I've got an old double-hung window from the 90s and the bottom of the frame is starting to look soft and crumbly. Water's been getting in there over the years. Do I need to replace the whole frame or can I just cut out the bad part and patch it somehow?
You can often save the frame by cutting out the rotted wood and filling it with epoxy filler or a wood repair compound, which hardens and can be sanded and painted to match. The key is getting all the soft, damaged material out first - use a chisel or screwdriver to probe and remove anything that's genuinely rotted - then let the area dry completely before applying filler. If the rot goes deep into the structural parts of the frame or if more than about a third of the frame is affected, replacement becomes more practical and cost-effective. For future prevention, make sure water drains properly from the sill and consider caulking any gaps where moisture can get in.
I had water damage creep into a frame corner at my place and caught it before it got too bad. If the rot's still shallow you can dig it out with a chisel, let it dry completely (this part matters, moisture will just cause more rot), then pack it with epoxy wood filler or a two-part repair compound. Sand it smooth once it hardens and paint over it. But if the rot goes deep into the frame's structure - like the wood feels hollow or spongy over a big area - replacing just that section or the whole sash assembly is worth considering because a patched-up structural piece might fail when you're trying to open or close the window.
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