Build a wooden workshop attached to the house

Now this is just theory! For that, you would need to know the structure of the exterior wall of the house (cross-section), heat pump planning. Otherwise, it is difficult to answer seriously from a distance.

The structure of the exterior wall from inside to outside. -160mm timber frame with insulation in between -12.5mm gypsum fiberboard -140mm insulation boards (expanded polystyrene rigid foam) -6.5mm exterior plaster

I don't know how it looks with the approval requirement.

But thanks for the hint.

Ignoring this hint from could make all other considerations pointless. You can risk that when building onto an old building, but with a new building? Maybe even in a new development area?

Yes, heated basically sounds like a living space expansion. That won't be approved that easily.

Ignoring this hint from could make all other considerations unnecessary. When attaching to an old building, you can take that risk, but with a new building? Maybe still in a new development area?

The architect who is designing our house is also handling the building application for the workshop/hobby room for us. He made sure during the preliminary design discussion that we comply with the building boundaries. That's why it is also connected to the house. The workshop/hobby room could also be positioned to stand free. But then I would have to cut off a corner of the workshop/hobby room to comply with the building boundary and would have a narrow passage of 1m between the house and workshop.