Regular glass is not a great transmission material for WiFi, but it's better than concrete or brick, as it absorbs WiFi less. The problem comes when you have speciality glass containing extra metals or a specialist coating. Even then, though, what's going to happen isn't absorption but reflection.
*You should probably check the strength of the WiFi signal, which you can do using a WiFi Analyser app on your phone.
**Worryingly, some new-build houses near me seem to have metallic coating on the insulation blocks and the backs of every piece of plasterboard in them - each room is going to be like it's own little Faraday cage for WiFi!
