In-roof vs on-roof solar UK 2026: cost, aesthetic, performance trade-off

In-roof solar replaces a section of roof tiles with integrated PV modules sitting flush in the plane of the roof. On-roof solar mounts panels above the existing tiles on an aluminium rail system, with a 50 to 100 mm air gap underneath. Both approaches use the same panels in most cases; the difference is the mounting system, the labour cost, the panel temperature in summer, and the visual finish.

In-roof typically costs £1,000 to £2,500 more on a 4 kWp install in 2026, runs 3 to 6 degrees hotter at peak summer output, and is realistically only worth fitting at the same time as a re-roof.

Last reviewed: May 2026

TL;DR

In-roof solar costs £1,000 to £2,500 more than on-roof for a typical 4 kWp install (MCS installer pricing, Q1 2026).
In-roof runs hotter in summer because of restricted airflow under the modules. Panel temperature coefficients of 0.3 to 0.5% per degree above 25C cut summer output by 2 to 4%.
The visual case for in-roof is strongest on new-build, re-roofs, and properties where planners or conservation officers expect a flush finish.
Permitted development in England and Wales generally accepts both approaches on a dwelling outside a conservation area. Listed buildings and AONBs need a case-by-case planning route.
Retrofit on an existing intact roof is rarely economic: the labour of stripping and refelting the affected section pushes in-roof close to the cost of a partial re-roof.

On-roof is the default in the UK domestic market. MCS deployment data for 2025 shows roughly 92% of residential PV installations used above-roof rail systems, with in-roof concentrated in new-build and major refurbishment projects. The two approaches solve different problems. Get them confused and the system runs hot, costs more, or loses planning consent.

What in-roof solar actually is

An in-roof system replaces tiles or slates in the panel footprint with a watertight tray or interlocking module that the PV panels slot into. The roof surface becomes part PV, part tile. The visual line of the roof is flat: panels sit in the same plane as the surrounding tiles, with a narrow trim around the array. Common UK in-roof systems include GSE In-Roof, Viridian Solar Clearline Fusion, and the integrated systems supplied by manufacturers such as Marley SolarTile and Redland SolarTile.

The watertight detail sits in the tray. The original roof felt and battens beneath the panel footprint are usually replaced during the install with a manufacturer-specified breathable membrane and a modified batten layout. That is what makes in-roof a re-roof-adjacent job: getting the watertight detail right requires lifting and reworking the affected section.

The cost gap

MCS-certified installer pricing across the UK in Q1 2026 puts a 4 kWp on-roof retrofit at £6,800 to £8,200 inclusive of zero-rate VAT, panels, inverter, mounting and labour. The same 4 kWp in-roof system installed at re-roof time sits at £8,200 to £10,000. On a retrofit to an intact roof, in-roof rises further because the existing tiles in the footprint need to be lifted, sorted, and either reused or replaced.

Scenario	4 kWp on-roof	4 kWp in-roof	Gap
New build (at construction)	£7,200	£8,400	£1,200
At re-roof (existing house)	£7,500	£9,200	£1,700
Retrofit to intact roof	£7,500	£10,000+	£2,500+

The cost difference is labour and materials around the watertight detail, not the panels themselves. Most in-roof systems take the same 410 to 440 W panels as a comparable on-roof install.

Thermal performance: the derate that matters

PV panels lose efficiency as they heat up. Standard test conditions for the rated wattage are 25C. Above that, output falls at the panel's temperature coefficient of power, which for most monocrystalline silicon panels available in the UK in 2026 sits between 0.30% and 0.40% per degree Celsius above 25C. Some premium n-type modules (TOPCon, HJT) achieve 0.25 to 0.29% per degree. An on-roof panel with a 75 mm rear air gap on a sunny June afternoon in southern England runs at around 45 to 55C cell temperature. An in-roof panel in the same conditions, with restricted under-panel airflow, runs around 50 to 60C. The 3 to 6 degree gap costs 1 to 2.5% of peak summer output, depending on the panel and the day. Across a full UK year the annual generation difference is smaller, typically 1.5 to 3%, because the temperature gap closes outside summer.

The catch is that the panel datasheet warranties assume Standard Test Conditions and Nominal Operating Cell Temperature. Manufacturers do not derate the linear performance warranty for in-roof installs, but real-world generation over a year still tracks the temperature curve. On a 4 kWp system generating 3,800 kWh on-roof in Leeds, the in-roof equivalent might land at 3,700 kWh on a like-for-like basis.

Aesthetics and the conservation case

This is where in-roof earns its premium. On-roof modules sit proud of the roofline by 60 to 120 mm, with visible rail brackets at the eaves. From a street view the array reads as a separate technological layer above the roof. An in-roof system sits flush; the array reads as part of the roof, particularly with black-frame all-black modules and dark trim.

That matters for three groups of properties. Conservation officers in conservation areas often prefer flush in-roof systems where PV is acceptable in principle. Listed building consent applications, which sit outside permitted development entirely, are more likely to succeed with an in-roof flush detail and a sympathetic trim colour. National Park and Area of Outstanding Natural Beauty authorities, particularly in the Yorkshire Dales and Snowdonia, have published informal preferences for flush installations in sensitive landscape settings.

In practice, a homeowner in a conservation area applying for planning permission for solar should expect the case officer to ask whether the installer has considered an in-roof option. The application can still succeed with on-roof, but the case is stronger with in-roof and the planning fee is the same. Outside conservation areas, permitted development under Schedule 2, Part 14, Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015 covers both approaches without an application, subject to the standard volume and projection limits.

Permitted development and listed buildings

Permitted development for domestic microgeneration in England, last consolidated by the Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2023, allows solar PV on a dwelling subject to a few conditions: the panels must not protrude more than 200 mm beyond the roof slope, must not sit above the ridgeline, must not be installed on a listed building without listed building consent, and must minimise visual impact in conservation areas.

Wales follows the equivalent permitted development regime under the Town and Country Planning (General Permitted Development) (Amendment) (Wales) Order 2023, with similar conditions. Scotland has its own regime under Class 6E of the Town and Country Planning (General Permitted Development) (Scotland) Amendment Order 2009, with comparable but not identical rules.

Here is where it breaks for in-roof on a listed building. Even with the flush finish, listed building consent is required because the works replace a section of the protected roof material. The application is judged on its merits, with reversibility a key test. In-roof is harder to remove cleanly than on-roof because the tile interface has been altered, which sometimes weighs against the application.

Retrofit difficulty

Fitting in-roof on an intact, sound, mid-life roof rarely makes financial sense. The watertight rework around the array footprint takes the labour close to a partial re-roof. By the time the affected section has been stripped, refelted, rebattened and detailed around the in-roof tray, the install is two trades on site for three to five days against one trade on site for one to two days for on-roof.

The realistic windows for in-roof are:

New build. Specified into the design at construction. The cost gap is smallest (£1,000 to £1,500 on a 4 kWp) and the watertight detail is integral to the roof build.
Re-roof. The existing covering is at end of life and is being replaced. The labour of detailing in-roof is part of the re-roof anyway. The cost gap is moderate (£1,500 to £2,000).
Major refurbishment. The roof is being opened up for other reasons (loft conversion, dormer addition, structural work). The detail can be integrated.

On the ground, an installer asked to quote in-roof on an intact 15-year-old concrete tile roof should be flagging the cost-benefit explicitly. The thermal derate, the higher labour, and the reversibility problem all push the rational answer toward on-roof unless the visual case is decisive.

Insurance, warranty and fire safety

The UK fire safety regime for domestic PV sits under the BS 7671 Wiring Regulations and the 18th Edition Amendment 3 in force since January 2024, with specific solar requirements covered in DC isolation and arc-fault detection. In-roof and on-roof are treated equivalently under the regulations. The differences sit in practical fire access and the panel-to-tile interface.

Buildings insurers will normally cover both approaches without a premium loading, provided the install is MCS-certified and the inverter and isolation gear comply with BS 7671. Some insurers ask supplementary questions about in-roof installs where the panels replace the primary watertight covering, particularly on older properties; this is usually a documentation matter rather than an additional cost.

Worked example: Cheshire detached house, 2026 retrofit decision

A homeowner in Knutsford with a 12-year-old concrete tile roof, no immediate re-roof need, and a south-facing 30 degree pitch capable of taking 6 kWp. MCS installer quote in March 2026: on-roof at £10,800 inclusive (6.0 kWp, 14 panels, hybrid inverter, no battery). In-roof at £14,200 for the same kit. Generation modelled at 5,700 kWh per year on-roof versus 5,550 kWh in-roof using the regional SAP 10.2 figure adjusted for orientation and the manufacturer's NOCT data.

At a self-consumption rate of 35% and an Octopus Outgoing Fixed export rate of 15p per kWh, on-roof saves and earns roughly £1,330 per year (April 2026 cap on imports). In-roof at the same self-consumption rate saves and earns roughly £1,295. Payback: 8.1 years on-roof, 11.0 years in-roof. The aesthetic premium for the flush finish costs £3,400 and roughly three years of additional payback.

Scotland and Wales: regional notes

Scotland's permitted development rules under Class 6E impose a 200 mm projection limit on a dwelling. Inside a conservation area, planning permission is required for both approaches; Historic Environment Scotland guidance updated in 2023 indicates flush in-roof is more likely to satisfy a conservation officer in a designated area, particularly in Edinburgh's New Town or the Glasgow West End.

Welsh Government's Optimised Retrofit Programme has tested both approaches across social housing in South Wales since 2019. Findings published in 2023 confirmed measurable summer-output suppression in in-roof installations on south-facing roofs with restricted under-panel airflow, supporting the 1.5 to 3% annual derate range observed in installer monitoring data.

Editorial note. This guide summarises publicly available UK energy market information for general reference. Tariffs, grant rules and regulator decisions change frequently. Always verify the current position on Ofgem, GOV.UK or the supplier's own page before acting. For complex financial decisions, consult an FCA-authorised adviser. Kael Tripton is an independent editorial publisher and does not sell energy contracts or earn commission from suppliers.

Frequently asked questions

Does in-roof solar generate less than on-roof?

Typically 1.5 to 3% less per year on a like-for-like basis, because restricted under-panel airflow raises panel temperature and silicon PV loses efficiency above 25C. The gap is largest at summer peak.

Is in-roof solar worth the extra cost?

The financial case for retrofit is usually weak. The aesthetic and conservation case is strong on new build, re-roofs, listed buildings and conservation areas where a flush finish is expected.

Can in-roof be retrofitted to an existing roof?

Yes, but the labour of lifting the affected section and detailing the watertight tray pushes the install cost close to a partial re-roof. Most installers will quote it only at re-roof time.

Does in-roof solar count under permitted development?

Yes, on most dwellings outside conservation areas and listed buildings, under Class A Schedule 2 Part 14 of the GPDO 2015 in England. Equivalent provisions apply in Wales and Scotland.

Is in-roof safer or more dangerous in a fire?

UK insurers treat both approaches equivalently under BS 7671 Amendment 3 (January 2024). The DC isolation and arc-fault detection requirements are the same.

Do conservation officers prefer in-roof?

Often, where solar is acceptable in principle. The flush finish carries less visual impact than a raised on-roof array. Always check with the local planning authority before applying.