Pct assignment

Daniel Palmer/0palmd78/ARC401

d) The primary function of a foundation is strength and stability. The total loads on a building should be transmitted to the ground without causing damage to the building. So the foundations must be designed and constructed to resist any movement, either settlement or heave and it must be limited and uniform under the whole of the building. (Emmitt and Gorse, 2010A p.38)

The suitability to carry loads will vary and the soil types are poor in this construction location e.g. silt, sandy clay and soft clay which are vulnerable to settlement. (Bird V, 2011A). If loads exceed 30kN/metre in these ground conditions, strip foundations would not be suitable. (BR Part A) The construction is for 3-storey flats, so the load could be quite excessive from both imposed and dead loads from the people, weather and the construction. A reinforced concrete raft foundation must be used where loads imposed on the soil must be limited due to poor ground conditions. This foundation uses concrete placed under the whole of the building and is designed to distribute the loads evenly over the whole raft and will therefore reduce the level of settlement. (Emmitt and Gorse, 2010A p.61). There are three different types of raft foundation, but the solid slab foundation will be sufficient for this construction under the conditions because it has a concrete base of equal thickness and is used when the soil is poor and with uneven bearing capacity. (Emmitt and Gorse, 2010B p.93). It is encouraged to use an extended toe to carry the brickwork on the exterior of the building to hide the concrete raft and start brickwork below ground level. These toes will be next to the downstand beams which are used to add rigidity and stability to the raft under the load-carrying walls. (Emmitt and Gorse, 2010B p.94).

A suspended floor will not be necessary with the conditions present because it will inhibit the stability of the floor and will not settle uniformly with the raft foundation which will cause cracks. A 100mm layer of tightly compacted hardcore is necessary under the raft to support the concrete floor and raise it high enough above ground level to hinder dampness from penetrating the interior of the building. (Autonopedia.org). A 50mm layer of concrete blinding will be placed on top of the hardcore to provide a flat base for the steel reinforcements. These will need to run perpendicularly to each other to strengthen and stabilise the raft and protect against tensile and compressive forces that may occur. (Lecture notes A 2012). Then, concrete is poured between the reinforcements to a depth of 200mm at the centre of the raft and 300mm where the edge requires to be thickened for the load-carrying walls. A Damp Proof Membrane is placed on top of the concrete raft foundation and up the interior wall to a height of at least 150mm above exterior ground level to prevent damp rising from the concrete. The DPM will be folded into the interior wall on top of the DPC in the block wall to prevent any gaps for damp to get through. Rigid board insulation must be placed on top of the concrete raft to a depth of 80mm and must also run up the side of the wall to prevent cold-bridging. A 65mm layer of sand-cement screed is to be put on top of the insulation to provide a finished floor surface. (Emmitt and Gorse, 2010A p.65). A sloping concrete layer should be placed at the bottom of the cavity to force water out of the building rather than inside. The floor will not require any other layers because all the functions have been addressed and economically considered.

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e) One of the main functional requirements of a roof is to resist the passage of heat to the outside. (Emmitt and Gorse, 2010A p.302). In a cold roof, the insulation is placed at ceiling level, either between or below the ceiling joists or roof rafters. (RIBA p.20). This means that when the rest of the house is heated, the roof will remain colder because the insulation is preventing the movement of air. Condensation is an issue that needs to be addressed with cold roofs because it occurs when warm moist air comes into contact with a cold surface or a space where the temperature is below the dew point and the water vapour condenses to moisture. (Bird V, 2011B). There are three solutions to controlling condensation: Prevent vapour entering structure, allow water vapour to escape and create ventilation.

Adequate provision must be made to prevent excessive condensation in a roof, (BR Part F) so this issue must be addressed when constructing roofs. To prevent this from happening in cold roofs where the insulation is at ceiling level, an impermeable vapour control layer is placed on the warm side of the ventilation to limit the amount of vapour entering the structure. A vapour permeable membrane is placed on the cold side of the insulation to allow vapour to escape. There should be cross-ventilation of the eaves to limit water vapour. A ventilated space must be provided between the insulation in the rafters and the underside of an underlay a high water vapour resistance (greater than 50MNs/g) to a depth of 50mm through the eaves and the ridge. (Roofing technical review RIBA). Inadequate ventilation will mean moist air cannot escape and condensation can occur. (Homes in Havering, pdf p.7). It is important, however, not to over ventilate a property as it will diminish the effects of air-tightness.

In a warm roof, the thermal insulation is fixed between the rafters and on the battens above the rafters of the pitched roof which will allow the roof space to be heated by the rest of the house. The insulation should be placed without any gaps and continuous up the cavity, over the eaves and on top of the ceiling to help prevent cold-bridging which will encourage condensation. The underlay should be placed under the counter battens and must comprise a vapour permeable membrane to allow water vapour to escape. (RIBA). For this warm roof I would use a low vapour resistant underlay such as “Permo Forte” (Klober.co.uk) which is BBA (British Board of Agreement) approved for creating no ventilation paths. The ventilation will be sufficient under and around the tiles. There should also be a vapour control layer behind the plasterboard to prevent condensation on the inside of the roof. If the permeability of this layer is likely to lessen over time then ventilating between the underlay and roof covering should be considered. (RIBA).

The warm roof construction differs with a cold roof construction in a few ways. The warm roof doesn’t need ventilating if there is a low vapour resistance underlay above the insulation as vapour will be able to escape from the inside. The insulation placement differs in a warm roof construction to allow the roof to be heated. Thus, the condensation patterns will be different due to the location of the insulation membranes that resist/not resist vapour.

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f) The functional requirements for a floor separating a flat are fire safety and acoustic dampening. (Emmitt and Gorse, 2010A p.119). High-density concrete transmits less sound than timber floors and can be used to prevent spread of fire, so this will be the base of my design. Generally, the materials used to create a sound protected floor will be a suitable fire resistant barrier. (Lecture notes B 2012).

There are 3 main ways of separating a floor that comply under building regulations part E. An effective floor type in use for flats is a floating floor where the floating layer is on top of a resilient layer which is placed upon an off-situ low-density concrete base. The resistance to sound depends on the density of the concrete and the type and isolation of the floating floor used. Each floor type requires a different ceiling treatment which can affect the level of sound-proofing. For this floor separation, timber battens will suffice as insulation and sound-proofing will be provided in the concrete base and floating layer. For this type of floor, joists should only be fixed to the surrounding walls as these will be load-carrying and must deflect some of the loading. (BR Part E). There should be a clearance of at least 100mm between the top of the plasterboard forming the ceiling and the underside of the base floor to allow space for the insulation. (BR Part E 3.19). The minimum density of this insulation has to be 10kg/m³ so mineral wool will be suitable. (BR Part E). The plasterboard should be fixed to the timber battens in the ceiling to act as dampeners and to increase the strength. The floating floor on top of the concrete consists of a floating layer and a resilient layer. For this floor, a sand cement screed should be used for the floating layer and the resilient layer consists of mineral wool with thickness 25mm. (BR Part E 3.65). The floating layer will not provide any noticeable sound-dampening and is mainly used as a floor finish, whereas the resilient layer is designed to act as a sound barrier.

This is constructed different to the first floor in a single domestic house because they are usually made of timber which is not needed to be as sound insulating as in a block of flats. The timber joists have to be between 38-75mm thick and have support from the walls or beams placed on wall plates on top of the blockwork and strutting is used to prevent twisting. Approved document A recommends the use of straps or joist hangers to provide lateral support for walls and transfer the horizontal forces to the floor. (Emmitt and Gorse, 2010A p.202). Insulation can be placed in the floor joists like the flats to create a barrier for sound and heat.

The junction between the first floor and external wall will require the same floor used in “a”. The external wall will be masonry with a cavity to provide space for insulation and barriers that may be needed from the flat below. The cavity needs to be fully filled where the concrete sits on top of the blockwork and a cavity barrier should be used to prevent sound transmission and spread of fire. This sound transmission reduction measure is not required in a single domestic house. Cavity closers are not required at every level of a house but are sometimes used at eaves level at the roof. The masonry inner leaf of an external cavity wall should have a mass per unit area of at least 120kg/m² to able to support the concrete floor and transfer the loads safely. The off-situ concrete base block should carry through to more than 300mm from the side of the wall.

The junction between the floor and an internal wall backing onto another flat will be described using the same floor used in “a”. Dense blockwork will be used for the internal walls as this is an acceptable sound insulator and more economical than other choices such as cavity masonry or independent panels. The concrete floor should not be continuous through a separating wall and should be filled to prevent sound transmission from flats below. (BR Part E 3.84). Gaps should always be filled with perimeter sealant in domestic houses and flats to prevent sound transmission. Wall plates are not required in domestic houses if the inner walls are constructed of timber.

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g) I will aim to create a warehouse structure primarily for hardwearing retail use such as “B&Q” or “Halfords”. As soil type is still poor with uneven bearing capacity, the foundation will have to remain a raft. If there were firmer soils below I would consider using pile foundations as this could be more economical and effective. I am going to use a long span portal frame of height 15m as the main structure of my warehouse because it is a more economical alternative to lattice truss and lattice beam roofs and it reduces the volume of roof space that has to be heated. (Barry’s Advanced p.173). The functional requirements of framed structures are strength and stability, durability and fire safety. (Barry’s Advanced p.161). Steel rolled into an “I” shape will be used as it is the most effective for strength and stability and has good compressive and tensile strength and strength-to-weight ratio. Steel will corrode easily when exposed to air and moisture, so it will be coated with zinc to inhibit the rust and will only require minimal maintenance. For shops and commercial structural roofs that form floors must have a minimum fire resistance of 60 minutes if the height is between 5-18m. (ODPM, 2002 B, Appendix A, Table A2). Elements of the structure that give support or stability to another element of the building must have no less fire resistance than the other supporting elements. (Barry’s Advanced p.163).

The pitched roof of the portal frame will be as low as possible (5-10°) to reduce the spread of the knee. The span of this structure is going to be 30m which is classified as medium span, and allows the ridge to be formed on site for convenience sake. (Barry’s Advanced p.173). I will put a masonry wall around the perimeter of the site for aesthetics and security. Bracing in the form of rafter bracing and sheeting rails is needed on the roof and walls of the structure to stabilise the frames and offer resistance to the wind. I will also fix purlins across the rafters and sheeting rails to provide support and fixing for roof and wall cladding and insulation. (Emmitt and Gorse, 2010B p.182). I will use galvanised Zed section purlins with anti-sag bars on the roof to stop them twisting during fixing of roof sheeting. Side rail struts will be used on the walls connected to the purlins to provide strength against the sheeting.

The functional requirements for roof and wall cladding are strength, weather protection, resistance to heat, freedom from maintenance and aesthetics. I will use profiled steel sheeting for the cladding because it can be attached to the structural frame to add strength and stability. The sheeting will be trapezoidal shaped because it can be attached to the zed purlins and can be more aesthetically pleasing than other profiles. The steel sheet cladding can resist the penetration of water if it is overlapped as it is impermeable to water and the side and end laps are designed to keep water out. (Emmitt and Gorse, 2010B p.208) However, steel can be prone to corrosion, so I will give it protection with a zinc coating and finish it with polyvinal chloride which is not affected by UV rays and gives it a long life expectancy. (Bird V, 2011C). The gutter and will also be steel, protected against corrosion and supported by steel brackets screwed to the eaves purlins whilst the ridge is secured to the steel cladding via the screws to the purlins in the roof. The wall cladding will be fixed vertically at the columns for the weather functionality and the eaves need to be closed to prevent leakage.

I will have a masonry brick and block wall 3m high built around the steel structure for increased security and a change in effect for aesthetics. I will install a window in the middle of every portal frame from 150mm off the ground to the bottom of the steel cladding which will make the warehouse more open and inviting.

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Bibliography

(Emmitt and Gorse, 2010A) Emmitt S and Gorse C, 2010; Barry’s introduction to construction of buildings; Wiley-Blackwell

(Emmitt and Gorse, 2010B) Emmitt S and Gorse C, 2010; Barry’s advanced construction of buildings; Wiley-Blackwell

(Bird V, 2011A) Foundations 1 accessed at 28/11/12

(Bird V, 2011B) Roofs and insulation accessed at 7/12/12

(Bird V, 2011C) Industrial roofs accessed at 8/12/12

(Lecture notes A 2012) Powerpoint and notes from lecture Ground and foundations V Bird 2012

(Lecture notes B 2012) Powerpoint and notes from lecture Floors J Merriman 2012

(RIBA) RIBA, Roofing technical review accessed at

(BR Part E) Building Regulations Part E 2004; NBS; at http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_E_2010.pdf accessed 6/12/12

(ODPM, 2002 B, Appendix A, Table A2) Source taken from Emmitt and Gorse, 2010B p.164

(BR Part A) Source taken from Emmitt and Gorse, 2010A p.51

(BR Part F) Source taken from Emmitt and Gorse, 2010A p.351

(Homes in Havering pdf) at http://www.homesinhavering.org/CHttpHandler.ashx?id=18387&p=0 accessed 29/11/12

(Klober.co.uk) 2010 at http://www.klober.co.uk/products.php?productsID=81&products=Permo%AE%20forte, accessed 2/12/12

(Autonopedia.org) 2010 at http://autonopedia.org/buildings_and_shelter/Rural_Building/Hardcore_Filling.html accessed at 5/12/12

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Pct assignment