In-roof solar panels: how they work and when they make sense

In-roof (or integrated) solar panels replace part of your roof's tiles or slates, so they sit almost flush with the roof instead of on brackets above it. A flashing kit around the panels joins them to the surrounding roof and keeps the rain out. Because less air flows behind them, they run warmer and produce a little less: about 3% less than panels mounted with open air behind them, in the European Commission's PVGIS model for UK cities. They make most sense when the roof is being built or re-covered anyway.

On-roof, in-roof or solar tiles?

Product names can blur the line: Marley's "SolarTile" is a full-size 445 W panel, not a tile-sized unit. Solar roof tiles compares tile-sized products.

How much output do in-roof panels lose?

Solar panels produce less when hot. The PVGIS manual says panels with restricted air movement behind them can run up to 15°C hotter in full sunshine; the model offers free-standing panels and "building-integrated" ones with no air movement behind them. We ran both for 1 kWp at 35°, facing south (PVGIS 5.3, SARAH3 data, 14% losses). These are long-term yearly averages:

In PVGIS, that is the gap between the two extremes. Ordinary on-roof panels have less air behind them than free-standing ones, so the gap between on-roof and in-roof panels should be smaller. Depending on how the roof is built, air can also move in the batten space under an in-roof panel.

A January 2014 study by the in-roof maker Viridian Solar, with Enphase and Cambridge University researchers, points the same way: it estimated that a panel above a tiled roof would produce 3.1% more a year than the same panel fitted in the roof (and a free-standing panel 6.0% more). That study's panels lost more power with heat than Viridian's current 445 W panel (−0.509% against −0.29% per °C, from the study and the datasheet), so we'd expect a smaller gap today.

What the MCS standard asks of an in-roof kit

• MCS 012 certification. The MCS installation standard (MIS 3002) says panels on or in pitched roofs must use kits certified to MCS 012, or, where no certified kit suits the roof, provide evidence that the fixing meets Building Regulations on structure, fire and weathertightness. The certificate declares test results rather than a pass mark: the approved roof pitches, the wind uplift resistance and the fire classification. Viridian's Clearline fusion portrait kit, for example, is approved for 20° to 60°, resists 4.65 kPa of design wind uplift with its current panels and is rated BROOF(t4).
• Fire rating and the boundary. The installer must show the roof's fire performance hasn't been reduced. The standard's worked example, based on Approved Document B (England and Wales), shows a BROOF(t4) kit can go anywhere on the roof, while lower-rated kits are limited by their distance from the property boundary. The rating holds only with the panel family it was tested with.
• Matching parts. If a kit is certified with named panels, only those panels may be used.
• Pitch. Low pitches raise the risk of rain being driven under flashings. Viridian says its kit passed the MCS 012 rain test at 20° and allows down to 14° only with a specialist low-pitch underlay.

When in-roof panels make sense

• New homes. From 24 March 2027, new homes in England must have on-site renewable electricity (Building Regulations requirement L3), unless building control was notified before that date and work starts by 24 March 2028. Approved Document L measures it against, for example, 0.22 kWp per m² over 40% of the ground floor area, facing south-east to south-west at 45°: 4.4 kWp for a 50 m² ground floor (20 m² × 0.22).
• Re-roofing. If your tiles or slates are being replaced anyway, the in-roof panels take the place of some of the new covering, and scaffolding goes up once.
• Appearance. Flush panels without rails on show can suit a prominent roof, though planning limits still apply.

On-roof panels are usually the simpler choice when your roof covering has years of life left, when the pitch is below an in-roof kit's approved range, or when you want every possible kWh from limited roof space.

What in-roof solar costs

There is no official price series for in-roof systems. DESNZ's 2025/26 figures for MCS-certified solar in Great Britain (per kW of panel capacity, including VAT, excluding batteries) give means of £2,109 per kW for systems up to 4 kW on existing homes and £1,518 per kW for the same size on new-build homes, without separating in-roof from on-roof. For 4 kWp on an existing home that is 4 × £2,109 = about £8,435: a reference point, not a quote.

Viridian, which makes in-roof kits, says its in-roof panels are "now at similar cost to above-roof panels" (datasheet v1.1, 2025) and that total installed cost is competitive with above-roof systems "when installing a new roof" (brochure v2.01, 2026). Test the maker's claims with on-roof and in-roof quotes for the same roof, each itemising panels, kit, roofing, scaffolding and electrics; solar panel cost explains what a quote should include.

VAT. When the installer supplies and fits the solar in your home, the VAT rate is 0% until 31 March 2027 and is then scheduled to be 5% unless extended; panels bought without installation are charged 20%. If a roofer's work is on the same contract, HMRC treats it as one supply or several, which changes the VAT on each part, so ask for the VAT on each part to be shown. Solar installed while a new home is being built is zero-rated along with the construction. See VAT on solar panels.

Warranties, weatherproofing and repairs

• Product and output warranties. Viridian's 445 W in-roof panel carries a 15-year product warranty and an output warranty of 95% after 10 years and 87% after 30 years. Marley's 15-year full-system warranty covers the compatibility and weathertightness of the roof system when SolarTile is installed as part of a complete Marley roof. For comparison, the JinkoSolar Tiger Neo on-roof panel gives 25 years' product and 30 years' output warranty on its datasheet (F1.3-EN). How long solar panels last explains what each warranty covers.
• Your roof warranty. If the roof is under warranty, the MCS installer should ask the warranty provider whether the panels will affect it, and get your written agreement if they might.
• Repairs. Replacing a faulty in-roof panel means opening part of the roof covering, so ask who is responsible for the weatherproofing: the solar installer, the roofer or both.

Planning permission

In-roof panels project very little, so they usually fall within permitted development: in England, no more than 0.2 m beyond the roof slope and not above the highest part of the roof (excluding any chimney). Listed buildings need consent in every nation. In a Scottish conservation area, permitted development excludes the principal (usually front) elevation and any side elevation fronting a road, and it doesn't apply at all in a Scottish World Heritage Site. In a Northern Irish conservation area or World Heritage Site, it excludes a roof slope facing and visible from a road. In England's conservation areas, the restriction covers walls, balconies and roof enclosures fronting a highway. Planning permission for solar panels has each nation's rules.

What to ask for on an in-roof quote

• The kit's MCS 012 certificate (approved pitches, wind uplift resistance and fire classification for your panel model) and the installer's wind-loading calculation for your roof.
• The panel make, model and datasheet, with the product and output warranty documents.
• A layout drawing, and who does the roofing and who does the electrics.
• VAT shown for each part of the work.
• Who puts right any leak, and for how long.

Comparing solar quotes shows how to line up the rest of the offer.

Frequently asked questions

Are in-roof solar panels less efficient?

They run warmer because less air flows behind them. In PVGIS, fully building-integrated panels in London, Birmingham and Glasgow produce about 3% less a year than free-standing ones; kits with some air space behind the panels should lose less than that.

How much do in-roof solar panels cost?

There is no separate UK price series for in-roof systems. DESNZ's 2025/26 means for systems up to 4 kW were £2,109 per kW on existing homes and £1,518 on new-build homes, including VAT. Viridian's 2026 brochure says its installed cost is competitive with above-roof systems when a new roof is going on; compare on-roof and in-roof prices for your own roof.

Can you fit in-roof panels on an existing roof?

Yes, by replacing the tiles or slates where the panels go, if your roof pitch is within the kit's approved range and the structure has been checked. If the rest of the roof needs replacing soon, do both together.

Do in-roof solar panels leak?

They are designed and tested not to: MCS 012 in-roof kits are tested for weathertightness, and each certificate lists the approved pitches. Check your roof is in range and who is responsible for any leak.

Do you need planning permission for in-roof solar panels?

Usually not, as they sit within the pitched-roof limits for permitted development. You need consent for a listed building and for any house in a Scottish World Heritage Site. In a conservation area you need it for the front or a road-facing side of the roof in Scotland, or for a slope seen from the road in Northern Ireland. Some councils have also removed permitted development rights locally, so check if you're unsure.