Subfloors, stumps and restumping: what to check under the floor
Houses with raised timber floors sit on stumps or piers, and the subfloor beneath is where decay, termites and movement usually start. Signs of trouble include uneven or sloping floors, springy or bouncy areas, doors that stick or swing, cracked plaster and gaps under skirting. Check the subfloor for clearance, ventilation, damp, decayed or leaning stumps and termite mud tubes; current housing provisions require at least 150 mm of ground clearance, and 400 mm where termite inspection is required. Restumping, also called reblocking, replaces failed stumps; in Victoria it needs a building permit and a registered builder.
- 01SupportStumps carry bearers, bearers carry joists, joists carry the floor
- 02AirCross-ventilation lets ground moisture escape
- 03Clearance150 mm minimum, 400 mm where termite inspection is needed
A floor that slopes is telling you something about what holds it up.
How a raised floor works
In a raised timber floor, stumps or piers carry timber bearers, the bearers carry joists, and the joists carry the floorboards. Older homes often stand on timber stumps, many of red gum; later homes use concrete, brick piers or adjustable steel stumps. The subfloor space below needs air moving through it and enough clearance for someone to inspect it, because that is where moisture, decay and termites do their damage unseen.
| Type | Where you find it | What to watch for |
|---|---|---|
| Timber stumps | Much pre-war and early post-war housing | Decay at and below ground level, termite attack, settlement |
| Concrete stumps | Common from the post-war decades and in restumping | Cracking, spalling, and timber packers between stump and bearer that decay |
| Brick or masonry piers | Many older and mid-century homes | Cracked or leaning piers, loose mortar, missing ant caps |
| Adjustable steel stumps | Newer homes and restumping | Corrosion in damp subfloors and coastal areas, and loose adjustment fittings |
Signs the stumps or subfloor need attention
| Symptom | What it can mean | Check next |
|---|---|---|
| Sloping or uneven floors | Settled, decayed or sunken stumps, or ground movement | Floor levels across rooms, and stump condition below the low area |
| Springy or bouncy floor areas | Decayed joists or bearers, missing supports or overspanning | Framing condition and support spacing below |
| Doors sticking, swinging open or out of square | Frame movement from stump or footing movement | Whether it is seasonal, and floor levels at the door |
| Cracked plaster, especially diagonal cracks from door corners | Movement in the frame | The pattern, read with the cracks guide |
| Gaps between skirting and floor | The floor dropping away from the walls | Stumps and bearers along that wall |
| Musty smell or damp underfloor | Poor ventilation, drainage or leaking plumbing | Vents, drainage and pipes; see the damp guide |
Clearance and ventilation: the numbers
The ABCB Housing Provisions set minimum ground clearances under suspended floors: at least 150 mm where termite inspection is not required, and at least 400 mm where a termite management system needs to be inspected. On sloping sites, the 400 mm may reduce to 150 mm within 2 metres of the external walls. The same provisions require cross-ventilation through openings in the walls, because ground moisture in a still subfloor encourages rot, fungus and termites.
Older homes were not always built to these clearances, and later work often reduces them: soil and paving built up against walls, garden beds, blocked vents, or storage pushed into the subfloor. Restoring clearance and airflow is often the cheapest improvement available.
| Check | Good sign | Concern |
|---|---|---|
| Clearance | Room to inspect; ground well below bearers | Ground or debris close to timbers |
| Ventilation | Clear vents on opposite sides; air moving | Blocked, painted-over or missing vents; still, humid air |
| Ground moisture | Dry soil | Damp soil, ponding, or water entering after rain |
| Stumps and piers | Plumb, sound, bearing evenly | Leaning, decayed, cracked or packed stumps; gaps to the bearer |
| Termites | No mud tubes; ant caps intact | Mud tubes on stumps or walls; damaged or bypassed ant caps |
| Plumbing and services | Dry pipes and connections | Leaks, wet patches below wet areas, sagging pipes; see the plumbing guide |
Do not disturb termite mud tubes; leave them for a licensed timber pest inspector. CSIRO's building technology resource on managing termites explains why visible, inspectable subfloors matter.
Restumping and reblocking
Restumping (often called reblocking) replaces failed stumps and re-levels the floor. It can be partial, replacing only failed stumps, or full. In Victoria, councils and the VBA list reblocking or restumping as work that needs a building permit, and it must be carried out by a registered builder; Macedon Ranges Shire's permit guideline also notes that domestic building insurance is required for registered builders where the work is over $16,000. Requirements differ elsewhere, so check with your state regulator or council.
Two things are worth knowing before you start. First, re-levelling a floor that has settled over decades can crack plaster, jam doors or open gaps that need making good, so budget for it. Second, "restumped" on a listing can mean anything from a few stumps to the whole house. Ask for the permit, the builder, the date and a plan showing which stumps were replaced.
Common misreads
| What people say | What is closer to right |
|---|---|
| "It has been restumped" | Ask how many stumps, where, when, with what material, and under which permit. |
| "The floor is level now, so the problem is fixed" | Levelling treats the symptom. Drainage, plumbing leaks and termites can keep causing movement. |
| "Concrete stumps cannot fail" | They can crack or settle, and the timber packers and bearers above them can still decay. |
| "Sealing the vents keeps the house warmer" | It also traps moisture under the floor. Insulate the floor instead of blocking the vents. |
Worked example: restumped, but the back room still slopes
Illustrative reasoning example, not an inspected property. A 1930s weatherboard was advertised as restumped. The front rooms are level, but the rear room slopes and its door sticks. The vendor provides an invoice for "restumping".
The invoice lists 24 stumps at the front of the house. The rear room is a later addition on its own stumps, with a downpipe discharging against the wall beside it. The next steps are a subfloor inspection of the addition, a check of the drainage, and a quote for that area alone. The front restumping is real evidence for the front of the house, not for the whole of it. See the interwar homes guide for the wider pattern.
Frequently asked questions
How do I know if my house needs restumping?
Common signs are sloping or uneven floors, springy areas, doors that stick or swing, diagonal cracks in plaster from door corners and gaps under skirting. A subfloor inspection showing decayed, leaning or sunken stumps confirms it.
What is the minimum subfloor clearance in Australia?
Current ABCB Housing Provisions require at least 150 mm ground clearance under suspended floors where termite inspection is not required, and at least 400 mm where a termite management system needs to be inspected. On sloping sites, 400 mm may reduce to 150 mm within 2 metres of external walls.
Do I need a permit to restump a house in Victoria?
Yes. Victorian councils and the VBA list restumping or reblocking as building work requiring a building permit, carried out by a registered builder. Domestic building insurance is also required for registered builders where the work is over $16,000.
What is the difference between restumping and reblocking?
They usually mean the same thing: replacing failed stumps and re-levelling the floor. Restumping is common in some states and reblocking in others.
Can restumping cause cracks?
Yes. Re-levelling a floor that has settled over many years can crack plaster, jam doors or open gaps, so allow for making good afterwards.
Should I block the subfloor vents to keep the house warm?
No. Vents let ground moisture escape; blocking them encourages rot, fungus and termites. Insulating the floor is the better way to improve comfort.
What do termite mud tubes look like under a house?
Pencil-width earthen tubes running up stumps, piers or walls. Do not break them open; arrange a licensed timber pest inspection.
How this guide was researched
We work from above-floor symptoms to subfloor evidence, set out current clearance and ventilation requirements, and separate partial from full restumping scope, with a fictional example.
Limits: Older homes may predate current clearance requirements. Permit and licensing rules vary by state; confirm with your regulator or council.
Sources
- Housing Provisions Part 6.2: Subfloor ventilationAustralian Building Codes Board · accessed
- Restumping or re-blocking a building: permit application guidelineMacedon Ranges Shire Council · accessed
- Do I need a building permit?Maroondah City Council · accessed
- Building Technology Resources (foundation maintenance, condensation, managing termites, asbestos)CSIRO · accessed
- Protect against termitesQueensland Building and Construction Commission · accessed