Perimeter insulation under the floor slab and still XPS under the screed?

Hello,

we have decided on 10 cm above and 10 cm below the floor slab. The payback period is 30 years if you only consider the floor slab insulation. However, since we achieve KfW 40 (+) through this, the overall structure pays off in 10-15 years, with the subsidy and the low-interest loan.

Regards
Judyyy

For KFW reasons, we do not need the extra insulation. Funding is not planned and therefore not included in the calculation.

As far as I have read into the topic so far, I can hardly "make it look better by calculation."

The energy cost savings would be between 60 and 120€ per year. It would take us about 25 years to offset the incurred costs.

That is a back-of-the-envelope calculation. Changes in energy costs, as well as interest rates, etc., are not included.

I personally find the 2300€ not much when considered in isolation. Also, 25 years is not long for a house, in my opinion. Of course, you can’t just spend an extra 2000€ on every trade. Couldn’t you, for example, lay the insulation under the screed yourself and save some money? Because as you say: you never get access again.

The BU would pass this on roughly at cost price if we insist - hence the price.

Including own contributions at these points is not an option for us. We have no experience there and hardly want to take anything away from the experienced team.

They just need to know whether they should carry out this additional service or not.

I would also like to revive the topic.

We are planning a construction project with timber frame construction and the whole thing is supposed to/will be KFW 55.

2 out of 3 providers offer a floor slab insulated with xps.

A third says he does not need the insulation for KFW55 and would forgo the insulation below the floor slab and instead increase the screed insulation. This would save costs.

Is this okay, up-to-date and reasonable?

Should we invest the money in the additional insulation if we can reach KFW55 that way?

Or could we have problems with the floor slab, e.g. moisture, if we do not insulate?

Thank you very much

Regards

Sky

Hello

a small thought to ponder: 1m² 10cm perimeter insulation costs about 9 euros. Installing it takes less than an hour. I mean installing over 100m².

Steven