Batten ends should be cut square and nails skew driven on each side of the joint. Not more than one batten in four should be joined over any one truss or rafter. Where proprietary eaves ventilators are used, they should be fixed in accordance with the manufacturer's instructions. All members should be accurately located. Purlins and binders should be built in, where necessary. In a typical traditional roof, the basic timber members are:

Conservative estimates would suggest there is somewhere in excess of 60 million trussed rafters in service in the UK. To date, there has been no known failure of a trussed rafter in its “ex factory” condition, a remarkable safety record. However, experience has shown that trussed rafters are not always well understood by the people who specify them or who erect them. Such misunderstanding can, in some circumstances, lead to poor installation or worse unsuitable alteration. Objective The system owner’s software is very sophisticated and not only designs the trusses, but also produces quotations, manufacturing information and production data. Advantages of Trussed Rafters For cold roofs that incorporate a low water vapour resistance (type LR) underlay, (e.g. a vapour permeable underlay) ridge or high level ventilation equivalent to a continuous opening of 5mm should be provided in accordance with the design. (b) underlays Two clips are used per roof truss. One is placed on either side, where the truss is fixed to the wall plate. Usually, the roof truss clip is installed on the inside wall plate. However, you can also fit these on the outside wall plate if the detail of the truss heel allows.

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Dormers should be framed up so they are independent of the window frame, using a suitable lintel over the opening. Where necessary to protect the heads of timber features, the underlay should extend 50mm beyond gable walls, bargeboards, etc.

Provides support to purlins to prevent deflection and to transfer roof loads to the load-bearing structure below. Ridge and hip tiles, for a distance of at least 900mm from the face of rigid masonry supports such as gables, abutments and separating walls, should be mechanically fixed. A truss clip should always be fitted vertically to a wall plate, never lying flat or horizontally. You must make use of every hole on the face of the roof truss clip, and nail all of these in. Some installers may only use four of the thirteen holes which are on the clip – this is not utilising the strength of the clip fully. STRUTS: give support to purlins to prevent deflection and transmit roof loading to loadbearing structure below.Cavity trays should be linked to the flashing to prevent water penetrating into an enclosed area where a: