Which stone is best for construction?

hello folks.
i am in the process of building an extension to the garden at my small terraced house where our living room is supposed to go. the plot is only 4 meters wide and the extension is supposed to be 3.20 meters long. so now i want to use a stone as narrow as possible on the right and left next to the neighbor in order not to waste too much space inside. what should i best use for this regarding thermal insulation etc.? can i use an 11.5 stone or is a 17.5 better or even thicker because of durability and insulation? can you recommend a relatively good stone that is narrow and has good thermal properties.
best regards axel

Hello, 24 cm aerated concrete (gas concrete blocks) is a bit more expensive, but provides very high thermal insulation, at least 17.5 cm aerated concrete (structural). Regards

ok thanks. can I also easily have a concrete ceiling poured at 17.5 or should I better use beams instead of concrete because of the statics. best regards Axel

Yes, of course. 17.5 cm is a load-bearing wall. The ceiling only needs to be statically calculated.

thank you very much! is a concrete ceiling to the outside sensible? i have my doubts because of cracks and then there also has to be roofing felt on it.

Certainly, you can also install a wooden beam ceiling on it (beams approx. 24/14cm min. + boarding and appropriate covering + of course insulation).