Facade insulation with mineral foam boards?

We are currently new owners of a single-family house built in 1954 with 0% insulation. [...] Insulation of an old building with (30cm expanded clay blocks)

1954 expanded clay may be possible, but is that a certainty or a guess? Pumice is not only found in the Middle Rhine region (and is sometimes confused with it).

1954 expanded clay may be, but is that a certainty or a guess? Pumice is not only found in the Middle Rhine region (and is sometimes confused with it).

Sorry, you are right, it is pumice.

I would check with the manufacturer to see what they include in their current products (there are some pumice products that integrate an insulation material as a wall shell, similar to milchschnitten. It should be well "compatible" with the building material of your house and could be a product that is also available individually.

With the proposed insulation, you should not even meet the Energy Saving Ordinance (standard approach: Bims masonry from the 50s with a U-value of 0.9). With the mineral foam board, you just reach a U-value of 0.30 for the wall. 0.24 is required. Definitely speak with the energy consultant. In my opinion, it would have to be at least the 0.32 EPS graphite boards.

ETICS are also available in "environmentally friendly" alternatives. Wood fiber insulation board + curtain facade as just one of many examples. A specialist (who?) should provide advice there. The energy consultant then calculates whether it fits (with the target specification).