Insulate house with 30cm wall?

Hello,

the question of whether to insulate or not is increasingly being discussed, and of course there are numerous issues related to it. I would be interested in the current knowledge of those who are more familiar with the subject than I am...

The property we purchased was built in ’65 and unfortunately only has 30 cm exterior walls. During the gutting, we didn’t notice anything negative except for 1-2 spots in the basement. However, now the basement and attic will be insulated and new windows (probably double-glazed) installed. Would you generally recommend an ETICS for the wall thickness?

Thanks for your effort!

30s what? - Solid brick, porous brick, pumice or ...?

The single-story new building is to be made of aerated concrete blocks and offer a wide window front.

That’s already not a stone for exposed masonry. Is it supposed to be plastered or clad? - in my opinion, that depends on the answers regarding the old part of the house. Even if the extension is to be visually completely separate, I would not use different philosophies for the wall construction.

A look at the static calculations from that time shows that the masonry consists of "Zementschwemmsteine 'V50' in Mörtelgruppe II". The planning regarding the extension was only loosely requested here and will of course be planned by a structural engineer/architect.

A look into the static calculations at that time shows that the masonry consists of "cement slurry stones 'V50' in mortar group II".

Cement slurry stone is a term for a type of pumice concrete stone, V50 is a compressive strength class, and these two tell you, if you Google them with "thermal conductivity", what your energy consultant has to continue calculating with. The mortar group only indicates for the statics what is used to "glue" the stones together into a wall; stone and mortar are a team there. Thermally, this is a negligible factor. When building an extension, spaces are repeatedly created that are partly bounded by old and partly by new walls. Therefore, I would try to achieve an "overall wall" with values adapted to the old building for the new construction (possibly with varied thickness of the wall or insulation layer). Hence my advice to consider this together.

Regardless of a possible extension, I would be interested to know whether it is generally sensible to install insulation on a 30 cm pumice wall or not.

whether it is generally advisable to apply insulation to a 30 cm pumice wall or not.

Advisable: what purpose do you have in mind?

Insulation always improves the thermal transmittance value - completely independent of my personal attitude towards the insulation craze.

30 cm pumice is at least no longer the current standard without cavity filling. Whether it meets the energy saving ordinance, I don't know - probably not for KfW55 anymore.

If you have a different attitude towards insulation than I do and would apply ETICS on porous bricks, you can do the same on pumice, I see no essential principle difference. 30 cm is considerably thicker than 17.5 cm - therefore, for similar overall values instead of 16 cm, you will probably only need 8 cm or maybe 12 cm of insulation.

You won’t freeze or waste all your money on heating with 30 cm pumice even without insulation, I myself live like that (30 cm pumice monolithic, probably also unfilled, without ETICS and without facing brick). From which proportion of new build you have to bring the old building up to today's standard, I don't know.

The frequently read warnings about mold damage will depend on ventilation and the professional correctness of the installation, also no different with pumice than with other materials.