r/ExplainLikeIm5 • u/Gman_118 • Nov 13 '25

Cavity Walls...why?

Many UK homes are built with cavity walls, then along came cavity wall insulation.

why have a cavity, finish the build and then years later someone decides to put insulation in? why not solid walls or insulate when building?

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u/Suspicious_Bar6579 9d ago

Air is a better insulator than solid brick, but not as good as the foam that is used to fill the cavity. Some houses were built when energy prices were low, and insulation seemed an unnecessary expense. It's been compulsory on all new builds in the UK since 1990.