House and garage, close the gap between both structures?

The facts. The house structure is made of Ytong. Plastered. Garage concrete, prefab garage. Both stand next to each other, close together. The house is not plastered where the garage adjoins, so pure Ytong. Should the gap be closed with PU or silicone or left open because of drafts? What is professionally recommended?

I add. The BU wants to apply a PU seal with Sikaflex or similar. Then it will be tight. Karsten

Absolutely untreated Ytong? The water that gets in between probably won't be good for the stone in the long run.

"Spalt" and "eng"
means in centimeters?

Ytong pure. The joints are already well protected because our roof overhang is really generous. They are about 1 cm thick, about the thickness of an index finger.

PU joint would mean completely sealed. PU material is really waterproof, even permanently underwater. Open would mean air would always get in. Like with clinker before Ytong. Karsten

A common expansion joint is 2 cm, that is a good amount to bridge as a joint. I would use a waterproof material to close this joint. And if necessary, install small tubes (about thin empty conduits ?) as ventilation approximately every half meter at the top, under the eaves and about a hand's width above the garage roof ending. At the bottom at plinth height horizontally as well, one on each side. This as a suggestion for good measure, so that the bare Ytong does not stand in thick air.

I had feared, for example, a 5 cm gap, which would have required more effort.