Most modern roofs are constructed with trussed rafters. These are slightly cheaper than traditional cut roofs, but their main advantage is that they can be erected on site with relatively unskilled labour. Conversely constructing a traditional cut roof can be a highly skilled job. Most dormer roofs are more easily constructed as traditional cut roofs.

The main issue with this type of roof is that, unlike with trussed rafter roofs, internal supporting walls will be required if the length of the ridge is much more than around 6m. These walls should be at right angles to the ridge and they should be positioned so that they can support the roof purlins. This is not normally a problem, but is does need to be incorporated into the design of the building

We need the following information to design a traditional dormer roof:

a drawing or sketch showing the overall dimensions of the building and the position of any internal loadbearing walls

the height of the roof

the type of roof covering

the position of the dormers

the approximate location of the building

Design information

All design work is carried out in accordance with BS5268 (The structural use of timber).

The calculations provided will be suitable for Building Regulation approval.