Roofing: DIY or Sub Contract?

The real question is: 'How have your skills developed?' Do you feel confident about tackling the entire roof structure, which in many ways, is a quite separate exercise from foundation laying and shell construction? Creating the structure of the roof and fitting it into position is only one part of the process. There is, in addition, battening, felting and tiling or slating, all of which involve different skills and trades.

If you have developed a forte for joinery, you might want to produce the main framework and then leave the installation, felting and tiling to an outside agency. Alternatively, if you have found working at height uncomfortable or you are under pressure to complete the dwelling before winter sets in, you might prefer sub-contracting the whole of the roof. To find a qualified roofing contractor in your area, contact the National Federation of Roofing Contractors at 24 Weymouth Street , London , WIG 7LX or telephone them on 020 7436 0387. They also have a useful website at www.nfrc.co.uk that includes a wealth of information, technical advice and manufacturer details for roofing products and systems. Whichever route you choose, the following explanation of roof assembly stages and the work involved should prove helpful.

With a traditional roof, it is essential that the wall plate, purlins and ridge section are parallel with each other and level. To achieve this, check the Building Regulation approval for a description of how to bed and strap the wall plate down along the top of the finished walls. If any hip work is required, the wall plate will need to change direction, and plates should be strapped across the corner with a length of timber, so as to resist any outward thrust.

The construction drawings will indicate whether 'pad stones' are required for seating the purlins into position. These will help to spread the weight and, by using heavy-duty straps, the timber ends can be tied into the gable walls. The purlins must be level throughout their entire length and, as with joists, any curved edges must always face upwards. The rafters will have a tendency to slide down the roof slope, and it is important you prevent this by cross bracing above the highest purlins or notching the rafters over the purlins and/or the wall plate. All the relevant sizes for timber spacing and position will be detailed on the construction drawings. The size of rafters will also be described and, where they meet along the ridge at the topmost part of the roof carcass, a ridge-board needs to be installed, into which all the top ends of the rafters can then be secured with nails.

Cutting the upper parts of the rafters is best done on the ground before fixing them into position. Each saw-cut will be identical, so a template can be made and used to mark the position for subsequent cuts on each timber length. The lower end rafter cuts are more difficult because the timbers will already be fixed onto the roof structure. It is common practice to employ a line-band running along the edge of the rafters and then use a plumb-line to mark the vertical saw-cut position. It is essential all vertical cuts are equal and level because the fascia-board will be fixed onto the cut ends, thus providing a firm base on which guttering can be installed.

The method of bracing into gables and framing for eaves boards will all be indicated on the drawings. Builders will not normally require any additional information, as these aspects of the structure are not subject to building control inspection approval and the likelihood is that the builder will have undertaken this kind of work many times before. However, if you are an inexperienced self-builder, you probably will need more detailed guidance and your architect can supply it, providing they are made aware at an early stage that you intend doing all of the work yourself.