Floor slab insulation "Yes!" or "No!"

Conclusion: With a well-insulated floor slab, you are always on the safe side. Even if many providers try to dissuade you, you should not be discouraged, as later improvements in this area are not possible.

A good insulation of the floor slab offers two advantages:
- On the one hand, reduction of energy consumption by preventing heat loss
- On the other hand, increased comfort through a pleasant, even floor temperature; especially in the edge area near the external components, cold drafts are eliminated.

Regards

T. H.

Hello,

our architect told us the following in response to our question about how the subsoil including the floor slab will be constructed:
1. approx. 30-40 cm gravel layer
2. 8.0 cm perimeter insulation
3. vapor barrier
4. 20-25 cm floor slab with wu-concrete (depending on soil conditions)

Can someone tell me if this is a "common" and "sensible" construction
(assuming that the soil report shows a load-bearing soil without near-surface water layers)?
Do I understand correctly that the perimeter insulation under the floor slab would then already count as additional insulation, because the "minimum insulation" of the floor slab is actually installed between the floor slab and the screed? Which types of insulation material are used between the floor slab and the screed?

Thanks in advance!

Regards
Tatze

Hello,

...The architect said that with additional insulation of the floor slab you can reach KFW 55. But the price for this additional insulation is not in proportion to the benefit from the repayment subsidy.

No reasonably sensible planner would come up with the idea to achieve KfW EH70 to 55 exclusively through insulation of the floor slab! Usually, other measures are required for that.

Basically, the minimum requirements for the reference building (0.35 W/m²K) must be met.
Whether further "additional" insulation is economically reasonable can be calculated. => energetic optimization. Often, the floor slab contributes only to a small portion of the total losses. Then improvements should rather be made elsewhere.
General statements are not very purposeful in this regard!

Best regards