KfW70 only with prescribed expansion packages?

Hello construction community,

I have a problem with a house seller.
We want to buy a prefabricated house (timber frame construction) as a shell construction, which meets the KfW70 requirements.
The seller now believes that I will only get the KfW70 loan from the bank if I purchase the concrete slab offered by him (approx. 8mx10m for €13,000) and the interior finishing packages ( €13,000) and heating/plumbing ( €18,000 without heating boiler).
The following reasons were given:
The concrete slab can supposedly only be made by ONE company in our federal state because it has a RAL and BDF certification. :confused:
For the paneling and insulation, only special materials may be used because otherwise the insulation value is not met and because the bank and structural engineering prescribe these materials. The drywall panels he offers have a special size which is not available on the open market and may only be installed vertically and not horizontally.
And regarding the heating package, the statement was made that this special underfloor heating is required by structural engineering.

I don’t know much about structural engineering, KfW, and financing, but in my opinion it should be sufficient for the insulation value if I can prove that I have installed insulation with the corresponding insulation value in the appropriate thickness.
Likewise, I think that for the wood-based panel and the drywall panel, the screw spacing and thickness matter more for structural engineering than the manufacturer and size.
What underfloor heating has to do with structural engineering, I have not yet understood. I understand the screed height and thus the weight.
I do hope that a thermally insulated slab can be built by any company that offers one.

You would really help me if you could give me some information here so that I can finally sleep better again. :(

Thanks in advance.

Regards

McPat

Hello McPat,

with the amount of misinformation, I would also reconsider buying the [Ausbauhaus] ;), none of it is accurate.

Hello 6Richtige,

thank you very much for your response and confirmation of my assumption.
Are the prices for the expansion packages roughly okay?
The house has a total usable area of 129 m².
The [Paket Innenausbau] includes the material for the complete insulation and cladding (once with wood-based panels and once with drywall).
The [Heizungspaket] contains the complete underfloor heating (material only) and the material and installation of 2 bathrooms (basic equipment: 1 shower, 1 bathtub, 2 toilets and 2 washbasins).
I personally find the floor slab too expensive (8mx10m, thickness 30 cm, thermal panel and earthworks).

Thanks for a feedback.

Regards

McPat

Hello McPat,

why are you interested in the prices? Just take the list of materials and go to 5 hardware stores, then you will know the prices.

But you do have experience in airtight installation of vapor barriers (missing in your package?), right? Just so it doesn't turn black in the wall too quickly later ;)

Hello 6 Right,

Well, the thing with the list is a bit tricky; it does show the individual items, but the most important details about areas, quantities, and lengths are missing. The price is also only noted by hand on the lists. So I don’t know if and how much commission might possibly be involved here.

The vapor barrier is probably included in the package. I don’t really have any experience with installing it. I assume it is stapled with overlaps and that the overlap and the "attachment holes" are additionally sealed with tape.