I've got some older double-hung windows in my house that have gotten really hard to open over the last couple years. They'll budge if I really force them, but it's frustrating and I'm worried I might crack the glass. Is this just paint buildup, or is something else going on?
When you say they've gotten harder over a couple years, have you noticed any changes to the frames themselves - like warping or swelling - or does it feel more like friction in the tracks?
Paint buildup is definitely one culprit, especially in older windows. The sashes get painted over repeatedly and the paint seals up the gaps between the frame and the sash, making them stick. You can usually feel this as resistance throughout the full range of motion. But there's often more going on. Double-hung windows rely on a balance system (either weights on cords or spring mechanisms), and if those fail, the sash becomes genuinely heavy and hard to lift. Also, dirt and debris accumulate in the tracks over time, and moisture can cause the wood to swell slightly, changing the fit.
Start by examining the tracks closely - get a flashlight and look for gunk buildup. Vacuum out what you can, then wipe them down with a damp cloth. If that helps, you're mostly dealing with dirt. Next, try breaking the paint seal by running a utility knife carefully along the inside edges where the sash meets the frame - go slowly so you don't gouge the wood. Once you've loosened the paint, try opening and closing the window gently a bunch of times. If it's still stuck hard after that, the balance system might be worn out, which is a more involved fix but doable. For now, avoid forcing it hard enough to risk the glass - patient, repeated small movements are safer.
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