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A truss is so much more than the sum of its parts. Any alteration to a truss once manufactured is likely to be involved and costly. Surveyors and Inspectors need to be vigilant in spotting unauthorised alterations. Sin No 2 Unauthorised alterations Battens should be set out in straight lines, parallel to the ridge and to the gauge required by the tile or slate. The lap should not be decreased because this would reduce weathertightness. The lowest batten should be fixed so that the tile projects halfway across the gutter. Notes for specifiers and builders. The advice provided by trussed rafters manufacturers should be carefully adhered to and bracing in non standard situations should be applied. Sin No 4 Overloading / under loading
For any further information or prices please do call our national sales office. Buy Celotex Insulation fixings for fixing Pitched roof insulation currently unavailable Dormers should be framed up so they are independent of the window frame, using a suitable lintel over the opening. Restraint straps, or a restraining form of gable ladder, are required to provide stability to walls. They should be installed as shown in the design.A strip of underlay, at least 600mm wide, should be laid over hips and above the underlay to the main roof. Proprietary gutter or valley systems should be fixed in accordance with the manufacturer's recommendations. (e) flat roof intersection The guidance above will assist in reducing the risk of condensation occurring but is not acceptable as an alternative to cross ventilation of the roof space. Always be on the look out for existing roofs that seem to have substantial amount or significantly heavy items stored in them. Books and paper in particular create high loadings.
Where cheek framing does not extend to floor level, a double rafter will give necessary support to the cheek. The two rafters must be fixed together. To reduce the risk of freezing and condensation on pipework, the following precautions should be taken: Roof truss clips are metal components that are designed to safely and strongly fit roof trusses to wall plates. This resists wind uplift on the roof truss which avoids any damage by skew nailing.Where necessary to protect the heads of timber features, the underlay should extend 50mm beyond gable walls, bargeboards, etc. When using the following materials, the detailing and workmanship should follow the design and recognised good building practice:
Where bedded in 1:3 cement : sharp sand with plasticiser mortar the following tiles should also be nailed: 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 Most often, roof truss clips are included in your overall quote. However, should you need to buy these, you would be looking at a cost of around 25-40p per clip – a very minimal cost. This is a small price to pay to ensure your designs are validated and safe. Ridge and hip tiles are bedded in 1:3 cement : sharp sand with plasticiser mortar or mechanically fixed using a proprietary dry ridge fixing system following the manufacturer's instructions. The method shown in the design should always be used.
Sin No 1 Not Understanding how Trusses Function
All abutments should be weatherproofed using non-ferrous metal flashings. Lead flashings should be at least Code 4 (colour coded blue), while soakers are normally Code 3 (colour coded green). Normally, lead flashings should not exceed 1.5m in length, with laps of not less than 100mm. Detailed guidance on the use and handling of trussed rafters is given in the International Truss Plate Association Technical Handbook available from trussed rafter suppliers. Where a pitched roof abuts the wall at an angle, a stepped cavity tray linked to a stepped flashing should be used. 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: Trusses are made by some forty four manufacturing companies dotted around the country. Trusses are engineered to suit the particular application requested. The software used by each manufacturer will be supplied by one of three companies who also make the connector plates used to fasten the members together (often referred to as “the system owners”). The major System Owners are
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