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Pitched roof: insulated between & below rafters - with Quinn Therm QR & QL-Kraft

Benefits

  • Suitable for new build and refurbishment projects
  • Quinn Therm QR rigid insulation is well suited to use in warm roof constructions whether on new build or on refurbishment projects
  • The low thermal conductivity of Quinn Therm QR insulation boards enables the required U-value to be
    achieved with a minimum thickness of insulation, which, in turn, minimises the thickness of insulation
    required beneath the rafters
  • The low emissivity facings of Quinn Therm QR increase the thermal resistance of the air space above the insulation, improving the overall thermal performance of the roof
  • Using Quinn Therm QL-Kraft insulated plasterboard as the under-rafter insulation speeds up the installation process

Design and Installation

Insulating a pitched roof at rafter line - to create what is usually known as a warm roof - makes full use of the building volume by making the roof space available for occupation.

Installing part of the insulation between the rafters reduces the depth of insulation required beneath the rafters, which minimises the loss of headroom.

To avoid interstitial condensation the roof structure should be progressively more vapour open from inside to outside. For new build, this can be achieved by specifying a vapour open underlay. In refurbishments where the roof covering is not being replaced, 50 mm vented air spaces should be maintained between the insulation and underlay.

The foil facing on the rear of Quinn Therm QL-Kraft has a very high vapour resistance and can be formed into an AVCL by sealing the joists between boards: set the boards onto a wide (30mm) bead of vapour resistant sealant
applied to the under surface of all the joints and cross noggins. Alternatively, a separate AVCL can be installed.

To limit heat loss and prevent problems such as condensation, mould growth and staining occurring at cold spots in the construction, insulation should be continuous at junctions between the roof and other elements,
particularly the eaves and gable. At eaves, wall insulation should be continued between the rafters until it butts the underside of the Quinn Therm QR boards. Where there is a cavity closer at the wall head the additional wall
insulation may be fixed to the wall plate.

Required thickness of Quinn Therm QR

New build: Quinn Therm QR and Quinn Therm QL-Kraft, unvented cavities

Quinn Therm QL-Kraft
Insulation below rafters
Quinn Therm QR Insulation between rafters (mm)
75 100 125 150 175
thickness (mm) U-value (W/m2K)
37.5 - 0.20 0.17 0.15 0.14
42.5 - 0.19 0.17 0.15 0.13
50.5 0.20 0.18 0.15 0.14 0.12
62.5 0.18 0.16 0.14 0.13 0.12
72.5 0.17 0.15 0.13 0.12 0.11
82.5 0.16 0.14 0.12 0.11 0.10
92.5 - 0.13 0.12 0.11 0.10

Refurbishment: Quinn Therm QR and Quinn Therm QL-Kraft, vented cavities

Quinn Therm QL-Kraft
Insulation below rafters
Quinn Therm QR Insulation between rafters (mm)
75 100 125 150 175
thickness (mm) U-value (W/m2K)
37.5 - - 0.19 0.16 0.15
42.5 - - 0.18 0.16 0.14
50.5 - 0.19 0.17 0.15 0.13
62.5 0.20 0.17 0.15 0.14 0.12
72.5 0.18 0.16 0.14 0.13 0.12
82.5 0.17 0.15 0.13 0.12 0.11
92.5 - 0.14 0.12 0.11 0.10


U-value results above based upon floor construction shown:
Quinn Therm QL-Kraft insulated plasterboard beneath rafters; 150mm deep rafters @400mm centres; Quinn Therm QR between rafters (new build); 50mm unvented cavity, vapour open underlay (refurbishment); 50mm vented cavity; bituminous underlay; large format concrete tiles. Calculations performed to BS EN ISO 6946, taking account of repeating thermal bridges.

Accrediations
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