What mass of plexiglass should I use to replace a fanlight pane?
Answers: If it is a regular glazed wood window ( putty & points) .no genuine limit exc for frame depth ...usually 1/8"
Grooved storm fanlight or door requiring a gasket or spline
1/8" is usually reqd to match unproved glass concentration
Do not use plexiglass to replace a window cup pane if you want it to perform economically. over time the plexiglass will become cloudy. Also the heat from the sun will raison d`¨ētre the plexi to sag and move which will break the stamp which in turn will lead to condensation.