Should I be worried about fire risks when using Multifoil Insulation?

30/08/2017

Post-Grenfell, there has been concern from householders about the potential of their roof insulation materials to pose a fire risk. Although tower block cladding is a completely different scenario, it has highlighted concerns about exactly what fire tests materials undergo and how they are used.

What's designed to protect us?

In a domestic situation it is considered that the plasterboard used for lining rooms is what provides fire protection – usually for 30 minutes or more – and by the time it is spread beyond this then the wooden rafters will be on fire as well as any insulation. Externally, roof tiles are what provide the protection from an external source of fire, or from flaming materials landing from adjacent burning buildings. There can be no question that both plasterboard and roof tiles (or slates) have been exhaustively tested and are suitable for the job they do.

Should I be worried about fire risks when using multifoils?

How do Multifoils compare?

The BBA certificates for TLX Silver and TLX Gold confirm these points in the section “Behaviour in relation to fire”.

  • When installed with an internal lining board, e.g. 12.5 mm thick plasterboard, the insulation will be contained between the roof and internal lining board, until one is destroyed. Therefore, the insulation will not contribute to the development stage of a fire or present a smoke or toxic hazard.
  • The use of the products will not affect the fire rating obtained by tile or slated roofs.
  • The products will melt and shrink away from heat, but will burn in the presence of a naked flame.
  • When the products are used unsupported, there is a risk that fire can spread if it is accidentally ignited during maintenance works, e.g. by a roofer’s or plumber’s torch. Care should be taken during building and maintenance to avoid the material becoming ignited.

So fire risks can be avoided with commonsense: don’t have blow torches around rolls of the material stored prior to insulation or during building works, and keep the material the recommended distance away from any flues and heat-producing light fittings.

What do the regs say?

In the post-Grenfell discussions it is apparent that there is lack of understanding about what the Building Regulations cover and how they relate to materials testing.

Part B of the Building Regulations (Volume 1 – Dwelling Houses) has separate sections pertaining to

  • B1 Means of Warning and Escape
  • B2 Internal Fire Spread (linings)
  • B3 Internal Fire Spread (structure)
  • B4 External Fire Spread
  • B5 Access and Facilities for the Fire Service

Appendix A - performance of materials, products and structures:

So the Building Regulations deal with fire safety in buildings as a whole, and are aimed at limiting fire hazards. Standard fire tests, which assess the response of the material or product, do not measure fire hazard.

There are both European and UK classifications for testing the reaction to fire of the material, and they use different test methods. (None of these, however, involve placing a Bunsen burner underneath square of material to watch it ignite, as certain of our competitors would have you believe!) The tests assess how the material would contribute to the spread of fire, and how much heat is produced, as well as how combustible it is.

So using a multifoil as part of an insulation buildup above or below wooden rafters is not of itself a fire risk, as there is plasterboard below and roof tiles above to provide protection both internally and externally.

An aluminium foil isn't necessarily the answer

multifoil fireHowever, the presence of a sheet of conductive aluminium foil is not without issues. In the US, there is recognition that in the event of a lightning strike, having aluminium foil under the rafters creates a conductive pathway from the roof to earth down which the lightning current can pass, self-igniting the aluminium sheet and resulting in a major fire. Fortunately these are relatively rare occurrences in the UK.

Where there are multifoils with outer surfaces that are aluminium foil (rather than just aluminised plastic film as with TLX Silver) some manufacturers recommend that they are earthed, but really it is advisable to consult a qualified electrician as to whether the Wiring Regulations BS 7671 would require a protective earth bond to be fitted, as every building is different.

TLX Silver multifoil has an outer film with the metallisation only nanometres thick - just enough to provide a high reflectivity, but that won’t carry electrical current. It will not present any electrical issues either by conducting current in the event of contacting a live wire or by causing interference with mobile signals – it just fulfils its role in reflecting heat.

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