Problem occurs only in north wind and
rain, in only one north-facing window, a
non-opening half-moon over a large sash
window. There is a substantial windowsill
below the half-moon and above the sash
window, and water enters where this horizontal
sill meets the vertical part of the window.
This leak first appeared last fall, when I tried to
fix it by silicone caulk outside, finger-smoothed
into two small visible cracks in exterior finish
(oil-based stain) in the vertical/horizontal corner.
This seemed to work OK but the problem recurred
recently (2 inches of rain in a day in north wind.)
But I now see outside no visible cracks down in
the corner -- only cracks along the edge of the
putty (20 years old) that holds the window glass,
extending about half the width (3 ft. overall.)
Could rainwater enter at this point and travel down
the wood (under the finish) at least one inch, and
then another two inches horizontally to enter the
That's possible, but somewhat unlikely IMO unless you have some pretty large
gaps in the putty. I think you should be looking higher up, maybe even as high
as the eaves or the roof. Water could be getting behind the siding, and
running down between the sheathing and the siding, until it reaches the
windowsill, where it has a point of entry to the inside.
The first place I'd look is the casing around the window. Make sure the gap
between that and the siding is caulked properly. If that looks good, then
check the siding above the window for cracks or gaps. Go all the way up to the
roof if you need to - I think you'll find a point of entry somewhere, that
allows water behind the siding.
Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
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