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IFM-01 07/97
LYNX TRUSSED RAFTERS
CONTRACTUAL RESPONSIBILITIES
GUIDANCE NOTES FOR T.F.S. CLIENTS
General
Timber Frame Services Ltd. wish to draw the attention of their customers to the areas of responsibility we accept with respect to the supply of products and services.
In addition we make reference to definitions, which we consider are important for our Customers to be aware of.
Timber Frame Services Ltd. requires details to be approved in writing before manufacture.
Definitions
The British Standard for Trussed Rafter Roofs, BS5268:Part 3:1985, defines the responsibilities of the “Building Designer” and “Trussed Rafter Designer”. In some projects a “Roof Designer” may also be involved. To assist in the understanding of the various roles, their areas of responsibility are defined in a Technical Handbook published by the Trussed Rafter Association (TRA). We include relevant extracts of this publication for our Customers information only.
We draw our Customers attention to the need for the “Building Designer” to be defined in order that the recommendations of BS5268:Part 3 are followed.
NOTE: Timber Frame Services Ltd. never adopt the role of Building Designer.
Manufacture and Supply of trussed Rafters Only
Timber Frame Services Ltd., as the Truss Designer take responsibility for their products (the prefabricated timber trusses) being manufactured and designed in accordance with the relevant sections of BS5268:Part 3.
We warrant that in the event of questions arising as a result of claimed faulty design or manufacture, we will investigate and make every effort to remedy matters to the satisfaction of our Customers.
Design and manufacture, however, is based upon information received from the Customer being correct at the time of placing the order. In designing to BS5268:Part 3 we comply with Section Ten and consider it is necessary for our Customers to be aware of the full implications of this Section. In particular, we draw our Customers attention to Clause 46.3 of this Section which requires a check to be made. (See this section reproduced below)
46.3 Information Required by The Client
The trussed rafter designer or fabricator should provide the client or his agent with the following information, preferably on detailed drawings, to enable a check to be made that the trussed rafters are suitable for their intended use:
a) Finished sizes, species, stress grades or strength classes of members.
b) The type, sizes and positions of all jointing devices with tolerances or the number of effective teeth or nails required in each member at each joint.
c) The positions and sizes of all bearings.
d) Loadings and other conditions for which the trussed rafters are designed.
e) The spacing, spans, pitches and any other relevant dimensional information.
f) The positions, fixings and sizes of any lateral supports necessary to prevent buckling of compression members such as rafters and struts.
NOTE: Details of the permanent bracing necessary to ensure the overall stability of the complete roof structure and supporting walls should be provided by the Building Designer.
g) The method of support for tanks and ancillary equipment together with the capacity or magnitude of additional load assumed.
h) The range of reactions to be accommodated at the support positions including those required to resist wind uplift forces.
i) The basis of design.
j) Details of any changes in spacing to accommodate chimneys or openings.
k) Any special precautions for handling and erection, in addition to those covered by by this Part of BS5268.
As Part 3 is referred to as an Approved Document under the Building Regulations, we consider compliance to be both essential and protective of both Customer and Supplier.
In the event that the Customer is uncertain as to the information listed in 46.1 of Section Ten, we will be pleased to assist.
46 Designer, Fabricator and Client
46.1 General
To ensure that trussed rafters are correctly designed and fabricated, and that they are suitable for their intended purpose it is necessary for them to be accurately specified and for adequate information to be available when required.
46.2 Information Required by Trussed Rafter Designer and Fabricator
The following information should be provided by the client or his agent:-
a) The height and location of building with reference to any unusual wind conditions.
b) The profile of the trussed rafter including camber if required.
c) The span of the trussed rafter.
d) The pitch or pitches of the roof.
e) The method of support and position of supports.
f) The type or weights of roof tiles of covering, including sarking, insulation and ceiling materials.
g) The size and position of any water tanks or other equipment to be supported on the trussed rafters.
h) The overhang of rafters at eaves and other eaves details.
i) The positions and dimensions of hatches, chimneys, and other openings.
j) The service use of the building with reference to any unusual environmental conditions & the type of preservative treatment where required.
k) The spacing of trussed rafters and special timber sizes where these are required to match existing construction.
Whole Roof Design and Supply
Timber Frame Services Ltd. offer this service and whenever entering into a contract to design and supply the whole roof, we adopt the role of the “Roof Designer” thus relieving the “Building Designer” of his responsibility for the roof design.
As Roof Designer we accept responsibility to provide a design and supply all structural elements of the roof necessary to form a three-dimensionally stable trussed rafter structure, which may be erected off the top of the wall plates to resist all vertical and lateral loads imposed upon the roof.
This service would therefore include the design, detailing and location of all trusses, loose infill timbers, roof stability bracing, and carpenters metalwork.
We do not include in this service the supply of wall plate, fascia, soffit, valley boards, wind girders or any fixings to the structural masonry except for gable end restraint strapping.
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