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Insulation for Between Rafters

High performance PIR insulation boards for use in between rafters in loft conversions.

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Sometimes our buildings do not make life easy for us when it comes to retrofitting them. In trying to bring them up to modern standards, particularly in terms of insulation and thermal performance, we’re faced with the impossible task of applying modern materials and processes to a structure simply not designed for them.

Original pitched roof rafters might be no more than 75mm or 100mm deep, which is around half of the depth of modern rafters, and rarely offer the luxury of excess headroom below the rafters to play with.

The only solution becomes a compromise one, on the basis that some insulation is better than no insulation at all - as long as it achieves the maximum U-value, specified in the building regulations to avoid the risk of surface condensation.

Where there is only room for insulation between the rafters to achieve that target, it makes sense to use a thermally efficient material and derive the maximum benefit from minimum space. Rigid polyisocyanurate (PIR) foam insulation boards from Celotex are among the most thermally efficient, commonly available insulation materials on the market.

The boards are easy to handle and easy to cut. They come in a range of thicknesses to suit most rafter depths and can be fitted accurately between the structural timbers. Being lightweight, they do not impose substantial loads on existing roof structures, and the ceiling only need be lined with a plasterboard to finish.

Without an additional layer of insulation lining the underside of the roof structure, the cold bridging effect of the rafters can result in some pattern staining of the plasterboard finish. Wherever possible, use a between and under rafter solution for upgrading an existing roof.

 

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