External Wall Insulation (EWI) Explained

External wall insulation wraps a building in a continuous insulation layer, improving thermal performance while preserving internal space and reducing cold bridging at junctions. This guide covers the layers involved, suitable wall types, render and finish options, and the key installation details , including movement joints and window reveals , that determine long-term performance.

For the wall substrate and moisture context behind this system, see our Solid Wall Construction Explained guide. The government’s Approved Document L provides technical guidance on energy performance and insulation continuity.