How to Fix a Sagging Sofa: Foam, Webbing and Springs Explained

A sagging sofa is almost never one problem. It is foam, webbing or springs – sometimes all three – and each has a different fix. This guide shows you how to diagnose which one you have, what it costs to put right, and when the frame is worth the effort.

Diagnose first: a five-minute check

1. Take the seat cushions off and press the deck (the platform they sit on) with your hand. If it gives more than 30–40 mm easily, the suspension is the problem.
2. Turn the sofa on its back and look at the underside. Peel back a corner of the black dust cover (it is stapled; you can re-staple it).
3. Look for webbing: bands of elastic or jute in a lattice. Loose, stretched or snapped bands mean a re-web.
4. Look for springs: zigzag (sinuous) wire or coil springs. Broken clips, springs sagging below the frame rail, or a loose spring mean a spring repair.
5. Put the cushions back and sit. If the deck felt firm but you still sink, it’s the foam.

Also check the frame while you are under there. A cracked rail or a loose corner block will not be fixed by any cushion.

Fix 1: Replace the seat foam

The most common cause on sofas under ten years old. Cushion foam loses height and resilience long before the cover wears. Unzip a cushion; if the foam is yellow, crumbly or has a permanent dip, it is done.

Replace with high-resilience 35 kg/m³ foam at the original thickness (usually 100–120 mm), cut 10 mm over the cover size, and wrap it in 200 gsm Dacron. Our HR35 seat foam is what the trade uses for this. Full measuring instructions are in How to measure and order replacement sofa cushion foam.

Cost (indicative): foam and wrap for a 3-seater is typically in the low hundreds of dollars, and it is a 30-minute job per cushion once the foam arrives. Get a firm figure from the product pages or our contact page.

Fix 2: Re-web the seat

Most modern sofas have elastic webbing under the deck rather than springs. Elastic loses its stretch after 8–15 years, and the deck drops. The fix is to strip the old bands and fit new ones under tension.

What you need

• 50 mm elastic webbing – about 8–12 m for a 3-seater
• A webbing stretcher (or a wooden block and a helper)
• Staple gun with 10–12 mm staples; 71-series stainless if the sofa lives near the coast
• Tack lifter and pliers for the old staples

The method

1. Note the pattern and spacing of the old webbing before you remove it – usually front-to-back bands 50–75 mm apart, with side-to-side bands woven through.
2. Remove the old bands and all the old staples. Old staples under new webbing cut it.
3. Staple one end of a new band to the rear rail with 4–5 staples in a W pattern.
4. Stretch it 10–15% (a 600 mm span becomes about 680 mm on the stretcher) and staple to the front rail. Cut, leaving 20 mm to fold back and staple again.
5. Repeat across, then weave the side-to-side bands through and tension the same way.

Elastic webbing should read as a firm trampoline when done: give when pressed, but no slack. Too tight and the sofa feels hard; too loose and you are back where you started. We stock several tensions in our webbing & springs range.

Fix 3: Repair or replace springs

Sinuous (zigzag) springs run front to back and are held by metal clips on each rail. Common failures: a clip pulls out of soft timber, a spring loses its arc and sits below the rail, or a connecting link breaks so springs splay apart.

• Loose clip: refit with a longer screw or move it 20 mm along the rail into fresh timber.
• Sagging spring: replace it. Springs are sold by gauge (9 gauge is common for seats) and cut to the original length plus arc. Re-link to neighbours with spring clips or tie wire.
• Whole set flat: replace all of them – mixing new and old gives a lumpy seat.

Coil-sprung sofas (eight-way hand-tied) are a different job. If ties have broken but the coils are sound, re-tying with laid cord is a skilled but learnable task; if the coils have collapsed, most home upholsterers will want help.

Fix 4: Add support without stripping anything

If the sofa is a stop-gap – a flat, or a rental – a 12 mm ply board cut to the deck size and laid under the cushions removes the sag for very little money. It makes the seat firmer and stops the sink, but it does nothing for worn foam and can stress the frame rails, so treat it as temporary.

Is the sofa worth it?

Sofa	Worth fixing?
Solid hardwood frame, good cover, tired suspension	Yes – re-web or re-spring, new foam
Good frame, worn cover, flat foam	Yes if you like the shape – reupholster with new foam
Particleboard/stapled frame, under 5 years old	Foam only; if the frame has gone, replace
Cracked frame rail	Only if it is a quality or sentimental piece

As a rule, a well-made frame outlasts three sets of foam and two covers. Spending a few hundred dollars on the suspension and foam of a good sofa buys another decade.

When to hand it over

Re-webbing and foam replacement are solid DIY jobs. Coil springs, frame repairs and anything where the seat deck is stitched into the cover are harder, and a sofa on its back in a small lounge is a two-person job. If you are in Auckland and would rather have it done, our sister workshop Upholstery World repairs sagging seats on-site – springs, webbing and foam – and warranties the repair. Indicatively, a suspension repair on a 3-seater in NZ runs from a few hundred dollars depending on the construction.