Vapour-balanced 'breathing' construction
A vapour-balanced roof construction allows moisture to permeate, removing the need for
ventilation of the roof construction. The vapour resistance on the inside of the construction should be five times
that on the outside. The impervious roofing felt is replaced by 'breather felt'.The 50mm ventilation gap, the
soffit and ridge ventilators as well as the polythene vapour barrier are all omitted.
This simplifies the construction and leaves more space for insulation. However, as the existing roofing felt
must be replaced by the vapour-permeable type, all the existing slates (or tiles) and tiling battens must be
removed and replaced.