Insulation Screed KFW 55 - No Perimeter Insulation?

Hello everyone,

I am still dealing with the insulation of the floor slab or the screed.

Currently, no perimeter insulation is planned under the floor slab for our KFW 55.

We have an offer for that, but I find it very expensive, about 3,000 euros for 100mm XPS WLG 040.

Therefore, I have considered maybe investing more in the insulation above, if that should not be so expensive.

So far, the following setup is planned:

65mm floating cement screed
30mm system board WLG 040
70 mm insulation WLG 035

I have thought about replacing the 70mm WLG with a PUR aluminum laminated board WLG 023.

Do you think this makes sense and what does it cost?

Do you perhaps have other suggestions?

Thanks

How large is the area? 3000€ net or gross? I honestly don't find it all that expensive spontaneously. The material price for the board is certainly around 15-20€/sqm, then add labor on top of that. You know the area yourself, so just calculate. EPS on top is certainly cheaper in terms of material than XPS underneath. But it won't make a huge difference. PUR is significantly more expensive, but less insulation thickness is needed. Saves construction height.

Why do you want to insulate more than planned?

The floor area is approximately 75 sqm

I have been considering whether it makes sense to do "a little" more than necessary, also with a view to the future. In principle, I am satisfied with kfw55.

As an option for about 900 euros, I have the possibility to upgrade the collar beam insulation from 240mm WLG 35 to 240mm WLG 32.

However, I have thought about the floor slab. Here is the option of perimeter insulation 100mm XPS WLG for about 3000 euros.

Now I have thought about improving the screed insulation as a "middle ground".

Is this sensible?

Thank you very much

In my opinion, that makes no sense at all. It’s better to reach the next KfW level right away. That increases the value of the house and gives you at least a bit more funding.

I find the plan very good. To save money, you could install the insulation yourself.

With the underfloor heating, you have higher losses towards the ground compared to radiators, precisely because a higher temperature is applied. This could lower the flow temperature, increase efficiency, and thus save money.

Especially if you lay the PUR layer yourself, which should not take more than a day. Maybe then it will be worth it.