ᐅ How do you properly balance the requirements of the Building Energy Act against the standards of KfW 55, 40, and 40 Plus?

We are planning a cavity wall construction and want a mechanical ventilation system with heat recovery for comfort reasons. We are now aiming for 55EE; the thicker insulation and additional ancillary construction costs result in approximately 10,000 euros in extra expenses compared to the energy saving regulation with mechanical ventilation. This means the subsidy option is financially attractive for us and provides an incentive to go beyond the minimum energy saving regulation. If I compare the technical minimum for the energy saving regulation (without mechanical ventilation) to 55EE, it is roughly cost-neutral. However, this of course also depends on the wall construction.

--Lars-- schrieb:

How to properly weigh the Building Energy Act against KfW 55, 40, and 40 Plus?

It’s not really possible to be entirely “correct” here, as there is no objective philosopher’s stone for this. Apart from the blurred lines between established facts and well-meaning hopes, this topic can never be viewed completely independently of some personal stance toward one ideology or another—so it would have to carry an allergy warning: “may contain traces of subjective opinion.” So be cautious about any claims that a particular recommended approach is purely “correct.”
My personal opinion doesn’t need much repeating here: the forum search could definitely work better, but searching my username along with “ETICS” or “mechanical ventilation with heat recovery” will still provide helpful pointers.
I have nothing “objective” to contribute here ;-)
But “statistically,” after four years of hanging around this forum, I can roughly summarize that some of my views are widely shared here, namely: compared to simply meeting the Energy Saving Ordinance, the “enhanced” levels labeled “KfW,” “KfW turbo,” and “KfW double turbo” are all what must be personally worth the extra cost to you. These are all grant programs designed by their creators to provide incentives and encourage a change in mindset—but they were never intended (nor ever meant) to make you “rich” by using them. So beware of the false hope that funding for a more advanced KfW “level” by itself (or combined with a secondary unit or something similar) will fully cover the additional expenses required or even offer a little “bonus” on top.
In summary, from my point of view: do what you believe is right—even a plus-energy house including heat recovery, even if driven by the anxiety about whether the effort is enough to meet all Greta goals—but don’t dream. Instead, keep Tim Bendzko’s reminder in mind that before saving the world you still have “just” 148,713 emails to check 🙂

--Lars-- schrieb:

With exterior insulation systems, KfW55 can be achieved using thinner walls, which on our narrow lot would allow about 10 sqm more living space.

No, not really. We are talking about thirty-six point five centimeters monolithic versus thirty-three point five centimeters total, made up of 17.5 cm brick and 16 cm insulation boards. You will never, ever gain 10 sqm in a single-family house from that.

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So if I did anything right with our project, and I mean really right, it was the decision to involve a competent energy consultant (in our case, an engineering office/expert) early on... especially since 60% of the costs are subsidized.

In the end, we achieved KfW40+ standard with about 10,000 euros in additional costs and received 15,000 euros in subsidies (although with timber frame construction).

nordanney schrieb:

Energy consumption is roughly 60% influenced by the user, 30% by the proper heating system design, and 10% by the energy efficiency standard.

I am a prime example that this isn’t quite true.

All rooms are constantly set to 23°C (73°F), and the bathroom to 25°C (77°F), with no night setback.
Ventilation happens whenever it happens; the heating is not turned down beforehand or otherwise adjusted. It has been running for years without any special attention or operation.

So I would consider myself an absolute worst-case user.

Annual costs for the 112 sqm (1206 sq ft) house with two people:
336€ gas
427€ electricity

No large system on the roof, just two collectors for hot water on sunny days.

I think this is absolutely acceptable.

Regarding the question of what energy efficiency level to build for:
If you are young, around 25 -> build as efficiently as possible.

If you are around 40 -> it’s less worthwhile, better to invest less and be debt-free before retirement.

If you are older, around 50 -> forget about additional insulation.

Expensive thermal insulation only pays off over time. I built young and therefore invested in KFW55.
If energy costs are three times higher by retirement, I can live with that. Without KFW55, three times higher energy prices would quickly mean six times what they are today. Unbearable.

Nutshell schrieb:

So, I’m a perfect example that this actually isn’t true.

All rooms are constantly set to 23°C (73°F) and the bathroom to 25°C (77°F), with no nighttime setback.
Ventilation is done whenever it’s done; the heating is not turned down or adjusted beforehand. It has been running for years without special supervision or control.

Therefore, I would consider myself an absolute worst-case user.

Why do you consider yourself a perfect example?
You pay exactly your price for gas because you use your house the way you do. If you ventilate differently and set rooms to 20°C (68°F), you might reduce gas consumption by about 25%.
Your usage patterns determine your consumption. Or do you have a comparison in your house with different usage behavior?

nordanney schrieb:

Why are you a prime example?
You pay exactly your price for gas because you use your house the way you do. Ventilate differently and keep rooms at 20°C (68°F), and you might reduce gas consumption by 25%.
YOU decide your consumption through your usage. Or do you have a comparison in your house with different usage patterns?

Exactly, but 25% is not 60%.

I am also convinced that building to KFW55 standards has reduced my consumption by more than 10% with the same usage.

No matter how incorrectly I use the house or heating, thanks to KFW55 insulation, I pay relatively little.
And that is what really matters in the end.

Your post suggests that you can reduce costs by 60% through different usage, which is not true... well, unless you turn off the heating in some rooms and keep the rest at 20°C (68°F) or lower. Quite unrealistic. Just like you won’t drive a BMW M3 at 7 liters per 100 km (33.6 mpg), even though hypermilers can easily achieve that.

In summary, I can only advise this: everyone must decide for themselves whether the insulation costs will pay off.
For example, someone who is 50 years old and wants to leave a nice house to their child, and has the necessary funds, should definitely insulate thoroughly.
Otherwise, after 30 years, the house will simply be outdated and operationally unattractive. You can’t expect much rent in 2050 if heating costs for a small property are over €1500 (approximately $1600) annually.