- If you inspect the underside of your couch and discover a crack or split in the wood frame that's causing the boards to sink, use plywood to repair the damage. A piece of plywood, cut to size with a handsaw and screwed to the frame board over the sagging wood board with wood screws, acts as a splint. The splint straightens the frame board and can restore a sagging sofa.
- Sofa springs can loosen or stretch over time, leading to sofa sag. Take the springs that have come untied or slipped out of their spring clip and pull them together to tighten. Use sofa clips to hold the ends of the springs and screw the clips to the frame of the sofa. Once the loose or stretched strings are tight again, the sofa should stop sagging.
- If old stretched strings are damaged beyond repair, replace them. Sofa springs come in standard sizes and can be purchased at home service centers. Unhooking the old springs from the clips and attaching new springs is a simple process. New springs should firm up the saggy spot on a couch.
- Sofas can sag due to extra empty space in your sofa cushions. If you check your cushion filling and discover a lot of extra space, use scissors to cut a square of foam pad to fit inside the cushion. Unzipping the cushion and positioning the foam pad underneath the cushion padding should firm it up.