ᐅ Bricks: Are differences in thermal conductivity of 0.03 noticeable?

I want to build a two-story single-family house with an air-to-water heat pump using filled 36.5 Poroton bricks. Since there is no longer any KfW 55 funding, I am generally wondering whether it is economically and energetically worthwhile to use bricks with a thermal conductivity of 0.07 W/mK or if that advantage only looks good on paper. Is the difference between 0.07 and 0.10 W/mK in the house really noticeable or is it more negligible? Will I have to heat significantly more if I choose the 0.10 value?

There are no longer any subsidies, but you still have to build at least to the KfW55 standard. This is the current norm.

Inside the house, you won’t really notice any difference. You could just as well build with 0.30 stones (units of thermal conductivity).

The difference shows mostly in heating costs. However, in your example, user behavior probably has a much greater impact than the type of bricks used.

Aside from that, personally, I would only choose to build this “poorly” for one reason: if I couldn’t afford anything better. Because you have to, or at least should, also consider the value of the house. And in that regard, KfW55 is already outdated and “poor” for future standards.

nordanney schrieb:

Apart from that, I would personally only build so “poorly” for one single reason: if I lack the money. Because you have to, or at least should, also consider the value of the house. And regarding that, the KfW 55 standard is already outdated and “poor” today in terms of future standards.

If you build to the 55 standard, you are very well positioned in terms of price-performance ratio. Even before 2020, the 40 standard was only conditionally economical.
Yes, energy costs are rising. But construction costs—and therefore the extra costs for better standards—are rising as well.
Economic efficiency ≠ energy efficiency

PhiIipp schrieb:

If you build to the 55 standard, you’re getting very good value for money.

You really can’t build any worse.

But in reality, for many market participants, KfW 55 is already a deal-breaker today, and every provider builds to KfW 40 (without all the NH hassle) for a small additional cost. Certifications and such for subsidies are quite demanding, but they’re not really necessary.

nordanney schrieb:

There is no longer any funding, but you still have to build to KfW55 as a minimum requirement. That is the current standard.

Is that really the case? Who enforces that? For example, do I have to do the blower door test?

nordanney schrieb:

You will notice the difference in heating costs. However, in your example, user behavior probably has a much bigger impact than the different types of bricks.

That interests me especially. If I have a photovoltaic system with storage and an air-to-water heat pump with underfloor heating, is it still relevant whether I use bricks with a thermal conductivity of 0.1 or 0.07? For example, doesn’t opening the windows immediately negate the difference?

IOSam23 schrieb:

Is that really the case? Who checks that? For example, do I have to do a blower door test?

When applying for the building permit (planning permission), you must submit the necessary calculations that demonstrate compliance with the building energy law standard (= KfW 55). Without proof, there is no permit.

IOSam23 schrieb:

I’m especially interested in this. If I have photovoltaic panels with storage and an air-to-water heat pump with underfloor heating, does it really matter whether I use bricks with 0.1 or 0.07? For example, doesn’t opening the windows immediately ruin everything?

Part one of your question: Yes, it matters. Whether there is a difference of about €10 or €19 in heating costs that affects you, you will have to decide. The wall is only one part of the house. There are also windows, exterior doors, floor slab insulation, roof insulation, and a few other details.
Part two of the question: Opening a window once doesn’t cause any significant loss. But regularly leaving windows open for long periods will definitely have an impact. The ventilation system also makes a difference. How noticeable the effects are can only be determined if you compare a year without opening windows at all to a year with regular airing.
Or if you always keep the temperature at 19.5°C (67°F) or 22.5°C (72.5°F). Or if the winter is a bit colder or warmer than usual.

All together—using less efficient bricks, frequently leaving windows open, having to sleep with the window open, and so on—these factors add up but won’t cause anyone financial hardship.

P.S. For my apartment (in a two-family house, with my own heat pump), renovated to the formal KfW 55 standard (actually better), I expect heating costs this year of €350-€380 (at €0.25 per kWh electricity) including hot water for 120 sqm (1,292 sq ft). I don’t mind if it sometimes reaches €400 because the kids keep going in and out in winter or for whatever reason the windows and patio doors were often open. You will always have moderate costs in a new build—the difference of about 10% more or less is not significant in the end.