ᐅ "Cavity wall construction," wall formwork, aerated concrete masonry

Hello dear forum members,

As I mentioned in the "Introducing Myself" thread, I would like to ask a question regarding external walls.

I have a concrete housebuilding offer from what I consider to be a fairly large, well-known construction company.
I’m not sure if it’s allowed to mention the name here in the forum.
Let’s just say the name starts with a “V” and there are a few model home parks in Germany.

My question:
The company describes the following wall structure in their building specification:
40.0 cm (15.7 inches) thick external wall:
Inner leaf of 15.0 cm (5.9 inches) aerated concrete masonry (thermal conductivity 0.10 W/mK) + 12.0 cm (4.7 inches) insulation made of high-quality core insulation (0.035 W/mK) + 1.5 cm (0.6 inches) air gap + 11.5 cm (4.5 inches) facing brick (no thermal conductivity value provided)

There is also an alternative (same price) where the facing brick is replaced by a second layer of 11.5 cm (4.5 inches) aerated concrete masonry plus a rendered facade.

First, I would like to hear your opinions on this wall build-up. The company promotes this structure as very durable and insulating. The sales representative said that because the render/facing brick is separated from the insulation, no moisture can penetrate the masonry.
Is the above-described structure really sensible?

While browsing the forum, I came across the following thread: https://www.hausbau-forum.de/Dämmung-isolation/4234-einschaliges-mauerwerk-vs-zweischaliges-mit-wdvs.html

This made me a bit cautious. Admittedly, I’m not an expert. Is this thread discussing a similar "issue"? Or is it about rendering directly onto the insulation?

Perhaps some of you can shed some light on this.

Thanks in advance!

Best regards,
Christian

Hello building expert,

thank you very much for the detailed answer!

So you visited the red competitor in Kaarst; sooner or later every home builder takes a look there 😀

😎

What always makes me laugh the most is - in my opinion - the brilliant move with the red tent 😀

Uh, I’m lost here. Tent?

People have different opinions about external thermal insulation composite systems (ETICS / EIFS) — I personally don’t like them but have to come to terms with them — in the long run and with respect to compliance with the 2012 Energy Saving Ordinance, you won’t be able to avoid them. Even the respected red colleagues — according to a recent finding by an expert at the Consumer Advice Center in Bergheim — have problems with facing brickwork and KfW 55 standard; whether it’s due to the insulation, the exhaust air heat pump, or a combination of both, he did not want to specify. But every other solid construction provider has to deal with this issue as well.

Okay, I’ll try to summarize (is that the right way to say it?):
ETICS are insulation materials not used by the company. They seem to have certain disadvantages. Still, they should be used to comply with the 2012 Energy Saving Ordinance. Is that correct?
Furthermore, the company seems to have problems with the combination of heat pumps and facing brickwork. Does this mean conversely that insulation with a second layer of aerated concrete plus plaster is better?

Best regards
Christian!

Hello Christian,

Christian1982 schrieb:

Uh, I’m confused. Tent?

Yes, a red tent – the advertising message for interested home builders behind it is: we can build regardless of the weather.

Christian1982 schrieb:

Ok, I’ll try to summarize (if that’s the right way to say it??)

I skip those constant considerations and stick to the spelling rules I learned in school. That, of course, means I’m often using outdated or incorrect spelling.

Christian1982 schrieb:

ETICS are insulation materials that the company doesn’t use.

Christian1982 schrieb:
They seem to have certain disadvantages. Still, they should be used to comply with the Energy Saving Ordinance 2012. Is that correct?

ETICS stands for External Thermal Insulation Composite System; a long term, so I abbreviate it. For full exterior wall insulation, ETICS are often used to reduce heating costs and meet the increasing requirements of the Energy Saving Ordinance. Other common terms include thermal envelope or full thermal insulation.

Only a few types of insulation materials are suitable for ETICS because the standards are very high. For example, renewable insulation materials (such as mineral-based insulation) are either unsuitable or only conditionally suitable because they are more flammable and have a high moisture absorption capacity.

Tests have shown that polystyrene insulation boards can produce toxic smoke and dangerous flaming droplets on the facade in case of fire, and can accelerate fire spread—especially if fire barriers or mineral wool fire stops are omitted. Therefore, proper planning and installation of ETICS is essential, as well as proof of approval through a general building authority permit (AbZ). This permit is exclusively issued by the German Institute for Building Technology (DiBt) in Berlin.

Installing ETICS is not a job for amateur builders because many building physics requirements, connection details, and possibly static considerations must be taken into account.

ETICS are usually offered by one manufacturer as a system with compatible components. The insulation material—insulation boards or panels—is glued or fixed with a rail system to the exterior wall and covered with a reinforcing layer. This reinforcement consists of a base coat mortar with embedded reinforcing mesh. The outer plaster serves as the finish and prevents moisture from penetrating the masonry. Additional mechanical fixings are only necessary if the substrate is not stable enough, such as sandy old plaster or old coatings.

Source: Energiewelt, my website

Christian1982 schrieb:

Furthermore, the company seems to have problems with the combination of heat pumps and brick cladding.

Not with heat pumps in general, but with the combination of KfW 55 standard and the currently installed exhaust air heat pump; that’s an important distinction! Exhaust air heat pumps are reasonably used only in genuine passive houses (PH). Usually, the home builder ends up at a disadvantage due to high electricity costs. Have a look around the forum and search for posts by €uro.

Christian1982 schrieb:

Does this mean that insulation with a second layer of aerated concrete plus plaster is better?

That’s one of those “religious” topics — there is no universally “good” or “bad” when it comes to exterior wall construction. Some prefer aerated concrete, others Poroton, and others double-layered walls or timber frame construction. Personally, I prefer monolithic construction, but that only works to a certain extent and must be decided on a project-by-project basis. If I don’t have the worst possible plot conditions (such as orientation to the sun), monolithic combined with the appropriate technology works up to KfW 55 standard. But—and this must be mentioned—this reduces usable living space because the wall thickness must be increased to 42.5cm (17 inches), and not every builder has a sufficiently large building plot.

Düsseldorf isn’t far for me; if you need more clarification, we can discuss all relevant aspects of a building project in person.

Kind regards

Good morning construction expert,

thank you again for your detailed reply!!

Take a look around the HBF and search for posts by €uro.

Unfortunately, I could only find two threads started by €uro. However, each of them contains only one post. Which one did you mean exactly?

Regards,
Christian!

In the advanced search, you can directly search for the username "€uro."
This way, you will find all posts by them.

Hello,

Christian1982 schrieb:
....Inner leaf made of 15.0 cm (6 inches) aerated concrete masonry (thermal conductivity value 0.10 W/mK) + 12.0 cm (5 inches) insulation using high-quality core insulation (0.035 W/mK) + 1.5 cm (0.6 inches) ventilated cavity + 11.5 cm (4.5 inches) facing brick (no information regarding thermal conductivity value)

I find this wall construction quite reasonable. However, individual details may be viewed differently. In principle, I consider "separation of functions" resulting from differentiated requirements and competing demands to be sensible.
Here, I agree with E. Curb, although he is an architect and I, having originally trained in a different discipline, completed a civil engineering degree much later.
In real practice, we apparently reach consensus ;-)

Best regards