With attic trussed rafters, prefabricated in a factory (now so commonly and economically available), a roof replacement is a much simpler and quicker operation than may at first be thought. Most trussed rafter manufacturers can provide a 'whole' roof design service, supplying not only the individual trussed rafters but also any girder trussed rafters, probably pre-nailed in the factory, together with all the necessary infill timber work and connecting light steel fabrications. Properly organised and planned, the stripping of the existing roof and the installation of an attic roof structure by crane is probably no more than a 2-day operation. If possible, the existing ceiling of the building below should be left in place, perhaps with some temporary support, and a contingency for weatherproofing will undoubtedly have to be considered.
Now, with the panel, insulated panel and cassette constructions available as reviewed in Chapter 4, the replacement option is even faster and offers instant waterproofing without even felt and battens in place. Whilst it is best to use mechanical lifting for the systems, the more simple basic panel designs could be manhandled into position, taking account of health and safety and manual handling recommendations and also the Work at Height Regulations. A competent DIY team could tackle such work providing that a good set of technical drawings had been supplied with the roof structure package. If it is not the intention to use a crane, it may be practical to dismantle part of the existing roof and replace it with the attic structure, providing felt and battens to the new attic area and thus reducing the temporary weatherproof-ing problems which will inevitably occur.
A method of attic construction known as Spatial Roof, is now available which allows fast construction of the floor and the attic roof. Although designed for new-build it is suitable for roof replacement whilst leaving the existing ceiling and its ceiling joists in place. Full details of this are described in Chapter 4 complete with illustration. This method provides a simple construction yet takes advantage of the very latest engineered timber technology. It provides a quickly assembled engineered waterproof floor diaphragm, which provides a safe working platform from which to assemble and erect the prefabricated lightweight attic truss components. This method is eminently suitable for knowledgeable DIY, as most components do not require mechanical handling.
Clearly, the roof replacement option is one which is best carried out at such times as before somebody moves into a new home, or in a building which can at least be temporarily vacated. Using this particular option, it will probably be practical to construct the new attic structure, completing the installation of dormers, weather-proofings, retiling, making good or extending up gable ends and carrying out much of the internal work before penetrating through the existing ceiling into the building below. This, of course, will keep disturbance to a minimum.
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