinforced concrete is exposed to the weather, to wateror to the ground, durability must be considered. Protecting thereinforcement from corrosion requires an adequate cover ofdensely compacted concrete with sufficient cement in the mix tomaintain the steel in an alkaline environment. Where thiscannot be achieved, other measures such as coating the concretesurface, or using galvanized or stainless steel reinforcement,may be needed. Chlorides in concrete must be restricted as theypromote corrosion of the reinforcement; they may arise fromthe use of marine aggregates or from the unwise use of certainadmixtures.

At the time of writing (1986), several cases of alkali-silicareaction (ASR) are being reported. This is a reaction whichoccurs between the alkali in the cement and certain types ofaggregate, leading to expansion and loss of strength. It appearsto be restricted to high-cement mixes, but there are as yet noreliable tests for aggregates. Although this problem is rare,advice on the latest knowledge should be sought before commit-ting the mix design on large or important concrete elements,particularly if the concrete will be exposed to weather or water.

Glass-reinforced cement (GRC) is a relatively new materialwhich utilizes alkali-resistant glasses developed in the 1970s. Atypical mix will contain cement, sand, glass fibre and water, withcement: sand-ratio of 2:1, a water: cement ratio of 0.3:1, and5% by weight of glass fibre. Careful detailing is needed toaccommodate initial drying shrinkage, which is higher than fornormal concrete. When young, GRC is a tough material whichcan deform without breaking. As it ages and weathers, thetoughness reduces to a stable level after 2 to 5yr. Severalmethods of casting GRC are used, but the normal method is tospray the constituents on a mould to form a layer 6 to 10mmthick. This is demoulded and carefully cured. Simple shapes canbe formed by folding flat sheets before they harden; complexshapes require purpose-made moulds. Glass-reinforced cementshares many applications with glass-reinforced plastic (GRP)but the GRC is heavier, stiffer and has better fire resistance. Themain applications are drainage pipes for use underground,permanent formwork for concrete, roof tiles, street furnitureand cladding panels. Cladding panels can be formed as a singleskin of GRC, or as a sandwich of two skins with insulationbetween.

2L16, Ll Fire protection

Fire protection of concrete structures is based upon the provi-sion of adequate thickness of construction and adequate coverto the reinforcement or prestressing tendons. Lightweight con-crete has an improved fire resistance because of its betterthermal resistance and with some artificial lightweight aggre-gates is virtually free of spalling during a fire.

21.16.2 SteelIn one form or another steel is extensively used in practically allbuildings. As a structural element it is available in a wide rangeof section and composition to suit the particular requirements ofstress, deflection, corrosion or jointing technique: (1) it is of highstrength; (2) in itself, occupies little space and is prefabricatedfor easy and rapid erection on site; and (3) it readily lends itselfto extension or alteration. Sections can be cold-curved to formarches or rings. It has two disadvantages: (1) fire; and (2)corrosion. Several methods exist to overcome its fire sensitivity -various coatings are applied to resist corrosion and some steels(Corten) can be left exposed without treatment. Castellatedbeams are useful to reduce deflection and to provide holes forthe passage of services. Hollow sections, of various wall thick-

nesses, are used in tubular structures, columns, trusses, spaceframes. Combined sections are commonly used and compositeaction, via shear connectors, with concrete floor constructioncan be advantageous. Sheet steel applications include roof andwall cladding, ducting and in floor slab construction, actingcompositely with in situ concrete topping.

21.16.2.1 Fire protection

Fire protection of structural steel has moved towards the use ofboarded lightweight encasements, sprayed surface materials andintumescent coatings. In situ concrete casing tends to slow downthe construction process, although this can be overcome byprecasting the concrete surround leaving only the junctions tobe dealt with on site.

Boarded systems. A variety of boards are available in thick-nesses from 6 to 80 mm giving fire periods up to 4 h. They aregenerally manufactured from vermiculite or mica using cementand/or silicate binders and are particularly suitable for columnprotection and for 'all dry' construction.

Spray systems. A wide variety of lightweight materials areavailable generally based on vermiculite plus a binder (oftencement) or mineral fibres. It is generally applied direct to thesteel surface, although1 in some situations it is applied to anexpanded steel lathing to form a hollow box protection. Fireperiods of up to 4 h can be achieved; mesh reinforcement may berequired for the longer periods.

Intumescent coatings. These thin film coatings or mastics swellunder the influence of heat and flames producing an insulatinglayer 50 times thicker than the original. Fire periods up to 2 hcan be achieved. A variety of products are available; not all aresuitable for damp environments and only a limited number areapproved for the fire protection of columns.

Fire-protection thickness. The thickness required for most steelmembers given in manufacturers' literature has been given bythe Association of Fire Protection Contractors and Constrado.12

This generally relates the thickness of protection to both the fireresistance period and the HJA value of the steel section, whereHp is the perimeter exposed to the fire and A the cross-sectionalarea. The lower this value, the lower the heating rate.

Structural fire engineering. Whilst it is convenient in mostsituations to adopt the regulatory approach to fire resistance, inspecial cases a more fundamental approach may be appropriateand acceptable to the authorities concerned. Fire engineering isdirected towards a more accurate assessment of the fire protec-tion required by considering the significance and severity of areal fire in the building and the response of the structure as atotality to it. The process involves the consideration of:

(1) The heating rate and maximum temperature in the compart-ment - related to the fire load, ventilation and insulation oflining materials.

(2) The temperature rise in the structural member - related tolocation, weight per metre and perimeter of the structuralmember exposed along with any fire protection applied and,in the case of beams, their height above the fire.

(3) The stability of the structure - related to the load applied,the grade of steel and the effects of any composite action,restraint, continuity and movement.

Such considerations are particularly applicable to buildingswhere the function and fire load are unlikely to change. Ex-amples are: schools, offices, hospitals, sports stadia, public

assembly buildings and transport terminals. The concept is mostcost effective when the analysis leads to the acceptance of thebare structure without fire protection.

The fire load is a measure of the amount of material availableto burn and is calculated as weight x calorific value of thecontents and building materials used in each compartment. Theresulting figure is often converted to the equivalent quantity ofwood having the same total heat content. In calculating theheating rate inside the compartment, the available ventilationand insulating properties of the compartment envelope aretaken into account. Well-ventilated fires are shorter and hotterand an insulated envelope retains the heat. On the basis of thisinformation, it is possible to predict the likely heating cyclewithin the compartment which can then be related to the heatingstrength/deformation curves for the steel.

21.16.3 Brick and masonry

Brick and masonry have the advantages of a long heritage ofexperience and simple construction based on traditional skills;building plant costs are low, but the labour content is high andnot always in sufficient supply. The common materials arebricks and concrete blocks of various types, finishes andstrength, and natural or reconstituted stone. The main applica-tions occur in load-bearing walls and piers, particularly in low-and medium-rise buildings, and as cladding. Internally they areused as the inner skin of cavity construction or as partitions and,within limits, may be used to brace framed construction. Rein-forcement can be added in the horizontal joints to producebeam action or vertically, in piers, for tying purposes.

In general, the massive nature of these materials providesgood sound and thermal insulation together with good com-pressive strength and durability. Movement due to shrinkage inthe case of concrete bricks/blocks and expansion in the case offired clay bricks, temperature and moisture change, and chemi-cal action must be allowed for and provision made in designagainst progressive collapse. The design of brickwork hasbecome more sophisticated both structurally and architecturallyin keeping with the swing back to more traditional forms ofconstruction.

21.16.4 Timber

The main advantages are: (1) it is readily available in a widevariety of types and section; (2) it is light in weight; and (3) it iseasily worked, employing traditional skills. Typical applicationsare in floors, roofs, framing to light buildings, cladding, walland ceiling construction and in surface finishings. It is oftenused in temporary buildings and for temporary works andformwork.

Size, form and consistency limitations have been reduced bythe introduction of glued laminates and special fastening sys-tems have made larger-scale structures possible. Combustibility,rot and insect infestation can be retarded by chemical impregna-tion while treatment with steam or ammonia gas introducesflexibility. Temperature and moisture movements remain prob-lems. Fire resistance of exposed timber members can be assessedfrom the rate of charring. This varies with different kinds oftimber but is generally about 0.6 mm/min on each exposed face.

21.17 Walls, roofs and finishes

21.17.1 External finishes, materials and weathering

The design of the external fabric requires a knowledge of thebehaviour of the materials and elements of construction andincludes consideration of weathering and water-shedding char-acteristics. External materials must be durable under the

influence of climatic extremes and the local environmentalconditions including wind velocity and prevailing direction, andwhether coastal, urban, industrial or rural. The cost of mainten-ance, and accessibility for maintenance are also important con-siderations. The major functional requirements for the externalwall include heat and sound insulation and damp-proofing.

Design elements range from screws to complete assemblies.Deterioration due to weathering may be aesthetic or functionaland may be visible or concealed, and design details should besuch as to avoid structural deterioration, especially in concealedsituations, and should be designed bearing the possible colourchange or staining effects of weathering in mind.

The weathering characteristics of the main materials usedexternally are described in detail elsewhere.13

Concrete finishes depend upon the moulds used, the materialproperties and surface treatment. Blemishes such as surfaceairholes cannot always be avoided and untreated smooth sur-faces generally weather badly, although when, with hard con-cretes of plain or white mixes, the surface laitance is ground offand sealed, good results can be obtained. Patterning and texturecan provide interesting finishes, as with rough board markings,or ribbed surfaces which may be hammered or tooled in variousways. Deep patterning can also be very effective. Exposedaggregate finishes are available from a wide variety of processesand aggregates, and these generally weather well.

Brickwork is traditionally used as external walling and avariety of colours and textures are available in facing bricks.Attention must be given to weathering performance, porosityand freezing effects, efflorescence, sulphate attack, etc. Whenassociated problems are recognized, solutions are available.Details must be designed to accommodate relative movement ofthe brickwork and other building elements.

Timber and timber products may be used as cladding, butcolour changes usually occur on exposure to light and water,which can also lead to damage such as splitting, warping anddirt penetration. Various preservation treatments are available,including the use of varnishes, synthetic resinous clear finishes,opaque paints and applied film overlays.

With the use of metals externally, their particular propertiesas to electrochemical corrosion in relation to weathering and theproblem of bimetallic electrolytic action need to be understood.Aluminium, bronze and copper weather well and are used inroofing, cladding, window framing and flashing applications.Lead may be used in sheet form for special roof covering andmore frequently for flashings. Zinc provides useful coatings andflashings. Outstanding durability can be obtained with the useof stainless steel, and low-alloy steels of good weatheringproperties are available.

Curtain walling can provide an economic form of claddingand glazing, with advantages of lightness, thinness (as affectingusable floor area), flexibility of fenestration and speed oferection without external scaffolding. It is provided in two maintypes: (1) unit assemblies in which self-supporting panels areprefabricated including glazing and solid infilling with interlockor lap joints; and (2) part assemblies in which frame membersare erected and the glass and solid sheets added. Weatherresistance and connection to the structure must be adequate tomeet high local wind pressures and conditions of driving rain.Sealing methods include the use of mastics, gaskets, cover tapesand spring strips. Thermal movements may be very large sincethe panels have low heat capacity and respond rapidly tochanges in temperature, giving rise to differential movementsbetween one part of the curtain walling and another, andbetween the curtain walling and the structure.

Different types of glass are available including: (1) clear,coloured, or opaque; (2) heat absorbing, filtering or reflecting;(3) toughened, single or bonded into insulated sandwich con-struction.

A wide range of plastics for external use is available, withdifferent resistances to ultra-violet light, temperature, water,oxygen, micro-organisms, atmospheric pollution and loading.These include PVC, used for rainwater goods, glassfibre-rein-forced polyester resins forming sheet or shell products, poly-methyl methacrylate providing transparent sheets of highstrength and durability and the phenolic and amino resins forlaminated sheets. Polymer films may be applied to othermaterials such as boards or metals to improve durability.

21.17.2 Floor, ceiling and wall finishes (internal)

Such finishes may be integral with the structure or applied. Typeof usage, cost, chemical resistance, aesthetic requirements, fireresistance or 'spread of flame' requirements, maintenance, aresome of the factors influencing selection.

Floor finishes integral with concrete rely on good workman-ship: power-float finish, use of hardeners, dust inhibitors, water-proofers, or the application of granolithic concrete finishes to'green' concrete. Timber and metal decking can also be in the'integral' category. Applied floor finishes can vary from simplesheet or tile materials stuck (or laid loose in some cases) to thestructural slab, with or without levelling screeds. Damp-proofmembranes or vapour barriers may be required for slabs on theground, depending on the type of finish to be applied and/or thegroundwater conditions. Screeds may need to be of adequatethickness to allow for the running of service conduits, orthickened, reinforced and isolated by insulation in the case offloors to be heated or used for impact sound insulation. Raisedfloors to accommodate electrical or other services have becomeincreasingly popular in modern office buildings.

Integral wall finishes result from the use of controlled shutter-ing on concrete work, fair-faced brick or blockwork or self-finished plane or profiled sheet materials. Applied wall finishescan be basically divided into wet and dry applications, plaster-ing - by hand or spray - being typical of the former, and dry-lining such as plasterboards and proprietary insulation boards,acoustic finishes, being among the final finishes that may berequired.

Integral ceiling finishes result from the use of untreatedstructural soffits such as concrete, metal or timber. Appliedfinishes may be divided into direct and suspended, the former, asindicated, being the application of wet or dry 'lining' or finish-ing direct to the structural soffit, such as paint, plaster, sprayedfinishes, plasterboards, acoustic insulation boards or tiles. Sus-pended ceilings can be used to conceal structural members, toprovide space for services, to reduce room heights for functionalor aesthetic reasons, to provide a grid for flexible layout ofpartitioning. Such ceilings may be partly or wholly demountablefor access to services or may be 'monolithic', e.g. plaster onexpanded metal.

Building regulations must be referred to when consideringinternal finishes, requirements for resistance to fire being par-ticularly stringent in areas such as staircases and circulationspaces, but also applicable to other areas and varying accordingto building use, area and volume.

21.17.3 RoofsRoofs must keep out the weather, be durable and structurallystable, provide heat insulation in most cases and in certainothers provide light and ventilation. The choice of roof structurewill generally be determined by the general form of the buildingand the activities for which it is designed. Unlike floors, there isnot usually any restriction on the depth of a roof and this gives awide flexibility for economical and appropriate solutions. Some-times the roof structure will be outside the main building.

A roof must carry its own weight together with imposed loads

of roof finish and usually insulation, snow, the effects of wind,normal maintenance and often plant. It must resist excessivedeflection or distortion which, though not leading to collapse,may damage decorations and services and if visible lead to lackof confidence and anxiety for the occupants. In accommodationfor sedentary work or living, heat insulation, lighting, ventila-tion and sound insulation are important.

In general, the spacing of supports should be as close aspossible consistent with present or possible future use.

Short-span roofs below 7.6m are generally used for houses,blocks of flats, many multistorey buildings and some ware-houses. On houses, roofs are often traditional in design. Sheetmaterials allow a lower pitch but the uplift effect of wind isimportant. Flats and multistorey buildings are normally roofedwith a concrete slab similar to the floor construction.

Medium-span roofs 7.6 to 24 m are generally used for indus-trial buildings, warehouses, transit buildings, etc. Here, inter-mediate supports are often a nuisance. Appropriate systems areprecast or prestressed concrete beams or steel trusses, latticegirders and portal frames.

Long-span roofs over 24 m are for exhibition halls, industrialbuildings, leisure buildings, sports stadia and transport build-ings. Many of these buildings require roofs which only keep theelements off the occupants. Systems would include steel latticegirders, space frames, roofs supported by suspended cables,prestressed concrete, arched construction, concrete folded platesand hyperbolic paraboloids.

Roof coverings include slates and tiles for houses, sheetmaterials flat or profiled, asphalt, felt, new materials based onsynthetic rubber, plastics, sprayed-on materials and glass. Itmust always be remembered that provision must be made forroof drainage.

Fire spread is important in relation to roof coverings and iscovered by BS 476:1975, Part 3.

Thermal insulation is often required to conserve heat in thebuildings and is covered by the Building Regulations, but it isalso important to reduce solar gain and avoid excessive expan-sion in the structure of the roof, which sometimes distorts thestructural frame and outside walls. A reflective external finish tothe roof also assists.

Condensation is a serious problem in roofs. Where thermalinsulation is provided below the roof deck at ceiling level, cross-ventilation should be provided above the insulation. In somesituations, a vapour check is necessary on the warm side of theinsulation (the face nearest the inside of the building). Conden-sation is a subject on which a great deal of research has beencarried out in recent years and deserves careful study.

21.17.4 Partitions

Partitions divide large areas into individual spaces for specificpurposes such as stores, offices, etc. and separate circulationfrom working or living areas. The type of partition is deter-mined by requirements of acoustic or thermal insulation, secur-ity, privacy, fire resistance and flexibility of planning. When thepartitions are structural, brick or blockwork or concrete arecommonly used; however, partitioning is generally kept separ-ate from the structures.

Commonly used partitions, in increasing weight, are: (1) lightframing with infilling of glass or building board; (2) plaster-board dry partition panels; (3) woodwool and compressed strawbuilding slabs; (4) sandwich composite panels; (5) precast auto-claved concrete panels; (6) light to dense blockwork; and (7)brickwork and concrete.

21.18 Interior design and spaceplanning

Space planning and interior design are the link between thedesign of the building itself and its eventual use by the occu-pants. In new building, space planning features at the initialbriefing stages, and later in the completion and fitting out of thebuilding for use. During the life of the building many changesare likely to occur in the utilization of the space provided andthe building design must allow for this. A structural engineeringinput is important not only in new building design but also inadvising on space utilization in existing construction.

In achieving an efficient, flexible and visually attractive en-vironment the space planner has to balance the client's needsagainst the restrictions imposed by the nature of the buildingand the requirements of the statutory bodies. Structural aspectscan have a profound effect on the success of the design and thefollowing factors should be considered:

(1) Structural grid related to floor size and shape and intendeduse.

(2) Actual location of columns and beams.(3) Form of the structure and its integration into the building

fabric including services.(4) Floor to ceiling heights.(5) Ability to make satisfactory fixings to the structure.(6) Floor loadings.

Modular co-ordination in building has not been completelysuccessful. Planning grids have never entirely resolved theconflict between, for example, the sizes of workstations andcellular enclosures on the one hand and the sizes of buildingboards, ceiling tiles and partitioning systems on the other.Tartan grids are more economic for the internal fitting-outprocess as there is less need to cut partitions for ceiling tiles.Open-plan arrangements within most buildings do not producemuch difficulty but modular co-ordination can become a prob-lem in cellular office accommodation. Offices, for instance, arenearly always 10, 15 or 20 m2 in area according to the status ofthe occupier. Building components are 1200, 900 or 300mm.The most widely used structural grids are 6.0 and 7.2 m; 6.0 mcan be subdivided to provide 4 x 1 . 5 m or 5 x 1 . 2 m windowbays while 7.2-m grids give rise only to 1.2 m window modules.Although 1.2m is very suitable for building boards and parti-tions it does not lend itself to the provision of individual offices -two window bays gives an office only 2.44 m wide or less. The1.5 m module is superior in this respect and can accommodatesmaller components such as ceiling tiles of 300 mm width; largercomponents of 1.2m or 900 mm cannot be installed economi-cally. Perimeter details can be critical: a continuous flush surfaceallows easy partition connection, avoids cutting around span-drel profiles and service runs, which is both costly and unsightly,and maintains continuity of acoustic insulation. It is moreexpensive to produce a flush window wall and it is not attemptedin speculative buildings. The form of the building often dictatesthe space-planning principles. Few buildings today are of thetraditional narrow form providing two rows of rooms dividedby a corridor; most are wider and the most effective use of thespace uses a mixture of cellular and open-plan accommodation.

For reasons of cost, buildings often have restricted floor-to-ceiling heights on, or slightly above, the statutory minimum.Alterations to the air-conditioning system are frequently neces-sary to service individual rooms or to deal with the 'wild heat'produced by the new technologies. Such alterations causedifficulties if the ceiling height is too low or if deep beams haveto be traversed; the formation of bulkheads causes problems ofanother kind. The major problem for the interior designer today

lies with the distribution of power, telecommunications anddata cables. Speculative offices and older building stock rarelyhave sufficient capacity to deal with the plethora of wires andthe new local area networks. The best solution appears to be theinstallation of suspended floors fed by extra vertical risers butagain the floor-to-ceiling height must be sufficient to allow forthis. If it proves impossible then the floor construction shouldallow for extensive trunking runs in the screed.

Fixings to an existing structure can sometimes prove difficultand in some cases it has not been possible to fix the supports fora plasterboard ceiling to a slab. The strength of the slab givesrise to quite a different set of problems. Even with the growth ofinformation technology there still seems to be more and morepaper produced and the filing and storage of bulk paper isdependent upon the floor loading. The mandatory minimum of2.5 kN/m2 is rarely enough - especially when the weight of asuspended floor forms part of the live load. Even normal filingunits require 5 kN/m2 and compactors, mechanical and powerfiles, safes, etc. can create serious difficulties. It is often possibleto position the storage on beam on lines or directly adjacent tothe core walls where maximum strength occurs, but theselimitations are detrimental to the functional efficiency of thelayout. A value of 4 kN/m2 live load plus 1 kN/m2 for partitions,etc. should be achieved if possible.

Similar cautions should be voiced concerning the strength ofroofs. It is common to site additional service plants in suchlocations and the strength of the roof construction is of primeimportance.

21.19 Structure

The design of building structures is an iterative process by whichthe type, shape, dimensions, materials and location of thevarious structural elements are initially chosen as a first approxi-mation; loads are then determined and the design developed bya process of adjustment and verification that structural perform-ance will be satisfactory. The structure must also satisfy thefunctional needs of the building, site factors and the manytechnical requirements concerned with the safety, health, com-fort and convenience of the occupants.

21.19.1 Structural behaviour

Assessment of structural behaviour must cover: (1) 'service-ability limit states'; and (2)'ultimate limit states'.

21.19.1.1 'Serviceability limit states'

These are concerned with acceptable vibration, horizontal andvertical deflections and structural cracking and the compat-ibility of these with the secondary elements supported by thestructure, such as partitions, cladding, finishes.

21.19.1.2 'Ultimate limit states'

These are concerned with the provision of adequate reserves ofstrength to cater for variations in materials, structural be-haviour, loading and consequences of failure. Partial factors areused for this purpose as follows:

ym allows for variations in strength and is the product of:ym j to take into account the reduction in strength of

materials in the structure as a whole, as comparedwith the control test specimen; and

Ym2 to take account of local variations in strength dueto other causes, e.g. the construction process.

yf allows for variability of loads and load effects and isthe product of:yf to take account of variability of loads above the

characteristic values used in design;Yf2 to allow for the reduced probability of combi-

nations of loads; andYf to allow for the adverse effects of inaccuracies in

design assumptions, constructional tolerances suchas dimensions of cross-section, position of steel andeccentricities of loading.

Yc takes into account the particular behaviour of thestructure and its importance in terms of consequentialdamage, should failure occur. It is the product of yc

and YC where:Yc takes account of the nature of the structure and its

behaviour at or near collapse (whether brittle andsudden or ductile and preceded by warning) andthe extent of collapse resulting from the failure of aparticular member (whether partial or complete);and

YC2 takes account of the seriousness of a collapse interms of its economic consequence and dangers tolife and the community.

Relevant structural codes do not give values for the subcompo-nents (ym , Ym , etc.) quoting only global values for Ym and Yr,which vary wiih the circumstances and load combinations beingconsidered. However, the subcomponent definitions are usefulreminders of the variables that need to be taken into account.

21.19.1.3 Hazards

Building structures may be subjected to such hazards as: (1)impact from aircraft or vehicular traffic; (2) internal or externalexplosion caused by, for example, gas or petrol vapour or bysabotage; (3) fire; (4) settlement; (5) coarse errors in design,detailing or construction; and (6) special sensitivities, e.g. as toacceptance of movement or differential movement or as toconditions of elastic instability, not appreciated or allowed forin design. Hazards involving risk of collapse or damage mayalso be introduced during design, construction or service. Theyderive from mistakes, ignorance or omission, inadequate com-munication or organizational weakness.

These hazards cannot be quantified except in special circum-stances. However, for buildings of five or more storeys, theBuilding Regulations requirements concerning progressive col-lapse provide a general level of protection whereby the stabilityof a building is not put excessively at risk as a result of localstructural damage arising from whatever cause. In cases ofknown risk the special requirements should be included in thedesign brief.

Many methods are available for confining the effects ofaccidental damage to the immediate locality of the incident.These include designing to accept the forces involved, theprovision of alternative paths for the loadings, 'fail-safe' and'back-up' structures. Research has been carried out on partial-stability conditions, whereby the remaining components of thebuilding framework are capable of bridging or stringing over anarea of total local damage by beam, catenary or membraneaction.

Statutory requirements as to fire resistance and means ofescape are devised to ensure continued stability for sufficienttime to permit evacuation of the building and fire-fighting toprotect adjoining property.

The introduction of new methods and materials requirescareful consideration of the structural response to all the eventsthat may occur during manufacture, construction and life of the