Mixing exterior wall masonry of a single-family house

Hi everyone,

we are currently building a single-family house and have very large windows on the garden side. Now, during the structural calculation, it was found that there are problems with the used Poroton bricks (17.5) for the outer wall in the areas of the very large windows, which make up almost the entire wall.

The general contractor is now using KS instead of Poroton bricks at the corners around the windows to ensure load-bearing capacity. According to the structural analysis, this should be okay. I have now read in forums that mixing Poroton and KS, even with Poroton on the exterior wall and KS on the interior wall, can lead to problems with cracks due to different shrinkage behaviors.

Can the ceiling become crooked over time because the KS bricks shrink, or could the load of the rear house no longer rest on them?

I hope you can help...

Best regards

According to the static calculation, this should also be okay. [...] Can the ceiling eventually become crooked if the KS blocks shrink or if the load from the rear house no longer rests on them?

The structural engineer will not base his assessment on forums - I think it will be fine. Monolithically, in such cases, stones of higher densities were often used in the past, e.g. in the form of solid bricks. This seems to me comparatively like "same old, same old," and it is probably not the first time that both have done it this way.

I have now read in forums that mixing Poroton and KS can already lead to problems with cracks when Poroton is used for the exterior wall and KS for the interior wall, due to different shrinkage behaviors.

I know such recommendations and usually relate them to wallpapering or plastering without expansion joints at those points where the other type of block is located "around the corner" behind.