Loft Insulation: Cost, Grants, the Right Depth and DIY Options

An uninsulated loft loses about a quarter of a home’s heat through the roof. Putting loft insulation in — or topping up a thin old layer — is still the cheapest big win in UK home energy: materials are inexpensive, the job takes a day, and the Energy Saving Trust puts the annual saving at around £250–£290 for a typical semi with a fully uninsulated loft.

This guide covers what loft insulation costs in 2026, the grants that replaced ECO4, how deep the layer needs to be, and where the DIY route is genuinely sensible.

Loft insulation cost: installer prices in 2026

Prices vary with loft size, access and how much clearing-out the fitters have to do, but for mineral wool laid to the full recommended depth these are realistic installed ranges:

Two things push quotes up fast: storage boarding (raised on stilts so the insulation isn’t squashed — roughly £15–£25 per m² extra) and downlight covers or pipe lagging, which any decent installer will insist on.

If a company quotes several thousand pounds for plain mineral wool in an accessible loft, get more quotes. TrustMark-registered installers are the safe baseline, and your local council’s retrofit partner list is often cheaper than the national lead-generation sites.

Loft insulation grants: what replaced ECO4

The two schemes that funded most free installs of the last few years — ECO4 and the Great British Insulation Scheme (GBIS) — both closed to new referrals at the end of March 2026. Their successor is the Warm Homes Plan, which took over as the main route to funded insulation from 2025/26.

What that means in practice:

• Low-income and benefit-receiving households remain the priority group. If anyone in the household receives a qualifying means-tested benefit, funded loft insulation is very likely still available — apply through the government’s Improve your home’s energy efficiency service or directly via your council.
• The council tax band + EPC route (band A–D homes with EPC D or worse) that GBIS used has broadly carried over for subsidised — not always free — measures.
• Social housing tenants should go through their landlord, who can access the Warm Homes Social Housing Fund.

Don’t pay a “grant agent”. Every legitimate route is free to apply to, and the installer is paid by the scheme, not by you.

The 270mm depth rule: how much loft insulation you need

The recommended depth for mineral wool in the UK is 270mm, usually laid as 100mm between the joists plus 170mm across them at right angles. Building regulations for new homes work to an equivalent performance, typically 270–300mm.

Depth matters because thin layers were the norm for decades:

• Pre-1982 homes often have no loft insulation at all.
• 1980s–90s installs are commonly 25–100mm — worth topping up, not ripping out. New rolls go straight over the old layer.
• 100mm → 270mm top-up still saves roughly £50–£70 a year for a semi, with materials often under £200.

Diminishing returns are real: going beyond 300mm rarely pays back. Spend the spare budget on draught-proofing the loft hatch instead — an insulated hatch with a compression seal is a £30 job that removes a surprisingly large cold spot.

One warning that applies to every depth: don’t block the eaves. Air must flow from the soffit vents across the roof space, so keep a 50mm gap at the edges or fit vent trays. A loft packed tight to the felt is how you get condensation and, eventually, rot.

DIY loft insulation: when it makes sense

Laying mineral wool is within reach of most people who can safely get into their loft. The DIY route makes sense when all of these are true:

1. The loft is empty or easily cleared, with safe access.
2. There’s no damp, no leaking felt, and no history of condensation.
3. Wiring is modern and any recessed downlights below get proper covers.
4. You’re laying rolls — blown or spray products are professional-only.

Buy rolls by the m² (measure the ceiling area of the rooms below and add 10%), wear a mask and gloves, and lay the cross-layer perpendicular to the joists. A weekend and £150–£350 of materials does a typical semi.

Go professional instead if the loft is boarded and you want to keep storage (the raised-deck work is fiddly), if there’s any moisture question, or if the house has a room-in-roof — that’s a different job (sloping-ceiling insulation) with different products and prices.

What loft insulation saves

Using Energy Saving Trust figures at January 2026 prices, going from nothing to 270mm saves roughly:

• Mid-terrace: ~£195 a year
• Semi-detached: ~£250–£290 a year
• Detached: ~£400+ a year

Against a £500–£900 install, the payback for a previously uninsulated semi is two to four years — and materials-only DIY pays back in under two. A 100mm→270mm top-up pays back in three to five years. Few purchases in home energy beat that; see our EPC rating guide for how the same job moves your certificate score, and the cavity wall insulation guide for the wall-side equivalent.

Frequently asked questions