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

Why basement?

(1) You need a lot of space for the technology, about 10 sqm. I hardly have space on the ground floor without making big compromises with the office, kitchen, living room. With the technology in the basement, I can better realize my desired living layout.

(2) For a music room, I have little or no space in the house. Yes, I could build bigger, but that in turn affects the floor plan. It is also difficult to achieve good sound insulation. And with a basement, it becomes more of a "music studio," which is even better. It is used by me every day and is fun.

(3) I am building with a carport and without a garage. With a basement, I have more storage space. Possibly also the option for a fitness room, sauna, etc.

Why KfW40+?

From KfW55 to KfW40, there is hardly any additional cost, and I also want a photovoltaic system. That is relatively well subsidized with KfW40+, so it does not make much difference in price to forgo it. Yes, it will be a bit more, but it is worth it to me.

So please don’t try to talk me out of KfW40+ or the basement. That train has left the station. That wasn’t even my question :)

I initially planned without a basement. But with floor plan planning, etc., I then decided on a basement. Excavation is not as expensive as I expected – I already have a soil survey and chemical analysis and an offer from an excavation contractor.

The basement offer includes 12 cm insulation for the walls and 14 cm insulation under the basement slab for about 10,000 euros; whether that is enough for KfW40+ I will only know when the energy consultant does the calculations, but he does not calculate for an offer. I don’t expect much more insulation effort, unless you have other experiences.

Next week I have an appointment with provider 2, then I can ask again.

I am certainly not the first to build KfW40+ with a basement in the thermal envelope, am I? :)

But those are the only measurable and for reasonable people also decisive reasons.

So, am I hearing correctly now that I might not be "reasonable" because I decided on a KfW40+ house with a basement? :)

KfW40+ is not much more expensive with a prefabricated house provider than a KfW55 house. The wall is already the same in most cases. In addition, a better insulated roof and better insulated base plate. However, the extra cost is almost offset again by the KfW40 subsidy (repayment grant). The photovoltaic system is also subsidized, it does not have to be large. A 5kWp system with a 5kWh storage costs about 13,000 euros.
The repayment grant from KfW40 to 40+ is at least 6,000 euros more, almost half of the photovoltaic system.

Without subsidies, it probably wouldn't pay off. And in 2021 it will be subsidized even more.

I can turn up my amp, learn drums, practice with a band without worrying about disturbing my neighbors. You can't measure quality of life :)

How many Porsches, Mercedes are driving around here? I just treat myself to a basement and drive a Golf. :)

Of course, KfW40+ is significantly more expensive than KfW55. That your house provider calculates this opaquely and makes the subsidy look better is their business and up to them. Realizing that the additional effort will not be saved during the lifetime of the house is therefore up to the customer. Everyone can do what they want, but in fact, KfW40+ is an expensive placebo; as a hi-fi enthusiast, you surely also know €1000 cables, which is a similar thing. P.S. I hope you are aiming with the soundproofing at the basement and not at the KfW40+ insulation. Thermal insulation has absolutely nothing to do with soundproofing; in a timber-frame house, it quickly becomes a completely different problem.

There are not only commercial reasons to decide on a building according to KfW40+ standard

But those who have non-commercial reasons for it are probably rather looking for a general contractor for whom this is an issue of opinion and not an option on the price list.

I am certainly not the first to have KfW40+ built with a basement within the thermal envelope, am I?

I would even say that for the opinion-based client, it is the standard case to prefer the "consistent" path. That means for them, the question of a downgrade hardly arises (instead, they find that borderline unethical). By the way, I treat myself to living in a multi-neighbor house, and for my individual traffic kilometers, I drive an Opel-labeled Suzuki (not only for commercial reasons, but also for two nostalgic ones).

KfW40+ is not much more expensive with a prefabricated house provider than a KfW55 house.

I used to think that too. Upon closer inspection, the perimeter insulation of the cellar (i.e., the real additional costs) has to be provided by the builder, so it does not appear in the company's price. If you build with a company that only offers KfW40 walls (Weberhaus, for example), you pay quite a bit of money for a wall you might not need. Then adding a cellar to KfW40 standard 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. And this is under the assumption that the photovoltaic system and the battery storage are installed anyway, which only makes limited commercial sense for the latter without subsidies.

Everyone should do what they want, but in fact KfW40+ is an expensive placebo, as a hi-fi enthusiast you surely also know €1000 cables, that goes in a similar direction. P.S. I hope you mean the basement with soundproofing and not the KfW40+ insulation. Thermal insulation has absolutely nothing to do with soundproofing, which is a completely different problem especially in timber frame houses.

I am a hobby musician, not a hi-fi enthusiast. My hi-fi system costs €300 and so do my speakers. I don't believe in €1000 cables.

And of course I know that thermal insulation has nothing to do with soundproofing. I'm not stupid.

But again some numbers: A 5 kWp photovoltaic system costs about €7,000, the 5 kWh storage about €6,000. The repayment subsidy from KfW40 to KfW40+ is another €6,000. So, the photovoltaic system is subsidized by about 50%.

With a 5 kWp photovoltaic system you get about 4000 kWh of electricity generation per year. That’s about €1000 saved annually. So you have amortized it in less than 10 years, right?

Example: A Fiat 500e consumes 13 kWh per 100 km. That’s about 30,000 km per year (4000 kWh * 100 km / 13 kWh). I work from home and can let my e-car charge all day. For a commuter that might not make sense. I probably drive about 8000 km per year.

That’s why KfW40+ makes sense for me. Or am I making a calculation error?

Now one might ask, does KfW40 make sense? Repayment subsidy an additional €6000 compared to KfW55. The wall from a prefab house supplier is usually already good enough for KfW40, only more insulation is needed in the roof and under the slab. Plus a heat pump with controlled indoor ventilation, but that is also subsidized by BAFA by about €10,000.

So, KfW40 even without a photovoltaic system makes sense to me (if you don’t build solid). Mathematically you might be slightly in the minus, but definitely not "significantly more expensive." Electricity will not get cheaper.

KfW subsidies for 2021 will be increased again.