Spray Foam Roof Insulation

Technical Overview

Failure to stop airflow through either the home, office or factory envelope means that new air constantly requires re-heating. Minimising areas where air can infiltrate helps to keep energy costs down. Research in America estimates that up to 40% of a typical home's energy waste is caused by air infiltration. Moisture and condensation have virtually no effect on sprayed polyurethane foam, which results in a cooler environment in summer and a warmer environment in winter.

Principally used as a stabilisation medium on pitched roofs, it forms a seamless weatherproof barrier stopping wind, driven rain, snow and dust. It contains no nutritive value and will prevent access to vermin and birds.

Technical Specifications

The polyurethane spray is a 2 compound system comprising isocyanate and resin in equal amounts. It is an open celled, spray applied semi rigid polyurethane foam system. Sprayed polyurethane foam cures within seconds of being sprayed and forms rigid foam. The spray foam is HCFC and CFC free and has zero ozone depletion potential. It is suitable for both internal and external roof applications and meets Part L of the Building Regulation Standards.

The application has a service temperature range of -15°C to 70°C.

Typical U Values

"U" FACTOR represents the measurement of the amount of heat which passes through a composite of materials (U heat loss). Typical foam thickness used in the encapsulation of domestic roofing materials achieves the following U values:

• 20mm .. U Value = .98
• 40mm .. U Value = .52
• 75mm .. U Value = .29
• 100mm .. U Value = .20 (recommended for new-build)
• 150mm .. U Value = .15

During installation the foam is sprayed to within 2" [50mm] of the eaves. This does not affect the U value but does allow for an acceptable airflow throughout the roof/loft space. The lower the U-value the greater the heat retention at a spray foam thickness of 40mm, there would be a need to incorporate the listed materials by the given percentage increase to achieve a comparable U-value and therefore the same degree of insulation but without either any degree of adhesion or increase to the stability of the roof.

• Polystyrene ..... 64mm ( 60%)
• Mineral Fibre .. 72mm ( 80%)
• Cork ................ 80mm (100%)
• Cellular Glass .. 88mm (120%)

However, all the alternatives listed above would be more difficult and time consuming to install. Each domestic spray foam installation is usually completed the same day providing minimal disruption with maximum benefit.

Moisture in Roof Timbers

Concerns and reservations about the product are often centred around the potential problems of water retention in the load bearing roof rafters that are partly encapsulated. These concerns are completely unfounded and have no scientific basis. On an average roof rafter measuring 100m x 75mm, 35% of the surface area is left exposed. This coupled with the fact that the polyurethane spray foam has the same ability to breathe as timber results in no greater moisture being transferred into the timbers once the installation has taken place.

Loft Conversion

In bonding tiles or slates to each other and to the load bearing timbers, ensures that the product insulates, stabilises the roof and eliminates condensation - all these factors make it ideal for the consideration of a low cost loft conversion.

The foam can either be covered with suitable boarding whilst ensuring adequate air flow or alternatively painted with an emulsion paint.