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When are we seeing bulk water leaks into windows and siding?

joenorm | Posted in General Questions on

There is a lot of discussion about WRB’s, proper window flashing, tapes, etc. to keep bulk water off and out of walls.

My question is in what situations are we seeing bulk water leaks into siding when there are proper overhangs built into the home?

What siding choice is ineffective enough to challenge the WRB to such a great degree?

I guess it’s when the building starts to get tall, or if people go for no or small eaves that siding and window detailing gets a challenge from the rain.

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  1. Expert Member
    Akos | | #1

    2nd story Juliet tilt and slide door, rain screen, sloped sill 18" overhang. A section was not caulked on the inside on the bottom, wind driven rain made in under the trim. Didn't do any damage just discolored the non finished side of the trim.

  2. Expert Member


    A lot depends on the site conditions. My own house is about 1/4 mile from the ocean on a heavily treed lot. Even during winter storms it is rare for rain to hit our windows, and the roof is able to take almost all of the burden off the walls. A house I designed at the bottom of our street is on an exposed site where one set of French doors, which was protected by a three foot overhang immediately above, suffered extensive moisture damage at the bottom of the glazing within two years.

    Most details are designed for the worse possible scenario, and in any cases prove to be unnecessary. But given the proper window installation isn't appreciably more work or cost that doing an inadequate job, why not?

  3. Expert Member
    Peter Yost | | #3

    Bulk water management is of course all about assessing exposure and your tolerance for risk. This is why Joe Lstiburek at BSC does climate-tuned Builder Guides and a Water Management Guide.

    If you are unable or unwilling to assess exposure, then best practice is your default. And that applies to design, specs, and then workmanship.

    There is no climate where reverse flashings are good idea. And yet, on more building investigations than I can count, the moisture mismanagement I got called about, the problem is reverse lapped WRB and flashing. Some folks assess risk based on simplicity of the solution for exactly this reason.


  4. GBA Editor
    Martin Holladay | | #4

    Gable walls see more rain than non-gable walls.

    Two-story walls see more rain than one-story walls.

    Walls in windy locations see more rain than walls in a still location.

    Walls in rainy climates see more rain than walls in dry climates.

    All claddings leak when exposed to enough wind-driven rain.

    When a strong storm hits, almost any wall can get soaked -- and if the WRB has reverse laps, or the window rough openings lack sill pans, or the door rough openings lack sill pans, you've got a water entry problem.

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