ᐅ Is water on a flat garage roof problematic or hazardous?

Created on: 14 Feb 2018 20:20
M
Marchonisch
Good evening

There is always water standing on our garage roof. In my opinion, the drain is incorrectly positioned.

The architect and the structural builder say this is normal and not a defect.

However, my roofer sees it as problematic. He says mold can develop...

What is your opinion or recommendation?

Flat roof with green roof waterproofing, construction wood remnants at the edge, autumn trees in the background.
H
HilfeHilfe
15 Feb 2018 06:45
We had a similar situation. Although there was a drainage system, water still accumulated in various spots from time to time. The developer said it evaporates and is within the standard.

In the end, he covered all the roofs, including the neighbors’, with plants at his own expense.
M
Marchonisch
15 Feb 2018 07:02
No, we want to use the roof as a terrace...

The drain is located roughly in the middle on the left side in the photo.

I think I need to take care of a new drain.

Since my architect says this is normal, I probably need an expert report to request that he address the defects.

What do you think?
S
Steven
15 Feb 2018 07:44
Hello Maronisch

The drain is at the highest point. There is no slope towards it. That is a problem.
Are you planning to build up the terrace? Then it could be leveled out again. But as it is now, it is incorrect. The drain should always be at the lowest point, otherwise it doesn’t work properly. In your case, it acts as an overflow.

Steven
B
Bieber0815
15 Feb 2018 07:50
Only a specialist construction lawyer can provide you with proper advice on this! First, it depends on what was agreed upon and with whom. Then, it is questionable whether having the right also means being granted justice. For a garage, I would advise against filing a lawsuit. Since you are planning a terrace, I see the situation somewhat differently.
Steven schrieb:
Are you adding a raised structure to the terrace? That could compensate for it.
The waterproofing layer will certainly not be affected by a terrace structure. It actually makes things worse because water accumulates under the terrace. As I said, in the case of a garage: it does not matter if the roof is watertight, the water evaporates. But when you place a terrace on top, water remains trapped under the terrace construction on the roof. It is better to use a structure that is as open as possible.

I would try again to discuss the matter objectively with the architect (assuming they are responsible). Demolition and rebuilding does not have to be the only solution. There should be an open discussion about how to achieve a technically sound condition without standing water, even with a terrace.
11ant15 Feb 2018 18:17
Marchonisch schrieb:
So, a defect. From the shell builder or the architect?

From the architect – unless the shell builder did not follow the plans.
Marchonisch schrieb:
What are the consequences?

Standing moisture.
ypg schrieb:
Still, they do what they are supposed to: they are watertight.

Even the watertightest pond is still a pond—not a roof. A drainage system should be designed so that evaporation is not needed to assist it.
Marchonisch schrieb:
No, we want to use the roof as a terrace...

Then it is often planned without a slope to keep the substructure of the surface covering simpler. I’m afraid there is a good chance that the inspector will then really approve it that way.
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M
Marchonisch
15 Feb 2018 21:37
Thanks a lot for your feedback.

The architect insists that everything is fine. The structural builder says he tended to position the drainage differently.

What would you recommend for a construction that can later be used as a terrace?