Window screens age quietly, and a screen that looks fine from across the room can still be failing its one job. Here are the signs it's time to replace.
Visible tears and holes
Any gap bigger than a few millimetres lets mosquitoes and flies through. Small punctures from pets or hail grow fast once the mesh frays, so a tiny tear this month is a swarm next month.
Sagging or baggy mesh
Mesh that's lost its tension bows outward and no longer seals against the frame. Bugs crawl under the spline edge where the mesh has pulled loose. Sagging is usually from years of heat and humidity — re-screening fixes it.
Rust or corrosion on the frame
Aluminium frames corrode at the corners, and steel hardware rusts, leaving rough edges and a weakened structure. If the corners are pitting, the frame is near the end of its life.
Bowing, bent or broken frames
A frame that's been forced out of square won't seat in the track, leaving gaps. Bent frames also scratch the window track and get harder to remove each season.
Faded, brittle mesh
Mesh that's gone chalky and brittle is UV-degraded and will tear at the lightest touch. If it crumbles when you press a fingernail into it, replace it.
If two or more apply, it's more cost-effective to replace the screen than to keep patching.