ᐅ Water on flat roof – double layers of roof waterproofing

Created on: 24 Feb 2015 07:46
H
HilfeHilfe
Hello,

On our attached structures (garage), we have standing water for an extended period (24-36 hours) after rain showers. I estimate about 5 cm (2 inches) and plan to inspect the roof soon.

The developer says this is completely acceptable for a flat roof or even good because of the waterproofing.

I’m having a hard time with that 😳
B
Bauexperte
25 Feb 2015 12:17
Hello,
HilfeHilfe schrieb:

On the outbuildings next to our house (garage), we have standing water after rain showers for an extended period (24-36 hours). I estimate about 5 cm (2 inches), and I plan to check the roof soon.
The developer says this is completely acceptable for a flat roof, or even good because of the waterproofing. I find that hard to believe 😳

I remember your builder as a reliable and competent partner – are you sure there is actually 5 cm (2 inches) of standing water? Our eyes can sometimes deceive us.

If this is indeed the case, it could mean that the required slope of 2% on the flat roof was not properly implemented ... assuming, of course, that the drains are not the cause, for example, clogged with leaves.

Best regards, Bauexperte
H
HilfeHilfe
25 Feb 2015 13:51
Hi Bauexperte,

for me, it means going up onto the roof with a spirit level. I hope it’s not 5cm (2 inches). In the meantime, we had a good conversation. I will keep you updated.
H
HilfeHilfe
26 Feb 2015 07:42
So, water stands about 1.5 - 2 cm (0.6 - 0.8 inches)....

The roof also has a slight slope, but only up to the corner where the gutter is installed. At that point, the roof is level again. Therefore, the remaining 1.5 cm (0.6 inches) of water can never drain off.

It’s somewhat comparable to a shower tray (I hope you understand what I mean).

Now, of course, the question is whether this is harmful or not.....
T
toxicmolotof
26 Feb 2015 08:15
How large is the puddle? I believe it’s probably harmless, BUT I’m not a roofer.

We also have small areas, roughly 20cm by 80cm (8 inches by 31 inches), where about 1cm (0.4 inches) of water tends to collect.
H
HilfeHilfe
26 Feb 2015 08:58
I need to measure again. But it is more like 3 x 3 meters (10 x 10 feet). Basically a low-profile shower tray............
H
HilfeHilfe
27 Feb 2015 09:19
upDate:

Water is standing between 0.7–1 cm (0.3–0.4 inches)....

The roof insulation makes the situation a bit misleading.

Now the question is whether to take action or not. I have always learned that water finds its way... but it could also be that everything above is sealed.