ᐅ Insulating a New Build with 36.5 cm Aerated Concrete Blocks?

The "Stone Age" is in quotation marks... It is simply the lowest possible standard at the moment. After the next revision of the energy saving regulations (EnEV), it will be outdated.

Of course, sound insulation is not always a concern everywhere, so what makes sense is individual. As I said, I just can’t stand this black-and-white thinking. Aerated concrete is affordable, and if you want, you can build monolithically with it—it certainly has its merits.

Tego12 schrieb:
And the U-value comments... Windows have a much greater impact than the wall area... Oh man. Troll.

I see it differently: with a state-of-the-art triple-glazed window, twice as much heat passes through compared to the same area of a wall built 50 years ago: a single-layer 30cm (12 inch) solid brick wall.

Regarding attitudes toward construction methods with or without insulation boards, one should not overlook that in new construction, achieving a certain standard is supported regardless of the approach; however, insulation boards are specifically eligible for financial incentives when used for retrofit projects.

Therefore, the perspective of the new construction contractor differs from that of the renovator.

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Triple glazing with a good U-value is now standard. There is not much room for improvement in that area anymore. The wall surfaces offer a significantly greater potential for improvement, especially if you only have 36cm (14 inches) aerated concrete walls.

I already have a preliminary calculation, which shows 42.7% of heat loss through ventilation, 26.9% through glazing, and 10.8% through the external wall. These figures are based on the heating energy.

If we assume 8,000 kWh of heating and 4,000 kWh of hot water (approximately 180–190 liters (47–50 gallons) of hot water demand per day for the whole family, including losses, etc.), that totals 12,000 kWh.

Of that, 10.8% (of the 8,000 kWh heating energy), equals 864 kWh through the external wall. Out of a total of 12,000 kWh!

If you save 25% (!) => 216 kWh per year => 10.41 EUR savings per year here with the current gas tariff => 87 cents reduction per month.

Sound insulation is harder to calculate precisely.

Aerated concrete 350 kg/m³ (22 lb/ft³) x 0.365 => 127.75 kg/m² (26.2 lb/ft²)
Sand-lime brick 1800 kg/m³ (112 lb/ft³) x 0.175 => 315 kg/m² (64.5 lb/ft²)

Initially, the mass is clearly higher for the sand-lime brick.

However, aerated concrete benefits from its porous structure, while sand-lime brick combined with EPS (expanded polystyrene) reduces sound insulation, since EPS actually amplifies sound (!), unlike mineral wool.

Regarding life cycle costs: Based on the minimal advantage of EPS insulation (for example, 10.41 EUR per year above, which is 520.50 EUR over 50 years), it becomes clear that the external insulation composite system (ETICS) does not necessarily fail or fall off the wall after just three years. It won’t. But even the smallest renovation damage removes the advantage over a monolithic wall. A single woodpecker hole, one mechanical impact, algae growth after 30 years, etc.

Basically, you will need to renovate an ETICS facade at least once. A monolithic wall will not. Here in our region, many ETICS facades are already undergoing renovation. Of course, you could argue that they were all installed incorrectly and that may be true in some cases. It is also noticeable that houses without roof overhangs are often affected. But for the 10 EUR per year savings, I wouldn’t want to bet on it.

In 2013, I assumed that anyone who needs to wrap a new house in expanded polystyrene insulation has done something wrong. So, I chose 36.5cm (14.4 inches) aerated concrete blocks and am satisfied. Considering the low heating costs, chasing the last few percentage points and spending a lot of money on it is economically unreasonable.

It may be true that a properly installed external thermal insulation composite system (ETICS) can last for decades. But who can be sure that the contractor works flawlessly and the designer plans without mistakes? If a system is so sensitive that even minor errors cause expensive repairs less than ten years later, I avoid that system. With the money saved, one can almost indefinitely cover any additional energy consumption if interest rates return to normal levels, without having to worry about defects occurring.

tomtom79 schrieb:
What would be a sufficient plaster thickness to prevent algae growth? Which type of plaster should be preferred?

From what I know:

- thick (>1.5cm (0.6 inches))
- mineral-based
- vapor-permeable, so no painting with water-repellent paint or similar

So basically the opposite of what is usually done (cheap thin-layer synthetic resin plaster, painted with water-repellent paint, probably including biocides against algae).

Grym schrieb:
If you save 25% (!) => 216 kWh per year => 10.41 EUR savings per year with the current gas tariff => 87 cents discount per month.

Well, where does the 25% come from, what is that target based on?
The point is that building monolithically is more expensive to achieve the same insulation standard as with ETICS (external thermal insulation composite system) – especially EPS. This is clearly shown in the offers we have. And everyone has to meet at least the minimum insulation standard, for example according to the energy saving regulations. Getting to KfW 55 standard is then relatively cheap, because it only requires a few centimeters more EPS. On the other hand, you have a 5,000 EUR repayment grant and interest benefits through KfW loans.
Therefore, I find the approach odd to assume a fictitious 25% “saving” and estimate some consumption. Instead, consider that every groove in the monolithic wall is a thermal bridge. The same applies to the floor slab exposed to outdoor air.
Don’t get me wrong, I would also like to build monolithically. It just feels like the “right” way to go. But the extra cost is simply there, I also quite like calcium silicate blocks, and a two-layer system with facing brick is not possible here (in my opinion the absolute ideal).

Grym schrieb:
A single woodpecker, one mechanical impact, one algae infestation after 30 years, etc.

If someone has the notorious woodpecker damage, they took the cheapest of the cheap options. Use a laminated EPS board, mineral wool, and/or thick-layer plaster, then that belongs to the realm of myths.
Algae growth can be reduced but does also occur on monolithic walls, although less frequently. Some environmental factors simply cannot be ignored, e.g., proximity to forests.

Currently, many people build houses with white plaster facades. No matter how you look at it, these will need cleaning at some point, whether there is ETICS underneath or a monolithic wall structure. Of course, if algae develop, it happens sooner and/or more often, but they all get dirty eventually.