New construction of a single-family house Single-family house 125 sqm in Brandenburg

What do you understand by "a very efficient energy-saving house"? Passive house, plus-energy house?

All of our domestic hot water is currently generated via the heat pump. It didn’t even struggle with 2 rain showers and simultaneous bathtub filling.

I would add the ventilation and replace the solar with a photovoltaic system.

Depending on what you understand by very efficient energy-saving house, the question is whether underfloor heating is necessary.

yeah yeah the evil WDVS...

I would recommend a decentralized ventilation system, always installed as a pair, 1 fan about 780€ net (including installation and drilling). It is not expensive and the window ventilation is additionally supported by it. 16cm WDVS is completely sufficient

According to the calculation of the construction company, the house with the 24cm HZL walls and the 16cm WDVS has a Kfw value between 40 and 55.

The house should be insulated in such a way that I don’t suffocate in summer and can heat with little energy in winter. In general, a constant 21 - 22 degrees is enough for us.

Regarding ventilation, I first need to get information. Currently, I didn’t want to install any.

Are there any improvements regarding the floor slab? Currently, it is 18cm wu concrete with 16.5cm warming screed.

The specified components correspond, to the best of my knowledge, to the current standard construction methods. It is suitable and proven. If you want more, just buy more! With 16cm insulation, it is of course even more efficient, but the windows also need to be upgraded accordingly, and so on.

For 120m², however, I consider the panic about heating costs to be nonsense. You just need to invite the neighbors for coffee and the place is warmed up.

You can also insulate under the floor slab You can insulate the walls thicker You can install better windows etc do you want that?

Between Kfw 40 and 55 is a good standard.

Window rebate ventilation also lets warm air in during summer. You can set the ventilation system to zero during the day or some lock automatically. There are also ventilation systems that can cool. Whether necessary, no idea. Mine can’t, haven’t missed it so far. In modern houses, shading is the be-all and end-all in summer to keep it comfortable.

Instead of solar, I would probably choose photovoltaics. In winter, when the underfloor heating is connected, you will miss the sun and now there is far too much.

Get advice and inform yourself from users. One has already mentioned his gas costs for domestic hot water.

What is somewhat confusing is that today everything happens under the terms [Klimawandel] and [Energiewende]!
In a single-family house, quickly 50 cubic meters of hazardous waste are built in, but hardly anyone cares!
If this hazardous waste would at least bring some benefit, then that would be okay.
There are tables from a research institute in Hannover listing selected exterior wall constructions. Maintenance intervals and costs over the next 80 years!
[Wärmedämmverbundsystem (WDVS)] 1314.05 Euro/sqm
Exterior wall with facing brickwork 284.73 Euro/sqm
Exterior wall with fine plaster 429.65 Euro/sqm

WDVS compared to facing brickwork + 460 percent!
At about 200 sqm exterior wall 262,810 Euro versus 56,946 Euro!
That should be enough to make you think!

Upside-down building world!

"According to the calculation by the house building company, the house with the 24 cm [HZL] walls and the 16 cm WDVS has a [KFW] value between 40 and 55."

That is a U-value house!

According to what is the calculation made?
According to the stationary U-value!
This U-value can only be achieved under constant conditions in the laboratory!
But houses still stand outside and are subjected to non-stationary conditions. For this there is the effective non-stationary U-value. It includes the solar input into the wall and the heat storage capacity of the building materials.
Only the single-layer or double-layer ventilated masonry remains.
Unfortunately, hardly anyone knows about the effective U-value!

That is why we launched the building revolution, so that we return to proper building!