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

For us, there was no price difference between monolithic construction and sand-lime brick with external thermal insulation composite system (ETICS). But even if there was, I would pay extra for monolithic construction. You simply have peace of mind. It’s worth it for just 10 EUR per year...

Just a slightly thicker plaster won’t keep the woodpecker away. You need a ceramic cladding on the outside that the woodpecker cannot penetrate.

And 1.5 cm (0.6 inches) plaster is not standard; you’d usually get about 2–3 mm (0.08–0.12 inches).

A U-value of 0.17 represents 25% less heat transfer compared to 0.23 (W/m²K). However, I’m not sure if this difference is linear. It hardly matters in practice, because it doesn’t have a noticeable effect. Compared to ventilation losses, window area, and hot water, the heat loss through external walls, roof, slab, front door, and roller shutter box is negligible.

Regarding KfW55: According to our planning, it would also work easily with a 36.5 cm (14.4 inches) monolithic wall but with a somewhat better brick (U-value 0.08), or with a standard brick (0.09) plus 42.5 cm (16.7 inches) thickness.

However, the entire set of KfW55 documents and calculations costs several thousand euros according to two providers (one offering over 4,000 EUR including all calculations, site inspections, verifications, etc.). This has been mentioned multiple times before in this forum.

And I don’t see any interest rate advantage with KfW55!?
2.25% over 20 years?
The current market interest rate at Commerzbank for 20 years with 2% repayment (so less than KfW) and 80% loan-to-value is 2.08%.

Grym schrieb:
For us, there was no price difference between monolithic construction and sand-lime brick with external thermal insulation composite system (ETICS).

That is, of course, a valid point. So far, it looks different here. Are you building with aerated concrete or with clay blocks?

Grym schrieb:
Just a bit of thick plaster won’t keep the woodpecker away. You really need a ceramic panel on the outside that the woodpecker can’t penetrate.

Simply put: Yes, it can. This is based on the architect’s experience and a demonstration on an actual building. The woodpecker only pecks when the sound is right. Thick plaster changes that sound.

Grym schrieb:
And you won’t get 1.5 cm (0.6 inch) plaster as standard, rather 2 to 3 mm (0.08 to 0.12 inch).

It depends on what you order. I’m building with an architect; I define the standards myself. But yes, building contractors/general contractors normally cut costs here, as I already mentioned. They do exactly the opposite of what would be needed to preserve an ETICS for a long time.

Grym schrieb:
However, all the documents and calculations for KfW55 certification cost several thousand euros according to two providers (one quoted over 4,000 EUR including all calculations, inspections, certifications, etc.). This amount has been mentioned several times here in the forum.

Current offer is 2,800 EUR, with 50% reimbursement from KfW. I don’t know what they would charge for the Energy Saving Ordinance documentation (you’ll still need that specialist).

Grym schrieb:
And I don’t see an interest rate advantage with KfW55!?
2.25% for 20 years?
Current market rate at Commerzbank for 20 years with 2% principal repayment (less than KfW) and 80% loan-to-value: 2.08%.

Yes, rates have gone up again—I hadn’t noticed. They were previously 1.75% for 20 years. But please don’t assume the 2.08% at Commerzbank are actual terms. KfW adjusts only in relation to market levels.

One experience: building with Ytong blocks, finished monolithically without external thermal insulation composite systems (ETICS), was the most cost-effective option in Schleswig-Holstein. Then came Poroton blocks with ETICS and plaster. Then Ytong with brick veneer. So the same house, sizes 163, 168, 176. I am not familiar with sand-lime bricks; in Schleswig-Holstein, sand-lime bricks are basically obsolete as a material for single-family houses.
Advice from the builder: If you use plaster, always make sure to have a good roof overhang. KfW energy efficiency ratings didn’t matter to me.

Alex85 schrieb:
That is, of course, a valid point. So far, it looks different here. Are you building with aerated concrete or clay blocks?

Probably aerated concrete on the outside and sand-lime brick for the interior walls.

Yes, they have just increased again—I hadn’t seen that yet. For 20-year loans, they were last at 1.75%. But please don’t believe that the 2.08% rate at Commerzbank reflects real terms.
The KfW only adjusts its rates in relation to the market level.

We also had a personal consultation once, and the interest rate was only slightly worse (less than 0.1 percentage points), but included 12 months with no commitment fees. If we had applied on that day, this rate would have been fixed.
So it seems that Commerzbank can really offer the online rates. Anything else would be fraud, wouldn’t it?

Nordlys schrieb:
I don’t know about sand-lime brick; sand-lime brick is basically dead as a building material in the single-family house sector in Schleswig-Holstein.

Since I’m from Schleswig-Holstein myself and have a relevant circle of acquaintances there, I can only say: No.
What do you think is behind the typical red facing brick?

If you have a good credit rating, I also consider a two percent rate realistic, especially when 10 years are currently agreed at 1.25 percent.