~£900 installed for 270mm from bare joists, ~£750 for a 120→270mm top-up (EST, May 2026) — the fastest-payback job in home energy. Full pricing, labour split and funded routes below.
Typical semi (~50m² loft): £900 from bare, £750 top-up — £18–£28/m² installed. Detached (~70m²): £1,100–£1,500. Materials are £4–£8/m²; the balance is labour, clearing and detailing around eaves, pipes and tanks. 0% VAT to 31 March 2027.
DIY at £200–£400 materials is viable for empty, accessible lofts — keep ventilation paths at eaves, don’t squash quilt under boarding (use loft legs), never cover recessed-light housings without covers. Professional pays for itself where storage boarding, awkward access or full clearance is involved.
Loft insulation is the most-funded fabric measure: ECO4 (to Dec 2026) and WH:LG (to Mar 2028, insulation = 24% of installs) both cover it — could be fully funded for some eligible households; eligibility does not guarantee installation or zero contribution.
~£200–£250/year savings on a typical gas-heated semi with a thin loft: payback in 1–3 years, then pure saving for decades. No other measure comes close — which is why every whole-home plan starts here. Check your home to see your order.
AC-coupled (battery has its own inverter) is the retrofit default: no rewiring of your array, works with any brand or age of system, £3,500–£6,000 installed for 5–10kWh usable. DC-coupled only makes sense if your inverter is due replacement anyway — a hybrid inverter + battery swap can be cheaper combined.
Feed-in Tariff payments are unaffected by adding storage — generation payments continue and deemed export isn’t metered down. On SEG, a battery lets you shift export into peak-price windows instead.
Match usable capacity to your evening consumption and summer surplus — the sizing guide has the tables. Most 4kWp homes land at 5–8kWh usable.
About £900 installed for 270mm from bare joists, £750 for a top-up from 120mm (EST May 2026); £18–£28/m².
Roughly £400–£600 of the installed price — materials are only £4–£8/m².
Via ECO4 (to Dec 2026) or WH:LG (to Mar 2028) it could be fully funded for eligible households — eligibility doesn't guarantee installation or zero contribution.
270mm is the standard because heat savings taper beyond it — topping up from 100–150mm still pays back in 2–3 years.
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
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