Who we help · Houses
Semi-detached house
Usual measures: Loft, cavity (or extraction and refill), floor, EWI on side and rear. Watch-out: Match the neighbour's look on the front.
Typical prices
Semi / end-terrace prices
- Loft insulation (new or top-up)£600–£1,300
- Cavity wall insulation£1,200–£2,500
- Cavity extraction and refill£3,500–£7,500
- Suspended floor insulation£1,500–£4,500
- External wall insulation + render£14,000–£24,000
- EWI with brick slip finish£18,000–£32,000
- Draught-proofing£300–£800
Before grants · updated 11 October 2026 · a survey confirms the final figure.
Read the full guide: Semi-detached homes
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Construction, heat loss and watch-outs
- Typical construction
- Mostly 1920s–1970s cavity walls; some Victorian solid
- Where heat is lost
- Three exposed walls and roof
- Usual measures
- Loft, cavity (or extraction and refill), floor, EWI on side and rear
- Watch-outs
- Match the neighbour's look on the front
Recommended
The insulation we usually recommend
Loft insulation
Mineral wool laid between and across the joists to 270–300 mm so heat stays in the rooms below.
Cavity wall insulation
A borescope survey, then blown mineral wool or bonded bead injected into empty cavity walls.
Cavity wall extraction and refill
Failed, wet or slumped cavity insulation removed, wall ties checked, then refilled.
Suspended timber floor insulation
Mineral wool or rigid board between the joists with an airtight membrane.
External wall insulation (EWI)
A complete certified build-up of insulation board, mesh and render from one system holder.
EWI with brick slip finish
External wall insulation finished in brick slips so it looks like real brick.
Draught-proofing
Sealing doors, windows, letterboxes, hatches, floorboards and unused chimneys — every home's quick win.
Prices
Semi / end-terrace price column
| Measure | Semi / end-terrace |
|---|---|
| Loft insulation (new or top-up) | £600–£1,300 |
| Loft clearance and replacement | £1,500–£3,000 |
| Room-in-roof | £4,000–£9,000 |
| Cavity wall insulation | £1,200–£2,500 |
| Cavity extraction and refill | £3,500–£7,500 |
| Internal wall insulation (whole home) | £10,000–£20,000 |
| External wall insulation + render | £14,000–£24,000 |
| EWI with brick slip finish | £18,000–£32,000 |
| Re-render only (K Rend silicone) | £6,500–£12,000 |
| Suspended floor insulation | £1,500–£4,500 |
| Draught-proofing | £300–£800 |
| Whole-house fabric package | £22,000–£45,000 |
Indicative ranges for London and the South East, supplied and installed, including VAT, before grants. Updated 11 October 2026. A survey confirms your final price.
Grants and savings that may help
- ECO4Closes in 73 days
Up to fully funded; paid by energy suppliers per measure
Grant via local councils (£960m nationally in 2026/27)
- Social Housing Fund
Landlord-led bids
Saves 20% VAT
- Local schemes
Varies
Eligibility depends on your circumstances and is confirmed by evidence and the funder or council.
0% VAT on energy-saving materials
Insulation, solar panels, batteries and heat pumps installed in homes in Great Britain are zero-rated for VAT until 31 March 2027. Windows and doors are not included.Houses
Other property types
- Detached house
- End-of-terrace
- Mid-terrace
- Townhouse
- Mews house and cottage
- Detached bungalow
- Semi and terraced bungalow
- Chalet and dormer bungalow
- Period home
- 1930s home
- Post-war and ex-council house
- Non-traditional / system-built
- Listed building or conservation area
- Farmhouse, barn conversion or rural home
- New build or self-build
- Park and mobile home
- Every property type
Begin your project
Price insulation for your semi-detached house
See a price range for your property type in two minutes, with grants and 0% VAT applied where they fit. A survey always confirms the final figure.