Photovoltaic system on flat roof / loads?

Hello everyone,

As part of our house planning, we want to make all the preparations now to later install a photovoltaic system on our flat roof. We have already planned a conduit for this, which will be laid from the flat roof into the utility room on the ground floor. Now the construction company is asking for which loads the roof should be designed. We are currently in the process of asking some suppliers.

Does anyone of you have any experience or reference values regarding this? We definitely do not want to have the system fixed to the roof / drilled into it. It should be mounted on supports, probably at an angle of about 25 to 30 degrees. On the internet, you always read something like about 10 to 30 kg per square meter. Is that plausible?

Thank you very much for your rough assessment.

Yes, that fits. As long as the flat roof is "hard," a photovoltaic system is no big deal in terms of the additional load.

nooo, rather not...

There are plastic carriers with aluminum profiles onto which the modules are screwed. The plastic carriers are filled with sand or similar. To counteract the wind load on inclined modules, you need more than the specified 30Kg/m²

Alternatively, aluminum triangles that are screwed to the modules, with weights like "concrete paving slabs" or similar. Here too, 30Kg is not enough.

And as always: beware, this is half-knowledge read up by an amateur, no guarantee on anything.

P.S. Consider combining a green roof with photovoltaics, I see that as the optimal combo...

Yes, you are right, if it is not to be anchored, more ballast is needed! Still shouldn’t be a big deal. Some systems reduce the necessary ballast by connecting entire rows. There are also special aerodynamic solutions.

They wanted to force a [Gründach] here as well, but that would have been economically nonsense. You put greenery and lay a photovoltaic module on top, very clever. Fortunately, they backed off from that.

Warning, this is only the acquired knowledge of an interested layperson and operator: The modules with a normal substructure alone weigh around 20kg/sqm.

Not drilling into the flat roof is definitely a good idea. But then, as already mentioned, you have to put ballast on the mounts. How much ballast depends on your wind load zone. Find that out and then look at the specifications of the parts for the mounting system.

Do you have a tip on which manufacturer or provider is best to contact for this? You can find many posts on the internet, but I need an exact calculation for the construction company. Of course, I am familiar with the common providers, but I am also very happy to receive recommendations.