Additional cost for 36.5cm aerated concrete plan block compared to 30cm plan block?

Hello,
we are planning a single-family house with a living area of approx. 150 m² / without basement / gable roof 40°
knee wall height 1m
external dimensions approx. 9.5 * 10.8m
Energy Saving Ordinance 70
to be built.
At the moment we are still in the selection phase of possible contractors.
As standard, one supplier offers the 30 PB plan block without ETICS in the EnEV 70 BB
existing.
However, we prefer the 36.5 PB plan block.
With what additional costs would we have to reckon for the masonry?
Thank you very much for the feedback

@Everyone
no one there?

Hello,

well, then I'll give it a try, even though I am unfortunately only a prospective builder and not an expert, so unfortunately no concrete prices from me but just some tips:

- Since construction companies are often very creative with their cost calculations, especially when it comes to hard-to-compare trades like shell construction, I have once directly contacted the manufacturer myself. In my case, a large brick manufacturer. So: I found a sales contact on the Internet, called, and was referred to a local sales office that helped me a lot both with prices and with arguments when negotiating with construction companies. Worth a try!

- 30cm aerated concrete is the lower limit in terms of thermal insulation; with a very porous plan brick with λ=0.08 W/mK and 30cm, you get a U-value of about 0.27, which is still okay but not good for the future. Because the rule is: Priority in energy savings goes to the building envelope (roof, walls, windows, base plate), only then comes the heating technology, which has a significantly shorter lifespan and is easier to replace.

Also, many experts don’t like the highly porous aerated concrete blocks because they crumble so quickly and look outdated in terms of dowels and slots. However, that is just hearsay...

- 30cm is very little for such a porous stone. I suspect a low sound insulation value. Personally, in your place, I would choose the 36.5cm stone, even if it costs a few thousand euros more and is not energetically cost-effective in the long run.

- If the wall is insulated as thinly as with the 30cm stone, then to achieve KfW 70 you need to invest more in technology. So I suspect it won’t work without a heat pump with a solar system. If the exterior wall and the roof had good insulation values, then you would have more leeway in planning your heating technology. You might then be able to fall back on a cheaper gas boiler without solar support. But the prerequisite for KfW 70 would then be: you invest in ventilation with heat recovery. That would be at least my choice if I were building your house...

Best regards Olaf

Hello o.s.
Thank you very much for the feedback. I will give it a try.
I am an absolute PB fan.
A brine heat pump is to be used as the heating system. We are still unsure about the controlled residential ventilation, whether decentralized or centralized. It is also a cost factor that must be taken into account. (Keyword: amortization) I tend to prefer a centralized system, primarily for comfort reasons.
We visited a house over the weekend where a decentralized system without heat recovery was installed. The supply air inlets were installed in the roller shutter box. It was quite drafty there. For me, more of an emergency solution.
Many greetings

Hello volkono,

A ventilation system with heat recovery will never pay for itself. It is purely a comfort gain! What the heat recovery saves is consumed by the motor's electricity and the maintenance costs for the filters. I myself also considered whether to take a decentralized system with heat recovery but have now decided on the central one despite the additional costs. The point of having a hole in the wall to the outside in every room put me off. Especially because of the noise. Otherwise, I personally also tend to save on heating technology and put the money into insulation. We are building quite similarly from the house perspective. We have 145m^2 with a gable roof and a kind of front gable and also achieve energy saving regulation 70. Roof 24cm WLG035, walls are 17.5cm aerated concrete with 160mm ETICS WLG035. Passive house windows, gas condensing boiler without solar and controlled residential ventilation with heat recovery.