For a typical UK 3-bed semi new build under the Future Homes Standard, you need 8 solar panels (3.4 kWp). For a 4-bed detached, 12 panels (5.2 kWp). For a 5-bed executive home, 18 panels (7.6 kWp).
The exact number depends on your ground floor area — the FHS rule is panel area equal to 40% of ground floor area. Below we walk through how to calculate it for any house type.
The FHS 40% rule explained
From 24 March 2027 every new dwelling in England must include solar PV with panel area equal to at least 40% of the dwelling\'s ground floor area. The rule is measured against ground floor area (not total floor area) and against panel area (not roof area). A standard residential solar panel measures roughly 1.7 m² and produces 425W of nameplate capacity.
The formula: Number of panels = (Ground floor area × 0.40) ÷ 1.7 m². For a 3-bed semi at 42.5 m² ground floor: 42.5 × 0.40 ÷ 1.7 = 10. We round up to 8-10 panels (closer to 8 in practice because typical UK new-build 3-bed roofs aren\'t configured for exact 10-panel arrays; suppliers fit the closest standard portrait array).
Panel count by house type — 2026 reference table
| House type | Ground floor | Panel area needed | Panels (425W) | System (kWp) | Annual kWh |
|---|---|---|---|---|---|
| 2-bed terrace | 28 m² | 11 m² | 6 | 2.55 | 2,400 |
| 2-bed semi | 36 m² | 14 m² | 7 | 2.98 | 2,800 |
| 3-bed terrace | 38 m² | 15 m² | 7-8 | 3.0-3.4 | 2,850-3,200 |
| 3-bed semi (typical) | 42.5 m² | 17 m² | 8 | 3.4 | 3,200 |
| 3-bed detached | 50 m² | 20 m² | 10 | 4.0 | 3,750 |
| 4-bed semi | 50 m² | 20 m² | 10 | 4.0 | 3,750 |
| 4-bed detached (standard) | 65 m² | 26 m² | 12-13 | 5.2 | 4,900 |
| 4-bed townhouse | 38 m² | 15 m² | 7-8 | 3.0-3.4 | 2,850-3,200 |
| 5-bed executive | 95 m² | 38 m² | 18 | 7.6 | 7,200 |
| 6-bed prestige | 120 m² | 48 m² | 22-24 | 9.4-10.2 | 9,000-9,700 |
Annual generation figures assume a south-facing 35° roof pitch in the South Midlands (Loughborough reference irradiance). North-facing or east-west split arrays produce 10-25% less; south-facing roofs in the South West and South East produce up to 8% more.
When you need MORE panels than the FHS minimum
Three scenarios where you should specify above the 40% rule:
- 1Heat pump heating + EV charging: If you\'ll have ASHP heating and an EV at the property, household electricity consumption rises to 8,000-12,000 kWh/year. A larger array (e.g. 5 kWp on a 3-bed) absorbs more of this demand and pulls forward payback.
- 2Battery storage planned: A 10-13 kWh battery only delivers value if it has surplus PV to store. Specifying 25-40% above FHS minimum and pairing with battery storage lifts self-consumption from 55% to 78%+.
- 3EPC band A target: Volume housebuilders selling at the premium end (~£500k+) increasingly target EPC band A (92+) rather than the band B that the FHS minimum delivers. A larger array helps cross the threshold.
When you can install FEWER panels than the FHS minimum
The Approved Document recognises four exemption categories: (1) flats in tall blocks where the building-attributable PV area is less than the per-dwelling 40%; (2) plots in heavy shade; (3) mansards and complex roofs in Conservation Areas; (4) listed-curtilage infill plots. Outside these cases the 40% rule applies. See our 40% PV rule page for the full Approved Document detail.
For an instant size for your specific plot, use our FHS PV calculator — enter ground floor area, get the exact panel count, kWp and installed cost in 30 seconds.