The short answer
Solid parquet needs an expansion gap around its perimeter and at every fixed object, because timber swells as it takes up moisture – even when it's fully glued to the slab. The size of the gap depends on the floor's width, the climate, the timber's moisture at installation and the adhesive and installation guidance for the job. The gap is hidden by skirting, scotia or trims.
Why solid parquet moves
Timber is hygroscopic: it gains moisture and swells in humid conditions, and loses moisture and shrinks in dry conditions, mostly across the grain. Typical Australian interiors cycle through about 8–14% equilibrium moisture content depending on climate and season (WoodSolutions), and ATFA gives about 11% EMC at 60% RH rising to about 16% at 80% RH (ATFA).
In a parquet floor, blocks run in two directions, so the floor moves in both directions across the room. The adhesive restrains each block, but the combined movement of hundreds of blocks still needs somewhere to go. Without room at the edges, swelling pushes the floor against the walls and it can peak (rise along joints) or lift.
Where to leave expansion gaps
Leave gaps wherever the floor meets something fixed.
| Location | Notes |
|---|---|
| All perimeter walls | Covered by skirting or scotia |
| Door frames and architraves | Undercut the architrave so the floor slides under it |
| Thresholds and doorways | Use a trim or expansion strip where floors change or rooms are large |
| Columns, pipes and penetrations | Use a rosette, collar or flexible sealant |
| Kitchen islands and fixed joinery | Lay before joinery where possible, or leave a gap under kickboards |
| Stairs and steps | Detail with nosings that allow movement |
| Other floor finishes (tiles, stone) | Trim or flexible joint |
What sets the size of the gap?
Gap size is set by how far the floor can move: wider floors, more humid climates and drier timber at installation all need more allowance. That's why the adhesive and installation guidance, not a rule of thumb, decides the figure on each job.
| Factor | Needs a larger allowance when… |
|---|---|
| Floor width | The floor is wide or runs continuously through several rooms |
| Climate | The site is humid, coastal or has big seasonal swings |
| Moisture at installation | Timber was installed toward the dry end of its expected range |
| Heating and cooling | Conditions swing between heated, dry winters and humid summers |
| Adhesive system | The adhesive maker specifies it |
| Pattern | Two-direction patterns spread movement differently from straight boards |
The single best way to keep movement small is to install at the right moisture content – within about ±2% of the expected in-service EMC. See acclimatising oak flooring and moisture content in timber flooring.
How to leave and hide the gap
Set the gap when cutting in the edge blocks, keep it clear of adhesive and debris, and cover it with skirting or a trim that isn't fixed into the floor.
- Plan at setout. Allow for the gap when balancing the pattern – see herringbone layout and waste.
- Use spacers at walls while laying edge blocks; remove them once the adhesive has set.
- Keep the gap clean. Adhesive, plaster or debris in the gap stops the floor moving.
- Undercut door architraves so the floor runs beneath them.
- Fix skirting to the wall, not the floor. It should cover the gap without pinning the timber.
- Use flexible sealant only where needed and allowed – for example at a visible tile junction.
- Record the gap used in the job file.
Signs a floor is too tight
Peaking, lifting, blocks rising near walls or doors that start to bind usually mean the floor has no room to expand – or has taken up a lot of moisture.
| Symptom | Likely cause | Action |
|---|---|---|
| Peaking along joints | Swelling with no perimeter allowance | Check gap, check moisture source |
| Edge blocks lifting | Floor pushing against wall | Relieve the perimeter; investigate moisture |
| Doors catching the floor | Swelling | Check indoor humidity and moisture sources |
| Hollow blocks | Bond failure, sometimes from movement stress | Investigate slab moisture and adhesive |
Don't sand a peaked or cupped floor flat until the moisture problem is fixed and the floor has stabilised – otherwise it will crown when it dries.
Questions to ask your installer
- What expansion allowance will you leave, and whose guidance sets it?
- How will the gap be covered – new skirting, existing skirting, scotia or trims?
- Will architraves be undercut so the floor runs under them?
- Where will thresholds or movement joints go in a floor that runs through several rooms?
- How will the floor meet tiles, stone or carpet at junctions?
- What moisture readings did you take before laying?
Clear answers to these questions are a good sign the installer has planned for movement rather than leaving it to chance.
Gaps at installation vs gaps in winter
The expansion gap at the walls is different from the small seasonal gaps between blocks that can appear in dry months. Seasonal gaps are normal timber behaviour and usually close again in humid weather. Both are reduced by good acclimatisation and stable indoor humidity.
Glued parquet over slabs
For full slab preparation, adhesive and barrier guidance, see installing parquet over a concrete slab – commonly flat within about 3mm under a 3m straightedge, with the adhesive manufacturer's limits governing (Bowens). Homeowners can ask a Timbo partner how expansion will be detailed in their home.
Sources
- WoodSolutions – Moisture guide
- ATFA (floorchoices.com.au) – Acclimatisation of timber flooring
- Bowens – Hardwood timber flooring
Frequently asked questions
Does glued-down parquet need an expansion gap?
Yes. The adhesive restrains movement but doesn't stop timber swelling as it takes up moisture. A perimeter gap gives the floor somewhere to go so it doesn't push against walls and lift.
How big should the expansion gap be for solid parquet?
There isn't one figure for every job. The size depends on the width of the floor, the local climate, the timber's moisture at installation and what the adhesive maker and installation guidance specify. Wider rooms and humid climates need more allowance.
Can skirting boards be fitted tight to the floor?
Skirting should sit on or just above the floor without pinning it, and must not be fixed into the flooring. Its job is to cover the gap while letting the floor move beneath.
What fills an expansion gap?
Usually nothing – it's left open under the skirting or trim. Where a gap is visible, for example at a doorframe or kitchen kickboard, a flexible sealant or compressible filler can be used if the installation guidance allows.
Do large parquet floors need intermediate expansion joints?
Large or long floors, and floors running through doorways between rooms, may need intermediate movement joints or thresholds. The adhesive manufacturer and installation guidance set when they're required.