Polyurethane foam can be used as a high performing insulant in self-build projects to meet or exceed today’s standards. When used for airtightness or stabilisation under the roof or within the cavity it outperforms most other materials.
For insulation purposes closed cell polyurethane should be chosen. This material is resistant to driving rain meaning that the material stays dry with no loss of thermal properties. The British Board of Agrément certification approves this insulant for cavity walls in all exposure zones. Closed cell foams which achieve a Class 1 fire rating when tested to BS476 Part 7 are available. Or, where non-Class 1 materials are used on internal applications these must be covered by plasterboard, or a similar thermal barrier.
Conversely, open cell polyurethane foams do not have the high insulation properties associated with the closed cell materials. They do not have the same fire performance as closed cell, so they should never be left exposed; they have no structural strength to stabilise roofs or walls. Open cell foam is useful in situations which require enhanced sound attenuation or to allow more air and vapour into a building’s interior.