ᐅ Insulating a 38 cm Brick Older Building with Aerated Concrete / Autoclaved Aerated Concrete (AAC)

Hello,

As mentioned at the beginning of my question, I am considering buying a house. According to an unclear floor plan, a 34cm (13 inch) brick wall was used (does such a size even exist? Maybe it is 38cm (15 inches)). In the future, I would like to insulate the house and I am researching the available options in advance. For several reasons, I am against using polystyrene insulation!
Now I am looking for a good alternative!
I came across aerated concrete / autoclaved aerated concrete (AAC) / aircrete / mineral foam / Ytong / and other similar materials.
Is it possible to place these blocks as insulation in front of or on top of the bricks?
Does anyone have experience with this? Any issues with moisture or mold?

Many thanks and best regards!

Kick_master schrieb:
According to an illegible floor plan, a 34cm (13.4 inches) brick was used (do such bricks even exist?)

The floor plan probably indicates the total wall thickness, with or without plaster. A single 34cm (13.4 inches) thick solid brick wall is quite rare in older buildings. Does the house have a brick veneer?

Kick_master schrieb:
I would like to insulate the house in the future and want to gather information about the available options in advance

Knowing the building’s construction year could help estimate the type of wall and whether insulation is necessary or beneficial at all.

Insulation options:

For cavity walls with an air gap: blowing in suitable insulation material
Otherwise: ETICS (External Thermal Insulation Composite Systems) using EPS (expanded polystyrene) or natural insulation materials such as wood fibers or jute, finished with a rendering layer
Or insulating the exterior wall with flexible insulation mats placed between wooden battens or other supports, combined with weather protection through a ventilated rain screen facade made of wood or cladding panels

Kick_master schrieb:
Can these bricks be used as insulation applied in front of or on top of the bricks?

In theory, this is possible, but it is difficult and rarely done because of many drawbacks. You would need an additional foundation surrounding the house, which may require renewing all connections. Also, the insulation must be installed tight against the exterior wall without an air gap, which is more challenging with a solid masonry wall than with individual insulation panels. If mineral insulation is preferred, a major aerated concrete manufacturer offers a fully mineral ETICS system based on lime, sand, and cement.

Generally, you should first assess the existing wall construction, its U-value, properties, and other weak points of the building. Exterior walls are often not the most effective place to start; there are usually simpler and more cost-effective energy-saving measures.

Addendum: I just noticed that the house was built in 1965. Which federal state is "OE" in, in other words, where is the house located? What does it look like? (plaster, brick veneer, other facade?)

Based on the construction year, for single-shell walls, pumice hollow blocks (in southern Germany) or hollow blocks filled with brick chips or also lattice bricks were typically used. Usually, the thickness would be around 30cm (12 inches). For a brick veneer facade, I would expect a 24cm (9.5 inches) load-bearing wall made of hollow blocks plus 11.5cm (4.5 inches) brick veneer without an air gap. Air gaps between the load-bearing wall and the facing wall were uncommon in the 1960s.

@dertill
Thanks first of all for your reply. The "fully mineral external thermal insulation composite system (ETICS) based on lime, sand, and cement" is exactly what I was looking for.
And
"OE" stands for Austria. Unfortunately, I don’t have more details about the façade. I can rule out facing bricks; it looks to me like a 38cm (15 inch) brick wall with plaster.

Kick_master schrieb:
"OE" stands for Austria. Unfortunately, I don’t have more details about the facade. I can rule out clinker brick; it looks to me like a 38 brick and plaster combination.

I see – I would have guessed "AT" instead. Clinker brick is probably quite rare in Austria, and I’m not familiar with the typical building types there. Whether it’s 38cm (15 inches) lattice bricks, pumice stones, old aerated concrete, or hollow blocks, whatever was used would have a U-value between 0.6 and 1.0 W/m²K. Personally, with that wall thickness and U-value, I wouldn’t add insulation on the outside but focus on eliminating other weak points. At most, I would insulate the north-facing side if it has few windows.

So far, I haven’t found any plan to be illegible. So feel free to upload it or send it to me via private message.

In Germany, until the post-war years, the old “Reichsformat” was still used; in that system, 38 cm (15 inches) would have been possible (exactly one and a half bricks, meaning one brick plus one header). It’s possible that Austria switched to the new standard later or still had leftover stock at that time.

However, these were typically solid bricks in the standard format back then. This might explain the wall thickness, which seems to be somewhat more generously dimensioned, especially in the Alpine federal states.

24 cm (9.5 inches) is also conceivable (one brick in the current format system), possibly as a large block if made from lighter material (pumice / tuff).

As for whether and what kind of insulation is applied inside or outside, we would need to know more about the building (photos help).

The forum software probably assigns “OE” automatically when Austria is selected as the country of residence.

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