KfW 70 - 36er Ytong - Ventilation system

Hello €uro,

A monolithic wall construction is a compromise regarding competing demands. [...] In the case of a custom build, one should be less willing to accept compromises. Although all functional requirements are met overall, the details look less good: (load transfer (thickness of the load-bearing shell), individual load distribution or entry, sound insulation, thermal insulation in relation to the thickness of the insulation layer, summer thermal protection, etc.
In other words: it somehow works, but it is not optimal!

Of course, I see this differently! If what you describe above were true, I would certainly have a lot of customer complaints. Besides, sound insulation is really not an issue with a wall thickness of 36.5.

Best regards from the Rhineland

Hello, an alternative would be a two-shell wall construction... We build as follows on the advice of our architect: 17.5 [Kalksandstein Tragschale], 15cm core insulation WLG032 and 11.5 [Klinker] as the outer shell. This provides good sound insulation, a good indoor climate, fairly good wall insulation values (approx. 0.19 W/m²*K) and a facade that lasts and does not wrap the house in plastic. However, the wall construction is somewhat thicker... 44cm. Regards Fragri

Hello, an alternative would be a double-shell wall structure... we build as follows on the advice of our architect: 17.5 cm calcium silicate load-bearing shell, 15 cm core insulation WLG032 and 11.5 cm clinker as facing shell. This provides good sound insulation, a good indoor climate, fairly good insulation values of the wall (approx. 0.19 W/m²*K) and a facade that lasts and does not wrap the house in plastic. The wall structure is somewhat thicker though... 44 cm. Regards Fragri

But you still wrap the house! You probably don't have a ventilation system – how do you get rid of the moisture through a 44 cm wall structure?

Hello,

....we are building on the advice of our architect as follows: 17.5 cm calcium silicate load-bearing shell, 15 cm core insulation WLG032 and 11.5 cm clinker as facing shell.

You have a good architect, although I would possibly ventilate the insulation, depending on the insulation material used. If clinker as a facing shell is too expensive, calcium silicate + plaster also works here. Basically, in my opinion, the best wall construction one could choose! Common ETICS, for example, never achieve comparable solar utilization of opaque components. Usually, the cost aspect is decisive why this optimal variant is rarely chosen. However, one could consider getting by with a few cubic meters less enclosed space, leaving out unnecessary frills, then the budget will also be right again!

Best regards

Hi
we just received the documents for the KFW-70 application. We are building with 36.5 cm Ytong elements. They are prefabricated to the height of the floor in the factory and delivered as approx. 1.8 m wide elements. This results in no horizontal joints as thermal bridges in the wall.
In combination with gas condensing boiler, solar for domestic hot water, and insulated floor slab, we can easily meet KFW 70 for our 100 sqm bungalow.
What worse performance is to be expected from a cleanly plastered Ytong wall than from other walls with polystyrene insulation on top?

Then the solar system must be very large. I personally can’t believe that or my general contractor is too stupid.

How much insulation do you have under the floor slab and on the floor slab?
How does the roof insulation start?

Is maybe biogas being used?

@ Euro, Thanks! Certainly this is not the cheapest wall structure but probably one of the best. I just overlooked the ventilation gap... you are of course right, but it is also included in the planning. Here it is about 1-2 cm that are added. A core insulation with mineral wool (Kontur KP 1-032) is planned.