Rafters and Roof Overhangs

One job that had to be done this week was sanding and staining the rafters for the roof. For this we have had to keep the temperature in the house above 10ºC, when it’s been down to -15ºC outside, so the air heater inside has been vital. It’s somewhat ironic that keeping this temperature will be easy once we have the insulation on…

Some people might be wondering why we have rafters at all when we have a solid CLT roof structure already. The answer is simply that the rafters support the roof overhang that is necessary to shade the upper storey windows on the south side from the direct summer sun, which is vital to stop the house overheating, while maximising solar gain in the cooler months. Inside blinds etc. don’t actually prevent summer overheaing as well because, while they act as a barrier to light, they still allow heat in to the house, and outside blinds mean extra complications. The veranda roof will do the same for the lower storey windows. The overhang will also make the roof area larger which will enable us to maximise our solar power generation (when we eventually fit panels). Roof overhangs do many other useful jobs, however unfashionable they currently appear to be with architects who want their roof edges to be flush to the walls, largely for the sake of a ‘clean’ look.

Given that we don’t need them to support anything more than the overhang, our rafters are only short and are screwed into the CLT roof structure. The insulation will be cut to fit around them, and they will then be covered with a further top layer of wood fibre insulation, then wide strapping (which has to be able to hold down the insulation as well as having steel and eventually solar panels screwed into it), and finally the steel roof.

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