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Community and Q&A

Water between the bottom of the window and rough opening?

whitenack | Posted in General Questions on

Building a home in zone 4A and we done with framing and setting the windows and house wrap. The windows have been flashed and the house wrap is taped to the window on all 4 sides.

This morning, the builder needed to take a window out, and when he did he noticed a lot of water under the window between the window and the rough opening. He said it was a lot of water.

Could there be a simple explanation for this, or is this surely a leak somewhere? We had cooler temperatures last night and a heavy dew this morning. Could it be condensation forming on the cooler surface under the window frame?

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  1. GBA Editor
    Martin Holladay | | #2

    Ideally, your builder remembered to flash the rough opening. Rough openings need a waterproof sill pan, installed to drain to the exterior.

  2. whitenack | | #3

    Thanks Martin. He did. But in his eagerness to air seal at every opportunity, he taped the outside of the rough opening shut. We are assuming that the moisture is coming from condensation, and since the exterior of the rough opening is blocked, there is nowhere for the condensation to go.

  3. GBA Editor
    Martin Holladay | | #4

    At this time of year, it's hard to imagine that you'd have a lot of water there due to condensation, unless you are operating a powerful air conditioner, and the weather outdoors is hot and humid. Even then, I'm not sure how the outdoor air would contact a cold surface that would lead to dripping onto the sill pan.

  4. whitenack | | #5

    Thanks Martin. I'm headed out there this morning to see if there is moisture again. No rain last night, so if it is wet again it has to be something other than rain. However, this is the side of the house that faces the weather, so it very well could be a leak coming in somewhere. If no moisture this morning I'm going to get out the water hose and see what I find.

  5. whitenack | | #6

    Well, the window failed the water hose test. I doused the window with water out of a hose for a few minutes and found plenty of water under the window on the inside. I tried a few of the other windows and they were dry, so it is something specific about this window or the flashing.

    I wonder if I could set up a mini "blower door test" for just this window. Seal up the inside of the window with a garbage back or something connected to a small shop vac. Turn the shop vac on and see where the air is coming through.

  6. whitenack | | #7

    For those that may read this in the future, it looks like the trouble was coming from the hinged nailing flange. The windows were flashed, but the flashing did not cover the connection between the flange and the window. This hinge is not water tight, and water was getting in that hinge and traveling down the track to the sill.

  7. GBA Editor
    Martin Holladay | | #8

    Thanks for pointing that out. Many window installers don't realize that window flanges aren't always part of the flashing system -- they are just a convenient method to fasten the window to the wall.

    Some window manufacturers make flanges that are watertight components of a flashing system -- others don't.

  8. whitenack | | #9


    These windows have a bottom nailing flange. Should I seal that bottom hinge also or leave it unsealed since you should leave the bottom of the window un-flashed?

  9. GBA Editor
    Martin Holladay | | #10

    As you probably know, the rough sill needs sill pan flashing that drains to the exterior (usually, to the exterior side of the WRB). The bottom window flange should not be sealed or taped -- you want any water that reaches the sill pan flashing to be able to dribble out, if possible. (In reality, most of this water is probably handled by evaporation, but you need to plan for drainage if possible.)

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