ᐅ Insulation Under Reinforced Concrete Slab for KfW 55 Standard

Hello everyone,

We are going to build a prefabricated house on a concrete slab foundation. Our builder told us that with KFW55 standard, insulation beneath the slab is not required.

Now we are wondering whether we should add it anyway and if it is a worthwhile investment.

The concrete slab:
Reinforced concrete slab as a load-bearing element made of in-situ concrete (c20/25, approx. 15-20cm (6-8 inches) thick, edge reinforced) with reinforcement according to structural requirements.

Costs for the insulation:
120 mm (5 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 3115€
160 mm (6.3 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 4930€
Will these costs ever be recovered through energy savings?

Best regards

How will the heating be done later, and what insulation is installed between the concrete slab and the screed?

What does the energy calculation say about this? You cannot just omit what may have been planned beforehand.

It makes sense, but the energy savings will never fully compensate for it.

At least not at those prices. Doing the work yourself is off the table?

In theory, doing some of the work yourself is possible, but I have no experience with that at all... What are the reasons for installing insulation?

@toxicmolotov
We will be heating with an air source heat pump.
I can’t really say how the insulation is done above the slab.

turbotopo schrieb:
In theory, do-it-yourself work is possible, but I have no experience with it... What are the reasons to install insulation?

Hello

I recently wrote: Perimeter insulation with 120mm (4.7 inches) thickness costs around 10 euros per m² (11 USD per square yard). Estimated labor time is about 4 hours. Required expertise: two hands. Enough.

Steven