ᐅ Insulating the basement floor

Dear community,
We recently purchased a terraced house with a basement located above an open underground garage. The concrete ceiling between the garage and basement is about 30 cm (12 inches) thick and quite cold during winter. We now want to convert the basement into an office. Therefore, we would like to insulate the floor, install underfloor heating, and cover it with a linoleum floor. Unfortunately, we can only allow a maximum of 6 cm (2.4 inches) floor height increase.

We are considering installing underfloor heating that already includes a thin insulation layer. My question is: How should I build up the entire floor structure? Where should a vapor barrier or vapor retarder be installed? Does anyone have experience with this? Widder says that the supplied PE foil should be placed above the heating system...

Thank you very much for your answers.
Best regards,
Patrick

Hello Patrick,
Your project will hardly be feasible. A construction height of 6cm (2.4 inches) is too low for a hydronic underfloor heating system. Even if these 6cm (2.4 inches) are enough for the pipes, heated screed, and linoleum, there would be no space left for the necessary thermal insulation. This would mainly heat the ceiling between the garage and basement, which is ineffective.
The floor might feel warm to the touch, but it would hardly be suitable for room heating—and if it is, the heating costs would be extremely high.

Hertweck schrieb:
Hello Patrick,
Your project is hardly feasible. A construction height of 6cm (2.4 inches) is too low for a warm water underfloor heating system.

Hello Hertweck, I would like to correct and add something here. Such systems are indeed possible in Switzerland. There are several companies offering these types of systems. I have encountered such cases quite often in my practice.

@Patrick
The vapor barrier, typically a bitumen membrane, must be applied directly on the raw concrete or its leveling layer. After that, install the insulation with the integrated heating system, followed by the special leveling compound, and finally the floor covering.

Hello BauLine,
What is this covering compound made of, and what thickness is typically applied in Switzerland?

I mean: If I take the bitumen vapor barrier (approx. 1cm (0.4 inches)) + linoleum (0.5cm (0.2 inches)), we still have 4.5cm (1.8 inches) left for the underfloor heating system and the covering compound.
Setting aside Germany’s strict energy-saving regulations for a moment, 4.5cm (1.8 inches) hardly seems sufficient for proper thermal insulation in Switzerland either—would you agree? And now add the thickness of the covering compound as well.

I’m very interested in how a thermally insulated underfloor heating system with heating screed/covering compound and floor covering can fit within a total build-up height of 6cm (2.4 inches)—Switzerland or not, this is a matter of construction.

Hello Hertweck

The manufacturer Sika probably won’t disclose the exact composition of the material. It was developed specifically for the requirements of, or in cooperation with, the system manufacturer.
The system, with a possible supply temperature of 25-35°C (77-95°F), only requires a build-up height of 10mm (0.4 inches). This leaves about 4.0 cm (1.6 inches) for good PUR insulation, which is definitely better than nothing if the user wants underfloor heating. Since this is for an office—or even just a personal study—it is probably not comparable to the usual living areas. Moreover, for tax reasons, he will likely carry out the installation internally and will not report the renovation to the local building authority (building permit / planning permission).

I hope I was able to at least partially answer your question.
Otherwise, when I write posts, I mostly promote myself, but not an infrared heating system, which unfortunately appears under my signature by necessity. So, I will keep it at this for now.
I wish you continued enjoyment and success with the Swiss construction world.

These 6cm (2.4 inches) are simply too little and don’t make sense. We had a similar situation, and the company explained that it doesn’t work that way. So, we ended up installing radiators.