A basement exterior wall as a dowel wood construction (wood + concrete)

Hello,

I have a question for the community that won't let me rest. We are planning a house with dowel wood construction and cellulose insulation. Since the plot has a slight slope, we have planned a basement apartment. To achieve a better indoor climate, the construction company offered us the mostly open south-facing basement exterior wall made of dowel wood (just like the house). The other 3 exterior walls will be made of 20 cm thick reinforced concrete and insulated from the outside with 14 cm of Styrofoam and 6 cm inside.

Since I am not a fan of Styrofoam etc. (especially indoors), I proposed calcium silicate boards as internal insulation for the basement apartment as an alternative. According to the construction company, that would be possible, but only if we make the 11 m long south basement exterior wall as a dowel wood construction. Because the calcium silicate boards have a poor U-value.

At first, I was excited about the idea of having less concrete + Styrofoam in the house. However, later some acquaintances expressed their thoughts that such a construction is not stable and that wood and concrete walls should rather not be combined. Also, there is a particular risk in very heavy rain that water might get into the wall after all. An employee of a competing company also commented on this and said something about the statics.

Has anyone already implemented such a concept? Or does anyone know someone who has something like this? Or is there an architect/expert here who can say whether it is all okay or if it is better to leave it alone.

Thanks in advance
Regards
Sergey

What speaks against insulating the concrete walls on the outside with, for example, 20 cm, in order to completely dispense with interior insulation? Has this alternative already been calculated? A better insulation of the basement floor can possibly compensate for a certain deficit of the walls, if necessary. In the end, this is a calculation regarding the thermal insulation values of the various components of the house, including the window U-values.

What energy standard should the house achieve overall?

Calcium silicate boards are a good solution for retrofitting insulation in existing buildings when exterior insulation is difficult. In a new building, I would avoid interior insulation of solid walls. This has, besides possible health aspects, other reasons: if the entire concrete exterior walls of the basement are part of the thermal envelope, the house will also cool down or heat up more slowly, meaning it will respond more slowly overall to temperature changes – which, in my opinion, is quite positive. And thinking practically: shelves, etc., can be more easily mounted on the wall without interior insulation.

You are planning wooden studs, right? Every manufacturer advised us against that, and so did the structural engineer. We now have concrete on the slope side, insulation from the inside and outside, the rest is solid wood.

Thank you BobRoss, see inline:

What speaks against insulating the concrete walls on the outside with, for example, 20cm, in order to completely do without interior insulation? Has this been calculated as an alternative?
Better insulation of the basement floor might also compensate for a certain deficit of the walls, if necessary. In the end, it is a calculation task regarding the thermal insulation values of the different components of the house, including the U-values of the windows.

I asked the construction company the same question. They told me they are not allowed to use insulation that is too thick on the outside because they are making a wooden dowel ceiling in the basement. And it won’t work if the wooden ceiling protrudes too far outward with 20cm thick exterior insulation (I hope I understood that correctly). It deviates a lot from their standard and they would not try to build it.

What energy standard should the house achieve overall?

40+

Calcium silicate boards are a good solution for retrofitting insulation on existing buildings when exterior insulation is difficult to implement.

For me, calcium silicate boards would be a solution to do without polystyrene in the living area if we still build our house with basement with wooden exterior wall and wooden ceiling with the company.

For a new building, I would avoid interior insulation of massive walls. This has, besides possible health aspects, other reasons: if the entire concrete exterior walls of the basement are part of the thermal envelope, the house will also cool down or heat up more slowly, i.e., overall react more slowly to temperature changes—which in my eyes is certainly positive.

I don’t like interior insulation either and that also worries me the most. As well as an exterior wall made of wood in the basement. That’s why I need the community’s opinion.
Actually, I wanted the south exterior wall made of wood in the basement because it has much better values regarding phase shift—19.3 (wood) versus 12.2 (concrete) hours. So, with the wooden wall, the basement should be cooler in summer (at least in theory).

And practically speaking: Shelves etc. can be more easily screwed to the wall without interior insulation.

If there is interior insulation, drywall will also be installed on it.

You’re planning wood studs, right?

Thanks haydee,
we are planning a wooden house. One company offers solid dowelwood walls with Regal cellulose insulation. The other offers wood studs with wood chips as insulation. The equipment is quite similar. Only the second is about 10% more expensive.
The first company offers an exterior basement wall and basement ceiling and all interior walls (!) made of wood but with interior insulation made of Styrofoam.
The second company is more conservative and did not speak very positively about the solution from the first. Not only about the interior insulation (I knew the disadvantages myself), but also about the wooden wall and wooden ceiling. That it is not safe in the long run and cannot be compared to a full concrete basement.

Every manufacturer advised against it as did the structural engineer.
We now have concrete on the hillside side, insulation from inside and outside, the rest is solid wood.

Did you also want a wooden basement wall? Did the structural engineer say anything specific about why it’s not good?
Why couldn't you do without interior insulation?

We have a basement level. We need the concrete wall as a retaining wall. Either basement, as far as necessary, in concrete or retaining wall with at least 1 m distance from the house in front. With solid wood on 3 sides and thick retaining wall and floor slab it worked. Reinforcement was insane. However, we still have a 13 m slope behind the house.

Insulation on both sides was a must to prevent condensation. After the architect, plasterer, concrete worker, and expert were all of the same opinion, I assume it has to be done.