A restump gives a house new legs. But the legs hold up a timber skeleton — bearers running along the stump lines and joists crossing them — and in a 60–100-year-old house that skeleton has spent a lifetime with moisture, borers and (especially in Queensland) termites. Replacing failed stumps under failing bearers is half a job. Here's the other half.
How a timber subfloor works
From the ground up: stumps carry bearers — the heavy timbers, traditionally 100×75mm hardwood or larger, spanning stump to stump. Across the bearers sit the joists, typically at 450mm centres, and across the joists the flooring itself. Every load in the house — walls, furniture, the piano, you — travels down through this frame into the stumps. When a bearer sags, rots or gets eaten, the floor above it dips no matter how good the stumps beneath it are; a bouncy or dished floor with sound stumps is almost always a bearer or joist story.
What kills subfloor timber
- Termites. The number-one subfloor killer in Queensland and a constant risk in Victoria. White ants hollow bearers and joists from the inside while the surface looks fine — the screwdriver test (firm pressure into the timber) tells the truth. Rusted or missing ant caps on old stumps are the open door.
- Moisture and rot. Blocked subfloor vents, leaking showers and downpipes discharging against the house keep the subfloor damp; fungal rot takes the bearer ends and the joists over wet ground first. Wet areas — bathrooms, laundries, kitchens — are always the first place we look.
- Borers in older hardwood and any softwood that found its way under there.
- Undersized or over-spanned timber. Plenty of old extensions were built with whatever was on the ute. Sagging between stumps with no decay is a span problem, fixed with a new properly-sized bearer or an extra stump line.
- Butchered timbers: joists notched for plumbing, bearers checked half-through for services — common, and structural.
The F17 standard — what goes back in
Structural timber in Australia is stress-graded, and F17 seasoned hardwood is the benchmark grade for bearers and joists — the grade an engineer's schedule will typically specify for subfloor members in older hardwood-framed homes. F17 supply pricing runs about $20–$50 per lineal metre depending on section size, against $8–$20 for treated pine framing and $15–$40 for engineered LVL. All three have their place — H3/H4 treated pine and LVLs are legitimate where the design allows — but like-for-like hardwood keeps the stiffness and fixings behaviour of the original frame, and termite-resistant species matter north of the border. What we don't do is drop a pine sleeper under a hardwood floor and call it repaired.
What repairs cost
| Job | Typical 2026 range |
|---|---|
| Single bearer replacement | $500–$1,000 |
| Joist repairs / small section of subfloor | $2,500–$4,000 |
| F17 hardwood (supply) | $20–$50 per lineal metre |
| Larger structural subfloor jobs | $3,000–$25,000 by scope |
The single biggest cost saver is timing: do subfloor repairs during restumping. The house is already supported on jacks, the load is already off the bearers, access is open and the crew is on site — replacing a bearer then is a fraction of the cost of mobilising a crew, re-jacking and re-supporting the house for a standalone repair later. It's why our restumping inspections condition-map the bearers and joists as well as the stumps, and why our quotes carry unit prices for timber found rotten once the floor comes up: no surprises, and no second mobilisation.
Signs your subfloor timbers — not your stumps — are the problem
- Floors that bounce or trampoline between firm spots (dead spans between sound supports).
- A dished dip mid-room rather than a slope to one side (slope = stumps; dish = joists/bearers).
- Sagging specifically near wet areas, or a springy hallway outside the bathroom.
- Mud leads (termite tunnels) up stumps or piers, or timber that sounds papery when tapped.
- Gaps opening between floorboards over one bearer line.
Repairs, done in the right order
- Inspect and map: every bearer and joist checked and condition-mapped along with the stumps — with photos you'll see.
- Fix the water first: vents cleared, drainage and leaks sorted, because new timber in a wet subfloor is a countdown, not a repair.
- Support and remove: load lifted on jacks, failed members cut out. Termite-damaged timber comes out — not "treated and left".
- Replace to spec: new F17 hardwood (or engineered equivalent per the design) fitted, packed and fixed; new ant caps on every stump.
- Level and certify: floor re-levelled, and the work certified under the same permit/approval as the restump.
Structural subfloor replacement is building work — in Victoria it rides under the restumping building permit and engineering, and in Queensland under the certifier approval with a QBCC-licensed contractor. One approval, one crew, one visit: the whole reason to do it while the house is already up.