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How to use this ManualThis manual is provided to give information aboutthe use of trussed rafters for roof construction and isintended to be of interest to Trussed RafterSpecifiers, Trussed Rafter Designers and Contractorsusing Trussed Rafters.

The manual is arranged in three sections:

SECTION 1Information for specifiers

SECTION 2Technical information

SECTION 3Information for site use

Trussed rafters are now used for the overwhelmingmajority of domestic roofs constructed in the UK andEire, and have an exceptional performance recordsince their introduction to the Building andConstruction Industries.

A nationwide network of Authorised Trussed RafterFabricators can provide a competitive, economicsolution to even the most complex of your roofingneeds. Using the MiTek Engineering Design System,these companies provide high quality, purposeengineered units to satisfy the need of an ever morecomplex market.

We are confident that this document will demonstratethe advantages to you in selection and buildingsuccessfully with trussed rafters.

SECTION 1 Information For Specifiers1.1 What is a trussed rafter?1.2 Design responsibilities1.3 Exchange of information1.4 Limits of use for trussed rafters1.5 Basic Design principles1.6 Guide to setting out and dimensioning1.7 Practical roof solutions1.8 Glossary of terms used

SECTION 2Technical Information2.1 Codes and standards2.2 Timber2.3 Connector plates2.4 Design method2.5 Roof and trussed rafter bracing2.6 Loading and load cases2.7 Selecting trussed rafter profiles2.8 Framing common roof shapes2.9 Connection details2.10 Problems to be aware of

SECTION 3Information for Site Use3.1 Do's and Dont's on site3.2 Supporting water tanks3.3 Hatch and chimney openings3.4 Two-Tier construction3.5 Hip ends and corners3.6 Valley intersections3.7 Bracing trussed rafters and roofs3.8 Loose timber connection details3.9 Bearing details3.10 Ventilation and condensation3.11 Site storage and handling3.12 Erection procedures3.13 Risk assessments & method statements3.14 Construction check list3.15 Nailing and bolting3.16 Attic Frames-2 & 3 part construction3.17 Attic Frames-bracing3.18 Attic Frames-environment3.19 General construction details3.20 Builders metalwork

This document is for general guidance only and the information contained in it is provided in good faith but without liability.MiTek Industries Limited gratefully acknowledge the provision of information from the Trussed Rafter Association.

MiTek Industries Limited

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Section1.1 Information for Specifiers

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What is a Trussed Rafter?Trussed rafters or roof trusses are now specified forthe majority of domestic roofs constructed in the UKand Eire. The trussed rafter is an individuallydesigned component, engineered to provide astructural frame for the support of roof or similarstructures.

Pre-fabricated from high quality, stress gradedtimbers and joined with steel nailplate fasteners, thetrussed rafter offers:

A flexible, practical and fully engineered solution toyour roofing requirements.

Economy of materials, as trussed rafters can use upto 40% less timber than a traditionally formed roof.

How to Specify Trussed Rafters

MiTek trussed rafters are available from anationwide network of Authorised Fabricators. A fulllist of these companies is available on request fromMiTek.

Please note that, unless a specific contract exists tothe contrary, the Fabricators liability is limited to thedesign and supply of the individual trussed raftercomponents only. The responsibility for the design ofthe roof structure as a whole lies with the BuildingDesigner (or Roof Designer if one has beenappointed). Please refer to section 1.2 on DesignResponsibility. There are, however, companieswithin the network of Authorised Fabricators thathave the necessary experience and resources toundertake design responsibility for the roof structureas a whole.

To obtain competitive quotations for the design andsupply of trussed rafters, contact one or more of theauthorised Fabricators. They will be pleased to assistyou in assessing your requirements.

Reduced labour costs on site, due to the amount ofpre-fabrications, releasing site joiners for morecomplex areas.

Quick erection of the roof structure enabling othertrades to commence quickly.

Reduction in site waste, loss and pilferage ofvaluable materials.

Space saving on site, with no need for timber storageor carpentry work areas.

Competitive pricing from a nationwide network ofAuthorised Trussed Rafter Fabricators.

The Fabricator will require sufficient, clearinformation regarding the roof structure to determinethe required trussed rafter profiles, dimensions,spacings, quantities, loadings, methods of supportand any special features to be taken into account;together with the requirements for timber treatment,extra items required (eg Builders metalwork),delivery date and delivery address. A check-list ofthe information required, together with a list of theinformation to be provided by the Fabricator to you,follows later in section 1.2.

Using the MiTek Design system, the required trusseswill be designed for your individual application andthe Fabricator will provide you with the detailsrequired to support the quotation.

If the quotation is successful, and subject to alldimensions being checked prior to the manufactureof the units, your trussed rafters will be supplied tosite ready for speedy erection of the roof supportstructure.

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Information for Specifiers

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Section1.1

The Project StepsTo illustrate the line of action for a project where trussed rafters are to be used, the following diagram may beof assistance:

Notes:On specific projects, the building designer may alsoencompass the function of Roof designer. This willgenerally be the case for small projects, where often,the Builder or his Architect will be the onlyprofessional people involved.

It is also possible for the roles of the Roof designer and the Trussed Rafter Fabricator to be combined, inthe case where, by specific contract, the fabricatortakes the responsibilities for the design of the wholeor part of the roof structure. This arrangement willhowever be generally undertaken by the Fabricatoron a professional, fee-paying basis.

Clienthas building to construct

Appoints

Architect, Engineer orContractor to act asBuilding Designer

Building DesignerDecides on required roofscape, anddecides trussed rafters provide the

economic solution

Approaches

If quotation successful, details confirmed,trussed rafters made and delivered.

Trussed Rafter FabricatorFabricator designs the required trusses

and provides a Quotation

Roof Designerdesigns TOTAL roof structure required

by Building Designer and returns detailsto give to Trussed Rafter Fabricator

for pricing

either: or:

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Section1.2 Information for Specifiers

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Design ResponsibilitiesThe areas of Design Responsibility for the roofstructure of a building are as follows:-

The Trussed Rafter Designer is responsible for thedesign of trussed rafters as individual components.

He or she must ensure the structural integrity of thetrussed rafter units and inform the Roof Designer (or

Building Designer where there is no specificallyappointed Roof Designer), of any stabilityrequirements needed in the design of the trussedrafters.

If the Building Designer has appointed a RoofDesigner, they are responsible for the design of theroof structure as a whole and must inform theBuilding Designer of all information pertinent to theroof regarding its interaction with the supportingstructure and adjacent elements of the building.

If no person is appointed specifically as the RoofDesigner it falls upon the Building Designer toundertake the responsibilities of the Roof Designer.

On every project it is essential that one personassume overall responsibility as Building Designer.

The Building Designer may be the owner of thebuilding, his appointed Architect, a StructuralEngineer appointed by the owner or Architect, or theContractor or Builder.

The Building Designer is responsible for providingthe information listed in Section: 1.3 (and in section11.1 of BS.5268-3) to the trussed rafter designer andfor ensuring adequate provision is made for thestability of the individual trussed rafters.

The Building Designer is responsible for detailing allelements of bracing required in the roof, includingthat necessary to provide the lateral restraints to trussmembers required by the Trussed Rafter Designer.

The Building Designer is also responsible fordetailing suitable fixings for both the trussed raftersand the wall plates to provide the restraint againstuplift required by the Trussed Rafter Designer.

1. Trussed Rafter Designer

2. Roof Designer

3. Building Designer

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Information for Specifiers

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Section1.3

Exchange of Information

Please refer also to BS.5268-3 Section 11

Information to be provided to the Trussed Rafter Designer by the Building Designer

Information to be provided by the Trussed Rafter Designer to the Building Designer

The Trussed Rafter Designer should provide the Building Designer with the following information, on suitablydetailed drawings, to enable a check to be made that trussed rafters supplied are suitable for their intended use:-

1. The position of