Wall insulation is harder to get right than attic insulation – more cuts, more cold bridges, and tighter spots around pipes and outlets. Here's the easy method.
For a stud wall at 195 mm thickness, plan around 1 m³ of insulation per 5 m² of wall. Packs vary, but typically 1 pack per 4–5 m² of wall at 195 mm. Add 10 % waste for cuts around studs.
Net area = wall area minus studs and any windows/doors. On a typical stud wall the net area is about 80–85 % of gross.
Volume = area × thickness. 10 m² × 0.195 m = 1.95 m³ of insulation.
Packs typically cover 4–5 m² at 195 mm thickness – round up and add 10 % waste on top.
20 m² × 0.85 (net) = 17 m² net area. At 4.5 m² per pack that's 17 ÷ 4.5 = 3.8 → 4 packs. Add 10 % waste for cuts and you're at 5 packs.
Enter your wall area and thickness – the calculator works out packs with waste included.
Depends on the construction. Stud cavity wall: 195–245 mm typically. Cavity wall fill / external insulation: often 60–100 mm. Always check current building regs for your project.
Studs are cold bridges in themselves. The insulation between them should be unbroken. Tape and vapour barrier handle the rest.
Almost the same insulation value. Rock wool is slightly more fire-resistant and moisture-tolerant. Glass wool is often cheaper and lighter.
No – just the warm side. The cold side needs to breathe out, otherwise moisture builds up.
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