What is under a timber floor
Worth having the vocabulary, because it makes quotes readable.
- Stumps. The posts carrying everything, set into the ground.
- Ant caps. Galvanised plates on the stump heads that make termite workings visible.
- Bearers. The heavy timbers running across the tops of the stumps, spanning between them.
- Joists. Lighter timbers running across the bearers, at right angles, at close spacing.
- Flooring. Boards or sheet fixed to the joists.
- Vents. Openings around the perimeter that let air move through the space.
Each of those can fail independently, and the symptom you feel upstairs does not tell you which one it is. A bouncy floor is usually joists. A sloping floor is usually stumps. A soft patch near a wet area is usually localised rot in the flooring and the joists under it.
The repairs that come up most
Bearer replacement or sistering
Bearers fail at the ends where they bear on stumps, and in the middle where a span is too long or the timber has been weakened. Where the damage is partial, a new bearer can be bolted alongside the old one, which is called sistering. Where it is extensive, the bearer is replaced outright, which means supporting the joists above while it comes out.
Joist replacement
Joists rot near wet areas and get eaten near entry points. They are lighter and shorter than bearers so replacement is more straightforward, but access is the constraint. Replacing a joist under a bathroom usually means lifting flooring above.
Ant cap replacement
Cheap, quick while the house is already up, and disproportionately valuable. A missing or corroded ant cap removes the early warning that termite workings would otherwise have to reveal.
Packing and refixing
Timber packers crush and rot. Fixings corrode. Re packing and re fixing bearers to stump heads is routine work during any restump and it is part of what brings a floor back true.
Ventilation
Blocked, painted over, built over or simply insufficient vents leave the subfloor permanently damp. This is the cause behind a lot of what looks like unrelated timber failure, and it is among the cheapest things to put right.
Why this shows up as a variation
Here is the honest version of a common frustration. A restump gets quoted from an inspection where the contractor can see the stumps and can see the underside of the bearers. What they generally cannot see is the top face of a bearer where it meets the joists, the inside of a member, or anything behind flooring above.
Damage in those places becomes visible when the old stumps come out and the frame is opened up. So it arrives as a variation, mid job, when you have already committed.
You cannot eliminate that entirely, but you can manage it.
- Ask for a provisional sum or an allowance for bearer and joist repair rather than a bare exclusion
- Get the rate agreed in advance, per metre or per member, so the price is not negotiated under pressure
- Ask to be shown the damage before it is priced, with photographs if you cannot get under there
- Where a building and pest report exists, give it to the contractor before they quote
A contractor who says plainly that there may be hidden damage and here is how it will be priced is being straight with you. One who quotes a suspiciously clean fixed price and then finds a lot of extras is a different proposition.
Ventilation, in a bit more detail
Subfloor ventilation does one job: it keeps air moving so moisture that gets under the house can leave again. When it stops working, the ground stays damp, humidity in the space stays high, and every piece of timber down there is in a worse environment than it was designed for.
The usual causes on the Gold Coast are straightforward. Garden beds and mulch raised over the vents. Concrete paths, driveways and paving poured up against the house at a level above the vent line. Decks and enclosed areas built onto the side of a house without maintaining airflow. Vents painted over. Stored material stacked against the perimeter inside.
Clearing them is cheap. In some cases additional vents can be added, and in persistently damp subfloors mechanical ventilation is sometimes used. Whether that is warranted is a judgement based on how wet the space actually is, so measure before spending.
What to ask for in a subfloor inspection
- Every stump probed, not a sample
- Bearers and joists checked for rot, splitting and termite damage, including at bearing points
- Ant caps checked and their condition reported
- Floor levels taken through the house
- Ventilation assessed, including what is happening at ground level outside
- Ground conditions noted, including standing water, damp patches and where stormwater discharges
- Photographs, so you can see it without crawling under there yourself