Building Construction Handbook, Eighth Edition

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