Insulation -Walls

The walls of the traditional houses of Cheltenham are overwhelmingly solid, consisting variously of render and stucco, dressed stone, rubble stone and brick, with the exception of post-war reconstructions which employ twentieth century building techniques such as cavity wall construction. As long as they are not exposed to driving rain, cavity walls are relatively easy to insulate because the cavity can be filled with an insulating material. Solid walls, on the other hand, are difficult to insulate because the insulation has to be installed on either the inside or the outside face of the wall and a new wall finish put on top. This is both technically complex and, in Cheltenham, aesthetically challenging.

Despite its problems, wall insulation is definitely worth considering, not least because 35% of heat loss is through the walls of an average unimproved home (though the share of heat loss is probably lower in the many terraced houses of Cheltenham because their design reduces the number of walls that are exposed to the outside). You basically have a choice between exterior or interior insulation. Each has its pros and cons: exterior insulation does a better job and is less disruptive during installation but has a major impact on how a building looks; interior insulation preserves the outward form of the building but changes the interior and is technically more problematic. Both tend to be expensive and disruptive to install.

There are some well-known risks involved in the installation of solid wall insulation in traditional buildings. These arise because the walls of traditional buildings are, to some extent, ‘moisture-permeable’. Unlike modern buildings, which are designed to keep moisture out of their walls, traditional walls work by absorbing moisture and then drying out through the action of the sun and the movement of internal air.

If you install wall insulation over the surface of a traditional wall, you will compromise its ability to sweat out any moisture within it. Moisture trapped within a wall will increase heat losses across the wall, encourage mould growth and potentially cause damage to timbers within the walls such as the ends of floor joists. These risks can be minimised with good design, appropriate materials and adequate ventilation. However, this is a complex issue and a careful assessment of the risks of damp within your walls must be made first. If you are considering installing wall insulation, seek professional advice.