Flat Roof Solar Panel Installations

Recent changes to legislation mean that there is no longer a need to obtain planning permission when installing on flat roofs. It was the case that permission was required for domestic installations (and for commercial installations over 1MW), which meant additional costs and lengthy delays – but no longer!

There are however other considerations to take into account when installing solar on flat roofs, as follows: –

Available roof space

When installing on flat roofs, it is important to observe a minimum 600mm exclusion zone around all roof edges, in order to keep the panels away from the worst of the effects of wind uplift. Panels installed closer to the roof edge than this may not be guaranteed in the event of damage, and could even be unsafe.

This means that the amount of space on small roofs is restricted, and many dormers are just not large enough for a viable array.

Construction and Fixing Method for Flat Roofs

Panels on flat roofs can either be fixed, or ballasted.

A fixed system penetrates the roof covering, fixing to the substructure below. A weathertight seal is then laid over the roof fixings. Usually this method is installed on new roofs, so we can tell exactly what the roof substructure is, and the roofers can create the weathertight seal (thus ensuring guarantees are unaffected).

Ballasted systems do not penetrate the roof covering – but instead rely on additional weight (placed on the mounting frame, usually in specially designed containers) to hold the system down on to the roof. The amount of weight (or ballast) required is calculated according to the location, size and height of the roof. It is important that a structural engineer then verifies the ability of the roof to withstand the additional load, as the weights involved can be significant.

Ballasted Solar PV installation on flat roofs
Ballasted Flat Roof Installation

Roof Access

While solar PV systems need little maintenance, panels on flat roofs can need a little more attention, so thought needs to be given to location.

Panels on flat roofs tend to be installed at a low pitch (ten degrees or so), which makes dirt build up more likely, and therefore cleaning needed more frequently. Visual checks should be carried out to ensure that no debris builds up under or round the array, and if there is no access to the roof, then it is not even possible to inspect the array, let alone clean it if necessary.

A decent inverter or monitoring system might let you know if there is a problem – but access to a dormer roof can be costly, so bear that in mind when making your decision.

At Ecocetera we are always happy to look at a flat roof and give you advice on whether or not an array would be suitable – do contact us for further information.