If your home was built before the 1920s, it almost certainly has solid walls — meaning no cavity between the inner and outer leaf of brick or stone. These walls have no insulation layer, and they account for a disproportionate share of your home’s heat loss. This article explains why, and what you can do about it.
A cavity wall — the standard construction from the 1920s onwards — consists of two layers of masonry with a gap between them. That cavity interrupts the path of heat conduction, and when filled with insulation, it provides a significant thermal barrier.
A solid wall has no cavity. Heat travels continuously from the warm interior, through the wall fabric, to the cold exterior. The rate of this heat transfer depends on the thermal resistance (R-Value) of the wall construction. An uninsulated single-skin solid masonry wall has an R-Value of around 0.18 m2K/W — very low. Heat passes through it with almost no resistance.
There are three main approaches to improving the thermal performance of solid walls:
At the standard 20mm ProofTherm base coat depth, ThermoSilicone increases the R-Value (Thermal Resistance) of a single-skin masonry wall from 0.18 to 0.738 m2K/W — a 310% improvement. At 30mm, the improvement is 406%.
Where external render replacement is not appropriate — for example, where external appearance is constrained by planning or the property is in a terrace where only the rear elevation can be treated — ProofTherm internal plaster provides the same insulating base coat applied to the internal wall face. No external works, no scaffolding, and the same 15-year warranty.