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Cool ceiling tile

Bingo!

You’re out if your element, Donny

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We use three horizontal strips of thin flat stock metal attached to the studs with truss head screws before sheetrock to provide solid blocking at top and bottom of upper cabinets and also at top of base cabinets. The stock can be 20 or 22 ga. And 6" wide. You still may want to catch studs as best you can. I posted a picture showing the two strips that hold the upper cabinets. I’m not sure what the metric equivalent to gauge would be but you guys probably have something similar.

Looks like the concrete falls off on the right.

The gasket at the bottom of your overhead compresses to help create a seal along an uneven surface, but it can only do so much. Your gap may be too large to seal before the door bottoms out completely on the left. That said, there is adjustments that set where the door comes to a stop when closing, check your manual and see if the overhead can lower further.