ᐅ Solid wood construction – what wall thickness and costs should you expect?

Hello everyone,

I have several points I would like to discuss here in the hope that someone can help me.

We are building a duplex using solid wood construction (cross-laminated timber). For the separation between the two units, each dwelling will have its own wall with a small cavity in between. The general contractor (GC) says this is the best approach in terms of sound insulation. Question: Is that really the case?

So far, the two walls were planned to be 19 centimeters (7.5 inches) thick each – including plaster on the interior sides (the other exterior walls are 36 centimeters (14 inches) thick). The GC has now informed us that they have achieved a reduction of 7 centimeters (2.8 inches) in wall thickness. Originally, the walls were planned to be this thick due to structural requirements. After calculations, they say thinner walls are possible, which is good in terms of gaining more interior space. The downside: to maintain the same level of sound insulation, they advise against installing deep electrical boxes in this wall. Question: What are your thoughts on this?

What I only realized after the conversation with the GC is that saving 7 centimeters (2.8 inches) of thickness on each of the two walls, over an eleven-meter (36 feet) long house with three floors, means saving around 12 to 15 cubic meters (425 to 530 cubic feet) of material. The GC did not mention any positive impact this might have on costs. Question: Can anyone roughly estimate what this material saving might mean in terms of cost savings?

Thanks and best regards
TheZim