How could I “flash” a sill replacement on an old window?
A recent project involved hoisting some lumber through an upper window. The lumber brushed the sill and it came apart like wet leaves. I already knew it was bad but hadn’t realized how dire the situation was.
I ended up ripping the thing off, but I’m a bit confounded about what to do for the repair. There doesn’t appear to be any flashing beyond a perfunctory caulking of joints. The tar paper appears to be just trimmed around the edges of the rough opening. I’m not really sure how to integrate any solution for adding a new sill that doesn’t either ignore the problem or potentially make things worse.
The underlying problem seems to be that the sill catches too much water and doesn’t get enough sun to dry out. See the picture attached for how slim the overhang is. An additional problem is that the head flashing could be nonexistent, which means water is probably leaking down behind the WRB.
I see a few options here but I’m curious what others think:
1. Remove all of the trim and see just how rotten the framing is and do a proper job of re-framing, flashing, etc. the cheap, single pane window. – I don’t have a ton of experience, so this feels really daunting.
2. Put in a piece of solid lumber, try to work something like a sill flashing with a tape or fluid applied product, caulk the joints, and come back on another day with more time and money. – This feels like the right thing to do, but I’m not sure if the extra effort will make a difference.
3. Don’t worry about the flashing, just shove a board in there and caulk it, without a proper flashing around the whole window and a better overhang, a bang-up flashing on the bottom of the window is just lipstick on a pig.
Let me know what you think!
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Attaching some photos.
Also, I just realized I ended up posting a bunch of duplicates of this question, but I'm unable to delete them because they're not associated with my account. Sorry about that!
I'm a fan of the permeable fluid applied flashings for these inevitably hairy new-meets-old transitions. Very forgiving and easy to engage whatever existing WRB is present. No tape origami needed. The existing sills on my 1941 cape had a few spots of dry rot that I rectified with two prosoco products, one for gaps the other for coverage. Not cheap but it priced out better than others, and saved time and worry. Covered with light guage aluminum for looks.
Guess that makes my vote for option 2. Cheers
Thanks Jason. Any resources on how to make that connection?
Not much solid lumber there left to connect, from the looks of it... you may have to get creative with long screws diagonal into jambs.
Photos attached if it helps. This was prep for new flangeless fiberglass windows set against existing interior trim. Not shown is the peel and stick (per window manufacturer) directly under the new window covering the uphill edge of aluminum and forming a backstop. Also not shown is the alum L profiles that covered the jamb and head faces and tucked behind new 2" brickmold trim. The flaw is the caulk joint needed from jamb to sill alum but all that's just cladding protecting the fluid-applied. I made it a BIG fillet bead.
For your new sill board I would include a kerf cut underneath to form a drip edge, along with a healthy top slope -- I like 14 degrees (1:4, 3:12 same thing).
Yeah, it looks as if I'll need to do some thinking about how to recreate the bottom of the rough opening, but otherwise the prosoco does a great job covering up past sins.