Roof-integrated vs on-roof solar panels

Roof-integrated and on-roof solar do the same job by different means. On-roof mounting fixes panels above the roof covering on a frame, and it is by far the most common option for domestic installations¹. Roof-integrated systems replace the covering itself, with solar tiles fitted to the roof instead of normal tiles so the installation does not affect the look of the roof².

The performance gap is smaller than most buyers expect. A government consultation on the Future Homes and Buildings Standards reported a 3% difference in annual generation between on-roof and in-roof systems³. The cost gap is larger: solar roof tiles are normally about 1.5 times the cost of a solar panel installation², and panels on top of the roof are described as the cheapest option while tiles are the most expensive for the equivalent system⁴.

The choice therefore turns on roof condition, roof covering and appearance rather than on output. Integration is an option for tiled roofs, offering potential savings if the tiles are near the end of their life anyway⁵. Where the roof is sound and staying as it is, on-roof mounting keeps the two layers separate and the work simpler.

Roof-integrated vs on-roof: the short answer

The two mounting styles differ in where the weatherproof layer sits. On-roof systems screw roof anchors directly onto the roof rafters and connect bars to those anchors to create a frame, with the panels sitting above the covering⁸. Integrated systems put the solar product into the roof plane itself, so the panel or tile is part of the weather envelope rather than an addition to it.

That single difference drives everything else. Because the covering is replaced rather than overlaid, integration is a roofing job as well as an electrical one. A professional roofer can carry out the installation of integrated tiles, but a solar electricity professional is required to wire them together⁹. On-roof work still needs a competent roofer for the anchors, but the covering stays in place.

Generation is close. The 3% annual difference reported in the Future Homes and Buildings Standards consultation is the most useful single figure for comparing like with like, because it compares on-roof and in-roof systems rather than panels and tiles³. Solar roof tiles are a distinct product and are less efficient per area than solar panels, typically producing only 80% of the electricity for the same surface². An independent guide reaches the same conclusion in different words: tiles are not as efficient as solar panels and will produce less electricity from the same surface coverage⁹.

For a household, the practical question is what the roof is doing anyway. If it is being replaced, integration folds a roofing cost into a solar cost. If it is not, on-roof mounting leaves the covering untouched and keeps the cheapest route to the same generation⁴.

What each mounting style actually is

On-roof mounting is a mechanical assembly. Roof anchors are screwed directly onto the roof rafters, and bars are connected to the anchors to create a frame that carries the panels⁸. The covering stays intact underneath, and the panels sit on top of it. This is the arrangement behind the great majority of domestic installations¹.

Integrated mounting removes the distinction between covering and generator. Solar roof tiles, also called solar slates or solar shingles, are fitted to the roof instead of normal tiles². They are built into the structure of the roof itself, which is what allows them to blend in as much as possible⁹. The same principle applies to in-roof panel systems, where a framed panel replaces a section of covering rather than sitting above it.

The mounting hardware market reflects both approaches. Flat roof systems have their own standards, and the MCS 012 v3.0 scope was expanded to include non-mechanically attached mounting systems alongside mechanically attached systems designed for installation on flat roofs of 10 degrees or less¹⁰. Pitched roof work, whether on-roof or integrated, follows the same principle of fixing into the structure.

Two consequences follow from the construction difference. First, integrated systems leave no gaps for birds or rodents to get into, because there is no void between panel and covering¹¹. Second, they can be complex to retrofit¹¹. The roof has to be opened up, and the covering around the array has to be made good.

Efficiency: on-roof edges ahead, but only slightly

The headline comparison is the 3% difference in annual generation between on-roof and in-roof systems reported in the Future Homes and Buildings Standards consultation³. That figure compares mounting positions for the same kind of generating product, and it is the fairest single number available for the choice this page covers.

Solar roof tiles are a separate case. They are less efficient per area than solar panels, typically producing only 80% of the electricity for the same surface². An earlier independent guide puts it as tiles not being as efficient as panels and producing less electricity from the same surface coverage⁹. The reason is geometric: a tile has to look like a tile, which constrains the cell area and the packing density compared with a framed module.

Orientation and pitch matter more than mounting style. An east or west facing roof produces 15% less energy, and a north facing roof around 30% less⁷. South facing roofs typically perform best, though north facing roofs can still benefit⁵. A 3% mounting penalty is small beside a 15% or 30% orientation penalty.

Roof area is the other constraint. The size of the roof may dictate the type or number of solar PV panels that can be installed¹². Because tiles deliver less output per square metre, a roof that is marginal for on-roof panels may be more marginal still for tiles, and a larger array may be needed to reach the same annual generation.

For a household, the honest reading is that mounting style is a second-order decision on output. The first-order decisions are orientation, shading and available area, which are covered in roof orientation, pitch and shading.

Cost: integration carries a higher upfront price

Solar roof tiles are normally about 1.5 times the cost of a solar panel installation². An older independent guide puts tiles at approximately double the price of solar panels⁹. The two figures disagree, and the newer one is the better guide to current pricing, but both point the same way.

The direction of travel is consistent across sources. Panels on top of the roof are the cheapest option, while tiles are the most expensive for the equivalent system⁴. Cost depends on size, how easy it is to access the roof, and whether panels or tiles are preferred⁵. Whether a system uses panels or tiles, and whether it is roof mounted or ground mounted, are both named as variables affecting the overall price⁸.

Two factors can narrow the gap. Integrated systems are an option for tiled roofs, offering potential savings if the tiles are near the end of their life anyway⁵, because the roofing cost would be incurred regardless. And the cost of rooftop solar installation may be 10% cheaper for new builds, according to Solar Energy UK³, which is where much integrated work happens.

Against that, the risk profile differs. The risk of damage to roofs is 20 times higher with roof-integrated systems than with roof-mounted systems, according to a government literature review on fire in solar PV systems⁶. That finding dates from 2017 and concerns roof damage during and after installation, but it is the only comparative risk figure available and it belongs in any honest cost discussion.

Prices for both routes are installer quoted, and no published UK price list applies across the market. The wider cost picture, including what drives quotes, sits in how much do solar panels cost in the UK.

Roof covering compatibility: what integration works with

Integrated systems are an option for tiled roofs⁵. Solar tiles and slates can integrate with new and existing roofs and are compatible with a wide range of roof tiles and slates⁴. That breadth is the point of the product: the array has to marry into whatever covering surrounds it.

The hard limit is timing. Integrated photovoltaic tiles can be installed as part of a new build property or as a roof replacement, but not into an existing roof⁹. This is the single most important compatibility rule on the page. A household with a sound roof and no plans to replace it is not a candidate for integrated tiles, whatever the appearance appeal.

Where a roof is being renovated, the position changes. Existing panels could be refitted to a renovated roof instead², which keeps the on-roof array and takes the opportunity to renew the covering beneath it. That route avoids the retrofit complexity of integration while still ending with a new roof.

Building regulations apply to roof work either way. If a solar panel is installed on a roof, building regulations will normally apply¹³. Where solar products form a roof covering, that is, where they are roof-integrated, a fire classification is required so that compliance with Building Regulations, specifically Regulation B4 on external fire spread, can be demonstrated¹⁴. Products that cannot meet that requirement cannot be integrated into roofs in compliance with the Building Regulations¹⁴.

Flat roofs are a separate case. Solar panels can be installed on both pitched and flat roofs, and on a flat roof the panels need to be tilted and spaced to avoid shading¹⁵. Flat roof mounting is not an integration question in the same sense, and the standards for it are covered in solar panel mounting systems.

Ventilation and temperature: why airflow matters

Roof ventilation is a building regulation matter before it is a solar matter. When ventilating a roof, air should be able to enter at one end and travel through to the other end where it can exit¹⁶. That continuous path is what keeps a roof void dry.

Introducing an opening into a roof covering does not remove the requirement. Ventilation of the existing roof void has to be considered, as air must still be allowed to flow from one void to another¹⁸. An integrated array changes the covering over part of the roof, so the airflow path has to be preserved around and through the altered section.

The temperature question is usually framed as panels overheating through reduced airflow. The published evidence here concerns the roof void rather than the modules. Insulating at ceiling level results in a colder attic space above, meaning an increased risk of condensation and pipe freezing¹⁹. That is the opposite problem to overheating, and it shows how sensitive roof voids are to changes in how they are ventilated and insulated.

Insulation itself is a separate layer with its own logic. Inverted roof insulation goes above the weather membrane, protecting it from heat and cold that can shorten its life and that of the roof deck²⁰. Insulation keeps homes cool in summer and warm in winter and means less energy is wasted through draughty windows, walls and roofs²¹. Room-in-roof insulation involves fitting insulation to provide a continuous thermal envelope around the room space²².

For a household, the practical point is that an integrated array is not a standalone change. It interacts with the roof void, the insulation and the ventilation path, and those interactions are what a competent designer has to resolve. The general retrofit context is set out in retrofit explained.

Which suits which home

The clearest split is by roof condition. A household with a sound roof that is not being replaced is served by on-roof mounting: it is the most common domestic option¹, the cheapest for the equivalent system⁴, and it leaves the covering undisturbed. A household replacing a roof, or building new, is the natural candidate for integration, where the roofing cost is being incurred anyway⁵.

Appearance is the other driver. Solar roof tiles are fitted instead of normal tiles so the installation does not affect the look of the roof², and they are built into the roof structure to blend in as much as possible⁹. Where a roof is prominent or the covering is being matched, that matters. Where it is not, on-roof panels deliver more output per square metre at lower cost.

Roof geometry constrains both. The size of the roof may dictate the type or number of panels that can be installed¹². South facing works best, east or west will work well, and north facing roofs can still benefit⁵. Skylights or roof vents may make it harder to install solar panels and increase the installation costs, and a steep roof might slowly build up dirt on the panels⁵.

Some settings impose their own rules. Under one local listed building consent order, solar panels should be installed on the inverted slopes of a butterfly roof, or a flat roof at a minimum of two storeys or six metres above street level²³. That is a site-specific condition rather than a general rule, but it shows how far local heritage controls can shape what is permitted. The wider constraints are covered in solar panels in a conservation area and listed building consent for solar panels.

For energy independence, the mounting choice changes little. Either route generates on the household's own roof and reduces the electricity drawn from a supplier, and either route remains grid-connected, dependent on a certified installer for the electrical work¹² and on the roof itself for the resource. What integration adds is a longer-lived roof under the array; what it removes is the option to treat the covering and the generator as separate layers when either needs work.