In-Roof (Integrated) Solar Installation

Panels in the roofline, not on it

If you are re-roofing, building an extension, or you cannot stand the look of panels standing proud of the tiles, in-roof — also called integrated or roof-integrated solar — is the installation type built for you. The panels sit in the roofline on plastic or metal trays (GSE, Viridian and similar systems), replacing the tiles beneath them entirely. The finished roof is flush, and on the right house the array reads as part of the building rather than an addition to it.

There is a price for the aesthetics, in two currencies. Money first: a typical 3.5–6 kWp integrated system runs £6,500–£11,000 installed, against £5,500–£9,500 for the equivalent on-roof array, because trays and flashing add cost — partly offset by the tiles you no longer need to buy or keep. And yield: integrated panels run warmer with less rear ventilation, so annual generation is typically 3–5% below on-roof for the same kWp — roughly 2,850–5,200 kWh a year from a typical system. An honest installer states that deficit up front and sizes around it. One who claims integrated yields the same as on-roof is either uninformed or hoping you are.

The rest of this page covers when in-roof genuinely makes sense — the economics hinge on one specific moment — and how the installation itself is done, because this install type is as much a roofing job as an electrical one.

The re-roof moment: the cheapest solar your house will ever buy

Here is the economic heart of in-roof solar. If your roof covering is coming off anyway — a re-roof, a new build, a full extension — the marginal cost of integrating solar is at the lowest it will ever be. The scaffold is already up and paid for. The tiles are already off. The roofing contractor is already on site with the felt and battens exposed. At that moment, adding solar trays across part of the elevation costs you the trays, panels and electrical work — while saving you the tiles that would have covered that area and a second scaffold hire later.

Modelled against the same array installed standalone at a later date, integrating during a re-roof typically costs around 60% of the standalone figure. That is the single strongest argument for this installation type, and it cuts the other way too: ripping tiles off a sound roof purely to fit an integrated system is usually poor value against an on-roof array on the same elevation. In-roof is a timing decision as much as a product choice. If your roof has a decade of life left and you want solar now, read the pitched-roof solar installation page instead — that is the better-value route for most sound roofs.

Tray by tray: how the installation is done

An in-roof installation swaps the tile covering for a weathertight tray system that the panels complete. The sequence matters, and so does who owns each part of it.

Survey and structural check

The survey covers everything an on-roof job needs — loft inspection, consumer-unit check, shading map, written planning position — plus a structural assessment specific to this method. Trays plus panels change the roof build-up: net load can actually come out lower than the tiles being removed (a point in this method’s favour on older timber), but the load path and fixing pattern differ, so the check is still required, not optional. On a re-roof, the survey also coordinates with the roofing contractor’s own plans for felt, battens and ventilation.

Strip and set out

The tiles across the array area come off, along with battens where the tray system requires it. The crew sets out the array zone precisely — integrated systems are far less forgiving of setting-out errors than on-roof rails, because the trays must course with the surrounding tiles and the flashing kit is dimensioned to the panel grid. Underlay is checked and made good; a re-roof gets new membrane across the whole elevation, which is part of why that moment is the right one.

Trays, flashings and the weathering detail

The trays fix through to the rafters and interlock with each other, forming a drained, ventilated tray field that carries water away beneath the panels. Around the perimeter, the flashing kit weathers the junction between tray field and tile courses — top flashing under the tile course above, side flashings interleaved with the tiles, bottom flashing lapped over the course below. This perimeter detail is where in-roof installations succeed or fail. It is roofing work, done to roofing standards, and the single most important question to ask any in-roof quoter is: who does the flashing work, and what does the weathering warranty cover? A solar crew improvising flashings around a system they rarely fit is how integrated arrays leak; a roofing contractor working with the tray manufacturer’s kit is how they stay dry for decades.

Panels in, tiles back, electrics

The panels drop into the trays and clamp down, completing the weathering layer — with in-roof, the panel itself is part of the roof covering, which is why like-for-like panel replacement matters more than with on-roof systems. The surrounding tiles are then cut and fitted back up to the flashings. In parallel, the electrician runs the DC cabling to the inverter position, fits isolators and any battery, connects into the consumer unit, and commissions: insulation-resistance and polarity tests, inverter configuration, monitoring walkthrough. Handover paperwork is identical to any MCS installation — MCS certificate, Electrical Installation Certificate, DNO evidence, warranty registrations — with the weathering warranty as the extra document specific to this method.

What a poor in-roof job looks like

The failure modes are roofing failures: flashings improvised from generic lead rather than the system kit, trays out of course with the tiles, no ventilation path behind the panels (worsening the heat-related yield deficit), and nobody clearly owning the weathertightness warranty between the solar firm and the roofer. Every one of those is a question you can ask before signing.

Costs, sizing and the honest yield deficit

A typical in-roof system is the same electrical size as its on-roof cousin — 3.5–6 kWp from 8–14 panels of 440–475 W across 18–32 m² — and the sizing logic is unchanged: start from your annual consumption, not the roof area. The premium over on-roof sits in the trays and flashing kit and the extra roofing labour, less the saved tiles; £6,500–£11,000 covers most domestic installations, benchmarked against the MCS-reported England average of roughly £1,565–£1,590 per kW (as at spring 2026) plus the integration premium. Installed at re-roof time, the marginal cost falls dramatically, as covered above. Domestic installations are zero-rated for VAT until 31 March 2027, when the rate reverts to 5% — a dated fact worth factoring into re-roof timing. Full system-size pricing is on the cost guide, and export payments and the VAT position are detailed under grants and funding.

On yield: budget for 3–5% below an equivalent on-roof array, because panels sitting in the roofline shed heat less effectively and warm panels generate less. Over a year that is roughly 2,850–5,200 kWh from a typical system, and payback stretches to around nine years against eight for on-roof. If the array is being sized to hit a specific self-consumption target — particularly with a battery in the design — the honest move is to size the integrated array slightly larger to compensate, and an installer who raises this unprompted is showing you how they work.

Planning position for integrated arrays

In-roof shares the on-roof planning position: for most houses in England, Class A permitted development under GPDO Part 14, with no application needed. The distinctive advantage is in conservation settings — where a conservation-area officer objects to panels standing off the roof plane, a flush integrated array is the usual route to approval, and at re-roof time it is frequently the only solar the elevation will ever be allowed. Listed buildings still need consent in all cases, and the England-only caveat applies: Scotland and Wales run their own planning regimes, so a UK-wide reader should check locally. The 27 August 2026 permitted-development changes (SI 2026/896) chiefly relax projection limits for on-roof arrays — an integrated array sits within the roof plane and was never troubled by projection limits in the first place.

Building Regulations apply as for any solar installation: Part P notifiable electrical work to BS 7671, plus Part A structural considerations addressed by the survey. On a re-roof, the roofing work itself may involve building-control notification depending on scope — the roofing contractor handles this, but it should be visible in the project plan.

Scenario: a 6 kWp integrated array during a slate re-roof

A worked scenario, modelled from the ranges on this page rather than a client project. A Victorian terrace is having its rear elevation re-slated. The owner takes the re-roof moment: a tray system replacing slate across the rear pitch, 13 panels at 6.0 kWp, with the flashing detail owned by the roofing contractor working to the tray manufacturer’s kit. The front elevation faces the conservation area; the rear array, flush to the roofline, satisfies the conservation officer’s objection to an on-roof system.

Modelled generation is around 4,700 kWh a year — the integrated array running roughly 4% below what an equivalent on-roof system would produce on the same pitch. Annual benefit models at £900–£1,100 across self-use and Smart Export Guarantee export (SEG rates roughly 12–16p/kWh on leading tariffs as at mid-2026 — check current rates), for a payback around nine years. The decisive number is the marginal cost: integrated during the re-roof, the solar work came in at roughly 60% of what the same array would cost standalone later, because the scaffold, strip and membrane were already in the roofing bill. The re-roof moment is the cheapest solar this house will ever buy.

Questions about in-roof installation

Is in-roof solar more likely to leak than on-roof?

Done properly, no — the tray-and-flashing systems are engineered roof coverings with drained, ventilated channels, and carry weathering warranties. The risk concentrates in workmanship at the perimeter flashings. Ask who does the flashing work, whether the manufacturer’s flashing kit (not improvised lead) is used, and what the weathering warranty covers and for how long.

How much less does an integrated array generate?

Typically 3–5% less than the same kWp on-roof, because integrated panels run warmer with less rear ventilation. On a 6 kWp system that is roughly 150–250 kWh a year. Sizing the array slightly larger compensates — the deficit is a design input, not a dealbreaker.

Is in-roof cheaper than on-roof?

Standalone, no — trays and flashings make it £1,000–£1,500 more for a typical system, partly offset by saved tiles. During a re-roof or new build the picture inverts: with scaffold, strip and membrane already paid for, the marginal cost of integrating typically runs around 60% of a later standalone install. Timing is the whole economics.

Can I fit in-roof panels to my existing roof without re-roofing?

Physically yes — the tiles across the array area come off and the tray system replaces them, without touching the rest of the roof. Whether it is worth it is another matter: on a sound roof you pay the integration premium without the re-roof saving, so on-roof is usually better value unless planning or aesthetics rule it out.

Does an integrated array need planning permission in a conservation area?

Often it is precisely the answer to conservation-area constraints: permitted development still applies to most elevations, and where an officer objects to on-roof panels, a flush integrated array is the usual acceptable alternative. Listed buildings always need consent regardless of method. Get the position confirmed in writing at survey — and note Scotland and Wales have their own rules.

Related pages

For a sound roof that is not being re-covered, the pitched-roof solar installation page covers the standard on-roof method and its costs. If your property’s pitched elevations are unsuitable altogether, a flat roof solar installation on an extension or garage may be the alternative. Then see how much it costs, check available grants, or get a free quote with a proper survey attached.