Build a single-family house as KfW55 or Efficiency House 70?

The subsidy for KfW55 is relatively low and as such not a particularly desirable goal. The question is how good or bad the insulation is in the standard without KfW already and what payback period is acceptable for you.

If you find out the H't value for both variants, you can calculate with it and roughly estimate the amortization. The value describes the insulation quality without influence from technology or other creative accounting. Alternatively, look at which components are exactly improved and what the insulation values are in each case.

Photovoltaics usually pay off, the occupied area should be as large as possible to increase the profit. Home builders are not necessarily the best partners for photovoltaic systems; I would plan and install them separately. Provide conduit to the roof. Installing a just barely sufficiently sized system because of a subsidy would be a mistake.

Photovoltaic system has hardly anything to do with KFW 55. It would be easier to use a heat pump instead of, for example, gas. 15,000€ for a photovoltaic system with a max of 10 kwp would be too expensive anyway. It could also be problematic for taxes if the general contractor does not issue an individual invoice for it.

Homebuilders are not necessarily the best partners for photovoltaic systems, I would plan and have them installed separately. Provide empty conduits to the roof. Installing a system that is just barely large enough for a subsidy would be a mistake.

Likewise, homeowners are not necessarily the best partners for systems whose purpose is related to efficiency. Every system is only as good as its design and sizing, and supplying the batch size "one dwelling unit" is sometimes a tight framework for an efficiency optimum – on the other hand, detached single-family houses are only limitedly suitable for systems for multiple units.

We were asked today for the first time why we actually want to build KfW55. An efficiency house 70 would be about €20,000 - 30,000 cheaper and additionally about €15,000 for the photovoltaic system.

How do you come to these additional costs?! In 2016, we had only about €4,500 for the whole house from KfW70 to KfW55 (a bit more insulation and better insulation under the floor slab). After subtracting the €5,000 subsidy, that’s a good calculation. Our basement is almost entirely in the ground (rock), and only the hallway/vestibule has underfloor heating, but all rooms have controlled residential ventilation. The values were so good that it easily qualified for the 55 standard.

We had about €4,500 for the whole house in 2016 from KfW70 to KfW55

Then the equipment without the upgrade was probably quite close to the threshold, a jump of a whole grade would probably have been somewhat more expensive.

Then the equipment without the upgrade was probably quite close to the threshold, a jump of a whole grade would probably have been somewhat more expensive.

If a heat pump is already present, the issue of primary energy is solved.

If an ETICS or two-shell wall construction is already used, it’s only a matter of a few centimeters more insulation, possibly a slight improvement in the window (although one can compensate for the other). If wood is already used for construction, the wall structure usually meets KFW 55 or better quality.

Five-figure surcharges are only to be expected in the following initial situation: Monolithic with gas heating.