Celotex Isover

Insulation for Upgrading Cavity Walls

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Masonry cavity walls as we understand them today have been around for about a century. Early cavity walls did not feature thermal insulation materials; the air space alone was relied upon for additional thermal performance. As national building regulations began to set target U-values for building elements, insulation materials started being used in the cavity - but not to the extent we see now.

In recent years, where assessment has shown it to be a suitable solution, many walls with a clear cavity have been filled retroactively. The performance of such a solution is dependent on the efficiency of the insulation material and the width of the cavity. Similarly, where walls were constructed with insulation, the performance is limited to the standards of the time.

For homeowners looking to improve the performance of their properties - perhaps to achieve compliance with modern building regulations, or perhaps to go beyond that and meet a retrofit standard such as EnerPhit - replacing or adding more insulation material in an already-treated cavity is not possible.

Using an insulated plasterboard product, either adhered to the masonry inner leaf or mechanically fixed to timber battens, represents an ideal option for improving the thermal efficiency of the wall. Lightweight polyisocyanurate (PIR) foam boards from Celotex are easy to handle, and their thermal efficiency means thicknesses can be kept to a minimum, reducing lost floor space.

As part of an holistic approach to upgrading you may also want to consider building fabric, airtightness and controlled ventilation along with improvements in thermal performance. The composite facing on the insulation board, behind the plasterboard layer, can form part of the air and vapour control layer when the tapered edge plasterboards are taped and jointed.

The building detail is for illustrative purposes only. It does not constitute advice and should not be relied upon.

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