ᐅ How is the "typical wall thickness" determined for cavity walls?

Hello,
I have read a lot about possible wall constructions, and it seems there is no single “right” solution, which is fine. However, when I add up the commonly recommended layers (assuming it’s better to insulate more rather than less), I end up with a cavity wall consisting of Poroton blocks on the inside and clinker bricks on the outside measuring about 1 cm (0.4 inches) (plaster) + 30 cm (12 inches) (Poroton) + 18 cm (7 inches) (mineral wool insulation) + 4 cm (1.5 inches) (ventilation gap) + 12 cm (5 inches) (clinker) = 65 cm (26 inches). On the other hand, when I search for “typical wall thickness,” I usually find values around 49 cm (19 inches) or less (for a standard KFW55 or KFW40 house). Where am I mistaken?
Karl

Isn't that in your case a three-layer construction?

For comparison, in a KfW55 building, we use 17.5cm (7 inches) calcium silicate brick and 21cm (8 inches) plastic insulation (plus plaster).

karl.jonas schrieb:

I have now read a lot about possible wall constructions; there doesn’t seem to be a single correct option, okay. But when I add up what is recommended

Just “google” here or elsewhere for “Steinemantra.” There you will find my recommendation (explained) that there are exactly as many recommended wall constructions as the number of options your builder has experience with in their portfolio.

karl.jonas schrieb:

Where am I wrong?

Simply put: you are mistaken where you do not make the structural masonry leaf slimmer if you include an outer masonry leaf. You are adding 100% on top, which always results in more than a whole.

Why do you want to saddle the horse exactly by wall thickness?

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30 cm Poroton with 18 cm internal insulation is unusual, which is why you end up with such a thick wall.

We have:
17.5 cm aerated concrete, 16 cm mineral wool, 2 cm air gap, 11.5 cm facing brick = 47 cm (18.5 inches)

Then there is also the interior plaster.

Mineral wool and facing bricks are more insulation materials than components of a wall structure. A wall is a structural element with a load-bearing function.

A cavity wall basically consists of an inner wall and an outer wall built together in a bonded masonry system. The open cavity between them was simply filled with air as insulation. In the past, for example, walls were built with facing bricks, with the inner wall being 12 cm (5 inches) thick, the outer wall 12 cm (5 inches) thick, and a 12 cm (5 inches) air gap between them. Both walls were bonded together with facing bricks across the cavity. That is why it is called bonded masonry.

Then interior and exterior plaster finishes are applied.

Our last new build, for example, consisted of 17.5cm (7 inches) calcium silicate brick + 14cm (5.5 inches) insulation + 11.5cm (4.5 inches) facing brick. An air gap is not necessary.