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Pitched roofs between & below rafters

Key Properties

QUINN-therm

  • does not readily absorb water, making it suitable for use in damp environments;
  • is light, robust and easy to handle; it may be worked using a saw or sharp knife;
  • is durable and will perform for the service life of the building.


Meeting Regulations


Required thicknesses of QUINN-therm QR (mm)
U-value (W/m2K) 0.25 0.20 0.18 0.16 0.14
Between Rafters 65 100 100 100 100
Below Rafters 25 25 40 55 75

Results based upon roof construction of:
12.5mm plasterboard, polyethylene VCL, 150mm deep rafters at 600mm centres, QUINN-therm QR insulation between rafters, 50mm QUINN-therm QR insulation above rafters, vapour open underlay, 50mm cavity formed by counterbattens and battens, large format concrete tiles. Calculations performed to BS EN ISO 6946:1997, taking account of repeating thermal bridges.
* Overall heat loss method
For U-value calculations for other roof constructions contact Quinn Technical Services.


Design Notes

  • depending on the depth of the rafters and the required U-value, it may be necessary to install QUINN-therm QR between the rafters and below the rafters.
  • a vapour control layer is required behind the surface finish to prevent condensation forming within the structure: that may be formed by taping the joints between the metallic surface of the boards with metalised tape. Contact Quinn Technical Services for further advice on condensation control.
  • a vented cavity at least 50mm deep should be maintained between the underside of the underlay and the top of the insulation to prevent condensation.


Introduction

QUINN-therm QR (Quinn Roof) is a PIR (polyisocyanurate) insulation for creating warm pitched roofs by insulating between and below the rafters.

Insulating an existing pitched roof at rafter line - to create what is usually known as a warm roof - is an ideal way of increasing the usable space within the building without having to extend the structure. In projects where the loft space is being upgraded without removing the roof covering the insulation should be installed either in one layer between the rafters or in two layers, one between the rafters and the other fixed to the underside of the rafters (installing the insulation wholly between the rafters will in most cases result in insufficient headroom).

QUINN-therm QR rigid insulation is well suited to use in warm roof constructions: it is robust enough to span the rafters and will resist moisture. Also, its high thermal resistance enables the required U-value to be achieved with a minimum thickness of insulation, which minimises the loss of headroom within the loft space.


Design

Thermal bridging

To limit heat loss and prevent problems such as condensation, mould growth and staining occurring at cold spots in the construction, junctions between elements should be designed to maintain continuity of insulation. For roofs the key junctions are those at eaves and gable, where wall insulation should meet roof insulation.

The thermal performance of existing gable walls should be upgraded with an insulated dry-lining system, such as QUINN-therm QL plasterboard laminate, or QUINN-therm QW wall insulation installed with plasterboard. Junctions with the roof slope should be designed to give continuity of insulation and sealed to prevent air leakage.

Given space constraints within existing roofs, it is usual to insulate the stud walls rather than attempt to extend insulation between the rafters as far as the eaves. The junctions between the stud walls and the roof insulation should be sealed. The roof between the stud walls and the eaves should be insulated between the joists, taking care to maintain any ventilation paths at eaves and ensuring continuity of insulation with the stud walls.

The details shown here are designed to minimise thermal bridging and air leakage.


Condensation Control

In refurbishment and loft conversion projects the underlay is likely to be of bituminous felt, which has a very high vapour resistance. To prevent moisture from the occupied space condensing on the underside of the underlay and damaging the roof structure ventilated cavities at least 50mm deep must be maintained between underlay and the upper surface of the QUINN-therm QR boards (see BS 5250:2002 for details).


1.QUINN-therm insulation boards
2.Existing membrane
3.Battens fixed to rafters through insulation boards: plasterboard fixed to battens
4.Undercloak
5.Lead lining on section of vapour open underlay or building paper
6.Timber stud
7.Battens to secure vertical insulation boards
 
 
 
1.QUINN-therm insulation boards
2.Existing membrane
3.Battens fixed to rafters through insulation boards: plasterboard fixed to battens
4.Battens to secure vertical insulation boards
5.Lead lining on section of vapour open underlay or building paper
6.Timber stud

In some projects the rafters may not be deep enough to accommodate the insulation and the necessary cavity. The problem may be resolved either by increasing the depth of the rafter space by fixing 50mm x 50mm battens to the underside of the rafters or by installing some insulation between the rafters and the rest on the underside of the rafters.

To reduce vapour transfer through the roof structure there should be a vapour control layer behind the internal finish: that may be formed from the foil facing of the QUINN-therm QR boards by taping the joints with metalised tape.

Condensation risk analysis should be conducted on all roofs using the method in ISO 13788:2001: consult Quinn Technical Services for assistance.


Fixings

QUINN-therm QR boards fitted to the underside of the rafter should be fixed in place with 25mm deep timber battens nailed through to the rafters. The timber battens form a series of voids between the insulation and the surface finish which may be used for running services without disturbing the insulation. The voids, in combination with the low emissivity foil face of the boards will also improve the thermal performance of the roof by reducing radiation heat losses.

In stud walls the QUINN-therm QR boards should be cut to fit between the studs and fitted against timber battens nailed to the inside of the studs to prevent the insulation shifting out of place.


Installation Guidance

QUINN-therm QR boards between the rafters

  1. If necessary nail 50mm x 50mm battens to the undersides of the rafters to increase the available depth.
  2. Cut boards to fit snugly between the rafters.
  3. Insert boards between the rafters, ensuring there is a minimum 50mm gap between the underside of the underlay and the upper face of the boards.
  4. Install the VCL and internal finish.

* see guidance on condensation risk


QUINN-therm QR boards between and below the rafters

  1. Cut boards to fit snugly between the rafters.
  2. Insert boards between the rafters, ensuring there is a minimum 50mm gap between the underside of the underlay and the upper face of the boards.
  3. Fix the second layer of boards across the underside of the rafters using 25mm deep battens.
  4. Tape the board joints with metalised tape to form a VCL.
  5. Fix internal finish to battens.


QUINN-therm QR boards in stud walls

  1. Follow the sequences for fitting boards between or between and below the rafters, but nail timber battens to the studs behind the boards to keep them in place.


Product Data
Properties Value QUINN-therm QR
Board width x length mm 2400 x 1200**
Board thickness mm 60 - 200
Board density kg/m3 26 - 32
Area per board m2 2.88
Edge profiles available   Butt edged
 
Performance Data
Properties Value QUINN-therm QR
Thermal conductivity* W/mK 0.022 - 0.023
Water vapour resistivity MNs/gm ~ 400
Compressive strength kPa >120

* quoted in accordance with BS EN 13165:2001 ‘Thermal insulation for Buildings - factory made polyurethane foam products’.
** other sizes may be available upon request.


Key Properties

QUINN-therm QR consists of a core of PIR foam bonded on both faces to composite aluminium facings; the gas filled cells give QUINN-therm its high thermal performance and strength.

When QUINN-therm QR is installed next to an airspace of at least 25mm deep the low emissivity surface of the insulation contributes to the thermal performance of the roof by reducing radiation heat loss across the cavity.


Notes

  • Butt boards tightly together to form a continuous layer of insulation.
  • Cut boards neatly around penetrations. Seal gaps with expanding foam.
  • At wall/roof junctions fit boards tight to the wall and seal any gaps with expanding foam.
  • At junctions between roof planes and stud walls cut boards to fit tightly together and tape joints with metalised tape.


Handling & Storage

QUINN-therm QR boards are supplied in shrink-wrapped packs. Store boards under cover and out of direct sunlight, keeping boards flat. When handling QUINN-therm QR do not knock corners and edges.

Whilst QUINN-therm boards are robust, they are not designed to support people: do not stand on the boards nor use them as a working platform.


Accrediations
Aventas Group
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Contact

QUINN-therm
Scotchtown,
Ballyconnell,
Co. Cavan
Tel : +353 49 9525600
Fax : +353 49 9525601

UK Tel: 0845 602 6870
UK Fax: 0845 602 7880

E info@quinn-therm.com

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