Houses 116 & 117 fascias & rooves are going on as I post.
The cavity system creates a space between the wrapped framework & the back of the cladding this space allows air movement and moisture to escape
A few details_
- the presence of mold is reduced by ventilating the cavity space and thus lowering continual humidity
- when working out spacing you must take exterior cladding fixing requirements & space the cavity battens to meet those requirements
- timber battens must be treated to H3.2 unless the timber is primed or has isolating element like bituminous paper, best just to use H3.2 unless retrofitting
- cavity battens are fixed to studs on top the the building paper: to allow vertical moisture runoff
- if horizontal cavity blocks are used they must be fitted at a minimum slope of 5°
- expanded or extruded polystyrene may be used instead of timber and glued to the building wrap