How to achieve KfW40? Energy technology / Economic efficiency

As mentioned, it is a calculation. You can also use another DStein with much better values. In the end, just calculate. But don’t forget the feel-good effect, because KFW is not a guarantee for feeling good. Upgrading will always cost something somewhere, it’s just a question of where it fits best and has the most effect.

As I said, it’s a calculation.

That of the general contractor. He builds with “his” brick, “his” insulation, his possibilities.
In this respect, you should communicate the Kfw40 requirement to the general contractor so that HE can implement it. If a general contractor generally builds with Poroton, he will not use Ytong.
The answer is not to you , but to the OP.

: Yes, you are right, and that’s exactly how we will do it.

I know many GU houses, and they all have a good price-performance ratio, the support is also top. But of course, these are budget builds.

Usually kfw55 houses made of aerated concrete, ETICS, ground source heat pump from Tecalor, deep drilling. Little fluctuation among the trades, always the same two or three site managers (good that way), materials affordable and okay, but nothing extraordinary outside the mainstream. Just quickly changing the insulation boards or the entire ETICS plaster system, etc. will probably not be possible. It’s off-the-rack fashion, not haute couture.

I am sure that in the end it will rather be the builders who afterwards install a photovoltaic system. And kfw40 or kfw40+ buildings will also be rather rare for him.

In this respect, I was particularly interested in your opinion regarding the size, orientation, and economic efficiency of a photovoltaic system on a 30-degree gable roof with east-west orientation. Although economic efficiency is not everything. We would also like to have a somewhat climate-friendly and future-proof feeling with the whole energy technology story. Especially since my wife has been committed for several years to saving the world. And I try to help as best I can. ;-)

We are building here for my parents, so we have to watch the budget. However, we definitely want to build in such a way that the house can someday be a possible retirement home for us. We would then sell our current one.

We will involve an energy consultant eventually anyway. But I’m more the type to at least try to form an opinion beforehand so that the statements from the trades are not Hebrew to me. So once again thanks to everyone for the advice. And maybe there will be more...

Happy New Year in advance to you all!

If your wife (and you as well) want to save the world, then buy an existing property. A new building, especially a single-family house, is the wrong ecological way ;) I am with build as your general contractor always builds. That is the most likely way it will work.

That sounds reasonable, because a reliable general contractor is already half the battle and saves you a lot of trouble and thus energy :D !!!
Regarding photovoltaics, there is a forum that you can find immediately on Google. In my opinion, however, they mostly speak "Hebrew" there..... luckily, it’s a bit more straightforward here, good for a simple character like me.
A photovoltaic provider was already mentioned to you here further up, if you now also include the electrician of the general contractor, that would already be more than a start. In our case, it was like this: the electrician from the general contractor made a very good offer and we will probably accept it because then everything comes from one source. Maybe it would be a few euros cheaper elsewhere, but having everything from one source is more important to me.
In the other forum, the opinion prevails that photovoltaics always pay off and you should make them as big as possible, even more than 9.8 kWp if possible.
Ultimately, there is no general calculation; we will achieve KfW40Plus but only because we wanted a high insulation standard anyway; therefore, we have to use a storage system anyway, which we will almost get paid for through the Plus subsidy.
As sometimes shown here, you can make a lot look good or bad with storage, and there are thousands of opinions about the modules: some offer longer warranties, others more performance, others a great price...... For me, reliable implementation would also be very important, it’s like with cars, there is a justification for almost everything from Dacia to Lexus.
For us, it will probably be the modules from Solarwatt with a 30-year warranty and made of glass, because the electrician sells and knows them, they are supposed to be good, but the other providers also have their advantages.
In your case, it might be difficult now to build the budget house for the parents, which they then want to live in later as the desired KfW-xy energy-saving house.
Just feeling-wise, I would therefore consider building the house for the parents now and complying with the current energy standard without KfW measures, with which you already have a really good house, the parents probably consume little energy anyway and are thus inherently economical in consumption. If you want to live in it yourself sometime in the future..... who knows what else will come in life, only then would I implement the good and then possible measures at that time, whether photovoltaics or anything else. Until then, today’s standards are already old news again.

The "saving the world" was related to energy technology and not meant entirely seriously. I just wanted to express that the economic side is not everything. The feeling for the technology should also be right.

Existing buildings are almost as rare here as plots of land. In this respect: nice dream...