Insulation in between rafters is an alternative to placing it above.
The following details show two possibilities, where if required
supplementary insulation can be secured to the underside of
rafters.
counter batten
insulation between rafters
vapour control layer
plasterboard inclined ceiling
Sealed Warm Roof
tile battens
tile batten rafter
vcl
plasterboard
Ventilated Cold
Roof (typical of
loft conversion)
vapour impermeable fibre-based
bituminous felt tiling underlay
50mm air space above insulation
insulation between rafters
breather membrane
or vapour
permeable tiling
underlay
Condensation can be controlled where a well sealed vapour control
layer (for instance, foil [metallised polyester] backed plasterboard)
is incorporated in the ceiling lining and used with a vapour
permeable (breather membrane) underlay to the tiling. Joints and
openings in the vcl ceiling (eg. cable or pipe penetrations) should
be sealed, but if this is impractical ventilation should be provided
to the underside of the tile underlay.
Pitched Roof--Insulation Between Rafters