U-value outer wall 0.26 - is that okay?

Hello dear ones,

we have now been offered the PP4 0.5 (also 36.5 cm) instead of the Ytong PP2 0.35 (36.5 cm) for better sound insulation. The PP2 has a λR of 0.08 (U-value 0.21) and the PP4 a λR of 0.10 (U-value 0.26). We are tempted by the higher sound insulation, but is the heat loss too high? Windows are equipped with a Ug of 0.6. The Energy Saving Ordinance 2016 allows a U-value of 0.28. Construction will be with an air-to-water heat pump + fireplace + (possibly decentralized ventilation with heat recovery).

What do you think? Couldn’t find anything on the internet or here. :-(

The 0.26 is tight but probably sufficient if the shell is otherwise okay. Your BU has to calculate that or have it calculated. I'll give you an example: we, 30 cm Ytong, monolithic, 110 sqm, U value per wall 0.25, need gas for 55,- per month. I think that's okay.

Thank you Nordlys! I think that the Energy Saving Ordinance is already being complied with. I am more concerned about the heat loss. Is the difference between the stones that big? I believe I researched that 0.26 as a u-value was already being discussed in 2009. 0.21 is probably today's KFW 55 standard value. The PP4 just has significantly higher sound insulation values and is more massive.

What does a "λR of 0.08" mean? If soundproofing is important to you, keep in mind that the windows let through more sound than the wall (even soundproof windows usually do not achieve the wall's value).

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

Yes, you are absolutely right. I already brought up this topic here in the forum. The best wall doesn’t matter if the windows don’t have a similar sound insulation value - that’s what I learned here. But for us, this consideration is about the increased massiveness due to the higher raw density with the side effect of better sound insulation. In principle, we are only talking about a street that might require increased sound insulation. On this side, we also have hardly any windows. That’s why I thought about switching to PP4. λR of 0.08 = lambda value = thermal conductivity; the lower, the better. 0.08 is really quite good. So could one switch without worries?

the increased solidity due to the higher bulk density with the side effect of better sound insulation. Basically, we are only talking about one street that might possibly require increased sound insulation. On this side, we also hardly have any windows.

Without being an expert: I would do that as well. 1) the wall definitely has more square meters compared to the windows 2) more bulk density helps against dull, booming road noise