ᐅ Underfloor Heating Installation on a Garage Roof Deck

Hello everyone,

I would like to get some advice on the renovation of our garage attic.
Our single-family house is directly connected to our double garage. There is a door providing access to the attic of the garage.
In March, we plan to install underfloor heating in both the house and the garage attic. For the house, we will use standard polystyrene / EPS insulation boards 50 cm (20 inches) thick.

Now we are wondering if we should use a different construction for the garage attic, for example, 50 cm (20 inches) thick extruded polystyrene (XPS) insulation boards.

Basic floor structure (15 cm / 6 inches):
- Floor covering 1.5 cm (0.6 inches)
- Screed 5 cm (2 inches)
- Underfloor heating (with mat system) 3.5 cm (1.4 inches)
- Polystyrene / XPS 5 cm (2 inches)

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

Looking forward to your feedback.

If you want to achieve better insulation values, you need to switch to PUR/PIR.

Andreas94 schrieb:

- Underfloor heating (dimpled membrane) 3.5 cm (1.4 inches)

Why is that? Why not staple it onto a vapor barrier and insulate better instead?

Andreas94 schrieb:

We are now considering whether to use a different structure for the garage roof floor, for example, 50mm (2 inches) Styrodur / XPS insulation boards.

Why would you want that?
XPS is mainly harder/stiffer/more rigid.
For better thermal insulation, @Benutzer200 has already given good advice regarding PUR/PIR. By the way, for ultimate insulation performance, there are vacuum insulation panels. Only 20mm (0.8 inches) provides the same insulation effect as 100mm (4 inches) EPS 035. However, they are also 5-6 times more expensive.

Benutzer200 schrieb:

If you want to achieve better insulation values, you need to switch to PUR/PIR.

Why is that? Why not staple insulation onto a vapor barrier instead for better performance?

Would you use the PUR board with an aluminum facing? Risk of condensation, etc.?

Our HVAC technician recommended these boards. However, we will discuss again whether it could be done by simply stapling them in place.

Tolentino schrieb:

Why would you want that?
XPS is primarily harder/stiffer/more rigid.
For better thermal insulation, @Benutzer200 has already given good advice regarding PUR/PIR. By the way, for ultimate insulation performance, there are vacuum insulation panels. Only 20mm (0.8 inches) of these provide the same insulation effect as 100mm (4 inches) of EPS 035. However, they are also 5–6 times more expensive.

As I said, we are here looking for the best possible solution...
Your experience on how and why we can do this is needed here 🙂

We will definitely consider the PUR boards. Thanks.

Andreas94 schrieb:

Would you use the PIR board with aluminum facing? Risk of condensation, etc...?

Yes. For example, you can tape the joints with aluminum tape and cover with a grid foil. You can staple directly into the insulation.