What’s in an EWI Quote? Every Line Explained

Why quotes for the same house look so different

External wall insulation is a system, not a product. The board is the cheap part; the labour-heavy work is in the preparation, the render build-up and the detailing around every window, door, pipe and eave. When one quote is far cheaper than the rest, it is usually because whole categories of that work are silently excluded — not because the installer has found a cleverer way to fix boards to a wall.

The honest arithmetic looks like this. Our headline system rate is £130–£140/m² — board, basecoat, mesh and render on a clear wall. But when we measure our completed, installed jobs and divide the final invoice by the treated area, they come out at £176–£232/m² all-in. The gap between those two figures is scaffolding, beads, reveals, sills, rainwater goods and making good. Every installer has that gap; the only question is whether it is printed on the quote or discovered mid-job. You can see the underlying data in our 2026 London price report.

Before any boards go on: survey, scaffold, preparation

Survey and design

A proper quote starts with someone measuring your actual elevations, checking the substrate (render condition, blown patches, hollow-sounding areas), noting every penetration — flues, vents, waste pipes, cables — and confirming the wall construction. If your quote arrived from a photo and a postcode, the surprises are still to come.

Scaffolding

Scaffolding appears on 88 of our quotes. For a two-storey house it is unavoidable and it is a significant line — priced by elevations, height and access, not by wall area. We cover why in our guide to scaffolding and access costs. A quote that omits it for a two-storey property is incomplete, full stop.

Substrate preparation

Boards need a sound, reasonably flat wall. Preparation can mean hacking off failed render, treating organic growth, filling voids or fitting a starter track perfectly level around the whole building — the starter track sets the line for every board above it, so an installer who rushes this hour pays for it for the rest of the job. Look for a preparation line, even a small one.

The insulation system: boards, adhesive, fixings

The quote should name the board and its thickness. We install EPS (on 128 of our quotes) and ROCKWOOL mineral wool (on 126), plus wood-fibre systems where breathability matters — see EPS vs mineral wool for the honest comparison. “100mm insulation” with no manufacturer or board type named is a red flag: you cannot verify the thermal performance, the fire classification or the warranty of an unnamed board.

• Adhesive: boards are bedded in adhesive, applied so there are no continuous vertical joints and corners are toothed together.
• Mechanical fixings: supplementary fixings through the board into the wall. The count per m² comes from the system design and the building’s exposure — more at corners, where wind load is highest. A quote with adhesive only, on a tall or exposed elevation, is under-specified.

One detail only installers tend to mention: board joints must never line up with the corners of window and door openings, because that is exactly where render cracks start. Boards are cut in an L-shape around openings instead. It costs nothing extra when done from the start and is unfixable afterwards without opening the render.

Basecoat, mesh, beads and the render finish

The render is what you look at for the next 25 years, and it appears in detail on 98 of our quotes. It is a multi-layer build-up, and each layer should be visible on the quote:

• Basecoat with embedded reinforcing mesh: the structural skin of the system. The alkali-resistant glass-fibre mesh is bedded into the wet basecoat with generous overlaps, plus extra diagonal “stress patches” at the corners of every opening. Skip the mesh and the render will map every board joint within a few winters.
• Beads and stops: corner beads, drip beads over openings so water sheds clear rather than tracking back to the frame, movement beads on long runs, and stop beads wherever the system ends — at a party-wall boundary, a roofline or a change of material. These are small-money items that decide whether edges stay crisp and dry.
• Finish coat: the named topcoat — we install Licata render systems — with the texture and colour specified in writing. Silicone, mineral and acrylic finishes behave differently; our render systems guide compares them.

Reveals, sills, rainwater goods and making good

This is the section that separates a system from a finished job — and the section most often missing from cheap quotes.

• Window reveals and sills (on 33 of our quotes): thinner insulation boards returned into every reveal, and sills extended or replaced so they overhang the new, thicker wall. Skipped reveals leave a cold frame of brick around every window — the classic mould line. Our reveals and sills guide covers this in depth.
• Gutters, downpipes, soffits (rainwater goods appear on 80 of our quotes; soffits, fascias and eaves on 24): adding 100mm or more to a wall moves everything attached to it. Downpipes need extending brackets or re-routing; eaves may need extending so the roof still oversails the wall. See what EWI does to the outside of your house.
• Making good: reinstating anything disturbed — external lights, satellite brackets, boiler flue extensions, paths and beds under the scaffold. Cheap quotes assume you will not notice this is absent until the installer has left.

What the suspiciously cheap quote leaves out

When we are asked to compare our quote with one 30–40% cheaper, the missing items are nearly always the same:

• No named board or manufacturer, or a thinner board than discussed.
• Adhesive-only fixing, no mechanical fixings specified.
• “Render” as one word — no basecoat, no mesh, no beads.
• Reveals and sills not mentioned at all.
• Scaffolding “by others” or absent.
• No rainwater alterations, no making good, no waste disposal.
• No warranty or guarantee terms in writing.

The honest caveat: a cheaper quote is not automatically a con. A single-elevation job genuinely costs far less than a whole house, and a plain rear wall with no windows is cheaper per m² than a detailed front. Compare scope line by line before comparing totals — if a line is missing, ask for it in writing. An installer who meant to include it will add it without fuss; one who did not will start negotiating.

If you want a benchmark to compare against, get a free, fixed, itemised quote from us — every line above will be on it, priced, with nothing left to discover later. Or start with our external wall insulation service page to see how we run the job itself.

EWI quote FAQs