ᐅ Thermal insulation for the concrete slab

Hello,

I have a question.

We are about to start building and are close to submitting the building permit / planning permission.

In our new development area, some concrete slab foundations are already in place. On some of these slabs, insulation is installed on the ends (at the edges), which I believe is extruded polystyrene (XPS), while other slabs have no insulation at all and just show exposed concrete.

Is this insulation necessary or beneficial? I just wanted to get some quick information before I call the construction manager and ask any awkward questions!

Thank you.

Hello,

Exterior insulation is definitely necessary when thinking about a single-family house. However, the insulation can also be added at a later stage. I would be more concerned if the perimeter insulation is installed too early, for example as formwork during casting.

Without the perimeter insulation of the slab against the ground, a corresponding thermal bridge would occur there. Whether this is strictly required by regulations or similar rules, I am not sure.

Knallkörper schrieb:
I would be more concerned if the perimeter insulation is installed too early, for example as formwork during the concrete pour.

Hmm, I’ve now seen dozens of construction sites where the insulation was installed before pouring. Are you saying that is incorrect?

Well, let’s put it this way. I spent quite some time on this during the planning stage. We had the issue that our foundation slab ended up a bit too large, and it was then broken out, partially exposing the reinforcement. During that process, the topic of waterproofing was also examined more closely. The question is: how can you properly waterproof the base area once perimeter insulation is already installed?

tomtom79 schrieb:
Hmm, I’ve seen dozens of construction sites where the insulation was installed before pouring the concrete. Are you saying that’s wrong?

For intermediate floors, that is the correct approach.
For a slab-on-grade, it depends on the waterproofing system; it is uncommon because water can seep behind the insulation through the gaps and joints between the insulation boards.

There are various waterproofing systems; one example is:
- First, pour the slab using formwork
- Build the walls set back from the edge (horizontal damp-proof course)
- Create a fillet between the slab and the wall (important)
- Apply a waterproof slurry coating in areas where higher moisture is expected
- Apply a thick protective coating (up to the base of the wall)
- Install the perimeter insulation in overlapping layers from bottom to top
- Install a dimpled membrane