36.5 aerated concrete
With that, even without extra insulation, you already have quite good values. We had once considered a variant with it; depending on the insulation under the floor slab, you are at KfW55 or Energy Saving Ordinance level. You can build with a heat pump. Hydrogen in the gas grid was not such a hype back then and was accordingly disregarded, "bio" gas from the worst industrial agriculture is a niche product and will remain so. There are only limited areas for agriculture, and right now we are seeing once again how important it is to at least cultivate staple foods in the country. And environmentally friendly is simply nothing about monocultures of rapeseed and the like. Gas from waste exists, but to produce gas on a large scale there is not enough waste. I can understand everyone who replaces an oil burner with gas in an old building. That makes sense if you don't want to carry out a complete renovation. But in new buildings, I am a bit more critical. There are reasons, e.g., if heating is mainly done with wood, but sometimes the house should be heated while absent. Then you might want to save yourself the more expensive underfloor heating. But otherwise, as of today, I see no point in planning a gas heating system in new buildings. Where construction is already running, you can still carry it out if you want ( that was for you :) ) By the way, you don't need photovoltaics for the heat pump. Electricity comes from the grid. At night and during a week of foggy-cold weather, you have no other choice anyway. Photovoltaics are a bonus, not a prerequisite.