Keeping rain out: Tips for a watertight window install?

I’m in the same boat with a 60s-era house and nothing lines up right. I used flashing tape and caulk when I did my kitchen window - tape first, then caulk on the outside after it was set. Didn’t mess with foam, mostly because I kept hearing it can warp the frame if you use too much. Has anyone here actually had foam cause problems, or is that just internet paranoia?

Didn’t mess with foam, mostly because I kept hearing it can warp the frame if you use too much.

- Had the same worry. Used low-expansion foam on two windows in my 1958 place - just a thin bead, didn’t go wild.
- No warping for me, but I was careful not to overfill. I think it’s only a problem if you really pack it in.
- Tape and caulk combo is solid. Foam just helped block drafts in my case, especially in winter.
- Honestly, biggest issue was getting the old frames square enough for anything to seal right... nothing’s ever level in these old houses.

I’ve always been a little nervous about foam for that exact reason - heard too many stories about bowed jambs. Did a couple windows in my 1960 ranch, just a light pass with low-expansion stuff, like you said. No trouble, but I triple-checked every step. Tape and caulk are my go-tos for water, but on those windy winter days, foam made a noticeable difference. Getting the frame square is the real headache, though... nothing like trying to shim a window when the wall’s gone wavy over the decades.

Getting the frame square is half the battle, especially in an old place - mine’s got walls that look straight until you actually measure. I’ve had better luck with flashing tape than caulk for water, honestly. Caulk shrinks and cracks over time, but the tape holds up if you overlap it right. I do a layer of tape on the sill, set the window, then more tape up the sides and top, always lapping it so water runs out, not in. Only a tiny bead of caulk outside, just to keep wind-driven rain out. Expanding foam, I use barely any - just enough to fill gaps, not jam the frame. Never had leaks, but I’m stubborn about following the order. Wouldn’t say it’s rocket science, but patience matters more than fancy products.

I’m with you on flashing tape holding up better than caulk, especially in older houses where nothing’s ever truly square. I’ve found patience is the key too - rushing the taping step always comes back to bite me when the first big rain hits. I go a bit further and use a sloped sill pan (sometimes just made from folded flashing), which helps direct any water out, just in case something sneaks past the tape.

Curious if you insulate around the frame for energy efficiency? I use low-expansion foam, but I’m careful not to overdo it so the window doesn’t get pushed out of alignment. I’ve read some folks prefer backer rod and mineral wool instead of foam for breathability and to avoid trapping moisture, but I haven’t tried that myself yet. Have you noticed any difference in drafts or condensation with your approach? Always trying to find that balance between watertight and airtight without causing other issues...

Yeah, I’ve had better luck with low-expansion foam too, but I get nervous about overfilling and messing with the window alignment - been there, done that. Tried mineral wool once on a basement window and it seemed to breathe a bit better, but I still noticed a little draft. Might just be my old house settling, honestly. The sloped sill pan trick is something I wish I’d known about years ago... makes a big difference in heavy rain.

I get what you’re saying about low-expansion foam, but I’m not totally sold on it being the magic bullet. I’ve seen it shrink back a bit over a couple seasons, especially if there’s any moisture sneaking in. Had to pull trim off and re-do a section last fall - what a pain. Sloped sill pans are good, but if the flashing tape isn’t just right, water still finds its way in. Sometimes I wonder if the old-school method of backer rod and caulk wasn’t more reliable in these drafty old places...

Totally hear you on the foam - I've seen it shrink too, especially in spots that get a little damp. It’s great for drafts but not a cure-all. Backer rod and caulk definitely have their place, especially in older frames where nothing is square.

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“if the flashing tape isn’t just right, water still finds its way in.”

Curious if anyone’s found a good way to deal with irregular stone sills - those always seem to be the leakiest spots for me.

- Seen the same thing with stone sills - never totally flat, always a pain.
- What’s worked for me: flexible flashing membrane (the stretchy kind), pressed into every dip and wrinkle. It’s not pretty but it does seem to help.
- I’ll run a fat bead of high-quality exterior sealant under the sill before setting the window, then tool it in tight.
- Sometimes I wedge in backer rod if there’s a big gap, but honestly, it’s just about getting as much coverage as possible.
- Tried liquid flashing once on an old fieldstone opening... messy job, but it held up through two winters so far.

Stone’s just tough - nothing is square or smooth. Just gotta layer it up and cross your fingers sometimes.

That’s pretty much my experience too - stone just never cooperates. I’ve tried the flexible flashing, but sometimes I wonder if it’s just hiding problems instead of fixing them. Ever used a sill pan with stone? I did once, but it was such a wrestling match getting it to sit right, not sure it made a difference. At this point, I’m convinced you can only make it “good enough,” not perfect. Water always finds the tiniest path...

At this point, I’m convinced you can only make it “good enough,” not perfect. Water always finds the tiniest path...

I get where you’re coming from, but I’m not fully convinced it’s just about “good enough.” I’ve had way fewer issues since I started using liquid-applied flashing, even with stone. Yeah, it’s a pain to prep and gets messy, but it seems to fill those weird gaps better than the peel-and-stick stuff. Maybe nothing’s totally waterproof, but I’ve noticed less staining and fewer callbacks. Might just be luck or maybe it’s the extra prep… hard to say.

I’ve had similar luck with liquid-applied flashing, especially in older brick houses where nothing is square and you’re always fighting weird gaps. The first time I tried it, I was skeptical - looked like I’d just painted on some goo. But a year later, no leaks, and the sills are still bone dry. The prep is annoying, yeah, but it seems to really bond with rough surfaces.

Peel-and-stick always felt like a shortcut to me, especially when you’re dealing with uneven stone or brick. It just doesn’t get into every nook. I still run a bead of sealant at the corners for peace of mind, but honestly, since switching to liquid, I spend less time fixing stuff after the fact.

Not saying it’s magic - water always finds a way if you give it enough time. But for me, the extra effort on prep and using liquid flashing has cut down on headaches. Maybe it’s overkill in some climates, but in the Midwest with all our freeze-thaw cycles, it’s been worth it.

Peel-and-stick always felt like a shortcut to me, especially when you’re dealing with uneven stone or brick. It just doesn’t get into every nook.

Yeah, I hear you on that. Tried peel-and-stick once on an old limestone house - total pain. The stuff just didn’t want to stick, and I ended up with gaps anyway. Liquid flashing was a game changer for me too, but the prep killed my weekend. Still, worth it in the long run. Midwest winters are brutal on anything that isn’t sealed up tight... seen too many folks deal with rot from little leaks that turn big.

seen too many folks deal with rot from little leaks that turn big.

- Totally get where you’re coming from about “peel-and-stick always felt like a shortcut.” On rough stone or brick, it’s just... not ideal. Those gaps are a nightmare to chase down later.

- Liquid flashing is a pain up front, but you nailed it - worth the effort. I’ve spent way too many Saturdays smoothing that stuff into every little crevice. It’s slow, but once it sets, you can actually sleep at night when the rain’s coming sideways.

- Midwest winters are no joke. Seen plenty of window frames swell or rot after just one season of leaks sneaking in. Even the tiniest missed spot can turn into a headache.

- If anyone’s on the fence about the extra prep, here’s my take: spend the time now, save yourself from tearing out soggy drywall later.

- For what it’s worth, I still use peel-and-stick on newer builds with smooth sheathing. But old stone? Not worth the gamble.

- Sounds like you made the right call switching to liquid flashing. Sometimes shortcuts just aren’t worth it in these climates...

I hear you on liquid flashing, but I’ve actually had decent luck with peel-and-stick even on older masonry - if you use a high-quality primer first. It’s definitely not as forgiving as liquid, but sometimes the mess and cure time of liquid flashing just isn’t practical, especially if you’re racing weather or working solo. I guess it depends how rough the surface is and how much time you’ve got. Maybe I’m just stubborn, but for smaller jobs or repairs, peel-and-stick still feels like a solid option if you prep right.

“peel-and-stick still feels like a solid option if you prep right.”

Totally get where you’re coming from. I’ve done a few window retrofits on my 1960s brick place, and yeah, peel-and-stick worked out as long as I spent extra time with a roller and made sure the primer was bone dry first. The one time I rushed it, though, it started peeling at the corners after a wet spring… lesson learned. For awkward spots or quick repairs, I keep a roll handy, but for anything bigger I usually bite the bullet and go liquid. Just less nerve-wracking in the long run.

That’s a solid approach - prepping makes all the difference. I’ve seen folks get frustrated with peel-and-stick, but honestly, most of the failures I’ve been called out to fix were from rushing or skipping primer. You nailed it with the roller, too; pressing it in really matters. For bigger jobs, I lean liquid as well - it’s just more forgiving if there’s any weirdness in the surface. Still, for those quick fixes or tight spots, peel-and-stick is tough to beat. You’re on the right track keeping both options handy.

I get the love for liquid, but man, I tried it on my first window and ended up with more of it on my jeans than the wall. Maybe I’m just clumsy, but peel-and-stick felt way less stressful for me. I will say, though, I skipped the primer once (because who reads instructions?) and yeah... that corner leaked like a sieve during the first rain. Lesson learned. For me, if it’s not a huge area, peel-and-stick wins just because it’s less mess to clean up after.

Yeah, skipping the primer is one of those mistakes you only make once, right? I’ve definitely been there - thought I could get away with it, then spent a Saturday chasing leaks. Peel-and-stick is great for smaller jobs or if you just want less mess, totally agree. But man, liquid can be forgiving if you’re dealing with weird shapes or corners. Ever tried using a cheap chip brush to control the splatter? Not perfect, but at least my jeans survived the last round.