Typical detail (warm roof) ~
Where a roof space is used for habitable space, insulation must be
provided within the roof slope. Insulation above the rafters (as
shown) creates a warm roof', eliminating the need for continuous ventilation. Insulation placed between the rafters creates acold
roof', where a continuous 50 mm ventilation void above the
insulation will assist in the control of condensation, (see next
page).
Suitable rigid insulants include; low density polyisocyanurate (PIR)
foam, reinforced with long strand glass fibres, both faces bonded
to aluminium foil with joints aluminium foil taped on the upper
surface; high density mineral wool slabs over rafters with less
dense mineral wool between rafters.
An alternative location for the breather membrane is under the
counter battens. This is often preferred as the insulation board will
provide uniform support for the underlay. Otherwise, extra
insulation could be provided between the counter battens, retaining
sufficient space for the underlay to sag between rafter positions
to permit any rainwater penetration to drain to eaves.
Pitched Roof--Insulation Above Rafters