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

Why a Basement?

(1) Technical equipment requires a lot of space, about 10sqm (108 sq ft). I hardly have enough room on the ground floor without making major compromises on the office, kitchen, and living room. With the technical equipment in the basement, I can better realize my desired living layout.

(2) I have little or no space for a music room in the house. Sure, I could build bigger, but that would affect the floor plan. Also, it is difficult to achieve good sound insulation without a basement. And with a basement, it becomes more of a "music studio," which is even better. I use it every day and enjoy it.

(3) I am building with a carport and no garage. Having a basement gives me more storage space. Possibly also room for a gym, sauna, etc.

Why KfW40+?

Upgrading from KfW55 to KfW40 involves hardly any additional cost. I also want a photovoltaic system. KfW40+ is reasonably well subsidized, so financially it doesn’t make much difference to take advantage of it. Yes, it’s a bit more expensive, but it’s worth it to me.

So please don’t try to convince me to skip KfW40+ or the basement. That ship has sailed. It wasn’t my question anyway 🙂

Initially, I planned without a basement. But with floor plan planning and so on, I decided in favor of the basement. Excavation isn’t as expensive as I expected—I already have a soil survey and chemical analysis, plus a quote from the excavation contractor.

The basement offer includes 12cm (5 inches) insulation for the walls and 14cm (6 inches) insulation under the basement slab for about 10,000 euros; whether that’s enough for KfW40+ I will only know after the energy consultant calculates it, but they don’t do calculations for quotes. I don’t expect to need much more insulation unless you have different experiences.

Next week I have an appointment with a second provider, so I can ask again then.

I’m certainly not the first to build KfW40+ with a basement in the thermal envelope, right? 🙂

apokolok schrieb:

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

So, am I hearing correctly that maybe I’m not “reasonable” because I chose a KfW40+ house with a basement? 🙂

KfW40+ with a prefab house provider isn’t much more expensive than a KfW55 house. In most cases, the walls are already the same. Then you have a better insulated roof and better insulated floor slab. But the extra cost is almost covered by the KfW40 subsidy (repayment grant). The photovoltaic system is also subsidized and doesn’t have to be big. A 5 kWp system with a 5 kWh battery costs around €13,000.
The repayment grant from KfW40 to 40+ is about €6,000 more, almost half the cost of the photovoltaic system.

Without subsidies, it probably wouldn’t be worthwhile. And in 2021 there will be even more support.

I can turn up my amp, learn drums, practice with the band, without worrying about disturbing my neighbors. Quality of life can’t be measured 🙂

How many Porsches or Mercedes do you see around here? I treat myself to a basement and drive a Golf. 🙂

Of course, KfW40+ is significantly more expensive than KfW55.
If your home builder calculates the costs non-transparently and offsets them with subsidies, that’s their business and up to them. It’s the customer’s responsibility to realize that the extra effort won’t be recovered during the lifetime of the house.
Everyone can do as they wish, but in fact, KfW40+ is an expensive placebo. As an audio enthusiast, you’re probably familiar with €1000 cables, which is a comparable situation.
P.S. I hope your soundproofing target is the basement and not the KfW40+ insulation. Thermal insulation has absolutely nothing to do with soundproofing, which is a completely different issue, especially in timber frame houses.

superzapp schrieb:

There are not only financial reasons to choose building to the KfW40+ standard

But those who have non-financial reasons for this probably look for a general contractor for whom this is a matter of personal opinion rather than a price list option.

KalterKaffee schrieb:

I’m probably not the first to build a KfW40+ house with a basement within the thermal envelope, am I?

I would even say that for the homeowner driven by personal views, the common approach is to prefer the “consistent” path. That means for them, the question of downgrading hardly arises (they would regard it as borderline unethical). By the way, I’m lucky to live in a multi-family building, and for my private travel kilometers, I use an Opel-branded Suzuki (not only for financial reasons but also for two nostalgic ones).

---

https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/

KalterKaffee schrieb:

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

I used to think that as well. But on closer inspection, the perimeter insulation of the basement (which are the real additional costs) has to be provided by the builder, so it doesn’t appear in the company’s price. If you build with a company that only offers KfW40 walls (for example, Weberhaus), you end up paying quite a bit for a wall that you might not actually need. Then upgrading the basement to KfW40 just to avoid “wasting” the better wall is not cheap and exceeds the €12,000 (about $13,000) subsidy by far. Not to mention the hidden costs of the more expensive wall itself. This all assumes that the photovoltaic system and battery storage are installed anyway, which in the case of the latter only makes limited economic sense without subsidies.

apokolok schrieb:

Everyone should do as they please, but in practice, KfW40+ is an expensive placebo. As an audiophile, you’re probably familiar with 1,000 euro cables, which is a similar concept.
P.S. I hope your soundproofing concerns refer to the basement and not the KfW40+ insulation. Thermal insulation has nothing to do with soundproofing, which can be a completely different issue, especially in timber frame houses.

I’m a hobby musician, not an audiophile. My sound system costs 300 euros and so do my speakers. I don’t believe in 1,000 euro cables.

And of course I know that thermal insulation is unrelated to soundproofing. I’m not stupid.

But to go over the numbers again: A 5 kWp photovoltaic system costs about 7,000 euros, and a 5 kWh battery storage around 6,000 euros.
The repayment grant from KfW40 to KfW40+ is another 6,000 euros. So, the photovoltaic system is subsidized by about 50%.

With a 5 kWp photovoltaic system, you get about 4,000 kWh electricity generation per year. That saves roughly 1,000 euros annually. So, it pays off in less than 10 years, right?

For example: A Fiat 500e consumes 13 kWh per 100 km. That is roughly 30,000 km per year
(4,000 kWh * 100 km / 13 kWh)
I work from home and can charge my electric car all day. For a commuter, this might not be economical. I drive maybe 8,000 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? The repayment grant is an additional 6,000 euros compared to KfW55. The wall from a prefab house manufacturer is usually already good enough for KfW40; only additional insulation is needed in the roof and under the floor slab. Also, a heat pump with controlled ventilation is required, but this is also subsidized by BAFA at around 10,000 euros.

So, KfW40 without a photovoltaic system also makes sense to me (if you’re not building with solid construction).
Mathematically, you might be slightly at a loss, but definitely not “significantly more expensive.” Electricity will not get cheaper.

The KfW subsidies for 2021 are going to be increased again.