My bedroom drywall started buckling near the window this summer after we had that crazy humid spell in July. It's not cracked, just wavy in spots about 3-4 feet up the wall. Do I need to replace the whole sheet or can I screw it back down somehow? It's bugging me more each week.
I've dealt with wavy drywall from moisture before, and the good news is you probably don't need to replace the whole sheet. Try screwing it back down with drywall screws spaced every 12 inches or so along the studs - the moisture likely just weakened the original fasteners, and new ones can pull it flat again. Make sure you're dealing with the humidity source first though (check the window seal, make sure your AC is running properly) or it'll just buckle again. If the waves don't flatten out after re-screwing, or if the drywall feels soft or crumbly, then you're looking at replacement, but honestly most of the time just anchoring it properly does the trick.
Before you touch those screws, make sure the humidity is actually stable now - if it's still damp in there, you're just gonna be chasing the problem. Grab a moisture meter and check the drywall around that buckling area. If it's reading above 16-17% or so, you need to fix the moisture source first (seal that window, check for leaks, get some air flowing). Once things have dried out for a week or two, the drywall might actually flatten back on its own.
If it stays wavy after the humidity's under control, then yeah, you can screw it down without replacing the sheet. The pitfall nobody mentions: don't just go crazy with screws thinking more = better. Spacing them too close together can actually cause more problems down the road. Put new screws in every 12-16 inches in that bulging area, and here's the thing - use slightly longer screws than standard (maybe 1.5 inches instead of 1.25) so they actually bite into the stud and pull the sheet snug. Pre-drill slightly so you don't blow through the paper. Then spackle over the heads and sand smooth.
One more thing: check what's behind that wall. Window bays can have insulation issues or air gaps that trap moisture. Even after you fix the drywall, you might want to make sure there's nothing going on with ventilation or condensation buildup around the frame. A small vent or dehumidifier in the room during humid months could save you from dealing with this again next summer.
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