The choice depends on what sort of useful space you want to have in the roof. If you are designing a house with a cold roof (ie one that is primarily used for storage rather than living space) then you will probably want enough space to accommodate a cold water tank and any storage. You will also want to design sufficient headroom to move about comfortably in the loft – so about six foot in the centre.
The result of these considerations is that the normal pitch of the roof on a domestic property is between 300 and 450. This is also the ideal pitch for installing Solar PV.
