Why floors bounce on stumped homes
A timber floor feels solid because every joist passes its load to a bearer within a metre or so, and every bearer passes it to a stump. Bounce means that somewhere in the chain, load isn't being carried. Three causes cover nearly all of it. First, a stump no longer bearing — it has sunk a few millimetres, or its top has rotted to mush, so the bearer above it floats free and spans twice the distance it was built for. The stump can look perfectly upright from the side and be doing nothing at all. Second, a rotted or termite-eaten bearer or joist: the supports are fine but the timber between them has lost its stiffness. Third, undersized spans — common in old lean-to additions, sleep-outs and enclosed verandahs, where the original builder stretched the timber further than it should go. That last one has bounced since day one and isn't getting worse; the first two are progressive.
Rot or structural?
The feel underfoot is a genuine clue. A springy, diving-board flex across a broad area — the whole room gives slightly and returns — usually means a bearer spanning further than designed, which points at a stump not carrying. A soft, mushy patch the size of a dinner plate or a doormat, often near a shower or an external door, is more likely rot in the flooring or a joist right there: the timber itself is failing, not the support under it. The distinction matters because the fixes are different trades. Localised rot is a carpentry repair; a stump out of action is a restumping job, and if several have gone in one zone, a partial restump of 8–20 stumps is the usual remedy.
The wet-area pattern
Bounce clusters around water, and it's worth taking the pattern seriously. Bathrooms, laundries and kitchens leak slowly for years; showers are the classic offender. The moisture rots timber stumps from the top down, rots bearer ends, and softens the soil so even sound stumps sink. Outside, a leaking downpipe or a garden bed watered against the wall does the same to perimeter stumps. If your soft spot sits within a couple of metres of a wet area or a downpipe, you've probably found both the symptom and the cause — and the cause needs fixing first, or the new stumps inherit the same wet ground (why houses sink covers the soil story).
How to investigate
If there's crawl access, a torch and ten careful minutes tell you most of it. Look for daylight or a visible gap between a stump top and the bearer above it, stumps leaning off vertical, and timber stumps crumbling at ground level. Then probe: push a screwdriver into stump tops, bearer ends and the underside of the soft spot. Sound timber resists; rot takes the blade with almost no pressure. Photograph anything suspect with something for scale. If clearance is too tight or you're unsure about wiring under there, don't force it — this is exactly what a pre-quote inspection covers, and the self-check guide lists what a contractor will look for.
One soft patch near a shower is a repair. Bounce across a room, or in more than one room, is a support problem — get the subfloor looked at before patching the floor above it.
Slope vs bounce, and next steps
Keep the two findings separate, because they say different things. Slope means something under the floor went down; bounce means something under the floor isn't carrying. A stump can rot at the top and leave the floor level but springy — no slope at all. Both together in the same zone make the stump diagnosis close to certain. Either way, the sensible sequence is: fix any water source, map the affected area, then get the subfloor inspected. If stumps are the answer, the cost guide sets fair expectations — localised jobs commonly land between $4,000 and $12,000 — before any quotes arrive.
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Common questions
Can a contractor just add a stump under the bouncy spot?
Sometimes, and for a genuinely undersized span in an old addition it's a legitimate fix. But if the existing stumps are rotting, adding one new stump among failing ones buys a year or two, not a solution. Ask the contractor to state the condition of the surrounding stumps in writing — that tells you whether you're repairing or postponing. Partial restumping covers where the line sits.
Is a bouncy floor dangerous?
Rarely in the short term — timber floors fail gradually and noisily, not suddenly. The real risks are a foot going through a badly rotted patch, and the slow structural cost of bearers working loose while nothing carries them. It's a fix-this-year problem, not a leave-the-house-tonight one.
Could it just be the floorboards, not the structure?
Yes. Old baltic pine boards flex between joists, and a floating floor laid over an uneven subfloor can feel spongy on its underlay. The test is area: board-level flex is narrow, between one joist and the next. If a whole section of room moves together, the problem is below the boards.