ᐅ Exterior Wall: Calcium Silicate Blocks with Polystyrene Insulation vs. Hollow Clay Bricks

Hello everyone,

I have a few questions regarding materials for exterior masonry walls.
The plan is for a single-family house, about 150 sqm (1,615 sq ft), two floors plus a basement, hip roof (urban villa style), not KfW-certified—so according to the Energy Saving Ordinance (technically like "KfW60"), air-to-water heat pump, underfloor heating, central controlled ventilation with heat recovery. The area is quiet.
According to the construction specification, the walls are to be built with 24 cm (9.5 inches) sand-lime brick plus 17 cm (7 inches) external insulation with EPS (expanded polystyrene) and an ETICS (external thermal insulation composite system). An alternative is perforated clay brick 36.5 cm (14.4 inches) without cavity insulation—but with an additional cost of about 10,000 euros for the whole house.
I’m not particularly eco-conscious 🙂 but here are my thoughts:
- I have read that EPS means the external insulation needs to be replaced after 20–30 years—is that true?
- Birds and small animals like to use polystyrene as nesting material, causing holes and heat loss.

The option with the perforated clay brick is offered without filling (according to the consultant, at a wall thickness of 36.5 cm (14.4 inches) it is not necessary).
- Is it really sufficient without cavity insulation?
- What are the experiences with moisture and mold inside the wall when the brick is unfilled?
- If filling/insulation is recommended after all, which is best: mineral wool, “small stones”?

And in the end: which of the two options would you recommend?

Many thanks for your opinions 🙂

Kind regards
NilsHolgersson

NilsHolgersson schrieb:

Hello everyone,

I have a few questions about materials for external wall masonry.
The plan is a single-family home, about 150sqm (1,615 sq ft), 2 floors plus basement, hip roof (city villa style), no KfW subsidy – so following the Energy Saving Ordinance (theoretically like "KfW60"), air-to-water heat pump, underfloor heating, central controlled residential ventilation with heat recovery. The area is quiet.
According to the construction specification, the walls will be built from 24cm (9.5 inches) sand-lime brick plus 17cm (7 inches) external insulation with ETICS (external thermal insulation composite system).
An alternative is a 36.5cm (14.4 inches) hollow brick without insulation - but for an additional cost of about 10,000€ for the whole house.
I’m not an eco-fanatic 🙂 but these are my thoughts:
- I once read that PS (polystyrene) means the external insulation has to be replaced after 20-30 years – is that true?
- Birds and small animals tend to use polystyrene as nesting material, causing holes and heat loss.

The hollow brick option is offered without cavity insulation (according to the consultant, with 36.5cm (14.4 inches) thickness it is not necessary).
- Is it really sufficient without insulation?
- What are the experiences with moisture and mold inside the wall with hollow bricks without insulation?
- If insulation is needed, which is best: mineral wool, or “small stones”?

And in the end: which of the two options would you recommend?

Thank you very much for your opinions 🙂

Best regards
NilsHolgersson

17cm (7 inches) XPS is definitely a completely different insulator than 36.5cm (14.4 inches) brick.
Also, sand-lime brick is actually the best brick for your house.
High thermal mass = very stable indoor climate.
It also stays cool for a long time in summer.
And excellent sound insulation.
Regarding moisture, I have a central ventilation system, but it surely works without it as well.
Just open the bathroom window for 10 minutes in the morning after showering. Done.

When I think about the fact that my controlled residential ventilation system with heat recovery, enthalpy exchanger, and so on cost me 8,000 (eight thousand) despite doing part of the work myself... well, it is definitely a luxury, but I think I could also do without it.

NilsHolgersson schrieb:

Which of the two options would you recommend?

Choose the one that the construction company is experienced with. Both options work well.

NilsHolgersson schrieb:

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

No.

NilsHolgersson schrieb:

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

That can actually happen. However, it usually occurs only in exposed spots, because the insulation is covered with about 1cm (0.4 inches) of plaster and reinforcing mesh.

NilsHolgersson schrieb:

- Is it really sufficient without any filling?

From an energy efficiency point of view, it really makes no difference.

NilsHolgersson schrieb:

- What are the experiences with moisture and mold in the wall when using bricks without filling?

Similar to sand-lime bricks with insulation. Mold is never caused by the wall itself. You need moisture, poor ventilation habits, and preferably cool surfaces for mold to develop.

NilsHolgersson schrieb:

- If filling/insulation is used, which is best: mineral wool or "small stones"?

Use the filling that won’t fall out when you drill into the block, for example, when installing a wall plug for a screw.

NilsHolgersson schrieb:

The version with the hollow brick is offered without brick infill (according to the consultant, it is not necessary for a wall thickness of 36.5cm (14.4 inches)).
- is it really sufficient without infill?

The thermal insulation is fine. Hollow bricks without infill are not great for soundproofing.

Hollow bricks result in slightly more thermal bridging and allow more external noise transmission. On the other hand, there is no need for external polystyrene insulation around the house. It’s purely a matter of preference. A 10,000 cost increase is quite steep.