A quick-reference guide to what’s available, what it costs, and what’s currently funded.
Insulation options available in the UK
- Loft/roof insulation — mineral wool laid between and over joists (or PIR boards/spray foam at rafter level for converted lofts)
- Cavity wall insulation — injected mineral wool, bonded bead, or foam through drilled holes in the outer leaf (post-1920s cavity walls)
- Solid wall insulation — external (board + render/cladding) or internal (dry-lining), for pre-1930s solid-wall homes
- Floor insulation — mineral wool batts between joists (suspended timber floors) or rigid boards above the slab (solid concrete floors)
- Draught-proofing — seals around doors, windows, letterboxes, and loft hatches
- Loft hatch insulation — an often-overlooked measure; an insulated hatch cover can reduce heat loss through the loft opening by up to 25%
- Double/triple glazing — window replacement to cut heat loss and draughts through the glass
- Hot water cylinder jackets & pipe lagging — simple DIY measures for unheated spaces like lofts and garages
Costs, savings and current grant status (2026)
| Insulation type | Typical installed cost (avg semi) | Annual saving (est.) | Payback | Grant status (2026) |
|---|---|---|---|---|
| Loft insulation top-up (mineral wool, 270mm) | £300–£500 in materials | £150–£250/year | 2–5 years | Often funded via ECO4 for eligible households |
| Cavity wall insulation | Around £2,700 | Meaningful; often paid back within five years | ~5 years | Funded via Warm Homes Local Grant / ECO4 where eligible |
| External wall insulation | Highest of all measures (scaffolding + render) | Largest single saving for solid-wall homes | 10+ years unfunded | Grants via HUG2, SHDF Wave 3, ECO4, Warm Homes Plan |
| Internal wall insulation | Mid-range, no scaffolding cost | Similar thermal gain to external, more disruption inside | Similar to external | Same grant routes as external, where applicable |
| Floor insulation | Lower than wall/roof work | Smaller than walls/roof but still worthwhile | Longer | Rarely grant-funded on its own |
| Draught-proofing | A few hundred pounds or less (often DIY) | Modest but immediate comfort gain | Under 2 years | Not typically grant-funded; too cheap to need it |
| Double glazing (full house) | £3,000–£7,000 | Around £120/year | 25+ years | Not part of standard insulation grants |
Grant scheme status — key dates
- Great British Insulation Scheme — closed 31 March 2026. Check any content still describing it as open.
- ECO4 — scheduled to end 31 December 2026. Still live, but on a countdown
- Warm Homes Plan / Warm Homes: Local Grant — the current routes to check alongside ECO4 before the end-of-year deadline.
- Warmer Homes Scotland — Scotland’s own scheme, funded by the Scottish Government, separate from the UK-wide schemes above.
Spray foam and mortgages
4 of 6 major UK lenders now require a roof-timber moisture survey on spray-foamed lofts, and 4 of 6 refuse open-cell foam outright. Closed-cell foam is mortgageable but flagged for a surveyor’s report. This is a gentle caution for anyone about to choose spray foam over mineral wool or PIR.
Notes: costs and savings are estimates for a gas-heated, semi-detached house and will vary by property size, construction, and location. Grant scheme details change fairly often — verify current eligibility and deadlines before applying.