ᐅ How to upgrade from KfW55 to KfW40+?

With the new subsidy, there is a 15% repayment bonus for KfW 40+, or am I mistaken?

dsin8788 schrieb:
With the new support program, KfW 40+ offers a 15% repayment grant, or am I mistaken?

Where can I find that information? I couldn’t find anything about it...

Bauexperte schrieb:
Good evening,
Aerated concrete is the best choice because, due to its uniform pore structure, it has consistent thermal conductivity and high thermal storage capacity. It also ensures high airtightness of the building envelope, which helps prevent corresponding energy losses.

The KfW calculation does not differentiate whether it is a brick with a lambda of 0.07 or aerated concrete with a lambda of 0.07. However, regarding thermal storage capacity, I have a different opinion. The PP 1.6-0.25, in my view, is the only aerated concrete block with lambda 0.07, and it has a density of 250 kg per m3 (250 kg per m3). The corresponding brick with lambda 0.07 and perlite filling has a density of 600 kg per m3 (600 kg per m3). For lambda 0.08, there is the PP 2-0.35 with 350 kg per m3 (350 kg per m3), and there are unfilled bricks from Freital with a density of 700 kg per m3 (700 kg per m3).
As far as I know, airtightness is achieved through the interior plaster. Why should a glued aerated concrete block be better than a glued brick?
Not that I generally have anything against aerated concrete, it’s a great building material. But regarding your statement about thermal storage capacity, I think bricks are better.

Everything starting from KfW 55 certainly raises the legitimate question of amortization. However, it does not matter whether construction is done with an exterior insulation system (EIFS) or monolithic construction according to KfW 55. The additional costs for both construction methods are almost identical.

To improve from a U-value of 0.20 to 0.16, for example, in monolithic construction you have to go from lambda 0.08 with a wall thickness of 42.5 cm (17 inches) to lambda 0.07 with 49.0 cm (19 inches). In sand-lime brick + EIFS, you simply increase the EIFS thickness from 160 mm (6.3 inches) to 200 mm (7.9 inches).

The additional cost for sand-lime brick + EIFS is about 3 to 5 EUR per m2 (square meter). The additional cost for monolithic construction is already 64 EUR per m2 according to list price, minus some small discount. The wall thickness without plaster for sand-lime brick + EIFS increases from 33.5 cm (13 inches) to 37.5 cm (15 inches) (+4 cm), but for monolithic construction from 42.5 cm (17 inches) to 49.0 cm (19 inches) (+6.5 cm).

The more extreme the requirements, the more worthwhile EIFS or timber frame construction become.

Passive houses have existed for years in monolithic construction with 36.5 cm blocks (14 inches); even as multi-story apartment buildings. By the way, anyone building a multi-family house as an investment primarily decides based on the yield calculation available to them; it can hardly be as uneconomical for builders as you suggest. It is understood that much of this is driven by environmental conscience as well as political will.

A passive house with 36.5 cm (14 inches) is not possible. By definition, a passive house requires a U-value below 0.15 for all exterior walls. With lambda 0.07 and 36.5 cm (14 inches), you can achieve at best 0.18.

Hello,

Grym schrieb:

A passive house with 36.5 is not possible. By definition, a passive house requires a U-value below 0.15 for all exterior walls. With a lambda of 0.07 and 36.5, the best you can achieve is about 0.18.

Yes, I should not have shortened it like that, my mistake, I should have checked my post again; sorry.

Here are the correct values. According to my table, a passive house needs:

24 cm (9.5 inches) aerated concrete 0.12 W/(mK) + 14 cm (5.5 inches) core insulation 0.032 W/(mK) + facing brick – for a cavity wall construction: U-value of 0.13 W/m²K, total wall build-up* 51.5 cm (20.3 inches)

or

49 cm (19.3 inches) aerated concrete 0.07 W/(mK) plus exterior plaster for a monolithic construction: U-value of 0.14 W/m²K, total wall build-up* 51.5 cm (20.3 inches)

Edit:

*air gap for facing bricks added like interior plaster (both wall constructions)

Regards, Bauexperte

Baufie schrieb:
Where can I read about this? I can’t find anything…

On the internet (KfW website) or here in the forum in the relevant subsection.

Bauexperte schrieb:
24 cm (9.5 inches) aerated concrete + 14 cm (5.5 inches) cavity insulation + facing bricks [...] total wall construction: 38.0 cm (15 inches)

38 cm (15 inches) + facing bricks.