@Puybaret, thank you very much. Following your pointers, I used Blender to create the glass blocks. It took me a while getting the right transparency parameters in Blender for the glass block.

Here they are....

Alpha: 0.617
Blend: 1.0
Fresnel: 1.5
Specular: 1.0


I have uploaded the .obj and .mtl to https://sourceforge.net/p/sweethome3d/d-models/485/


Night time view from outside.


Day time view from inside.

I think the existing service window in the library can be too much of a hassle to use with this glass block. I'll see if I can create a dedicated window model using these glass blocks.


Existing service window without glass blocks