BS 5268 Guidelines

7/29/2019 BS 5268 Guidelines

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MAIN CHANGES IS193 2006

DRAFT ISSUED FOR PUBLICCOMMENT JULY 2005

EARLIEST IMPLEMENTATION MID 2006

MOVES CLOSER TO BS 5268 Part 3

REFERENCES MORE ENs


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MINIMUM TIMBER THICKNESS 35mm TOCOMPLY WITH EN 1995 (EUROCODE95)

SPAN TABLES OMITTED ALL TRUSSES TO

BE DESIGNED

MAXIMUM BAY LENGTHS FOR EACH

TIMBER SIZE EFFECTIVELY GOVERNS

MAXIMUM SPANS FOR EACHCONFIGURATION


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PRINCIPAL GIRDERS

Girders supporting other girders, trusses,

or supporting a roof area more than 2.5

times the standard truss

CEILING TIE MUST BE BOLTED, OTHER

MEMBERS CAN BE NAILED

OTHER GIRDERS

Typically those in hip systems and multiple

trusses around openings of less than

2.4m width

ALL MEMBERS CAN BE NAILED


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REFERENCES PRODUCTION CODE EN

14250

AND FACTORY PRODUCTIONCONTROL (QA)


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SITE INFORMATION PACKAGEREQUIRED

TO INCLUDE;

ROOF PLAN SHOWING TRUSS LAYOUT

WITH TRUSSES LABELLED

NUMBER OF PLIES FOR MULTIPLE

TRUSSES


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LOADING FOR SLATES 0.400 kN / sq. m.INCLUDED

BRACING SIZE REDUCED FROM 2,500

sq. mm. TO 2,200 sq. mm

MINIMUM TARGET THICKNESS OF

25mm (25 x 88 mm.)


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SIGNIFICANT CHANGES TO BS5268

TIMBER QUALITY

Fissures greater than half the thickness are

only permitted at the ends of a member and

for a length not greater than the width of thepiece

NO LONG FISSURES ACCEPTED


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LOADING

To recognise the possibility of future conversion of

roof trusses where habitable room areas may be

provided, the designer should apply to the habitableroom area a minimum live load of 1. 5 kN/ sq. m. and

an appropriate dead load which should include an

allowance for partitions. In the absence of detailed

loading information a minimum floor dead load

allowance of 0. 55 kN / sq m should be used.

IF IT LOOKS LIKE AN ATTIC, LOAD IT

LIKE AN ATTIC


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LOADING

Unsupported eaves overhangs 600mm and above in

length, measured on plan, should be designed to

carry a concentrated load of 0.9kN 300mm from thetip of the overhang measured on plan


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LOADING

Ceiling tie loads for water tanks should be ;

2 x 0.45 kN for 230 or 300 litre tanks

2x 0.675 kN for 450 litre tanks

or design to specific requirements


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GIRDERS

Gaps greater than 3mm between chord members

should be packed with suitable material


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GIRDERS

Effective thickness of the girders shall be Kr x N x B

Where;

Kr 2 ply = 0.7

Kr 3 ply = 0.6

Kr 4 ply = 0.5

N = number of plies

B = thickness of each ply


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DESIGN RESPONSIBILITIES

It is important that the deflection of wind girders be

limited. To avoid structural damage to walls or wall

and ceiling finishes the Building Designer shouldprovide the trussed rafter manufacturer with the

maximum permitted deflection for the (wind) girders.

In the absence of any other guidance, it is suggested

that the maximum permitted deflection of wind

girders should be taken as 10mm

LIMIT DEFLECTION OF WIND GIRDERS TO

10mm MAX. UNLESS OTHERWISE

INSTRUCTED BY BUILDING DESIGNER


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STANDARD ROOF BRACING

ANNEX A NOW GIVES STANDARD

BRACING PATTERN FOR SPANS UP

TO 17M

APPLICABLE TO ALL BUILDINGS


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WALL PLATES AND TRUSS FIXINGS

Wall Plates

Wall plates less than 3m long in one piece

Wall plates longer than three metres can be in

two or more pieces but only two pieces can beshorter than 3.0m and none shorter than 1.5mlong.

TRUSS FIXING TO WALLPLATE

All trusses should be fixed using proprietarytypes of fixings nailed in accordance with themanufacturers requirements

SKEW NAILING OF TRUSSES TO WALLPLATE BANNED


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WATER TANKS

Platform should support tank over whole area

Platform should be minimum 18mm material

For 450 litre tanks, changed member size

minimum, maximum span for finks and

maximum bay sizes for other truss

configurations

All support members for tanks should be C16 orbetter


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FABRICATION

For trussed rafters manufactured with punched

metal plates fasteners the requirements on EN

14250 apply


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ERECTION

Under Damage between manufacture

and erection the new 5268 allows;In any chord or web member, bow of 0.003 of

member length or 20mm whichever is the lesser,

may remain after erection.


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INFORMATION TO BE PROVIDED BYTHE TRUSSED RAFTER

MANUFACTURER TO THE BUILDING

DESIGNER

Now includes;

The number, type, size and position of all

fasteners required to join girder trusses together

NAILING AND BOLTING DETAILS FOR

GIRDERS REQUIRED

Documents

BS 5268 Guidelines