Guides
Guides to insulation and render
Costs, rules and materials explained before you spend — checked October 2026.
How much does external wall insulation cost in 2026?
External wall insulation typically costs £105–£170 per m² of wall in 2026, plus scaffolding, depending mainly on the insulation board and the finish. A three-bed semi wit…
Is external wall insulation worth it?
External wall insulation is usually worth it on solid-walled and concrete houses that are hard to heat, especially when the outside needs re-rendering anyway. It's less w…
External vs internal wall insulation
External wall insulation usually performs better, keeps room sizes and renews the outside, but changes the look and needs scaffolding. Internal insulation keeps the façad…
EPS or mineral wool: which EWI board?
EPS is lighter, cheaper and slightly thinner for the same U-value, and is the usual choice on low-rise houses. Mineral wool is non-combustible, vapour-open and better for…
Do you need planning permission for external wall insulation?
For a house in England, external wall insulation is often permitted development if the finish looks similar to the existing walls. You'll usually need planning permission…
Building Regulations for wall insulation and re-rendering
In England and Wales, insulating, re-rendering or replastering more than half of a wall's area — or more than a quarter of the whole building's envelope — counts as renov…
Wall insulation grants in 2026
In 2026, funded wall insulation mainly comes from ECO4 (until 31 December 2026, for eligible households), Warm Homes: Local Grant schemes run by some English councils, Ho…
Is there VAT on external wall insulation?
Installing insulation for walls in residential accommodation is zero-rated for VAT in Great Britain from 1 April 2022 to 31 March 2027, and in Northern Ireland from 1 May…
Silicone, monocouche or acrylic render?
Silicone render is a thin, water-repellent, vapour-open finish that stays clean longest and is the usual finish over insulation. Monocouche is a thicker one-coat cement r…
How to tell if your house has solid or cavity walls
Measure the wall at a door or window: about 225mm (9 inches) usually means solid brick, while 260mm or more often means a cavity. On exposed brick, a pattern that shows t…
External wall insulation problems and how to avoid them
Most external wall insulation problems come from detailing rather than the insulation itself: cills too short, gaps around pipes, the system starting below the damp-proof…
Why is my render cracking?
Render cracks are usually caused by a mix that's too strong for the wall, water getting in at details, missing or corroded beads, movement in the building, or render appl…
Covering pebble dash: your options
Sound pebble dash can usually be rendered over (about £60–£95 per m²) or insulated over (about £110–£175 per m²) without removing it. Hollow or failing dash should be cut…
Non-traditional houses and external wall insulation
Most non-traditional houses — concrete, steel-framed or system-built homes from the 1940s to 1970s — have no fillable cavity, so external wall insulation is the usual way…
External wall insulation and fire safety
On houses, EWI systems with EPS or other combustible boards are widely used within tested systems. On taller buildings, the rules tighten: England bans combustible materi…
How long does external wall insulation take?
A typical semi-detached house takes about 2–4 weeks for external wall insulation, from scaffold going up to it coming down. Most render systems need temperatures of about…