Install windows flush with the exterior wall (WDVS)

Hello,

I am currently renovating an old building where all the windows are to be replaced and an [WDVS] is to be installed.

I would therefore like to have the new windows installed flush with the outer wall. My question now is whether the old plaster on the reveal should be left, which would make the window slightly smaller, or whether the plaster should be removed. The masonry is made of aerated concrete.

Best regards

I am currently renovating an old building where all the windows are to be replaced and an external wall insulation system (WDVS) is to be installed.

Since it is made of aerated concrete, it is probably more of an "existing building" than an "old building." Aerated concrete only became popular around 1980, not before Adenauer.

I would therefore like to have the new windows installed flush with the exterior wall. My question now is whether the old plaster on the reveal should be left, which would make the window slightly smaller, or whether the plaster should be removed. The masonry consists of aerated concrete.

After removal, the reveal will have three sections: old interior plaster – breakout wound all around in the installation plane of the old window – exterior plaster. So your question really only arises then; currently, you can hardly realistically predict the damage. I would initially not deliberately chip anything off. I hope you have a good window installer, who preferably is also the supplier and should already remove the old windows. I say this as a former window manufacturer and later dealer. The order is significantly important: the installer should first remove and then measure and so forth – is that even ideal or is the property inhabited during the measures?

Thank you for your response. Yes, the building is from 1978, so not ancient. For the installation, I have an acquaintance who professionally installs windows, but I would order the windows myself online. So removing all the windows and then ordering is not an option, even though the house is currently unoccupied. Otherwise, I would just chisel off the exterior reveal plaster everywhere and then measure the masonry, or as I said, alternatively leave the old exterior plaster on the reveals and make the windows smaller. Although I find option 1 somehow more consistent, who knows how firm the old plaster still is.

Just to put this into perspective: We are having the windows in our old building replaced (built in 1930). Our window installer measures, removes, delivers, and installs. Just measuring took him a whole day for 17 windows, 1 terrace door, and 2 doors. He measured pretty much everything that can be measured and only then placed the order.

"It's not just a matter of quickly measuring a window."

My acquaintance will assist me with the measurements. Do you remove all the windows and then leave the house open for weeks until the ordered windows arrive, or how is it supposed to work? I thought the measurements could be done with the old windows still installed.

As you like.

Do you all remove the windows and then leave the house open for weeks until the ordered windows arrive, or how am I supposed to imagine that? I thought the measurements were possible with the old windows still installed.

The normal case is indeed measuring when the windows are in place. Measuring after removal only if you can leave the place open for three months.
It also has no real advantage and is not more accurate.