I get what you’re saying about hiding gaps with trim, but I’m a bit more picky—especially around the sills. If you just slap on caulk everywhere, you can end up with drafts or water sneaking in later. I’d rather spend the extra time getting things tight, even if it means fussing with shims for a while. The patchwork look drives me nuts down the road.
If you just slap on caulk everywhere, you can end up with drafts or water sneaking in later.
I hear you on wanting things tight, but honestly, a high-quality elastomeric caulk—properly applied—can actually outperform shims in some situations, especially with older framing that’s not square. It’s really about the prep work and making sure you’re sealing against the right surfaces. I’ve seen jobs where folks spent ages fussing with shims, but still ended up with air leaks because they missed small voids behind the trim. Sometimes a hybrid approach works best.
I get what you’re saying about caulk—if you do it right, it’s a solid seal. But I’ve run into issues where relying mostly on caulk led to cracks down the line, especially with wood movement in older houses.
That’s usually where I land too. I’ll use shims to get things square and stable, then go in with caulk or low-expansion foam for the gaps. The last time I did a window, skipping shims made the frame flex just enough to mess up the operation. Maybe it’s overkill, but I’d rather spend an extra hour upfront than deal with drafts later.“Sometimes a hybrid approach works best.”
Totally get the urge to just caulk and call it a day, but yeah, wood’s got a mind of its own—especially in these old houses. I had one window where I skipped the shims thinking “eh, close enough,” and six months later it was like trying to open a medieval portcullis. Ever try explaining to your partner why the new window whistles in the wind? Shims first, sanity later... That’s my motto.
I ran into the same thing with our kitchen window—thought I could fudge the shimming, and now it scrapes every time the weather changes. It took me way longer than I planned, mostly because I kept second-guessing measurements. Did you find yourself having to redo any, or did you get it right on the first go?
I get what you mean about second-guessing the measurements. I’ve replaced five windows over the years and honestly, I haven’t gotten a single one perfect on the first try. The first two I did, I was convinced a little “close enough” was fine—fast forward to winter and one of them wouldn’t even close all the way unless I put my shoulder into it. That was a fun weekend tearing out the trim and redoing the shims while cursing myself for not just slowing down.
Shimming seems like such a minor step, but if it’s off by even a hair, it’ll drive you nuts every time you open or close the thing. I started using those plastic shims instead of wood after my second window because they don’t compress as much over time. Not sure if that’s your issue, but it helped with mine.
I also learned (the hard way) that you can’t really trust old houses to be square—my place was built in ‘52 and nothing lines up anymore. Measuring at three points—top, middle, bottom—saved me from having to redo as much. Still, there’s always one window that ends up being stubborn.
All told, I’d say each window took me about three times longer than I thought it would. The last one went in smoother, but only because I finally stopped rushing and just accepted it would take all day. Not sure if anyone actually gets these things right on the first go unless they’ve done a hundred of them.
Funny how something that looks straightforward on YouTube turns into an all-day project once you’re knee-deep in insulation dust and splinters...
You nailed it about the “close enough” trap—been there, regretted that. I’ve learned the hard way that a window that’s even a smidge out of square can kill your energy efficiency, too. Drafts sneak in, condensation builds up, and suddenly your heating bill’s creeping up for no good reason. I started getting a lot more meticulous after I noticed one room was always colder than the others, only to find a tiny gap at the top corner of a window I’d installed the year before.
Plastic shims are a solid move. I used wood for my first two windows and they compressed just enough over a season to throw things off. Switched to composite shims after that, which made a difference. Still, getting everything plumb and level in an older house is its own beast. My place is from the late ‘40s, and nothing is straight—sometimes I feel like the walls are actively fighting me.
I’m curious if you did anything special for insulation around the frame? I started using low-expansion foam after reading up on air sealing, but I’ve heard mixed things about how much it really helps versus just packing in fiberglass. For me, the foam made a noticeable difference with drafts, but it’s easy to overdo it and bow the frame if you’re not careful.
Did you notice any change in your heating or cooling bills after you finished your windows? That was the big motivator for me—my old single panes were basically just decorative at that point. Would love to hear if all that extra time paid off for you in terms of comfort or energy use.
I’ve seen a lot of older homes where fiberglass just doesn’t cut it for air sealing—especially if the framing’s not square. Low-expansion foam is my go-to, but you’re right, too much can push the jamb out of alignment. I usually do a light bead, let it cure, then check the operation before trimming. In terms of energy bills, clients almost always report a drop after we’re done, but it’s not always dramatic unless the originals were really bad. It’s more about comfort—no more cold spots or mystery drafts.
I hear you on the comfort factor—after we did our front windows, it wasn’t like the house suddenly used half the gas, but those weird breezes near the couch just stopped. The funny thing is, I thought I’d knock out all the windows in a weekend, but with our 1920s place...not a chance. Each opening was a little off-plumb, so I ended up spending ages shimming and tweaking to get things square before even thinking about insulation. I tried fiberglass at first too, but it felt pointless with those gaps.
Curious if anyone’s had luck with other sealing methods? I’ve seen people swear by backer rod plus caulk for tricky spots, but never tried it myself. Wondering if that’s any better for old, uneven frames or if foam’s still king.
Backer rod plus caulk actually worked better for me than foam in the weird, uneven gaps around my old windows—especially where the frames were really out of whack. Foam just made a mess and didn’t always fill the space right. Ever try using low-expansion foam instead of the regular stuff? That’s supposed to help with older wood frames warping, but I’m not sure it’s much easier.