Premier Mastic Asphalt

Thermal Insulation

The statutory requirements for the thermal insulation of roofs are set out in approved document L- Conservation of Fuel and Power to the Building Regulations 1991 (as amended).  This document requires roofs to have the following maximum U values.

Buildings other than dwellings

Dwellings

Residential

Other

 

0.25 W/m2k

0.25 W/m2k

0.25 W/m2k



These requirements are usually achieved by the inclusion of insulation boards beneath the waterproofing in a warm room system or above the waterproofing in a protected membrane system.

There are several types of insulation suitable for use in mastic asphalt roofing specifications.  The following types are the most frequently used.  All must be laid strictly in accordance with the manufacturer’s instruction.

POLYISOCYANURATE FOAMS

Suitable formulations of polyisocyanurate boards are available for use under mastic asphalt.  As mastic asphalt retains a high temperature for long periods after application the board used must be designed to maintain dimensional stability during the application and cooling of the asphalt.  It provides a substrate that is an ideal base for mastic asphalt.

CORK

Cork is resistant to moisture and decay and provides a substrate of good laminar strength making it an ideal base to receive mastic asphalt.

Cork/polyurethane foam composites boards provide good insulation within acceptable thickness limits.

CELLULAR GLASS

This type of board is non combustible, impermeable to water and can normally be laid without a vapour control layer.  The products high compressive strength makes it an ideal base for asphalt, particularly in situations where pedestrian traffic is anticipated.

When asphalt is applied over cellular glass insulation, two layers of non-bituminous building paper are required between the slabs and the sheathing felt to prevent adhesion.

PERLITE/POLYURETHANE

Perlite offers a high  level of dimensional stability with good fire resistance.  Perlite/Polyurethane composite boards provide a stable base for mastic asphalt together with good insulating properties.

EXTRUDED POLYSTYRENE

Extruded polystyrene is used in the Protected Membrane Roof system. Full details regarding the use of this type of board together with thermal insulation values are to be found under the Protected Membrane Roof system

 

TABLE OF THERMAL INSULATION VALUES

DECK: 150mm IN SITU CAST SLAB AND SCREED

Insulation

U-Value (W/m2k)

 

0.45

0.35

0.25

Polyisocyanurate foam

50mm

65mm

100mm

Cork / Polyurethane Composite

60mm

70mm

110mm

Cellular Glass

80mm

90mm

140mm

Perlite / Polyurethane Composite

60mm

70mm

110mm

DECK: 100mm PRECAST LIGHTWEIGHT CONCRETE UNITS

Insulation

U-Value (W/m2k)

 

0.45

0.35

0.25

Polyisocyanurate foam

35mm

50mm

90mm

Cork / Polyurethane Composite

50mm

60mm

100mm

Cellular Glass

70mm

90mm

130mm

Perlite / Polyurethane Composite

50mm

70mm

110mm

DECK: 19mm TONGUED AND GROOVED BOARDS

Insulation

U-Value (W/m2k)

 

0.45

0.35

0.25

Polyisocyanurate foam

50mm

65mm

100mm

Cork / Polyurethane Composite

60mm

70mm

110mm

Cellular Glass

70mm

90mm

140mm

Perlite / Polyurethane Composite

50mm

70mm

110mm

DECK: 50mm WOODWOOL SLAB

Insulation

U-Value (W/m2k)

 

0.45

0.35

0.25

Polyisocyanurate foam

40mm

55mm

90mm

Cork / Polyurethane Composite

50mm

70mm

100mm

Cellular Glass

60mm

90mm

130mm

Perlite / Polyurethane Composite

50mm

60mm

110mm

DECK: STEEL OR ALUMINIUM DECKING

Insulation

U-Value (W/m2k)

 

0.45

0.35

0.25

Polyisocyanurate foam

50mm

65mm

110mm

Cork / Polyurethane Composite

60mm

80mm

120mm

Cellular Glass

80mm

100mm

150mm

Perlite / Polyurethane Composite

60mm

80mm

120mm