Why is my floor bouncy or springy?

Bounce ranges from an accepted characteristic of an old house to a warning of structural failure, and the difference is mostly in whether it is changing.

Safety

Step by step

1. Work out whether it is changing.A floor that has always been slightly springy is usually a design characteristic. One that has become bouncy is telling you something has moved or failed, and that is the case that matters.
2. Look for the accompanying signs.Sagging, gaps opening at skirtings, doors that have started catching, new cracks in the ceiling below. Bounce with any of those is a structural question rather than a comfort one.
3. Get underneath if you can.A cellar, a crawl space, or lifting a board. Most causes are visible in five minutes from below and invisible from above.
4. Check for missing noggins.Short timbers between joists at mid-span, which stop them twisting and share load between them. Their absence is a common cause of bounce in older and cheaply built floors, and adding them is the easiest real fix.
5. Check the span against the joist size.Joists have a maximum span for their depth. An old floor, or one altered when a wall was removed, is frequently over-spanned, and that is a genuine structural shortfall rather than a nuisance.
6. Look for notched or drilled joists.Plumbers and electricians cut joists to run pipes and cables, often deeply and in the wrong place. A notch near mid-span or on the bottom edge removes a large part of the strength.
7. Check the bearing ends for rot.Where joists sit into a wall is where damp reaches them. Poke with a screwdriver — soft timber there is a serious problem and it explains sudden movement.
8. Check the boards as well as the joists.Chipboard that has got wet swells and loses strength permanently, and thin boards over widely spaced joists flex between them. This is a floor-surface problem, not a joist one.
9. Add noggins if they are missing.Solid timber the same depth as the joists, staggered so they can be nailed, at mid-span. Genuinely effective for a mildly bouncy floor and within normal DIY.
10. Consider sistering a joist.Bolting a new joist alongside a weak or notched one. Effective, but it needs to bear correctly at both ends and it is worth advice before doing it.
11. Do not just add more boards on top.Overboarding stiffens the surface a little and adds weight to a floor that is already deflecting. It treats the symptom and occasionally makes matters worse.
12. Get an engineer for the structural cases.Over-spanned joists, sagging, rot at the bearings, or anything that changed after a wall was removed. A structural engineer's report costs a few hundred pounds and is the right spend.

Tips

• The question that separates nuisance from problem: has it changed? A floor that has always flexed slightly is usually fine.
• Missing noggins are the most common fixable cause and the cheapest to put right. Look for them before assuming the joists are undersized.
• If a wall was removed at any point, treat bounce as structural until an engineer says otherwise.

Common mistakes

• Overboarding a bouncy floor — It adds weight to a floor that is already deflecting and does not address the cause. It stiffens the surface slightly and hides the problem.
• Notching joists to run pipes — Notches in the wrong position, particularly near mid-span or on the bottom edge, remove much of a joist's strength. There are permitted zones and depths for a reason.

If it doesn't work

Questions people ask