Question 1

How thick should wall insulation be?

Accepted Answer

In a temperate climate, 100–150 mm is typical depending on the wall; in colder regions 150–200 mm. The proper figure comes from a thermal calculation for the climate zone and wall build-up, but a 100 mm basalt slab plus cladding is often enough.

Question 2

Insulate from outside or inside?

Accepted Answer

Outside is the right way: it pushes the dew point out of the wall, keeps the room's floor area, and protects the wall from freezing. Inside insulation is a last resort (protected façades, etc.) and risks condensation and mould on the wall.

Question 3

Do I need a vapour barrier?

Accepted Answer

When insulating from inside, yes — on the room side, always. With external mineral wool, use a diffusion membrane outside and no vapour barrier, so the wool can breathe. Rigid XPS does not breathe, so it must be fully sealed.

Question 4

How many fixings do I need?

Accepted Answer

About 5–6 plastic anchor "mushrooms" per m², 10–12 mm into brick or 120+ mm into aerated concrete — so 25–30 per 5 m² pack, plus adhesive for the initial bond.

Question 5

When is the right season for façade work?

Accepted Answer

A wet-rendered façade needs at least +5°C, ideally +10°C. A ventilated rainscreen façade can be installed year-round at any temperature. Adhesive render must not freeze — it cracks on the first freeze cycle.

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