The headline figure from the FHS Impact Assessment is an additional £4,350 per dwelling in build cost (weighted average, 2025 prices). This page breaks the figure down line-by-line and shows how it varies between a 3-bed semi and a 5-bed detached.
The line-item breakdown
Air source heat pump system: £2,800
Solar PV array (3.4–5.2 kWp): £4,500–£7,000 (gross) — but offset £1,400 of legacy SAP-required token PV, net £3,100–£5,600
Enhanced fabric (walls, floor, roof): £1,200
MVHR ventilation: £2,800
Improved windows/doors: £600
Less: gas boiler removed (£900) and other savings
Net average: £4,350
How it varies by house type
Smaller dwellings see lower absolute premium but higher percentage cost. 2-bed flat: £3,200 (1.1% of build cost). 3-bed semi: £3,800 (1.4%). 4-bed detached: £4,800 (1.5%). 5-bed executive: £6,200 (1.6%). The Government Impact Assessment's £4,350 is a national weighted average across the 2025 housing mix.
Why developers can deliver below £4,350
The Impact Assessment uses retail benchmark pricing. Volume housebuilders buying at scale can come in below this figure.
How the homeowner recoups the premium
The PV+battery component alone delivers ~£950–£1,400/year saving at 2026 tariffs (86% bill reduction per Sunsave's 150-system sample). Adding ASHP efficiency gains and SEG export tariff brings the total saving to £1,150–£1,650/year. A 3–4 year payback on the FHS premium is typical for owner-occupied properties.
Impact on house prices
Multiple studies (Nationwide, Energy Saving Trust, Sunsave) put the home value uplift from a domestic solar+battery system at 2–7%. On a £325k median new build that is £6,500–£22,750 — typically 1.5–5× the FHS cost premium. Buyers reward FHS-spec homes through higher bid prices and faster sale times.