I hear you on the Zip tape—it’s not a miracle worker, but it really does handle oddball framing better than metal. I’ve run into that same issue in older homes, especially where nothing is square and the sills are all over the place. The flexibility of the tape helps, but like you said, surface prep is everything. If there’s even a little dust or dampness, it’ll start peeling at the corners after a season or two. I’ve had callbacks on jobs where folks skipped cleaning the sheathing, and the tape just didn’t hold up.
I’m with you on hitting the corners with sealant. Might seem like overkill, but in my experience, those are the first spots to fail if water finds a path. I usually run a bead of polyurethane sealant before taping, especially on rough or uneven joints. It’s a little extra time, but it beats having to tear open a finished wall later.
One thing I’ve noticed—sometimes folks get too confident with the tape and skip the flashing pan or don’t slope the sill. Even with good tape and sealant, if water can sit there, it’ll find its way in eventually. I always try to pitch the sill with a shim or a strip of beveled wood, then tape over that. Not everyone bothers, but it’s saved me headaches, especially in basements where any leak turns into a bigger mess.
Curious if you’ve tried any of the newer fluid-applied flashings? They’re a bit messier to work with, but I’ve found they can get into those weird corners even better than tape sometimes. Not cheap, though, and you still need to let them cure before setting the window.
In the end, I don’t think there’s one “right” way—just what keeps the water out for your setup. I’ll take a little overkill over a wet basement any day...
I always try to pitch the sill with a shim or a strip of beveled wood, then tape over that.
That’s such an underrated step. I’ve seen so many otherwise solid installs where water just sat on a flat sill and caused trouble later. Have you noticed any difference in energy bills after swapping windows and really dialing in the flashing? I’m always curious if the extra effort pays off on the heating/cooling front.
Pitching the sill is one of those little things that makes a *huge* difference down the line, but most folks get in a hurry and skip it—then wonder why the trim’s rotting out in five years. I’ve done a lot of window swaps, especially in older homes where nothing is square and you’re fighting 70 years of “character.” I always tell people: if you’re going to go to the trouble of replacing the windows, spend the extra hour or two getting the sill right and flashing everything like you’re waterproofing a submarine.
As for energy bills, yeah, there’s usually a noticeable change, but it depends on what you’re starting with. If your old windows are single-pane wood from 1950 and you swap to new double-pane with proper air sealing and flashing, you’ll see a decent drop in both heating and cooling costs. In my own place, I saw about a 15% drop over the year—not earth-shattering, but enough to notice. The key, though, is making sure you don’t just slap the new window in the old hole. Air leaks around the frame can kill any gains from better glass.
Here’s how I usually attack it:
1. Check the rough opening for rot or weirdness. Fix that first.
2. Pitch the sill with a shim or beveled wood strip—just like you said.
3. Flash under the sill with self-adhesive membrane, lapping it up the sides.
4. Dry fit the window, check for plumb/level/square (never all three at once in my house).
5. Set the window, shim as needed, and foam the gaps (low-expansion only—learned that one the hard way).
6. Flash over the flanges, making sure water always sheds *outward*.
I’ve seen some folks skip steps, especially with caulking or flashing, and end up paying for it with moldy sills or drafts. It’s not glamorous work, but it pays off every time it rains sideways or you get a cold snap.
Honestly, if you’re handy and patient, swapping windows yourself isn’t the worst DIY job out there. Just budget extra time for surprises—old houses love to throw curveballs. And yeah, dialing in the flashing and pitch does seem to help with both durability and energy bills, at least from what I’ve seen on my own projects and clients’ places.
That part about nothing being square in old houses hits home. Ours was built in the late 1940s, and every “simple” project turns into a bit of a scavenger hunt. Last spring, I decided to tackle swapping out the two worst windows myself after watching way too many YouTube tutorials and thinking, “How hard can it be?” Turns out, it’s not rocket science, but it’s definitely more than just popping out the old and dropping in the new.
I probably underestimated how much time would go into prepping the opening. One side had some crumbly wood under the sill—nothing catastrophic, but it added a couple hours to my Saturday. I almost skipped pitching the sill since I honestly didn’t see what difference a few degrees would make. Glad I didn’t. We had a nasty storm a few months later, and water was pouring down the glass, but nothing got past the trim inside. If I’d just leveled it flat, I’m pretty sure I’d have been dealing with soggy drywall.
Energy bills... I was hoping for more dramatic savings, but like you said, it’s not life-changing. Our old windows were leaky single-panes, so there was a noticeable drop in drafts and the house feels less “breezy,” especially on windy days. The bill went down maybe 10% over last winter—not bad, but not quite the miracle I’d hoped for.
One thing that tripped me up: foam. I thought more was better and used regular spray foam around one window. Big mistake. It bowed the frame just enough that the sash sticks now when it’s humid. Lesson learned—low-expansion only.
All in all, it was worth doing myself for the sense of accomplishment (and saving some cash), but it took longer than I expected and I had to redo some caulking after the first rain showed where I’d missed. Not sure I’d want to do all the windows in one go, but it’s manageable if you’re patient and okay with surprises.
Totally get what you mean about the foam—did the exact same thing with my first window and had to shave down the jamb just to get it to close. My house is from the '30s, and I swear nothing lines up. I thought window swaps would be a weekend job... three weekends later, I was still patching weird gaps with shims and cursing whoever invented plaster walls. But yeah, the draft situation is so much better now, even if the energy savings weren’t wild.