As of patch 1.05 the windows in nearly every building can be accessed by crouching through them even if there is a wooden cross/metal cross or curtain that is covering the window.
Some windows can just be jumped/vaulted through if they're big enough.
One of the buildings I didn't manage to do it yet is the brown wooden house.

I don't know if it was intended to be like that as I've seen other bug reports that state, that you CAN'T enter through windows.

The only thing I read in the patch notes was that the windows should be open for throwing stuff (grenades etc). So if it was intended to be like that please let me know.

See video link below.