ᐅ Single-shell vs. double-shell facade

Hello dear forum community,

After visiting several construction companies, the question of the optimal facade system has come up for me—specifically, what are the pros and cons of the different options?

First of all, the goal is to at least meet the KfW55 standard. A simple online search yields the usual advantages and disadvantages of all materials, but I would like to rely on the community’s arguments and experiences. The focus is explicitly not on aesthetic factors like “brick looks much nicer” or similar, but rather on practical experience, risks, and useful information about the different materials.

- In the single-layer category, I have so far only seen a Poroton facade (T7 MW, T8), which at 36.5 cm (14 inches) is quite narrow and is usually finished with an external render or optionally brick veneer.

- For double-layer systems, I was typically shown a naturally thicker facade consisting of aerated concrete, mineral wool insulation, and brick cladding. What we definitely want to avoid is polystyrene insulation.

I realize it’s hard to say that one option is clearly better than the other, but please be so kind as to share your personal opinion and feel free to explain your reasons.

Have a nice evening!
Regards, Rafael

T7 bricks are problematic when it comes to any kind of fastening. If you damage the brick, your insulation will be compromised. For example, installing electrical outlets in window reveals is not possible. In cavity wall construction, the insulation and load-bearing elements are separated, which also improves sound insulation. Additionally, you should consider whether you really want a plastered facade in terms of maintenance effort.

The best option is a ventilated curtain wall façade. Freezing wind is slowed down and doesn’t reach the house behind it. In summer, the sun doesn’t hit the wall directly (only the façade), leaving a 3cm (1.2 inches) gap behind that is open at the top and bottom, allowing air to circulate through a chimney effect. Any moisture coming from inside can easily dry out.

I especially noticed this last summer: even with sunlight, it was 25°C (77°F) inside and 35°C (95°F) outside. Then with the air conditioning on, you could look outside covered in frost 😀
I also like the appearance; I added a wooden cladding that doesn’t need to be painted again.

I would definitely recommend a cavity wall construction. Especially if you do not want a ventilation system, a cavity wall solution is always the better choice. If using ETICS (external thermal insulation composite systems), then one with mineral-based components. We built with aerated concrete + mineral wool + facing bricks and will move in at the end of the month. The building drying process worked extremely well for us.

It's also a matter of cost. A double-shell (cavity) wall is clearly more expensive. For a bungalow, for example, the effort for repainting the facade after 10 years is manageable since no scaffolding is needed. The roof overhang also provides good protection for the facade. Therefore, for a bungalow, a single-shell (solid) wall is acceptable. For a taller house, you need to consider it carefully... Both options are possible, but then a double-shell construction would be better—if affordable.

TobiasW. schrieb:
Especially if you don't want a ventilation system, a double-shell construction is always the better choice.

But practically, there is no connection. Or are you thinking of complicated wall penetrations in double-shell construction for the pipes? Hardly...