Wall Insulation Choices

What this is

Walls are the largest single surface of most homes, and the right approach depends entirely on how the wall was built. A cavity wall has two leaves with a gap between them, and that gap can sometimes be filled. A solid wall has no gap, so insulation has to be added on one face or the other. Getting this identification right matters more than any product choice that follows.

Telling whether your home needs it

Cold internal wall surfaces, condensation appearing on external walls in winter, and rooms that cool quickly once heating stops all point at uninsulated walls. Wall construction can often be read from the brick pattern: a repeating pattern of short brick ends bonded through the wall usually indicates solid construction, while a uniform run of long faces more often indicates a cavity.

What the job involves

Cavity fill is injected through small drilled holes and is survey-led work, not a do-it-yourself job. Internal insulation means fixing insulated board to the inside face, then dealing with every skirting, socket, window reveal and radiator that the new surface meets. External insulation wraps the outside of the building and needs eaves, sills and door thresholds extended to suit.

Things to watch

Every one of these approaches changes where the wall is warm and where it is cold, which changes where moisture will condense. Junctions left uninsulated become cold spots that attract condensation and mould. Cavity fill is unsuitable where the wall is exposed to driving rain, where the cavity is narrow or already partly blocked, or where the outer leaf is in poor repair. This is a case where a survey before a decision saves a great deal of remedial work.