36 cm Ytong exterior wall, solid construction, mold formation, insulation

Hello, we have now received an offer from a BU for our planned single-family house, which we actually liked.

Now we were told (by a prefabricated house builder) that if it is built solid, insulation should definitely be installed, otherwise mold problems will occur.

What do you think? KfW values can be neglected here.

.... The question is, however: Is a 36 cm aerated concrete (porous concrete) wall really massive?

I can only agree with that. The various "crumb stones" are sometimes a joke. Given today's requirements, "separation of powers" makes sense, i.e., assigning the partly competing demands each to a "specialist." Ideally, this ends with a two-shell wall structure plus a solid facing. Many people do not want or cannot afford this, as golden door handles, marble in the bathroom, or a dormer are usually preferred. It is no coincidence that the need for technical cooling is increasing in so-called "lightweight construction." If you calculate the real energy balance here, a passive house (PH) or KfW55 quickly turns into a simple energy-saving ordinance standard.
Best regards

Hello €uro

(...) The various "crumb stones" are sometimes a joke.

Can you explain that in more detail? ETICS made of styrofoam crumbles at least just as much. Do you see differences in stability between aerated concrete, perforated bricks, and bricks filled with perlite or mineral wool?

With today's requirements, "separation of powers" makes sense, i.e., assigning the partly competing demands each to a "specialist." Ideally, this ends with a two-shell wall construction + massive facing. Many either don't want or can't afford that since golden door handles, marble in the bathroom, or a dormer are usually preferred

In our case, that would be at least 22,000 euros more – representative hand-formed facing bricks not yet included. We neither want nor can afford that, even without golden door handles...

It is not without reason that the need for technical cooling is increasing in so-called "lightweight construction." If you calculate the real energy balance here, a passive house or KfW55 quickly becomes a simple energy saving ordinance standard

Don't not understand.

Regards Olaf

Hello,

.... The question is, however: Is a 36 cm aerated concrete wall really solid?

There he is again; I really appreciate your subtle sense of humor

And keep in mind that the masonry must also have other properties --> Statics / Soundproofing. So when choosing the right building material always look beyond the famous horizon

Aerated concrete

It is a highly thermal insulating solid building material that, due to its closed-cell pore structure, can take on both static and building physics properties – usually without additional measures and complementary building materials.

Sound insulation:

Aerated concrete relativizes the physical principle "The heavier a component, the better the airborne sound insulation." Because aerated concrete has, due to its pore structure, a kind of internal damping. DIN 4109 also takes this into account: Aerated concrete walls with an area-related mass of up to 250 kg/m2 receive a bonus of 2 dB. New component measurements even show further improvements. With walls and solid roofs made of aerated concrete, all exterior noise level ranges can be covered acoustically.

According to suitability test III for DIN 4109, double-shell party walls made of aerated concrete with 17.5 cm PP4-0.6 each and a 50 mm shell gap, fully filled with mineral insulation, even meet the requirements for increased sound insulation.

Source: my homepage

Kind regards

Hello,

Now we were told (by a prefabricated house builder) that if you build with solid construction, you absolutely have to install insulation, otherwise mold problems will occur.
What do you think? KfW values can be neglected here.

I really appreciate these "qualified" statements By now it should be well known that I am not a fan of hazardous waste; ergo my answer will not surprise anyone.

As my perceptive friend has already pointed out, there is nothing against a monolithic wall structure. However, it must also be noted here – according to the Energy Saving Ordinance, houses have to be built quite airtight (in my opinion too airtight). So you have to ask yourself whether you have time to ventilate your rooms accordingly; especially in the first year after moving in. Even if the aerated concrete is glued, a lot of moisture enters the house through the screed – and subsequently through human breathing. You should at least consider a ventilation system.

With monolithic construction – and if a partner is permanently at home – you can (just barely) do without ventilation. If you additionally put your house in an ETICS – I would, however, reduce the stone thickness, unless you are aiming for KFW 55 – then you no longer have this option, because mold is guaranteed. So much for the statement of your prefabricated house builder

Kind regards

Hello,

... However, a second protective layer is missing, so the structural builders have to work properly to avoid thermal bridges ...

That on the one hand, and on the other hand, today an ETICS is often installed because the hairline cracks caused by normal settlements then "hide" behind the Styrofoam.

Kind regards