ᐅ Green Roof on Flat Roofs: Managing External Drainage Outlets

Hello everyone,

I am currently building my own home with a flat roof. It needs to be greened, which I would like to do myself. Most things are clear to me, but I still need some advice on one point: How should I deal with our external drainage (the spot where a pipe passes through the parapet)? I probably shouldn’t put gravel directly in front of it. But should I simply leave a gap in the gravel, or would it be better to install a barrier made from L-profiles?

I hope I was able to explain my concern clearly enough.

Best regards,
Daniel

Hello, L-shaped concrete blocks are overkill. Planting something right in front of them is not a good idea because the roots will eventually constrict or even block the pipe. I would place large river stones in that area. You can find these at hardware stores. This way, the whole area remains accessible (e.g., in spring) for inspection and cleaning.

Planting usually does not extend all the way to the parapet but is typically separated, for example, by gravel strips. The roofer will of course ensure that openings or penetrations remain clear.

Are there any long-term experiences with green flat roofs on single-family houses? They have recently become quite common in development plans due to regulations, but how durable are they compared to, for example, a traditional pitched roof? It also seems (just a feeling) initially more expensive and risky, with the possibility of needing more frequent and extensive repairs over 40 years than the proven alternative.

BackSteinGotik schrieb:

Are there any long-term experiences with green flat roofs on single-family homes? They have become quite common in recent building plans due to regulations, but how durable are they compared to, for example, a traditional pitched roof?

They are two completely different things. A pitched roof has a slope, and roofing tiles usually come with a 30-year warranty if they are not damaged, and require little maintenance. A green roof is always installed on a flat roof (only a slight slope is possible without extra effort) and carries a higher risk, for example, due to leakage.

We have two houses with green pitched roofs in the wider neighborhood. They look great. The roof pitch is… hmm, definitely less than 45° (122°F).