House planning 135m2 in Austria

I like the idea.

The first years will be spent playing in the all-purpose room – there is no space there now

Guest room as a storage room for 2x use per year

Have a look at Stiebel Eltron LWZ 604 air or Tecalor TCO 2.5 is for houses similar to passive houses

We have infrared mirrors. They radiate heat immediately

Austria is large - where exactly do you want to build? - 50 cm aerated concrete sounds pretty alpine

What insulation regulations apply to you (do you know the Energy Saving Ordinance valid in DE and can you say how similar your regulations are)?

Southern Lower Austria, about 50km southwest of Vienna.
Not exactly "alpine" but at least the foothills of the Alps. I think Austria is generally colder than DE.

If I understand the Energy Saving Ordinance correctly, it is somewhat more relaxed than here in Austria.
In short: basically almost anything can be built here, but the criterion is the "eligibility for funding". This depends on the A/V ratio and the HWB. For an assumed A/V ratio of 0.6, for example, an HWB of 0.31 (without solar or photovoltaics) or 0.35 (with solar/photovoltaics) would have to be achieved. According to my understanding, this corresponds to a KFW house better than KfW40?

- Hpts. for the children (or rather our very little one, because the older one only comes rarely and not for much longer, and if he does, he just sits at the PC anyway),

I don’t quite get that: You are only twenty-eight yourself, but the older son is already studying ? ? ?

With an assumed A/V ratio of 0.6, for example, an HWB of 0.31 (without solar or photovoltaics) or 0.35 (with solar/photovoltaics) would have to be achieved. According to my understanding, that corresponds to a KfW house better than KfW40?

That mainly corresponds to my lack of understanding (A/V, HWB - complete gibberish).

Ant, it doesn’t matter whether someone is studying or living more with their mother or if it’s some kind of kfw something standard, because it doesn’t change the floor plan, which by the way already seems very well developed, if you want to put it that way. But the small storage room is probably only good for cans and such because it will probably get too warm if there is a cooler inside, since what cools inside heats outside. That’s how it is. You leave that thing out. It has to be done differently. K.

HWB = Heating demand (kWh / m²a)

That should be exactly the value on which your Energy Saving Ordinance or KfW is based.

In Austria, it also depends on the A/V (shell surface to volume) ratio of the building. The worse the A/V ratio, the better the insulation must be. Every bay window, dormer, recess, etc. increases the surface area of the house more than the volume is increased => bad for eligibility for subsidies. The ideal A/V ratio is a sphere. A cube (multi-story with a basement) is still relatively good. The more rectangular or unusual the building shape becomes, the larger the surface area, the worse the A/V ratio.

Da komme ich nicht ganz mit: Du bist selber erst Achtundzwanzig, aber der größere Sohn studiert schon ? ? ?

The older son is 11, goes to school and mainly lives with his dad in Vienna (shared custody). Every 2nd weekend and during school holidays, he is with us. Here in Austria, he is legally allowed from his 12th birthday to freely decide when and where he wants to be. From that point on, it is just as possible for him to decide to be full-time with us as it is for him to decide not to come at all. Very pragmatically thought, at the latest when his first girlfriend arrives (in 2-4 years), he will tend to come less or not at all. It’s sad but we just have to be that realistic.

Further "small" children are also not planned, by the way. Or rather, they would have been planned, but due to "fate" it is no longer possible. Except through adoption, which is still an option on the table...

And how many kWh are 0.31 and 0.35 respectively?

Building envelope/building shape basically have an impact on the overall energy consumption. That applies to us as well. Therefore, any advantage or parts of the garage included in the building envelope are expensive.