How to achieve KfW40? Energy technology / Economic efficiency

With Ytong, you can achieve KfW55 with a 36.5 cm block through creative calculations ("Mit detailliertem rechnerischen Nachweis auch 36,5 cm Ytong PP 2-0,35 lambda = 0,08 W/(mK) für KfW-Effizienzhaus 55 Förderung möglich."), with 42.5 cm even without calculation tricks. KfW40 also seems possible monolithically if you offset it against the photovoltaics and insulate a bit more elsewhere. Otherwise, a 48 cm block. Although Ytong is not just Ytong. On the website, there are the editions ThermStandard, ThermSuper, and ThermUltra... In terms of costs, there does not seem to be a clear trend whether monolithic or ETICS. At least I haven’t found anything clear about it on the internet. Personally, I think it’s better if no styrofoam is glued on and the higher-quality insulations also come with their price.

Hello, this is a building-integrated system and therefore more expensive, more complicated (cooling & sub-roof), high efficiency losses and last but not least: warranty issues.

Building-integrated: yes More expensive: yes (that is the only real disadvantage) More complicated: no - no separate cooling necessary, no special sub-roof needed Efficiency losses: moderate (not a real disadvantage if the design matches the demand) Warranty: unproblematic, since the trade handover is very well regulated. There are advantages too:

[*
simply a beautiful roof [*]only low voltage on the roof (<120V) [LIST] [*]no fire load introduction [*]reduced electric fields (if you consider that relevant)
[*]flexible planning and good area utilization due to small module sizes (irrelevant for us, can contribute to more architecturally free design (positioning of dormers, windows, choice of roof shape...) [*]barely sensitive to shading (parallel connection instead of series connection (irrelevant for us)

If you consider the photovoltaic system purely as an investment good, it is not worthwhile (unless you assume a higher added value to the property) If you consider the aesthetics, you simply invest – similar to flooring – in the look and enjoyment. Technically it is mature, no need for concerns. I would choose this option again for the next house and understand anyone who prefers to mount the large panels on the roof. Either way, photovoltaics on roofs is a good contribution. The OP can make up their own mind. It is always a pity when people say "if I had known this existed, then..."

As a note: Our architect and energy consultant (who builds almost exclusively KfW40/ passive houses) once said that most KfW40 houses are timber frame construction because it is relatively easy with this construction method and suitable insulation to achieve the appropriate values without extremely thick walls.

For comfort: My sister and her husband built a log house (I think 14cm) over 20 years ago. That was energetically sufficient at the time. Always a great indoor climate – the best I have ever perceived / felt. Years later, my parents built another log house 2 or 4cm thicker than this one at a distance. Again: great indoor climate. A few years ago, both houses were retrofitted with 8cm wood fiber insulation boards + cladding. This was also about getting rid of the old ugly (too dark) color. Sanding would have been more expensive than adding insulation :cool:

Quite simple: max. 70% of the nominal power is the possible maximum feed-in.

Ok, thanks!
Do you also know about the above-mentioned statement that if you take advantage of, for example, Kfw40Plus, you are NOT allowed to claim another subsidy, such as storage funding (in our case, the state of Saxony)?

As a note: Our architect and energy consultant (who builds almost only KfW40/passive houses) once said that most KfW40 houses are built with timber frame construction because with this method it is relatively easy to achieve the required values with suitable insulation and still not extremely thick walls.

That is often said and at first glance one is inclined to believe that it is easier to stuff some thicker mineral wool between the wooden studs than to apply an external thermal insulation composite system or fill bricks with insulation wool. On the other hand, switching to a 6cm thicker Ytong is also not exactly groundbreaking on the construction site. And the timber frame walls in KfW40 also have about 40cm thickness. I think this is more a story of the prefab builders to differentiate themselves from the solid construction builders.

That is often said, and at first, one tends to believe that it's easier to stuff slightly thicker mineral wool between the wooden studs than to install an ETICS or fill bricks with insulation wool. On the other hand, switching to a 6cm thicker Ytong is not exactly groundbreaking on the construction site. And wooden stud walls in KfW40 also have about ~40cm thickness. I think this is more a story from prefabricated builders to differentiate themselves from solid builders.

We are building monolithically with "normal" 36.5 brick, and according to the binding statement of the energy consultant, it is already calculated for Kfw40Plus. There are simply too many parameters and adjustment options with which one can achieve something. Any general statement can be wrong.