ᐅ PPW4 instead of PPW2 / Subsequent modification of the thermal insulation verification

For our new build (KfW40 standard), the exterior walls are constructed using aerated concrete blocks, which are then insulated and subsequently clad with brick slips. According to the energy performance calculation and the building specification provided to us, blocks of strength class 2 (lambda value of 0.10) should be used. However, during a site visit, we noticed that PPW 4 blocks (lambda value of 0.16) and in some cases PPW 6 are being installed. Upon inquiry, the site manager informed us that the structural engineer required this change and that the thermal insulation certificate would be revised accordingly.

Is this reasonable and acceptable?

Unlike the energy performance calculation, we do not have the structural calculation. Both the structural and energy reports come from the same engineer, who regularly works with the construction company. I suspect that the wrong building material was ordered and installed, and that the thermal insulation certificate is now being adjusted afterward to compensate. Or am I being too skeptical?

What can or should we do?

That is not entirely unreasonable.
Is the contractually agreed standard KfW 40 or the brick?

@BeHaElJa

Both KfW40 and the building materials are specified in the contract. Any changes to "equivalent" materials would need to be agreed upon.

Ordering the wrong building material is probably less common. It’s more likely that it’s deliberately ordered because it’s cheaper or structurally really necessary. Make sure to get the structural calculations. You probably won’t use them much yourself, but whoever might renovate your house and remove a wall in 30 years will be grateful!

As long as you still meet the KfW 40 standard, that’s fine. The contract will probably include a clause like: "deviations are allowed if technically necessary." However, they should have at least informed you, so a mild reprimand is justified.

Best regards,

Andreas