Question 1

How many packs of insulation do I need for a 20 m² floor?

Accepted Answer

For a 20 m² floor using mineral wool slabs (5.76 m² per pack) with 10% waste, you need 4 packs. The formula: ceiling((20 × 1.10) ÷ 5.76) = ceiling(3.82) = 4 packs. Coverage varies by product — always check the pack label.

Question 2

What is the difference between mineral wool rolls and slabs?

Accepted Answer

Mineral wool rolls are flexible and suit loft floors and large open areas between joists. Mineral wool slabs are semi-rigid and hold their shape better — ideal for walls, between rafters and vertical applications. Slabs are easier to cut precisely and less likely to sag over time.

Question 3

Do I need a vapour barrier with insulation?

Accepted Answer

In most cases yes, especially for floors and walls in cold climates. A vapour barrier prevents moisture from migrating into the insulation, which reduces its thermal performance over time. Install the barrier on the warm side of the insulation — typically the interior face.

Question 4

How much waste should I add for insulation?

Accepted Answer

Use 5% for simple rectangular areas with few cuts, 10% as standard for most rooms, and 15% for areas with many pipes, beams or awkward shapes that require lots of cutting. Insulation off-cuts cannot always be reused, so it is better to over-order slightly.

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