ᐅ KfW55 with 36 cm brick wall – feasible or not?

Hello.

We are planning a single-family house together with an architect, aiming for KfW55 standard. According to the architect, using 36.5 cm (14.4 inches) bricks should not be a problem. With these dimensions, everything is now also approved for the building permit / planning permission.
The structural engineer is now skeptical, and the energy consultant said this wouldn’t be possible at all.

So basically the question is: Has anyone successfully done this before?

Also to be installed: air-to-water heat pump, controlled ventilation with heat recovery.

Thank you.

Many things matter
The KfW rating depends not only on the bricks but on the entire house. Windows? Heating? Controlled ventilation? Photovoltaic systems? Solar thermal energy? Roof insulation? And so on.

Specific answers with the respective implemented measures will surely follow...

bluminger schrieb:

Basically, the question is: Has anyone successfully done this before?

Yes; repeatedly.

As nordanney already mentioned, an energy-efficient building—constructed to KFW 55 standards—is not just about the building envelope. An air-to-water heat pump and controlled ventilation with heat recovery are already good components; if the masonry is chosen accordingly (for example, insulated), and windows and roof insulation are properly addressed, most likely the only remaining aspect is insulation beneath the foundation slab. Unless, of course, you plan to build on the Brocken.

Best regards, Bauexperte

We once had a conversation with a nationwide general contractor in Germany, and they said that KfW 55 standard could be achieved using 36.5 bricks (although you would need to use a Tx brick (I think size 8?) instead of the standard size 9 brick).

Therefore, it should basically be possible.

This is determined by the structural engineer in the thermal performance calculation, which takes into account all heat-transferring exterior components and the heat generator (heating system, renewable energy sources) in the overall balance. In general, a wall thickness of 36.5cm (14 inches) will already be challenging to meet the new Energy Saving Ordinance 2016 requirements. For a monolithic wall structure, the wall material must have a thermal conductivity significantly below λ = 1.0. With aerated concrete building materials, structural issues may arise, and also hollow clay bricks may no longer be sufficient since they are only load-bearing in one direction (anisotropic building materials).
Insufficient sound insulation can be an issue with very lightweight wall materials, which is an important consideration in urban or village edge locations with traffic noise.

We are building a KfW55 house with a 36.5cm (14.4 inch) brick wall. Air-to-water heat pump and controlled residential ventilation with heat recovery. We needed 2cm (0.8 inch) more perimeter insulation, plus a small additional detail. But not much. I think it is even a T9.