Why wood moves: furniture that splits or warps

I have heard it on the phone: 'your colleague made me a magnificent table, it split in the first winter'. It is almost never the wood's fault. It is the design, sometimes the drying, often the stove installed one metre away. To understand, you need to know one thing: a piece of solid wood furniture is never finished. It keeps exchanging water with the air of your house, all its life.

Wood is a sponge that breathes

Wood is a material: it settles into balance with the moisture in the air. In a heated house, wood stabilises between 8 and 12% moisture content. In the depths of the heating season, the air dries out and the wood drops towards 7 to 8%; in summer, it climbs back up. With every exchange, it changes dimensions slightly: that is what we call wood 'moving', le bois travaille in French, literally 'the wood works'.

The detail that changes everything: wood does not move the same way in every direction. Along the grain, it barely moves at all. Across the width, a lot. That is why a top expands across its width and never along its length, and it is the first thing a cabinetmaker has in mind when drawing a piece of furniture.

Dimensional change in wood between the very damp and the dry state, by direction of cut. Average orders of magnitude, varying by species.
Direction of the wood	Total shrinkage	In practice
Length (along the grain)	Almost nil (under 0.5%)	A 2 m board keeps its length
Radial (from heart to bark)	3-5%	Moderate change across the width
Tangential (along the growth rings)	6-10%	A 100 cm top can vary by about 1 cm between summer and winter

The gold-underlined words are explained on hover. All definitions are in the joinery glossary.

Heating, the number one enemy of mountain furniture

Here in the valleys of the Hautes-Pyrénées, the problem has a name: the wood-burning stove. We heat hard, for a long time, and the air in the rooms turns very dry from November to March. A solid top standing one metre from the stove also suffers brutal drying on one face only: the exposed face shrinks faster than the other, and the top or splits. The wood is not to blame: no species can take that indefinitely. The remedy is simple: never put a solid wood piece right up against a direct heat source, and accept that the wood lives a little with the seasons.

How I plan for it in the workshop

My whole trade consists of letting the wood move without it breaking. In practice:

Dry wood, at the right level. I work with wood dried to around 10% moisture content, close to the balance it will reach in your home. A piece made with wood at 16% is doomed from the start.
Grain direction thought through. On a top, I alternate the orientation of the growth rings from one board to the next so the deformations cancel each other out instead of adding up.
Joints that let it live. A table top is never screwed down rigid: the fixings run through slotted holes that let it slide across its width. Door panels float in their frames, without glue, as on antique furniture that has crossed two centuries.
Acclimatising on site. For a wood floor or a large top, the wood spends time in the room before fitting, to finish settling into balance.

On this last point, I am unbending: laying a solid wood floor on delivery day, I refuse to do it. The boards must spend one to two weeks in the room, heating on, before I nail or glue them. It stretches the job, it forces me to come back, but it is the difference between a floor that stays flat and a floor that opens 3 mm gaps in the first winter. On the renovation of a floor and its joist structure, that is exactly what we did: the wood lived in the house before being fixed to it.

If you are choosing the species for a future piece, also read which wood species for a piece of furniture: some species move far more than others. And for a project, see my bespoke furniture and wood floor renovation pages.

Three questions that come up often

My furniture creaks at night, is it serious?

No, it is even a good sign: the wood is relaxing as it follows the room's variations in temperature and humidity. The creaks are more frequent at the start of the heating season, when the air dries out fast. If a creak comes with a crack opening up or a joint working loose, then call me.

Is a crack in a solid wood top a defect?

Not necessarily, but it is never a foregone conclusion. A hairline crack at the end of a top during a very dry winter can happen. A clean split running right through, on the other hand, almost always signals badly dried wood or a joint that stops the wood from moving. On my furniture, that case is covered: I come and see, and I repair.

Do you need a humidifier to protect wooden furniture?

In most houses, no. If you heat hard with wood and the air stays below 35% humidity for long spells, a small humidifier near precious furniture can help, and your airways will thank you too. The most effective measure is still keeping solid wood furniture away from direct heat sources.

Why wood moves, and how the artisan plans for it