External wall insulation cost

External wall insulation, often shortened to EWI, is a system of insulation boards fixed to the outside of a wall, then covered with a reinforced base coat and a render or cladding finish. Because it is a complete system rather than a single material, published per m² prices vary widely depending on what each source includes. The table below shows the figures as published, with the date each page gave.

Checkatrade says its figures cover the insulation board, fixings, render or cladding and labour, and that most contractors include scaffolding, though not all do. Its table headers read 'Cost+VAT', and the page does not say whether that means VAT is included or added on top, so ask any installer to state VAT clearly. HomeBuilding's material figures are lower, and it lists render finishes separately, so check whether any quote you compare against them covers both the boards and the finish. The safest reading is that the sources describe different scopes of work, which is why a written quote matters more than any single figure.

The single biggest factor is the area of wall to be covered, after windows and doors are taken off. Beyond that, the type and thickness of insulation board makes a difference, with mineral wool usually priced above EPS in Checkatrade's figures. Mineral wool is often chosen where fire performance or breathability matters, while EPS is lighter and widely used on standard cavity and solid walls.

Detailing adds a surprising amount of time. Window sills usually need extending, downpipes, satellite dishes, meter boxes, outside lights and boiler flues have to be taken off and refitted, and the roof edge may need altering so the insulation is protected at the top. Houses with bay windows, porches or lots of corners take longer than a plain flat-fronted terrace.

The condition of the existing wall matters too. Loose render, failed pebbledash or damp problems need dealing with before boards can be fixed, and Checkatrade puts removal of existing external wall insulation at £30 to £40 per m². Labour is a large part of any quote, and FMB gives a figure of about £250 per day per tradesperson.

• Wall area and the number of elevations being insulated
• Insulation type and thickness needed to meet building regulations
• Preparation, including removing old render or pebbledash
• Sills, roof edges, pipework, flues and fittings to alter or refit
• Access, scaffolding and the height of the building
• The finish chosen, from standard render to brick slips

Almost every external wall insulation job on a house needs scaffolding, and it can run for several weeks while boards, base coats and finishes go on and cure. FMB puts scaffolding hire at around £625 a week, and HomeBuilding.co.uk suggests around £1,000 for a typical three-bed semi. Checkatrade says most contractors include scaffolding in their price, but not all do.

When you compare quotes, check whether scaffolding is included, how many weeks it covers and what happens if bad weather extends the job. Terraced houses with no side access or homes on steep plots can need more complex scaffolding, and a few properties need permission to place scaffolding on the pavement, which your installer or scaffolder should arrange.

Payback is hard to put a figure on, because it depends on how poorly insulated the walls are now, how you heat your home, what you pay for energy and how long you stay. Solid-walled houses tend to gain the most, since they have no cavity to fill, while a house with an already insulated cavity will see a much smaller change. For most homeowners, payback through lower bills alone takes many years, so the decision often rests on comfort, reducing condensation risk on cold walls and renewing a tired exterior at the same time.

If your household is on a low income or receives certain benefits, you may be able to get some or all of the work funded. Our guide to external wall insulation grants in Sussex explains ECO4 and the Warm Homes: Local Grant, and our pros and cons guide covers the wider trade-offs. You can then fill in our short form or call 01273 115520 for up to 3 free quotes from checked local plasterers, with no obligation.