External Wall Insulation Guides | Costs, Rules, Grants & Systems

Corner mock-up showing each layer of external wall insulation: brick, adhesive, board with anchor, mesh and render

What is external wall insulation and how does it work?

External wall insulation explained: the layers, how it is fixed, what it achieves and when it suits a home. Plain-Englis…

Bay-fronted 1930s semi finished in white silicone render with a grey plinth

How much does external wall insulation cost in 2026?

EWI costs in 2026: guide prices per m² by system and finish, whole-house ranges for terraces, semis, detached houses and…

Thermal image of two semi-detached houses: the uninsulated house glows orange, the insulated one shows cool blue

External vs internal wall insulation: which is right for you?

Compare external and internal wall insulation on cost, disruption, room size, cold bridging, planning and moisture risk,…

Mid-terrace house finished in pale grey insulated render between red brick neighbours

Do you need planning permission for external wall insulation?

When EWI needs planning permission in England, Wales, Scotland and Northern Ireland: similar appearance, conservation ar…

Surveyor using a thermal camera on a red brick semi-detached house at dusk

Building regulations for external wall insulation

How building regulations apply to EWI: renovating a thermal element and the 0.30 U-value in England, building control in…

Street of post-war semi-detached houses with matching grey and white insulated render

External wall insulation grants and funding in 2026

What funding is open for EWI in October 2026 across England, Wales, Scotland and Northern Ireland, and what has closed. …

Mineral wool insulation slabs being fixed to the blockwork of a three-storey block, with wrapped slabs on the scaffold

EPS vs mineral wool: which EWI board should you choose?

Compare EPS and mineral wool for external wall insulation: thickness, fire class, breathability, weight, noise and cost,…

Close-up of light grey textured silicone render at a crisp corner beside a window with a grey sill

Choosing a render finish for external wall insulation

How to choose the finish on your external wall insulation: silicone, mineral and silicate render, pebbledash, brick slip…

Insulating lime render being floated onto the rubble stone wall of an old cottage

Does external wall insulation cause damp?

When EWI causes damp and when it prevents it: detailing, ventilation, vapour-open systems for old walls, and the faults …

Grey graphite EPS insulation boards fixed to a red brick wall with white anchor discs, a spirit level on the scaffold

EWI U-values: how thick does external insulation need to be?

Typical U-values for solid walls before and after EWI, and the board thickness each insulation type needs to reach 0.30 …

Post-war concrete semi-detached house half clad in insulation and mesh under scaffolding, the other half showing panel joints

External wall insulation on non-traditional houses

Insulating system-built homes: no-fines concrete, precast concrete panel and steel-framed houses. What EWI can and can't…

Failed render and insulation boards being stripped from a damp-stained brick wall under scaffolding

Why external wall insulation fails, and how to avoid it

The detailing faults behind failed EWI, what the 2025 NAO and Ofgem audits found about ECO4 and GBIS installs, and what …

EWI guarantees, system certificates and installer schemes explained

What BBA and ETA system certificates, TrustMark, PAS 2030 and PAS 2035, INCA and SWIGA mean for external wall insulation…

Pallets of insulation boards, bags of render and buckets on a driveway beside a brick house

VAT on external wall insulation: 0% until March 2027

How VAT applies to EWI: the 0% rate on installing insulation in homes until 31 March 2027, the return to 5%, and why mat…

Three-storey block of flats in scaffolding with yellow mineral wool insulation and new white render

External wall insulation and fire safety

Fire rules for EWI: reaction-to-fire classes, the 1m boundary rule, the 11m and 18m thresholds in England, Scotland's 11…

Plasterer on a scaffold pressing reinforcing mesh into basecoat over white insulation boards on a brick house

How external wall insulation is installed, step by step

The EWI installation process from survey to sign-off: preparation, starter track, boards, anchors, mesh, render and deta…

Rear of a Victorian terraced house finished in pale grey insulated render with bins in the yard

External wall insulation for landlords: EPCs and rented homes

How external wall insulation helps landlords improve EPCs on solid-walled rental homes, the minimum energy efficiency st…

Guides to external wall insulation