ᐅ Water on a concrete garage roof

Hello,

We have attached the garage directly to our house. It is built with masonry and the roof is made of concrete. The waterproofing between the garage and the house has already been completed. On top of the garage, there is now a black membrane, and metal flashing has been installed all around the outside.

Near the house and garage, there is a drainage outlet. Gravel is planned to be spread over the garage roof later.

We have often noticed that after rainfall, water remains standing and does not drain away, only disappearing through evaporation. The water also stands on the side of the garage facing away from the house, where there is no drainage.

A colleague suggested that we could pour screed on top and then create a slope towards the drainage outlet. Does this method work with screed? Are there any concerns to consider, such as frost or other factors?

Do you have any other suggestions on how to create a proper slope here? Or any other ideas on how to solve this issue?

Thank you.

Best regards,
xdiver

Who installed the roof on the garage? In the end, they must also ensure professionally that water drains properly according to the specifications.

Adding another layer of screed could cause structural issues. Have the garage builder come and request a correction. The slope on the roof must be directed towards the drain (you can check this using a spirit level).

Hello,

xdiver schrieb:

We have often noticed that after rain, the water always remains standing and does not drain away, disappearing only through evaporation. The water also sits on the side of the house half facing away (there is no drainage here).

Did you build the garage yourself or did you hire a contractor? And who came up with the idea to slope the surface toward the house?

xdiver schrieb:

A colleague suggested that you could pour a screed on top and then create a slope toward the drainage. Does this work with screed? Or are there any counterpoints (frost, etc.) that need to be considered?

The garage is based on structural calculations; therefore, it depends on how load-bearing the existing masonry is. Only once this is known, can such a measure be considered.

xdiver schrieb:

Do you perhaps have another way to create a slope here? Do you have other ideas on how to solve this problem?

The slope should be greater than 2%.

Either way, it reads like a botched job and, from my point of view, the responsible party must be determined. If you built the garage yourself, you will have to take responsibility and cover the repair costs. If there is a formal contract for the construction of a masonry garage, hold the contractor accountable and immediately demand a written remedy of the defect.

Regards, Bauexperte

Bauexperte schrieb:
Hello,
Did you build the garage in shell condition or did you hire a contractor? And who came up with the idea to slope the drainage towards the house?

The garage was built by the contractor.
The idea to place the drain there came from the architect. When I asked why the water doesn't flow away here, he just said it’s not a big deal.
Just put stones on it and it will be fine.
He also believed that the drain could be relocated, but without a slope, the water won’t flow.

Bauexperte schrieb:

There is structural engineering behind the garage; so it depends on how load-bearing the existing masonry is. Only when this is clear can such a measure be considered.

The slope should be greater than 2%.

I will give that to the architect as something to look into.
Do you have any links or regulations regarding garage roof construction that I could refer to?

Can screed that much affect the structural integrity? As far as I know, the roof is designed for 85 kg/m² (17.4 psf). So adding 5 cm (2 inches) shouldn’t cause any structural problems, or am I mistaken?

Bauexperte schrieb:

Either way, this looks like poor work, and in my opinion, it needs to be clarified who is responsible. If you built the garage in shell condition, you have to take responsibility and cover the repair costs yourself. If there is a formal contract for the construction of this masonry garage, you should hold the contractor accountable and immediately demand written rectification of the defect.

Best regards
xdiver