External wall insulation for solid-walled houses

It suits houses with solid walls, typically built before the 1920s or with non-traditional construction, where there is no cavity to fill. It keeps internal floor area, avoids disrupting rooms and covers the junctions where floors and internal walls meet the outer wall, which internal insulation struggles to treat.

It is a poor fit where the outside of the house is its main character: decorative brickwork, stone detailing or a street of matching frontages. Mid-terraces can have the rear done while the front stays unchanged, but then the job is partial. Walls that are damp because of defective gutters, leaking downpipes or high ground levels need fixing first; insulation is not a damp cure.

Outside protected areas, cladding a house does not normally need planning permission if the materials look similar to those the house was built with. In a conservation area, national park, Area of Outstanding Natural Beauty or the Broads, cladding the outside with render, stone, pebbledash, timber, plastic or tiles needs planning permission first. Listed buildings need listed building consent for significant works, inside or out. Article 4 directions can remove permitted development rights on particular streets.

If a wall stands on the boundary, the added thickness could project over your neighbour's land or the pavement. Settle that with the neighbour or the highway authority before work starts.

Approved Document B sets reaction-to-fire standards for the outer surface of external walls. On a house of 11 metres or less, walls less than one metre from the relevant boundary need a minimum fire classification, while those further away have no specific provision; residential buildings over 11 metres face much stricter requirements. Blocks of flats are a specialist area, and building owners should expect detailed fire engineering.

Rendering or cladding a quarter or more of an external wall normally triggers the thermal requirements of the Building Regulations. Approved Document L gives an improved U-value of 0.30 W/m²K for walls upgraded with internal or external insulation. Installers registered with a competent person scheme for external wall insulation can self-certify the work.

Window sills usually need extending so rain drips clear of the new, thicker wall. Downpipes, gas meters, satellite dishes, lights and air bricks have to be moved or extended. Air bricks that ventilate a suspended timber floor must stay open through the insulation. At the eaves, the insulation should meet the roof overhang; if the overhang is too short, the roof edge may need extending. At ground level, the system needs a proper starter track and should stay clear of damp ground.

Gaps at window reveals are the classic weak spot: skipping the reveals leaves cold strips where condensation and mould appear inside.

• insulation type and thickness, render or cladding finish and colour
• treatment of reveals, sills, eaves and the base of the wall
• moving pipes, meters, lights and air bricks
• scaffolding and any neighbour access needed
• planning or listed building consent, and Building Regulations route
• guarantee and who stands behind it

Installing insulation in a home is zero-rated for VAT until 31 March 2027. In Scotland, Home Energy Scotland offers a grant and loan towards solid wall insulation where your EPC recommends it; in England, the Warm Homes: Local Grant and ECO4 can fund wall insulation for eligible low-income households.

On Offrano, installers in your area see the request without your name or contact details, and only one firm can buy it. It pays us; you pay nothing. We email you its name, address and phone number before your details are released. There is no guarantee the request is taken, and you can get other quotes as well. Check the installer's registration with TrustMark or a competent person scheme yourself; Offrano does not inspect its work.

Source: gov.uk