ᐅ Wall U-value 0.26 – Is that acceptable?

Hello everyone,

We have now been offered the PP4 0.5 (also 36.5 cm (14.4 inches)) instead of the Ytong PP2 0.35 (36.5 cm (14.4 inches)) for better sound insulation. The PP2 has a thermal conductivity (λR) of 0.08 (U-value 0.21), and the PP4 has a thermal conductivity of 0.10 (U-value 0.26). We are tempted by the better sound insulation, but is the heat loss too high? The windows have a Ug value of 0.6. The 2016 energy saving regulation (EnEV) allows a U-value of 0.28. The building will have an air-to-water heat pump + a fireplace + (possibly decentralized ventilation with heat recovery).

What do you think? I couldn’t find anything about this online or here. :-(

The 0.26 is tight but probably sufficient if the building envelope is otherwise good. Your energy consultant will need to calculate this or have it calculated.
I’ll give you an example: We have 30cm (12 inches) Ytong blocks, monolithic construction, 110 m² (1,184 ft²), wall U-value 0.25, and we need gas costing $55 per month. I think that’s reasonable.

Thank you, Nordlys! I believe the energy saving regulations are already being met. My concern is more about heat loss. Is the difference between the bricks really that significant? From what I have researched, a U-value of 0.26 was already being discussed around 2009. A U-value of 0.21 is now the KFW 55 standard. The PP4, however, offers significantly better sound insulation and is more solid.

What does a "λR of 0.08" mean?
If sound insulation is important to you, keep in mind that windows transmit more noise than the walls (even soundproof windows usually do not achieve the same value as the wall).

For comparison:
House from the early 1990s, 56 dB wall, 0.27 W/m² (should this be the U-value?), 49 EUR/month for gas.

Yes, you are absolutely right. I have already brought up this topic here in the forum before. The best wall is useless if the windows don’t have a similar sound insulation rating – that’s something I’ve learned here.

But in our case, the focus is on the increased solidity due to the higher bulk density, with the added benefit of better soundproofing. Essentially, we are only talking about a street that might require enhanced sound insulation. On that side, we also have very few windows. That’s why I was considering switching to PP4.

λR of 0.08 = lambda value = thermal conductivity; the lower, the better. A value of 0.08 is already quite good.

So, would it be okay to switch without worries?

Bauherr&-Frau schrieb:
the increased solidity due to the higher bulk density, with the added benefit of better sound insulation. Basically, we are only talking about one street that might require enhanced soundproofing. On that side, we also have very few windows.

Without being an expert: I would do the same.
1) The wall has significantly more square meters compared to the windows.
2) More bulk density helps against dull, booming road noise.