Garage on the slope, external sealing, is Styrodur necessary?

Hello everyone,

We had to build a double garage into the hillside due to lack of space. The soil is very clayey and drains water poorly.

The wall thickness of the garage is 25cm, cast with WU concrete. Bitumen primer and bitumen have already been applied. The plugs in the wall were additionally sealed on the outside with bitumen roofing felt.

Now the following question:
How would the garage be properly sealed on the hillside side? Should Styrodur boards be glued to the bitumen on the outside and then the dimpled membrane? Then frost protection gravel?

Are there good experiences with this?

Photo attached.

Many thanks in advance.

Best regards, Richie

Was only WU concrete poured or was a WU basin constructed? In other words: including sealing of all joints as well as limiting crack widths through reinforcement?

If a complete WU construction, why was bitumen additionally applied? It is rather redundant. If not, then WU concrete was not necessarily required either, since sealing is supposed to be done by bitumen.

The Styrodur boards have no sealing function at all. In this case, they only serve as mechanical protection for the bitumen sealing (or as thermal insulation, if necessary, but then everything would have had to be insulated accordingly). You can do it, but depending on the drainage concept, it might make more sense to bond XPS drainage boards.

Thank you for your reply.
On the edge of the base slab, where the wall was erected, 20 cm high sealing strips were cast in between the reinforcement.

We applied bitumen on the outside as additional protection, also to prevent the dimpled membrane from being damaged later on the exterior wall of the garage.

For drainage, we plan to lay drainage pipes around the garage. First, stabilize the ground with gravel. Then place fleece over the pipes and gravel again before filling with backfill soil.

The garage space is intended to be "just" dry and occasionally used as a party room.