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Bouncy Or Sinking Floor
The floor gives under your weight, dips in one spot, or makes the furniture and glassware move when you walk past.
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What's happening?
Deflection you can feel is different from a squeak. Something under the covering has lost stiffness — a joist, a deck panel, or the bearing at the end of a joist. On a suspended timber floor the usual causes are a joist notched too deeply for pipes or cables, a joist end sitting on damp or crumbling masonry, or a deck of chipboard that has swollen and lost its strength after a leak. Downstairs on a solid floor, a sinking area is more often a failed screed, a void beneath it, or a subfloor that was never flat enough for the covering laid on it. A localised soft patch that has appeared recently deserves attention rather than a new carpet over the top.
What usually causes it?
- A joist notched or drilled too deeply for pipework or cabling, losing much of its depth
- Chipboard or OSB deck panels swollen and delaminated after a leak or a washing machine overflow
- Rot or insect damage at a joist end where it bears into a damp external wall
- Joists undersized or spaced too widely for the span, common in older conversions and loft rooms
- A missing or failed noggin or strutting run between joists, so the joists roll rather than share the load
- A hollow or debonded screed on a solid ground floor
- A heavy new load — a bath, a kitchen island, a large aquarium — placed on a floor never designed for it
Is it dangerous?
It can be. Visible deflection, a soft spot underfoot, cracking sounds or a floor that has dropped away from the skirting are signs that something structural has lost capacity, and that needs assessing rather than covering. Keep heavy loads off the affected area and stop using the floor for storage until it has been looked at. A floor that is bouncy but sound is annoying; a floor with a rotted joist end is not.
Can I fix it myself?
Investigation only. Lift a small area of covering or a floorboard at the softest point and look at the joist and the deck. Check for damp, staining, crumbling timber and any notch cut deeply into the top of a joist. Look under a suspended ground floor at the airbricks — blocked airbricks are a common reason joist ends stay damp. Do not add screws or packing to hide a dip without knowing why it is there.
When should you call a flooring fitter?
Call a flooring fitter to lift and assess the deck and to replace swollen or delaminated panels. Bring in a builder or a structural engineer where a joist is rotted, split, undersized or has been cut through for services, because that is a structural repair and not a floor covering one. If you can see the floor moving relative to the walls, treat it as urgent.
What will the flooring fitter actually do?
- Lift the covering and the deck at the worst point to expose the joists and their bearings
- Check joists for deep notches, splits, rot at the wall bearing and missing strutting
- Replace swollen or delaminated chipboard and OSB deck panels with correctly supported boards
- Refix and level the deck, packing where joists have dried out of line
- Report structural findings honestly and hand off to a builder or engineer where the joists themselves are the problem
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