ᐅ Aerated concrete exterior wall vs. energy efficiency regulations

Hi,

I hope this topic hasn’t been asked before; otherwise, I must admit I didn’t use the search function thoroughly enough.

We are planning to build a single-family house and are currently in the preparation phase. The plan is for a townhouse-style villa (2 full floors) with 150m2 (1,615 sq ft). Right now, I’m looking into exterior walls, energy-saving regulations, etc., and I’ve come across some fundamental questions—or rather, several.

According to our builder, standard exterior walls will be made of aerated concrete blocks (brand Ytong) with a thickness of 24cm (9.5 inches) without any additional insulation or external thermal insulation composite system (ETICS). Assuming the blocks used have a thermal conductivity of 0.09 W/(m·K) (there are different blocks ranging from 0.07 to 0.18), my rough calculations lead to a U-value of 0.37 W/(m²·K), or about 0.3 W/(m²·K) if we opt for 30cm (12 inches) thick walls. In terms of energy efficiency and future-oriented building, this is obviously insufficient.

I’ve read that according to the 2009 Energy Saving Ordinance (EnEV), exterior walls are allowed a maximum U-value of 0.28 W/(m²·K).

My specific questions are: Is this a regulation the builder is legally required to follow? What wall thickness would you recommend? Also, is what I’ve described correct?

I’m hearing different opinions, ranging from “Go for a 36cm (14 inches) wall thickness because of better insulation” (from someone who has built twice) to “I’d choose 24cm (9.5 inches) so the house can breathe and put enough solar panels on the roof for self-consumption” (an architect).

Thanks a lot for your feedback!
Sebastian

Walls do not breathe, and what does that have to do with solar energy (specifically photovoltaics)?

You have to comply with the energy saving regulation – that is mandatory. Without insulation, it won’t work – for a monolithic construction, you’ll need something better from the realm of masonry.

Wow, the statements from the "architect" are quite questionable. In a new house, nothing breathes—and above all, it shouldn't. Why would you want to “breathe out” all the valuable heat? In the past, this was more due to poorly sealed windows than solid masonry walls, at least to a relevant extent.

Solar thermal systems are even less economical than minimal setups, and in summer you often can't use all the hot water produced.

Depending on the overall concept, photovoltaic systems are usually a better choice.

This is simply not allowed in construction...
Starting in 2016, stricter regulations of the Energy Saving Ordinance 2014 will apply again... then you will no longer be allowed to build like this three times over.

At least 360... if not even 425.

I didn’t want to focus too much on the architect’s statement.
Why does a developer build a standard 24cm (9.5 inches) aerated concrete exterior wall if it does not meet the guidelines? Although it has triple glazing, that doesn’t compensate for it. Who is liable if energy saving regulations are not followed, and how or by whom is this checked or approved upon completion?

Thanks in advance for your feedback.

Well, that sounds like Town & Country, which was the first company I ruled out...
The house wouldn’t meet KfW 70 standards (which would still be tolerable given the interest rates) but it wouldn’t comply with EnEV 2016 either. With 24 cm (9.5 inches) walls, even with solar collectors for hot water (possibly also for underfloor heating), mechanical ventilation with heat recovery, triple-glazed windows, and the new requirements for roof insulation, it just doesn’t add up.
Town & Country couldn’t even provide the U-value, and Ytong doesn’t even list the 24 cm (9.5 inches) option on their website anymore. So, in my opinion and that of several other solid construction providers, they probably shouldn’t be building like this at all?!