The short answer
This is about how standard panels are mounted, not a different type of panel. On-roof (the default) fixes panels to rails that sit a few centimetres above your existing tiles or slates, leaving an air gap underneath. In-roof (or integrated) removes a section of tiles and sets the panels flush into the roof using a special tray and flashing kit, so they sit level with the surrounding covering. On-roof is cheaper, quicker and keeps panels cooler thanks to the air gap, which slightly aids output, and it is the most common UK choice. In-roof looks much neater and more flush, can suit new builds and conservation areas, but costs more, runs slightly warmer and removes part of your roof covering. For most retrofits, on-roof is the practical default.
Most UK solar installs use standard panels; the choice is whether to bolt them above the tiles or recess them into the roof. The decision affects cost, looks and a little of the performance. Here is how the two mounting methods compare.
On-roof vs in-roof
- On-roofAbove tiles on rails
- In-roofFlush, replacing tiles
- Lower costOn-roof
- Neater lookIn-roof
- Cooler runningOn-roof (air gap)
How each is mounted
On-roof mounting is the standard method. Roof hooks are fixed to the rafters under the tiles, rails are bolted to the hooks, and the panels clamp to the rails. The tiles stay in place and the panels sit a few centimetres proud of them, with an air gap underneath. It is fast, well understood and works on almost any sound pitched roof.
In-roof mounting removes the tiles where the array will go and fits the panels into a waterproof tray or frame with flashing around the edges, so the panels become part of the weatherproof surface and sit flush with the surrounding tiles. It takes longer, needs more careful detailing to stay watertight, and replaces rather than covers the roof covering in that area.
| Factor | On-roof | In-roof (integrated) |
|---|---|---|
| Mounting | Above tiles on rails | Flush, replaces tiles |
| Cost | Lower | Higher |
| Appearance | Panels stand proud | Flush, neater |
| Cooling | Better (air gap) | Slightly warmer |
| Install speed | Faster | Slower |
| Best for retrofit | Yes | Possible, costlier |
| Best for new build / re-roof | Possible | Strong fit |
Indicative comparison for guidance. Sources: Energy Saving Trust; MCS.
Performance, ventilation and looks
The air gap under on-roof panels lets air circulate and keeps the panels cooler. Solar panels lose a little efficiency as they heat up, so better ventilation gives a small generation advantage. In-roof panels sit tighter against the roof structure with less airflow, so they tend to run slightly warmer and can lose a fraction of output on hot days. In the UK climate the difference is small, but on-roof has the edge on cooling.
Looks usually pull the other way. In-roof panels sit flush with the tiles for a clean, recessed finish that many people much prefer, particularly on a front-facing or prominent roof. On-roof panels are clearly raised above the tiles, which is perfectly acceptable but more visually obvious. If appearance is a priority, in-roof generally wins; if generation and budget lead, on-roof does.
Leaks, cost and which to choose
Because on-roof leaves the existing tiles intact, the waterproofing is barely disturbed, and any future panel work is simpler. In-roof relies on the integration kit and flashing to keep water out where tiles have been removed, so the quality of the installation matters more; a well-fitted in-roof system is reliably watertight, but poor detailing creates a leak risk, which is why an experienced installer is important.
On cost, on-roof is the cheaper option in nearly all cases because it is quicker and uses standard mounting hardware. In-roof costs more for the tray and flashing kit and the extra labour, though if you are re-roofing anyway the marginal cost is smaller, since the panels offset some of the roof covering you would otherwise buy.
For a typical retrofit on a sound roof, on-roof is the sensible default: cheaper, faster, slightly cooler and easy to service. In-roof comes into its own on new builds, full re-roofs, and homes where the flush look or planning sensitivities justify the premium. A reputable MCS-certified installer can advise which suits your roof and detail an in-roof system properly if you choose it.
Frequently asked questions
Is in-roof solar more likely to leak?
Not if it is fitted well. In-roof systems use a waterproof tray and flashing to replace the tiles, and a competent installation is reliably watertight. The risk is higher only with poor detailing, which is why an experienced MCS-certified installer matters. On-roof keeps the original tiles in place, so it disturbs the weatherproofing less.
Does in-roof solar generate less electricity?
Slightly, in some cases. In-roof panels sit tighter to the roof with less airflow, so they run a little warmer and can lose a small fraction of output on hot days, since panels are marginally less efficient when hot. On-roof panels have an air gap that keeps them cooler. In the UK climate the difference is small.
Is on-roof or in-roof cheaper?
On-roof is cheaper in nearly all cases. It uses standard rail-and-hook hardware, is quicker to fit and leaves the tiles in place. In-roof costs more for the integration kit, flashing and extra labour, though the gap narrows if you are re-roofing anyway and the panels offset some roof covering.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.