In-roof solar integrates PV panels into the roof structure below the tile line, providing weatherproofing and electricity generation in a single flush layer — the default choice for FHS-compliant UK new builds at £1,150-£1,290 per installed kWp.
How in-roof solar is built
An in-roof system has four physical layers from inside out: (1) the roof structure (timber rafters or steel trusses); (2) a sarking membrane (typically Tyvek breathable membrane); (3) the in-roof mounting tray that holds the panels in a recessed array; (4) the panels themselves, sitting flush with the surrounding tile or slate roof covering.
The mounting tray includes integrated flashings that lap underneath surrounding tiles or slates and over weatherproofing membranes. Manufactured by GSE Integration (the dominant UK supplier), Marley SolarTile and similar systems, the tray is rated to BS EN 13501-5 fire spread and BS EN 12865 driving rain. Installation requires the mounting tray to be set into position during the roof tiling stage, not after.
Panels are then dropped into the tray (or, in factory pre-fit programmes, pre-installed at a panelised roof cassette factory before delivery to site), cabled, and connected to a hybrid inverter typically located in a utility room or plant cupboard.
Why volume housebuilders specify in-roof for FHS
Five reasons in-roof has become the default for FHS-compliant volume housebuilder work:
- 1 Aesthetic — sales appealIn-roof systems sit flush with the tile line. Show-home photography and street elevation imagery aren\'t dominated by a clearly-industrial panel array. Buyer surveys show a measurable preference for in-roof aesthetics on premium plots.
- 2 Programme — concurrent with roofingOn-roof solar requires the roof to be 100% complete before installation begins, then a dedicated 1-day install crew per plot. In-roof installs concurrently with the roof tiling — no separate install visit needed. Factory pre-fit extends this further: 2 hours of on-site labour per plot vs ~10 hours on-roof.
- 3 Net cost — tile offsetIn-roof panels replace the underlying tiles or slates they displace (~£35-50/m² saved). On a typical 3.4 kWp installation that\'s a £420 saving — making in-roof £120 cheaper net than on-roof on new builds.
- 4 Warranty — straightforward acceptanceNHBC, LABC, Premier Guarantee and Buildmark all accept BBA-certified in-roof systems without warranty reserve. Documentation requirements are well-established at the warranty surveyor level.
- 5 Wind resistance — coastal performanceIn-roof systems are wind-loaded as part of the roof structure, not as a separate mounted element. For coastal new-build sites (Blackpool, Hull, Brighton, Plymouth) the wind-resistance rating is materially better than on-roof — relevant for the FHS-era specification of larger arrays.
In-roof solar costs in 2026
Volume developer pricing for in-roof solar (3.4 kWp, 3-bed semi):
| House type | Panels | kWp | Volume install | Self-build retail |
|---|---|---|---|---|
| 3-bed semi | 8 | 3.4 | £3,380 | £5,200 |
| 3-bed detached | 10 | 4.0 | £3,950 | £6,400 |
| 4-bed detached | 12-13 | 5.2 | £4,500 | £7,550 |
| 5-bed executive | 18 | 7.6 | £6,270 | £9,970 |
For full cost breakdowns including ASHP, battery and EV charger packages: see our 3-bed cost guide, 4-bed, and 5-bed.
In-roof vs on-roof vs BIPV — which to choose
Three roof-integrated approaches exist for FHS-compliant solar PV:
- In-roof panels: Default for FHS new builds. Cheapest net cost, best programme integration, mainstream warranty acceptance. Full in-roof vs on-roof comparison.
- On-roof panels: Cheaper per kWp on a like-for-like basis but no tile offset, separate install programme, lower aesthetic appeal. Best for retrofit or non-aesthetic-sensitive sites.
- BIPV (solar tiles/slates): Highest aesthetic, indistinguishable from a non-PV roof at 50m+. Required for Conservation Areas, Article 4 zones and listed-curtilage plots. 2× the cost of in-roof. Full BIPV vs in-roof comparison.
For an in-roof installation quote on your new build, request a fixed-price quote or size your specific plot with the FHS PV calculator.