We have a basement flat and we suspect that the bathroom exhaust fans do not go anywhere, which causes a fair bit of damp in the flat which manifests itself as condensation on the windows in the winter.

I'd like to fit an extractor fan, or at least some sort of vent to allow the air to circulate (this should help with the condensation shouldn't it?), but don't want to drill through the wall as there is a damp proof membrane in there. Can I fit something into the window, and how do I go about cutting a hole in the glass to accommodate it? I've seen those cat-flaps that are in the windows so I assume it must be able to be done...

2 Answers 2


Sure you can - just depends on how you want to attack the problem.

You could either replace the window sash with a mount for the fan (removing the window itself - minus the frame and replacing it with finish grade plywood), or build a frame over the rear of the window and hang a fan from it. That way you don't actually need to cut the glass.

Here's one example

Here's another

  • thanks for the suggestions. I have a fixed window and don't really want to block out the light with plywood..
    – Sam Holder
    Aug 4, 2010 at 11:21

Does the window open? Or is it a fixed pane? If it opens (or if you can find one the same size that opens) you could install a window exhaust fan like this one that mounts in the window frame. That way you don't have to mess with cutting a hole in the glass.

Another option would bet to place a dehumidifier in the bathroom.

  • Also, I couldn't resist posting this from thereifixedit.com: thereifixedit.files.wordpress.com/2010/07/…
    – Doresoom
    Aug 3, 2010 at 20:31
  • no the window does not open, its just fixed pane. I'd prefer to fix something into the existing glass if possible. Maybe not an extractor fan maybe just a vent with holes which would allow some air circulation
    – Sam Holder
    Aug 4, 2010 at 11:20

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