What is Flat Roof Solar Mounting
What is Flat Roof Solar Mounting
To many people it seems that flat roofs should offer a far simpler starting point for a solar system than sloping roofs. In some ways that’s true, but there are a number of issues that need to be taken into account:
All solaracks flat roof solar installations require planning permission, whereas pitched roof installations are generally covered under ‘permitted development’. Non-domestic flat roof systems are usually fine without planning permission, but see our page on planning for more details.
Flat roof systems take up more space per kW than sloping roof systems, as separation between rows of panels is required to prevent one row of panels shading another.
Space becomes even more restricted given the fact that there usually needs to be a 0.5-1m border between the system and the edge of the roof.
Flat roof solar is usually ‘free-standing’ on the roof. The mounting frames are not secured to the roof and therefore the system has to be weighted down using ballast. The structure of the roof needs to be able to support the ballast.
The panels can be mounted east-west or south facing (or in between, depending on roof orientation). To mimimise ballast and optimise space, they are usually mounted at an angle of 10-12 degrees to the horizontal, as opposed to the ‘UK optimal’ angle of 30-40 degrees (see below).
On commercial properties, flat roofs tend to be a repository for air conditioning systems and lift motor housing. These need to be avoided to minimise shading. Furthermore, as always, health and safety is a key consideration, both for initial installation and on-going maintenance.
Roof warranties It is important that the system does not compromise the roof warranty. Most roof warranties are compatible with a free-standing, ballasted solar system. But with some roof types and membranes – e.g. Bauder roofs – a specialist fixing system may need to be used. If the system is fixed to the roof, it is important to check the impact on the roof warranty and to ensure water tightness is maintained.
Roof condition Before installing solar it is important to make sure that the roof is in a good condition. It’s clearly easier to take ‘free-standing’ panels off a flat roof than it is to take bolted panels off a sloping roof, and on a flat roof upgrade a few years into the solar system installation won’t actually be too disruptive. That said, if your flat roof uses standard roof felt, it would be worth ensuring it’s in tip top condition before installing solar.
Some felt roofing can melt in the summer heat and then become brittle in lower winter temperatures. It can also be affected by UV rays. It therefore tends to develop leaks and needs replacing every 10 years or so. It may be worth upgrading the roof membrane ahead of installation – these days there are maintenance free membranes that are guaranteed for 15-20 years and should last 30 years.
Roof structure All new-build flat roofs require a warm roof construction to comply with Part L of the Building regulations. Again, it is important that the solar system does not compromise the functioning of the warm roof and that this is taken into account when designing the solar system.