Wall construction of a country house

I actually thought so too. But now I have noticed in the neighborhood that houses with thin stones and Styrofoam whose main living areas (and windows) face east are very warm in summer. Houses built with thicker stones (all Poroton T12) without insulation and whose larger windows face south and west are significantly cooler in summer. Likewise, our current prefabricated house (built 08, Kfw 60): in winter it is really cozy warm, but unfortunately also in summer. We were also allowed to test different insulations when we were still looking for our home builder: hemp and Styrofoam were evenly heated with a radiant heater. After 2 minutes, the Styrofoam was hot on the back, while the hemp was still noticeably cooler. The heavier the material, the more it protects against heat.

That is due to the better heat absorption capacity of hemp or wood wool compared to Styrofoam.

What about KSstein + WDVS?
The high mass can certainly not hurt in summer...

(from outside to inside) 10.5 cm facing bricks, 2 cm air layer, 22 mm wood fiberboard (this material has, for example, good heat protection), 6x20 cm KVH timber frame insulated with 20 cm mineral wool insulation, 15 mm OSB as a vapor barrier layer, 6x8 cm KVH battens as an installation layer insulated with 6 cm mineral wool insulation, 12 mm OSB and 12.5 mm gypsum board. All dry, KFW 70 and better (depending on the remaining construction), clean interior work especially from the electrician and plumber, easy and simple to install your own items such as LAN cables or speaker cables, etc., much can be done yourself especially in the interior construction, the wood fiberboard is windproof

Poroton is recyclable, Styrofoam is hazardous waste.

Styrofoam is also recyclable and thus a valuable material
Apart from that, you shouldn't look any further. Every house is full of "hazardous waste."

That is due to the better heat absorption capacity of hemp or wood wool compared to Styrofoam.

What about KS stone + ETICS?
The high mass surely can't hurt in summer...

Besides the high heat storage capacity, also good static properties and good sound insulation.

Polystyrene can be fully recycled... however, it contains a few things; the flame retardant hexabromocyclododecane is hardly biodegradable and classified as very toxic for aquatic environments with long-term effects and toxic. In addition, in the ETICS area, a plaster is used with pesticides/algaecides which are washed out by weathering, causing the plaster to lose its protective effect. I know from customers that after about 8 years, for example, black algae and the like begin to settle on the plaster. One should also not overlook that the substances washed out end up in the garden (vegetable bed nearby?) or that birds or cats/dogs may drink it from puddles, or it enters the sewage system and from there into nature.

Hexabromocyclododecane is water-insoluble and forms a strong bond with the polystyrene, which does not dissolve easily. This requires elevated temperatures. Therefore, EPS is not non-flammable but flame-retardant. Alternatively, there is now EPS available that does without Hexabromocyclododecane. It can be recognized by the blue angel. Of course, when it comes to paint, one can also opt for paint without fungicides. Algae are found not only on [WDVS] façades but also on other plaster façades or sometimes on clinker. Whether and to what extent façades develop algae also depends on the location/shading and especially on adjacent vegetation.