Underfloor heating installation on garage roof attic

Good day everyone,

I would like to get advice on expanding our garage attic.
Our single-family house is directly connected to our double garage. It is accessible from the attic via a door.
In March, we want to install underfloor heating in both the single-family house and the attic of the garage. In the house, we will use "normal" Styrofoam / EPS 50 mm.

We are now wondering if we should use a different construction in the garage attic roof. For example, Styrodur / XPS insulation boards 50 mm.

Basic structure of the floor (15 cm):
- Floor covering 1.5 cm
- Flow screed 5 cm
- Underfloor heating (nop plate) 3.5 cm
- Styrofoam / XPS 5 cm

Basically, I want to get recommendations. Since the ground floor of the garage is not heated and the concrete ceiling would only be insulated via the underfloor heating. The garage is intended to be used as a party room in winter.

Looking forward to your feedback.

If you want to achieve a better insulation value, you have to switch to PUR/PIR.

- Underfloor heating (studded covering) 3.5 cm

Why like this? Why not staple onto foil and insulate better instead?

We are now asking ourselves whether we should resort to a different construction in the garage attic. For example, Styrodur / XPS insulation boards 50 mm.

Why would you want that? XPS is especially harder/ stiffer/ more solid. For more thermal insulation, has already given good advice about PUR/PIR. By the way, for the ultimate insulation effect, there are vacuum insulation panels. 20mm are enough for the same insulation effect as 100mm EPS 035. However, they are also 5-6 times more expensive.

If you want to achieve a better insulation value, you have to switch to PUR/PIR. Why is that? Why not staple onto foil and insulate better that way?

Would you use the PUR board with aluminum foil facing? Risk of condensation, etc...? Our HVAC technician recommended these boards to us. However, we will discuss again whether it could be done with simple stapling.

Why should you want that? XPS is above all harder/stiffer/denser. For more thermal insulation, has already correctly advised on PUR/PIR. By the way, for the ultimate insulation effect, there are vacuum insulation panels. Only 20mm of those are enough for the insulation effect of 100mm EPS 035. But they are also 5-6 times more expensive.

As said, we are here looking for the best possible solution.. How & why we do it, your experience is needed here :) We will definitely deal with the PUR board. Thanks.

Would you use the PUR board with aluminum coating? Risk of condensation etc...?

Yep. Then, for example, bond joints with aluminum and put raster foil on top. You can staple directly into the insulation.