Polycomp Products Limited

PART 1 - INTRODUCTION

Polythane is a PIR (polyisocyanurate) insulation for flat roofs by insulating between and below the rafters. Polythane rigid insulation is well suited to use in flat 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 minimizes the loss of headroom within the loft space.

PART 2 - TECHNICAL CHARACTERISTICS

2.1 Design Notes

• depending on the depth of the rafters and the required U-value, it may be necessary to install Polythane 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 metallised tape.
• 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.

2.2 Meeting Regulations

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

2.3 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 Polywarm plasterboard laminate, or Polythane 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 minimize thermal bridging and air leakage.

FIG

2.4 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 Polythane boards.

FIG

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 Polythane by taping the joints with metallised tape.

Condensation risk analysis should be conducted on all roofs using the method in ISO 13788:2001:

2.5 Fixings

Polythane 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 Polythane 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.

2.6 Key Properties

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

2.7 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 metallised tape.

PART 3 - INSTALLATION GUIDANCE

3.1 Polythane 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.

3.2 Polythane 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 metallised tape to form a VCL.
5. Fix internal finish to battens.

PART 4 - HANDLING AND STORAGE

4.1

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

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

Product Data
Board width x length	2400 x 1200 mm**
Board thickness	60 -200 mm
Board density	26 -32 kg/m3
Area per board	2.88 m2
Edge profiles available	Butt edged
**other sizes may be available upon request

Performance Data
Thermal conductivity*	0.022 - 0.023 W/mK
Water vapour resistivity	~ 400 MNs/gm
Compressive strength	> 120 kPa
*quoted in accordance with BS EN 13165:2001 "insulation for Buildings -factory made polyurethane foam products"

4.2 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 metallised tape.