Flat concrete roof for garage that becomes a puddle when it rains

[Bosegosen]

Hello,

We have a garage that has been excavated from the slope and then cast. The roof is a concrete rectangle with a smaller outhouse built on top. When it rains, the water doesn't drain off the roof but instead collects in various smaller valleys and depressions. The drainage channels that exist are also somewhat unintelligent as they are deepest in the middle.

I probably don't need to say that we have a moisture problem in the garage. ;-)

What can I do? My thought is to first level the roof with some leveling compound and then, similar to a self-leveling compound, create a slope from the middle outward. Suggestions/thoughts?

Best regards

 

[Peter2400]

Hello,

We have a garage that has been dug out of the slope and then cast. The roof is a concrete rectangle on which a smaller shed has also been placed. When it rains, the water does not run off the roof but gathers in various small valleys and indentations. The drainage channels that exist are also somewhat unintelligent as they are deepest in the middle.

Needless to say, we have a moisture problem in the garage. ;-)

What can I do? My thought is to first level the roof with some leveling compound and then like self-leveling compound, create a slope from the middle outwards. Tips/thoughts?

Best regards

What type of waterproof membrane is on the roof?
It shouldn’t matter if water remains as long as it is tight.

 

[Bosegosen]

Don't know. It was built in the mid-70s and the blueprints are sparse regarding information. What I can see from the outside is concrete and from the inside (the ceiling) that kind of insulation that resembles tagliatelle (pasta) that has been painted on. I know, the world's worst explanation but an attempt at least.

I would guess that it is not completely airtight.

 

[Bosegosen]

This is what it looks like when it has rained a little.

 

[Rabbithole]

One option is to apply filler to create a slope and seal.

Otherwise, it's possible to frame up a sloped roof. Like metal, channel plastic, etc.

 

[Bosegosen]

What filler? I'm somewhat of a rookie here.

The idea is to have a sofa set or something similar up there eventually. There is already a small cabin (as seen in the picture) and there's a fence.

 

[Rabbithole]

Putty can be applied thinner than concrete. There are lots of different types and I'm not the right person to say which type. 1cm/decline and something to seal with.

 

[Peter2400]

This is what it looks like after a bit of rain.

If you can attach an EPDM rubber sheet properly, it will last at least 30 years. It doesn't matter for the sheet if there is water on top.
https://www.bauhaus.se/gummimatta-firestone

 

[Rickard.]

I am actually quite pessimistic about EPDM roofs aimed at private individuals as they mix factory-vulcanized seams (100% tight and incredibly strong) with seams joined in roughly the same way as underlay fabric, which becomes a bit ridiculous.

But in your case, I think it is a really good solution; order a sufficiently large piece of fabric that covers the entire roof and a little extra, and all the upturns and ends are glued with contact adhesive. On top of that, you can build a deck if you want to utilize the space.