Estimate insulation costs for cavity walls, solid walls, floors and flat roofs by area and insulation type.
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How This Works
Cavity wall insulation (injected): cheapest at £10–20/m², often funded via ECO4. Solid wall insulation (external or internal): £50–150/m² depending on approach — external adds render finish, internal reduces room size. Floor insulation: rigid PIR boards between joists at £40–70/m². Flat roof insulation: above or below deck at £80–130/m².
Houses built after 1920 in England usually have cavity walls. Check by measuring the wall thickness: a cavity wall is typically 250–300mm thick (two skins of brick + 50–100mm cavity). A solid wall is 215–220mm (single brick) or 325mm+ (stone). You can also look at the brick pattern — cavity walls have an even stretcher bond (all bricks laid lengthways). Solid walls often show headers (bricks laid end-on) every few courses to tie the wall together.