How to Waterproof a Window in a Shower

Modern domestic bathroom with window in shower
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Windows are built to withstand the elements, especially moisture. But that's just on the outside. Window interiors are not meant to be water-resistant.

If you have a window in the shower, unchecked moisture can lead to serious, costly damage. It is critical to waterproof the window to protect the window, wall studs, insulation, and siding.

Why Your Shower Has a Window

Older homes sometimes have a full-size window in the shower because the shower had once been a bathtub. As a bathtub, it would have been acceptable to have a window in the bathing area because splashing water was kept to a minimum.

As bathtubs fell out of fashion, they were frequently converted to showers. The tub basin and controls remained, and a vertical water supply line was added to bring the showerhead to around 80 inches high. With a tile surround installed inside the enclosure and a shower curtain added, the tub was ready to be used as a shower—though imperfectly.

Shower Window Waterproofing Basics

All areas of a shower enclosure are subject to water, but none more so than the zone below the showerhead. This includes the window, a major intrusion point for the inside of the wall system.

A collection of waterproofing techniques can help to limit water intrusion and slow down damage to the wall. Some solutions are very temporary—for instance, draping a shower curtain in front of the window. Other solutions are a bit less temporary—re-sloping the window sill, replacing the sill, or replacing wood windows with rot-free vinyl or fiberglass windows.

Ultimately, though, the best waterproofing solution for a window is to remove the window or relocate it above the showerhead.


If relocating the window, it helps to decrease the size of the window. The window should be fixed, not openable. The window should be vinyl or fiberglass, not wood.

Ways to Waterproof a Window in a Shower

Add Shower Curtain on Inside

Adding a shower curtain on the inside of the shower is a fast, inexpensive way to prevent water from reaching the window. This can be an effective, short-term fix for homeowners planning a long-term, permanent solution in the near future.

On the exterior wall, run a shower rod from wall to wall in the alcove. Place a shower curtain on the rod. This effectively protects the window until you're ready for a more permanent solution.

Remove or Replace Window Trim

Water-logged wood window trim will eventually develop rot. Trim also provides an easy avenue for water to enter behind the window.

With a tile surround, it's best to entirely remove the wood trim and then bring the tile up to the edge of the window opening. You can also check the caulking around the window trim periodically for signs of wear, and wipe the window sill dry after each shower to help guard against rot.


If you want to have trim, replace it with PVC (plastic) trim. PVC does not rot. Stick it in place with construction adhesive to avoid creating nail holes for water to enter.

Slope Tile Window Sill

Anything flat in a shower will pool up with water. The sills of shower windows tend to collect water and send it running down into the wall.

Wood window sills should be removed and replaced with tile. The tile should be sloped down toward the shower to promote drainage.

Replace Window Sill

While a tiled window sill is better than a wood sill, an even better option is solid surface material.

Solid surface material eliminates seams. One continuous piece of solid surface material can run from end to end, instead of the numerous grouted seams found with tile sills.

Install Vinyl or Fiberglass Window

If you have a wood frame window in your shower, you can stop the deterioration of the window unit itself by replacing it with a vinyl or fiberglass window. All parts of a vinyl or fiberglass window are water-resistant.

Install Glass Block

Natural light in the shower saves energy and goes easy on weary eyes in the morning. Installing glass blocks in place of the current window will bring in diffused light, ensure privacy, and provide better moisture protection.

Glass blocks are heavy. One glass block measuring 6 inches square by 3 inches thick weighs more than 3 pounds. Due to the weight of the glass blocks, the wall will likely require additional support. Because glass blocks have only a minimal R-value (about 1.75), exterior use is limited to temperate climates.

Close up the Window

If you have repeated waterproofing issues with a window in your shower, it's time to give serious consideration to removing the window and closing up the space. 

While rebuilding this portion of the wall is a major project that requires a building permit, it does cure the problem once and for all. It also gives you the opportunity to view and fix water damage to the wall studs and to remove and replace moldy insulation. A brief overview of the process:

  1. Remove the tile surround, window, casing, and trim.
  2. Remove all of the moldy insulation.
  3. After supporting the exterior wall, remove the wall studs on each side of the old window.
  4. Remove the partial studs below and above the window, as well as the header stud.
  5. Assess the wall for other wall studs that may need to be removed and replaced.
  6. Install full-length wall studs.
  7. Insulate the wall.
  8. Add a 4-mil or greater vapor barrier on the inside.
  9. Add drywall or cement board on the inside.
  10. Add siding on the outside.