Exterior wall: lime sand + polystyrene vs. hollow brick

Hello everyone,

I have a few questions about materials for exterior wall masonry.
The plan is a single-family house, about 150 sqm, 2 floors + basement, hip roof (city villa), no KfW - so according to the Energy Saving Ordinance (theoretically something like "KfW60"), air-to-water heat pump, underfloor heating, centralized controlled residential ventilation with heat recovery. The area is quiet.
According to the construction specification, the walls will be made of 24 cm calcium silicate bricks + external insulation with 17 cm PS with ETICS. Alternative - hollow bricks 36.5 cm without filling - but at an extra cost of about €10,000 for the entire house.
I’m not an eco-type :) but the thoughts are:
- I once read that PS means the external insulation (PS) has to be replaced after 20-30 years - is that true?
- Birds/small animals like to use polystyrene as nesting material = holes + heat loss

The option with the hollow brick is offered without brick filling (according to the advisor, it is not necessary with a wall thickness of 36.5 cm).
- is it really sufficient without filling?
- what are the experiences with moisture and mold in the wall with bricks without filling?
- if filling/ insulation is used, which is best: mineral wool, “small stones”?

and in the end: what would you recommend of the two options?

Thank you very much for your opinions :)

Best regards
NilsHolgersson

Hello everyone, I have a few questions about materials for exterior wall masonry. The plan is a single-family house, approx. 150 sqm, 2 floors + basement, hipped roof (town villa), no KfW – so according to the Energy Saving Ordinance (theoretically like "KfW60"), air-to-water heat pump, underfloor heating, central controlled living space ventilation with heat recovery. The area is quiet. According to the construction specification, the walls will be made of 24cm calcium silicate blocks + external insulation with 17cm PS with ETICS. Alternative – hollow bricks 36.5cm without filling – but with an additional cost of approx. €10,000 for the whole house. I am not an eco-type :) but the thoughts are: - I once read that PS means that the external insulation (PS) needs to be replaced after 20-30 years – is that true? - Birds/small animals like to use polystyrene as nesting material = holes + heat losses The variant with hollow bricks is offered without brick filling (according to the consultant, at the wall thickness of 36.5cm it is not necessary). - Is it really sufficient without filling? - What are the experiences with moisture and mold in the wall with bricks without filling? - If a filling/insulation is used, which is best: mineral wool, "small stones"? And ultimately: what would you recommend from both variants? Many thanks for your opinions :) Best regards NilsHolgersson

17cm XPS is definitely a completely different insulator than 36cm bricks. Besides, with calcium silicate blocks you actually have the best stone for your house. High heat capacity = very homogeneous indoor climate. Stays cool for a long time in summer as well. And top-class sound insulation. Regarding moisture, I have a central ventilation system; it certainly also works without one. Just open the window for 10 minutes in the bathroom after showering in the morning. Done.

When I think about the fact that my controlled residential ventilation with heat recovery enthalpy exchanger etc. cost me 8k despite my own work...mh it's quite a luxury, but I think I could also do without it.

what would you recommend from both options?

Take what the construction company is good at. Both options work well.

- I once read that PS means the external insulation (PS) has to be replaced after 20-30 years - is that true?

No.

- Birds/small animals like to use polystyrene as nesting material = holes + heat loss

That can actually happen. But usually only in exposed spots, because the insulation is covered with about 1 cm of plaster and mesh reinforcement.

- is it really sufficient without filling?

Energetically it's actually the same result?

- what are the experiences with moisture and mold in the wall with the brick without filling?

Just like with aerated concrete and insulation. Mold is never caused by the wall itself. You need moisture, poor ventilation behavior, and preferably cool surfaces for that.

if with a filling/insulation, which is best: mineral wool, "small stones"?

The filling that doesn't pour out when you drill into the brick, for example to insert a plug for a screw.

The variant with the perforated brick is offered without brick filling (according to the advisor, with the wall thickness of 36.5 cm it is not necessary). - is it really sufficient without filling?

The thermal insulation is OK. Unfilled bricks are not great for sound insulation.

Hollow bricks lead to slightly more thermal bridges and are noisy to the outside. However, there is no styrofoam around the house. Purely a matter of taste. A 10k surcharge is steep.