ᐅ Thermal Insulation, Energy Saving Regulations, KFW 70 / 55 / 40 – Your Experiences

Hello everyone, as we would say here,

since I have now become quite engaged with this forum and am interested in more and more topics, the question of the right and “best” insulation has come up for me recently (still purely out of interest for now, but surely also practical at some point). I deliberately put the word best in quotation marks because there will always be different preferences and use cases.

I am fully aware that a standard house usually does not require insulation below U=0.14 W/(m²K). Therefore, I tried to look up the following values regarding the energy-saving regulations and the KfW houses 70 / 55 / 40.

I came up with the following values for the thermal transmittance coefficient:

Reference building according to Energy Saving Ordinance 2014
U-value | Roof 0.20 W/(m²K), Windows 1.30 W/(m²K), Exterior wall 0.28 W/(m²K), Basement wall 0.35 W/(m²K), Floor slab 0.35 W/(m²K)

KfW Efficiency House 70
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.23 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)

KfW Efficiency House 55
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.18 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)

KfW Efficiency House 40
U-value | Roof 0.15 W/(m²K), Windows 0.80 W/(m²K), Exterior wall 0.14 W/(m²K), Basement wall 0.20 W/(m²K), Floor slab 0.20 W/(m²K)

With the above values, it becomes clear what needs to be done regarding home insulation to meet certain standards. As mentioned above, other factors also play a role, such as roof, upper and ground floor windows, possibly the ceiling in the upper floor, exterior wall including roller shutter box, exterior door, exterior wall, and floor slab. But you have to start somewhere.

What I am curious about as a layperson is the comparison between the KfW 70 standard and the KfW 55 regarding the exterior wall. For me, this point represents basically the only difference related to the values mentioned above. Of course, you are also welcome to share your information and experience regarding windows, for example.

To achieve an exterior wall U-value of about 0.18 W/(m²K), there seem to be different options, as I have read in other threads, such as:

• Monolithic wall construction
• Functional exterior wall
• Double-shell exterior wall

For me personally, only the monolithic wall construction is really an option. Of course, you have to consider that you end up with, for example, a 40cm (16 inches) thick wall to achieve certain values. Often, the windows are then described as “loophole-like” because there is so much material around them. How did you decide, or how would you evaluate this from your experience?

What types of blocks or bricks have you had good or bad experiences with? For example,

• Aerated concrete plan block NeoStone U-value 0.17 W/(m²K)
• Aerated concrete plan block “SK08” U-value up to 0.18 W/(m²K)
• ThermoPlan MZ8 (mineral wool) – 42.5 cm (17 inches) 0.18 W/(m²K)
• Poroton T9 – 36.5 cm (14 inches) 0.23 W/(m²K) – therefore only suitable for KfW 70
• Poroton T8 – 42.5 cm (17 inches) 0.18 W/(m²K)
• Poroton T8 – 49 cm (19 inches) 0.15 W/(m²K)
• Poroton T7 – 42.5 cm (17 inches) 0.15 W/(m²K)
• UNIPOR W09 - Approval Z-17.1.-1042 | 0.20 W/(m²K) – therefore only suitable for KfW 70
• UNIPOR WS07 CORISO | Approval Z-17.1.-1074 0.18 W/(m²K)
• Ytong aerated concrete 0.07 – 36.5 cm (14 inches) 0.18 W/(m²K)
• Ytong aerated concrete 0.08 – 42.5 cm (17 inches) 0.18 W/(m²K)
• Ytong aerated concrete 0.09 – 48 cm (19 inches) 0.18 W/(m²K)

Now, go ahead and type away!

You are approaching this the wrong way – the wall construction is only ONE factor in the calculation – even the choice of heating system earns you points for KFW calculations.

Why only monolithic?

In any case, this approach won’t help you. You need to look at the complete package... and that’s what a planner does.

Lexmaul79 schrieb:
You are approaching it the wrong way – the wall structure is only ONE factor in the calculation – even the choice of heating system gives you points for KFW calculations.

Why only monolithic?

In any case, your approach won’t help; you have to look at the overall package... and that’s what a planner does. .

Good morning Lexmaul79,

Yes, I do understand that in the end the overall concept has to be right and fit together, and as mentioned above, there are many influencing factors. As you already said, heating, windows, and so on also play a role. Nevertheless, I think the facade or external wall (the wall structure) and the insulation make up a large part, don’t they?

My main question here is whether any of the bricks for the monolithic structure should be preferred, or if there are bricks, for instance filled with perlite, that one should rather avoid and instead choose options with mineral wool insulation.

The reason I ultimately decided on a monolithic structure is primarily because I do not want external insulation. Perhaps this is currently a personal preference, or maybe also a cost issue. Last week I attended a lecture on energy-efficient building. There, “prefabricated walls,” meaning pre-made elements from wood and other materials, were presented. It was also explained that the basic framework of the house can be completed within 3-4 days and that the wall thickness is about half compared to traditional masonry construction while achieving the same U-value. However, I still tend to prefer the monolithic structure.

There are different manufacturers, bricks, and especially variations available. I would be very interested to hear about your experiences, if any. Also concerning the topic of thick walls and the possible “loophole” appearance.

Regarding the loophole-style appearance, I would like to share my perspective.
On the ground floor, we have a wall thickness of 43.5 cm (plus interior plaster, brick veneer), and on the upper floor, 35.5 cm (plus interior plaster, external thermal insulation composite system). In both floors, the feeling at the window openings is the same; loopholes are not visible from either outside or inside.
I believe this "issue" only arises with very small windows, for example, narrow strips of glazing — although I have no experience with that.

We never really focused on the building materials in detail. The requirement was brick veneer on the ground floor and plaster on the upper floor — the planner was instructed to design at least a KfW 70 energy standard house meeting these specifications. How this was achieved was not important since everything is a matter of belief.

Hello,

Häuslebau3r schrieb:

My main concern here is whether one type of brick should be preferred for a monolithic construction, or if there are bricks filled with perlite, for example, that should rather be avoided in favor of options with mineral wool.

There is no single “best” wall construction; people have very different preferences, and all can be accommodated.

What you forget – despite all the information you seek – is that if your plot, for example, is located in an earthquake zone, you might have to give up your “preferred” brick. It’s also possible that you choose a building partner whose preferred material is hollow bricks, but you previously fixed on aerated concrete. And then?

Häuslebau3r schrieb:

Also regarding the topic of thick walls and possibly the loophole appearance.

You only find “loopholes” in genuine passive houses, and even then only if the budget does not allow for windows that meet passive house standards (which are usually twice as expensive as regular windows).

Best regards, Bauexperte

nordanney schrieb:
Regarding the loophole-style appearance, I would like to share my thoughts.
On the ground floor, we have a wall thickness of 43.5 cm (plus interior plaster, brick facade) and on the upper floor 35.5 cm (plus interior plaster, external thermal insulation composite system - ETICS). In both floors, the feeling around the window openings is the same; loopholes are not visible from either outside or inside.
I think this "issue" only arises with very small windows, for example, narrow strips of daylight — but I have no experience with that.

We never really focused deeply on the building materials. The desire was brick on the lower floor and plaster on the upper floor, so we commissioned the planner to design at least a KfW 70 house with these specifications. How that was achieved was not important to us, as it is ultimately a matter of belief.

Thanks already for your feedback regarding the loophole effect.
Is there any particular reason why you chose a brick facade with larger bricks on the lower floor and a smaller version including ETICS on the upper floor? So two different approaches? Of course, probably to meet the U-value requirements for KfW 70, but why the difference?