I'm doing a bathroom remodel and want to partially cover and tile over an existing window. Partial, because it's the only source of natural light, and because I live in a townhouse with an HOA, so I'm not permitted to change the exterior, otherwise I'd swap out the huge window for a smaller linear version.

The window is pretty large and the neighbors are RIGHT THERE, so it's a really stupid design to have a window over a bathtub with neighbors on top of each other. But, I like the natural light, and from a resell perspective, I think it makes sense to keep at least some of the window exposed. The HOA is ridiculous - first and last experience with an HOA. Won't do that again. The window is just under 4 x 4'. I'd be keeping the top 1' open and covering the remainder. I'd be adding support lumber along the lines where the mullions/grids are.

So, my question is, if advisable: Can I tile over using a backer board, and if yes, will I need some kind of insulation on the portion that I am closing? If yes to both, any suggestions? I will also be using a window film to cover the entire window, so no one can see any obvious irregularities from the outside. I live in U.S. hardiness zone 7 and have 2x4 exterior walls; the house was built in 1999. I welcome advice and suggestions.

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    – isherwood
    May 31, 2022 at 20:08
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    I have "stained glass print" privacy film over bathroom windows. Works fine. Also easily reversible. This approach seems odd, to say the least. Other folks put curtains over them (but I hate curtains in general.)
    – Ecnerwal
    May 31, 2022 at 20:12
  • @isherwood, the dual reasons are for both privacy and for waterproofing - tub is right below the window and it will remain there, but the shower is moving next to the tub (creating a shower room).
    – teeemdee
    May 31, 2022 at 20:18
  • @Ecnerwal - basically doing the same thing re a print of window film to help conceal what I am planning on doing inside, but want the added privacy of covering the lower window portion.
    – teeemdee
    May 31, 2022 at 20:20
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    The only requirement you have stated is privacy. At the risk of repeating what others have said ... why use tile for privacy? You can use window film, you can even get window film with an image of mosaic tiles on it. Or, a plastic venetian blind.
    – jay613
    May 31, 2022 at 22:40

1 Answer 1


Sure, you can float cement board over a window, but it needs to be supported. You'll need to either line the cement board with heavy plywood or put a frame of lumber behind it. Tile is not tolerant of substrate flex.

Insulation isn't needed. You'd have to seal it to the window itself, and the energy savings would be negligible over the window itself, so the payoff would be long. It complicates the project too much to be worth doing.


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