KfW40+ with a basement inside or outside the thermal envelope?

A photovoltaic system can also be built without subsidies and it usually pays off quite quickly. The problem is that the high electricity consumption usually occurs (heat pump in winter, cooking in the evening) when electricity generation is not particularly good. A storage system can help, but usually electricity from the storage then costs more than from the grid. Ergo, this has to be rephrased: your photovoltaic system is not subsidized at 50% but your storage system at 100%. The jump from 40 to 40+ is therefore more or less cost-neutral.

But the problem is the jump from 55 to 40 with a basement. Have concrete offers made, once for basement and house suitable for KfW55 and once suitable for KfW40. That is significantly more than €6000 that you have to invest in it.

As far as the new subsidy is concerned, nothing is fixed yet, so you should not count on it. For example, it is not clear whether 40+ houses will actually receive more than 25% subsidy. New concepts are supposed to come like "KfW55 + renewable energy," whatever that specifically means. A photovoltaic system could fall under that, for example. Whether that is really relevant... the new subsidy is also supposed to move the project start from the start of construction to the contract signing. So it may be that you have to wait until July with a signature and then get a price increase from the manufacturer that ends up being more expensive than the subsidy. This deal is by no means free money as the manufacturers want you to believe. I just went through this phase a few weeks ago ;)

Bringing a basement up to KfW 40 standards at the back just so you don’t waste the "good wall" is not cheap and far exceeds the €12,000 subsidy, not to mention the hidden costs of the more expensive wall.

Provider 1: (Not Weberhaus)

Offer: House including floor slab according to KFW 55, almost finished: 345,000 euros
For KfW 40: Additional insulation under the floor slab 5,000.00

For KfW 55, no controlled living space ventilation is required, but it is still interesting with a €10,000 BAFA grant. And I want controlled living space ventilation, with or without KfW 55. Therefore, the same air-water heat pump with controlled living space ventilation, whether KfW 55 or KfW 40.

A "good" (insulating) wall is not necessarily expensive, as the thermal insulation often comes from Styrofoam. Yes, Weberhaus has the ÖvoNatur Therm, which uses wood fiber insulation.

Ok, the basement complicates things here. But I gladly spend an additional €10,000 on insulation; you also benefit from it.

Did I miss something here? Maybe it’s something personal, not "de facto" nonsense.

We are talking about basement insulation and you bring an offer for the base slab. These are two completely different worlds since the basement still has 4 walls that need to be insulated. You won't get anywhere near that with a total of 10TE. And whether you want to slap Styrofoam on the outside... personally, I don't want that. Buried under the base slab I already don't find particularly nice, but on the outside of the wall, I definitely don't want it.

The jump from 40 to 40+ is more or less cost-neutral.

Ok, I agree (at least not more expensive), which is why I decided on the "Plus".

But the problem is the jump from 55 to 40 with a basement. Get some concrete offers, once for basement and house in KfW55 and once suitable for KfW40.

I have that from provider 1.

Offer for KfW55 on slab foundation.

Additional cost 5000 euros for KfW40 (insulation of slab foundation)

Additional cost 8000 euros for KfW40 (insulation of basement ceiling, stairwell, interior door, if built with basement)

But then the basement is not part of the thermal envelope. However, I want a comfortable, almost livable basement: music studio with underfloor heating and controlled residential ventilation.

From provider 2: offer is KfW40+, I do not have an offer for KfW55. Provider 2 has a higher quality wall than provider 1!

Offer from provider 2 is cheaper than offer from provider 1 (KfW40 plus basement)

However, I admit that I do not know for sure whether 12cm + 14cm basement insulation (about 10k euros) is enough for the basement to be part of the thermal envelope. But I believe I am not too far off. It may be a bit more. Maybe not.

Therefore, I would be interested to know if anyone has built KfW40 with a basement, what insulation was used? Will 10k euros be far from sufficient?

We are talking about basement insulation and you are bringing an offer for the floor slab. These are two completely different worlds because the basement still has 4 walls that need to be insulated.

I present it like this because that is how it is stated in the offer: Basic offer KfW55; Option KfW40 with floor slab, Option KfW40 on basement (outside thermal envelope).

At least I could compare KfW55 to KfW40 with floor slab. And there, KfW40 pays off.

Yes, the basement complicates it, I admit that.

For 12cm + 14cm insulation there is an extra charge of 10,000 euros. If that is not enough, what can I expect? (12m x 8m) -- 20,000 euros?

Maybe I estimate that too optimistically. I admit that. But with how much and what kind of insulation can I expect?

Thank you

I use this every day and it’s fun.

Possibly also the option for a fitness room, sauna, etc.

If you already make such statements, then the basement definitely belongs in the thermal envelope!