Repeated opening and closing, rough handling and humidity can cause swinging shower doors to sag. Typically, this sagging occurs on the door's handle side. When a shower door sags, it is nearly impossible to close it snugly, if at all. Damage to the door and frame can result, as well as water damage to the floor. To avoid sagging shower doors, tighten the door screws regularly and avoid slamming the door. To fix a sagging shower door, all you'll need is a screwdriver, hammer and scrap wood.
Loosen the screws in the corners of the shower door and the door handle. Open the shower door.
Place a two-by-four block beneath the door's outer, bottom corner.
Wedge plywood or a wood shingle shim between the block of wood and the bottom of the door.
Hold a small block of wood against the bottom corner of the door, near the edge. Tap the wood up against the bottom of the door several times with a hammer. Make sure that the shim is wedged in tightly. Repeat the wedging and tapping as necessary.
Re-tighten all of the screws. Remove the shim and two-by-four block from beneath the door. Close the shower door. If the door is still out of alignment with the frame, loosen the screws and repeat the procedure. One or two tries are usually sufficient.