What is moisture content?
Moisture content (MC) is the amount of water in timber, expressed as a percentage of the timber's oven-dry weight. A board at 10% MC contains water equal to 10% of the weight of the dry wood in it.
Timber is hygroscopic: it constantly exchanges moisture with the surrounding air. When the air is humid, timber takes up moisture and swells; when the air is dry, it releases moisture and shrinks. Most of that movement happens across the width of a board rather than along its length.
MC vs EMC
MC is what the timber is now; equilibrium moisture content (EMC) is what it will settle at in a given environment. The goal of drying, storage and acclimatisation is to get MC close to the in-service EMC before the floor is laid.
| Term | Meaning | Example |
|---|---|---|
| MC | Measured water content of the board | Meter reads 11% |
| EMC | Level the timber settles at in given temperature and humidity | ~11% at 25°C and 60% RH (ATFA) |
| In-service EMC | The EMC range in the finished, occupied building | ~8–14% in typical Australian interiors (WoodSolutions) |
Key numbers for Australia and New Zealand
Australian-made boards average about 10–12% MC at supply, interiors sit at about 8–14% EMC, and timber should be installed within about ±2% of its in-service EMC.
| Figure | Value | Source |
|---|---|---|
| Average MC of Australian-made floorboards | ~10–12% | ATFA specification |
| EMC at 25°C / 60% RH | ~11% | ATFA |
| EMC at 80% RH | ~16% | ATFA |
| Typical Australian interior EMC | ~8–14% | WoodSolutions |
| Installation tolerance | within ±2% of in-service EMC | WoodSolutions |
| NZ slab benchmark (solid strip flooring) | ≤75% RH at slab surface | BRANZ BU644 |
Specifiers can also refer to NATSPEC's technical note on moisture content in timber floors (NATSPEC DES 002).
Imported timber passes through very different climates during shipping and storage, so its MC on arrival can differ from what it left the mill at. Timbo does not publish a dispatch MC figure on this website – measure the timber on arrival.
How to measure timber moisture content
Use a calibrated moisture meter with the correct species setting, take readings from several boards across several boxes, and record them.
- Choose the meter. Pin (resistance) meters read between two pins driven into the wood; pinless (capacitance) meters read through the surface. Both need correct settings for oak.
- Set species and temperature corrections. Readings on oak can differ from a default setting; use the meter's oak setting or correction table.
- Sample widely. Take readings from a selection of blocks from different boxes – not just the top box.
- Read away from ends. Board ends dry and wet faster than the middle.
- Measure the site. Record indoor temperature and relative humidity over several days to estimate in-service EMC.
- Compare and decide. If boards are within about ±2% of the target, proceed; if not, keep acclimatising or investigate why.
- Record everything – readings, locations, meter, settings and date – in the job file.
For the process of getting timber to target, see acclimatising oak flooring.
Slab moisture is a separate test
Concrete slab moisture is not measured with a timber meter; it's tested with the method and against the limit the adhesive or moisture-barrier manufacturer specifies. In New Zealand, BRANZ uses ≤75% relative humidity at the slab surface as the benchmark for solid timber flooring. In Australia, the adhesive maker's limits govern (Bowens). See installing parquet over a concrete slab, the NZ slab guide and adhesives and moisture barriers.
What goes wrong when moisture is out
Too wet at installation means shrinkage and gaps later; too dry means swelling, cupping, peaking or lifting.
| Symptom | Likely cause | First step |
|---|---|---|
| Gaps between blocks or boards | Laid too wet, or very dry indoor air (heating) | Check indoor RH; compare with MC at install |
| Cupping (edges high) | Moisture from below – damp slab, leak, poor ventilation | Find the moisture source |
| Crowning (centre high) | Often from sanding a cupped floor too early | Let the floor stabilise first |
| Peaking or lifting | Swelling with no room to expand | Check expansion allowance and moisture source |
| Hollow-sounding blocks | Bond failure – often slab moisture or poor preparation | Investigate adhesive and slab |
Seasonal movement is normal. Solid oak floors open slightly in dry months and close up in humid months. Good acclimatisation and correct expansion gaps keep that movement within acceptable limits.
Moisture through the life of the floor
Moisture management doesn't stop at installation – the floor responds to its environment every season.
| Stage | Moisture risk | Good practice |
|---|---|---|
| Delivery and storage | Damp site, open boxes, rain during unloading | Deliver to an enclosed, dry site; store off the slab |
| Installation | Damp slab, wet trades, timber outside ±2% | Test, record, acclimatise |
| First year | Floor settling through its first seasons | Keep indoor conditions steady; expect minor seasonal movement |
| Everyday life | Spills, wet mopping, leaks, pot plants | Wipe spills quickly; fix leaks; use the finish maker's cleaner |
| Long absences | Closed-up house swings in humidity | Ventilate or condition the home where practical |
For installers, a short moisture record – slab readings, board readings, indoor RH and the products used – is the best evidence if a question arises later.
Practical tips for homeowners
- Keep indoor humidity steady. Avoid running humidifiers or dehumidifiers to extremes.
- Watch the first year. New floors settle through their first full set of seasons.
- Fix leaks fast. Water from a dishwasher, fridge line or pot plant can damage a floor quickly.
- Ask your installer for the moisture readings they took – they're part of a good job record.
Sources
- ATFA – Specification for solid timber flooring
- ATFA (floorchoices.com.au) – Acclimatisation of timber flooring
- WoodSolutions – Moisture guide
- NATSPEC TECHnote DES 002 – Moisture content in timber floors
- BRANZ BU644 – Solid timber strip flooring on a concrete slab
- Bowens – Hardwood timber flooring
Frequently asked questions
What moisture content should timber flooring be when installed?
Within about ±2% of the equilibrium moisture content it will reach in service. In Australia that in-service EMC is typically somewhere between about 8% and 14%, depending on location, season and heating or cooling.
Are pin and pinless moisture meters accurate on oak?
Both can be reliable when used correctly. Pin meters need the right species setting and temperature correction; pinless meters need the right density setting and a flat, clean surface. Check several boards and compare with a calibrated reference where possible.
Can I use a timber moisture meter on a concrete slab?
Not for an acceptance test. Timber meters read timber. Slab moisture is tested with the method the adhesive or barrier manufacturer specifies – often relative humidity – and compared with that manufacturer's limit.
What moisture content is imported European oak flooring supplied at?
It varies with the mill's drying, packaging, shipping and storage, so don't assume a figure. Measure a sample of blocks on arrival and compare with the site's expected in-service EMC. For context, the ATFA specification says Australian-made boards average about 10–12% MC.
What causes cupping in timber floorboards?
Cupping – edges higher than the centre – usually means the underside of the boards is wetter than the top, often from a damp slab, a leak or poor sub-floor ventilation. Find and fix the moisture source before considering any sanding.
Does a finished floor stop moisture movement?
No. Finishes slow moisture exchange but don't stop it. Timber floors keep moving a little with the seasons, which is why acclimatisation and expansion allowances matter.