Posted by Tom Raftery PV Product Manager on 29 Oct 2015 at 10:42am - tagged with pv, solar, design

Working in the solar industry it is easy to think that our former leaders are somehow against us, however, over the past year the re-occurring message from government ministers has been that they want to ‘put rocket boosters under rooftop solar’ with a particular focus being on commercial and mid-scale rooftops. Whether this becomes a reality is yet to be seen, but the benefits of installing PV on our schools, offices, shopping centres, factories, police and fire stations, hospitals and other larger scale properties are easy to identify; these buildings generally have large energy usage, which is weighted towards daylight hours making solar PV a perfect fit.

As the industry adapts and evolves to install more and more commercial schemes and therefore flat roofs, it is essential that solar installers and designers understand the varying roof types that they are installing on and ensure that the systems they are installing have as minimal an impact as possible on the roof membranes they are sitting on and in turn the buildings structure. 
The following design considerations should therefore be taken into account on every flat roof project whether new build or refurb:

How old is the roof membrane? Is it due to be renewed? Are there existing leaks? If a roof already has a history of problems, ballasting a PV array on top of it is not only likely to exacerbate the problem but make it very difficult to find the source of any future leaks. If you are looking at a schedule of projects, install PV on the schemes at the time of re-roofing and this will not only reduce install costs but ensure best practice as the roof will be up to the task of supporting the PV array. In new build scenarios, ensure the roof membrane being selected is up to the task. If you are installing the PV on a vulnerable single-ply or liquid system, a protection layer must be in place and the installation team must be very careful not to cause leaks whilst installing.

Unfortunately, flat roof mounting systems are not covered within either the MCS or the upcoming IET guidelines and so there are no regulations in place to ensure that mounting systems are of a quality that will stand up to 20 years plus of wind action. Choosing the right mounting system/anchoring method should be as important as what module you choose to use, especially when you consider the consequences of a system failing. 

When mechanically anchoring solar arrays it is important to understand that any penetration is a risk and that this should be avoided wherever possible. If you must mechanically fix due to wind loads then ensure that the penetration is installed by an approved method from the roofing warranty provider to avoid invalidating guarantees that may be in place.

A better solution is generally to either ballast or weld the mounting system to the roof. These days there are many very good options for flat roof mounting solutions that are both low-ballast and simple to install and far more cost effective than mechanically anchoring.

When ballasting, it is important to ensure that a protection layer is installed and that this is compatible with the roof membrane. It is also important to avoid point and line loads as these could cause the waterproofing to fail over long periods if not checked. Getting the ballast requirements correct is a balancing act between keeping the system light enough to ensure no damage to the building structure and ensuring you don’t end up with panels in your car-park, either of which could be catastrophic. Low ballast does not mean no ballast - in some cases lightweight systems have been known to flex and move damaging the membrane through wear and tear if the correct protection layers are not utilised.

A welded solution can provide the best of both worlds, as there are no penetrations and no ballast to worry about. However, care must be taken that the welding products are compatible with the roof membrane and that if installed as a retrofit the entire roof build up is known and has been installed to the correct standards, as wind loads are transferred  through the whole roof build up.

In conclusion, flat roofs are a perfect location for solar PV - out of the way, easy to install and access, and are generally found on buildings that have the correct type of energy profile. It is paramount however that installations on flat roofs have the above elements considered when designing and installing PV arrays on them. To find out more about how you can benefit from using Bauder roof survey services with roof moisture detection methods contact us on 0845 2718800.

Tom Raftery
PV Product Manager