The glasses in the china cabinet are how most people find out.
Someone walks past it and the stemware rings. Or the washing machine hits spin and you can feel it through your feet two rooms away. Or there's one spot in the hallway, always the same spot, where the floor gives a bit more than the rest and everyone in the house has quietly started walking around it without ever discussing it.
A place at Corrimal, timber floor, 1950s, and the owner had convinced himself it was the washing machine. New machine, same bounce. He'd been living with it for six years and had built a whole theory about the concrete slab in the laundry. There was no slab. There were two bearer ends sitting in wet dirt where a brick pier had sunk about 40mm sometime during his ownership.
Bounce and drop are not the same problem
Worth separating these before anything else, because people use them interchangeably and they point at completely different faults.
A floor that bounces is a stiffness problem. The floor is still being held up, it's just flexing more than it should between supports. That's usually joists that are too small for the span, or spaced too far apart, or a span that got longer at some point because someone took out a wall that was quietly doing more than they realised. It feels springy everywhere in the room, fairly evenly, and it's often been like that since the house was built.
A floor that has dropped is a support problem. Something underneath has failed — a pier has sunk, a stump has rotted at the base, a bearer end has gone soft where it sits. That one is local. There's a low spot, and it gets worse over years rather than being there from day one. Put a marble down and it'll tell you.
The reason it matters is that bounce is a design fix and drop is a repair, and they cost different money and take different amounts of time. Roll a marble across the room and stand a spirit level on the floor in a few spots before you ring anybody. Five minutes, and you'll know which conversation you're having.
Get under there, or get someone to
Everything above is guessing until somebody looks underneath. On most older houses around here you can, because they're up on piers or stumps with a crawl space.
Take a torch that actually works, wear something you don't care about, and go in on a dry week rather than after rain so you're seeing the normal state of things and not a one-off. What you're looking at is the top of the piers where the bearers land, the base of any timber posts, and the joists over the wet rooms.
The screwdriver is the whole test. Push it into the bottom of every post and into the end of every bearer where it sits on a pier. Sound timber stops the tip dead. Punky timber takes it and keeps going, and if it goes in to the handle you've found your low spot. Same test I use on decks and stair stringers, and it's in the deck repair signs post too, because it's the only field test that's worth anything.
While you're down there, have a look at the vents. It's the detail that catches modern owners out on old houses. Subfloor vents in the brickwork want air moving through them, and over fifty years people bank garden beds up against the wall, pour a path hard against the house, build a deck over the side, or lay pavers that end up above the vent line. Choke the airflow and the ground under the floor never dries out. Then the bearer ends go, and everyone blames the timber.
The three things that actually cause it
Rot is the common one, and it's nearly always a moisture path rather than bad timber. A leaking shower waste that's been dripping onto a joist for a decade. A downpipe discharging next to the wall instead of into a line. Blocked vents. It shows up first where timber meets something damp and can't dry, so bearer ends on piers, the base of posts, and the joists directly under a bathroom or laundry.
Termites are the one people are frightened of, and reasonably. Timber framing is cheap and it works, but it's subject to termite attack when the protection isn't up to it, and the Illawarra has plenty of them. What you find underneath is mud leads running up the face of a pier, or a joist that looks completely fine and is hollow when you tap it because they've eaten it from the inside and left the paint. If you see mud tubes, stop. Don't knock them off, don't spray them, don't poke around. Ring a licensed pest inspector first and a carpenter second, in that order, because disturbing the workings scatters them into somewhere else in the house.
The third one is the least dramatic and the most common in houses that have "always been a bit bouncy". The floor was never stiff enough. Joists at 450 centres that should have been closer, or undersized for a 3.6 metre span, or somebody notched half the depth out of a joist to run a waste pipe forty years ago and nobody ever looked. You see the notching one under bathrooms constantly. A joist with a big notch out of the bottom edge in the middle of its span has lost most of what makes it a joist.
What the fix looks like
Depends entirely which of the three you've got, which is the point of doing the diagnosis first.
A dropped bearer end is generally a jack, a new pier or a repacked one, and the rotten section of bearer cut out and spliced. That's a day or so on a good crawl space, and it's a genuinely satisfying repair because the floor above comes back to level while you're standing there.
A bouncy span is a different job. You're either adding joists between the existing ones, doubling up what's there, or putting in a new bearer and a line of piers mid-span to halve the span. That last one is usually the cheapest way to fix a springy floor properly. Treated pine bearers and joists run somewhere around $60 to $110 a square metre in materials on a standard job, which is the figure I use in the hardwood versus treated pine post, and materials are the small half of it under a house.
Because access is what actually sets the price. A metre of crawl height and a hatch you can get a length of timber through is one job. Six hundred millimetres of clearance, a hatch inside a linen cupboard, and every stick of timber cut outside and passed in is the same repair at double the labour. Nobody enjoys quoting that and nobody enjoys doing it, which is reflected in the number.
And if the bounce turns out to be because a wall came out at some point, you're in structural territory rather than floor repair. That's the same conversation as taking out a load-bearing wall — engineer first, then the carpentry.
Two things not to do
Don't pack a sunken pier with bricks, timber offcuts or bits of paver. I find this constantly and I understand the logic, but a dry-packed stack under a bearer moves again the first wet season and it hides the fact that the pier itself has failed. It's a fix that lasts exactly long enough to be somebody else's problem.
Don't bolt a new joist onto the side of a rotted one and call it done. If the old one has gone, the reason it went is still there. Sister a good joist onto a wet one and in five years you own two rotten joists.
Who does it
Subfloor work is carpentry — bearers, joists, piers, the connections back into the frame — and it's the kind of repair worth having someone licensed do, because everything above it is relying on the outcome. Carpentry is its own licence category in NSW, and anything over $5,000 all up wants a written contract as well. Smaller stuff, one soft board or a pier that needs repacking properly, sits under property maintenance with the rest of the running list. Termites are a pest inspector's job before they're mine.
The Corrimal floor took a day and a half in the end. Two new piers, about two metres of bearer spliced out, and a garden bed cut back off the wall so the vents could breathe again. He kept the new washing machine.
If your floor moves when someone walks past it, get a torch and a screwdriver under there before you spend money on anything else. Or ring Dave on 0414 007 351 and tell me which room and whether it bounces or dips, and I'll tell you what I expect to find.
Want a hand with this at your place? Get a free quote or call 0414 007 351.
