Wood Has a Season: Why Your Fitted Furniture Changes Shape Through the Year

We get two kinds of phone call about the same wardrobe. The first lands in late July, usually after a muggy fortnight: a door that shut sweetly in April now catches on the frame, and the owner is convinced something has dropped. The second arrives around February, when the heating has been running flat out for months and a fine dark line has appeared along a joint that was tight as a drum in autumn. Same cupboard. Same joiner. Same timber. Nothing has failed in either case.

What has happened is that the wood has done what wood does, and done it in a house with a British climate attached.

What's actually going on inside the board

Timber is hygroscopic, which is a fancy way of saying it drinks. Not liquid water — moisture vapour from the air around it. The amount it holds at any given moment settles into an equilibrium with the relative humidity of the room, and that equilibrium shifts constantly.

A typical UK home runs somewhere between 30% and 50% relative humidity in winter with the heating on, and can push well past 70% in a damp July. Outdoors it swings wider still. Each of those swings pulls moisture into the cells of the timber or lets it out, and the cells swell or shrink accordingly.

Here's the bit that surprises people: the movement is almost entirely across the grain, not along it. A two-metre length of oak will barely change at all from end to end. A 300mm wide panel of the same oak can move several millimetres across its width between one season and the next. That's not a defect. That's the material being honest with you.

Why some pieces move more than others

Two boards from the same tree, cut differently, will behave differently. Timber cut straight through the log — quarter-sawn — moves roughly half as much in width as timber cut through the middle — flat-sawn. Flat-sawn gives you the cathedral grain most people picture when they think of oak or ash, and it also gives you more movement. Neither is wrong; they're just a trade-off, and a joiner should be able to tell you which one you're looking at and why they've chosen it.

Species matters too. Oak and ash are lively. Poplar, tulipwood and most softwoods are calmer. Sapele sits somewhere in the middle. A pine blanket box in a spare room will behave quite differently from an oak dresser beside a kitchen range.

Acclimatisation isn't a box to tick

Before anything gets machined, timber needs to sit in the room it's destined for, or somewhere close to it. Stacked with spacers between the boards so air can move all round, left alone for days or — with solid timber in an older house — a few weeks.

This is the part of a lead time that clients sometimes find hard to swallow, and it's the part we're least willing to skip. Wood that arrives from the yard at 16% moisture content and gets cut and fitted the same week will spend the next twelve months finding its new equilibrium in situ, and it will do that finding at your expense: gaps opening, panels cupping, a painted finish splitting along a seam.

A moisture meter reading before machining, and another one after acclimatising, tells you whether you're starting from a sensible place. It's not glamorous. It is the whole game.

The allowances a good joiner builds in

Here's where design quietly earns its keep. Good fitted furniture isn't glued rigid against the movement it's going to experience; it's built to accommodate it.

Frame-and-panel construction. A traditional door is a frame with a panel floating inside a groove — loose, never glued across its width. The frame holds the shape; the panel swells and shrinks inside it. That's why old panelled doors survive centuries.

Slotted fixings. Tabletops and wide panels get screwed through slots rather than round holes, or held with buttons or figure-eight fasteners, so the timber can slide as it widens. Solid surfaces bolted down hard in every direction will split eventually. It's just a matter of when.

Reveals and tolerances. Doors are hung with two or three millimetres of reveal rather than a hairline, because hairline in June is a scrape in August. Drawer boxes are built a touch under the opening. Hinges are adjustable so a seasonal bind can be tuned out in five minutes without taking a plane to anything.

Grain direction, considered on purpose. Where a wide panel runs horizontally through a set of doors, we think about which way each board will move and how the joints should be allowed to behave.

Engineered boards aren't a shortcut

Ply, veneered MDF, moisture-resistant MDF and the better furniture boards are more dimensionally stable than solid timber, full stop. For wide painted doors, carcasses and shelving, an engineered core with a solid lipping is usually the sensible choice — you get a flat panel that stays flat, with real timber where you see and touch it: edge details, mouldings, frames, drawer fronts if you want the grain.

A lot of the best fitted furniture in British homes is a hybrid: stable boards where stability matters, solid timber where feel and appearance matter, and a design that respects the difference. Anyone insisting on solid timber throughout, in a centrally heated room, has either explained the consequences very carefully or hasn't thought it through.

What you can do as the seasons turn

A few practical things, all cheap:

• Don't push furniture hard against radiators or block background ventilation in an older property trying to dry out.
• A bathroom extractor fan and a working kitchen extractor do more for your cabinetry than any polish.
• If a door starts to bind in a humid spell, leave it. Check the hinges and the strike before you touch a tool. Nine times out of ten it'll free itself by October.
• If a hairline gap appears at a joint in winter, don't fill it. It'll close again. Filler squeezed into a joint that's going to tighten will push out and look worse than the gap did.
• Keep a note of the date when something changes. Two dates and a description tell a joiner far more than "it's gone funny".

The long view

A piece of fitted furniture that never moves at all is probably made of something that isn't wood. Real timber, well chosen and properly detailed, will shift a millimetre here and open a hairline there over the course of a year — and it will still be sitting square in your room in thirty years' time, long after the flat-pack it replaced has gone to the tip.

Movement isn't the flaw in the material. It's the material. The job is to plan for it, and that planning is a large part of what you're paying a joiner for.