Solid wood swells and shrinks across its grain every season as the moisture in the surrounding air changes. The amount can be calculated before a piece is built: seasonal movement equals the board's width times the species' dimensional change coefficient times the swing in moisture content, in percentage points [1].
Why wood keeps moving
Dried wood cell walls keep absorbing and releasing moisture from the air for as long as the wood exists. When the cell walls take on moisture, a board gets wider. When the cell walls give moisture up, the board gets narrower.
Seasonal wood movement repeats every year. A board milled in winter is a different width in summer.
Seasonal wood movement is small, but it is enough to split joints, stick drawers and crack breadboard ends when a design does not allow for it.
Movement is different in each direction
Along the grain (longitudinal), seasonal wood movement is negligible for furniture design.
Across the grain on a quartersawn face (radial), seasonal wood movement is significant and has to be designed for.
Across the grain on a flat-sawn face (tangential), seasonal wood movement is the largest of the three directions. A flat-sawn board moves more than a quartersawn board of the same species and width under the same humidity swing.
Quartersawn lumber costs more than flat-sawn lumber, and its lower movement across the width is a structural reason to pay for it on wide panels, not only an appearance choice.
The movement calculation
Seasonal movement across a board = width × C × moisture content swing in percentage points. C is the dimensional change coefficient per 1% change in moisture content: the tangential coefficient for flat-sawn boards and the radial coefficient for quartersawn boards [1].
Dimensional change coefficients for five furniture species, tangential then radial, per 1% change in moisture content [1]:
- White oak: 0.00376 tangential, 0.00194 radial.
- Black walnut: 0.00274 tangential, 0.00190 radial.
- Black cherry: 0.00248 tangential, 0.00126 radial.
- Hard (sugar) maple: 0.00353 tangential, 0.00165 radial.
- Bigleaf maple: 0.00248 tangential, 0.00126 radial.
A species' total shrinkage from green to oven-dry, such as 10.5% tangential for white oak, is not the per-1% coefficient. Putting total shrinkage into the seasonal movement formula overstates movement by about 2.8 times [1].
Worked example: a 12-inch flat-sawn white oak panel through a 6% moisture content swing moves 12 × 0.00376 × 6 = 0.27 inch across its width [1].
Worked example: a 12-inch quartersawn white oak panel through the same 6% swing moves 12 × 0.00194 × 6 = about 0.14 inch, roughly half the flat-sawn figure [1].
Constrain or accommodate
A solid-wood design can either constrain seasonal movement or accommodate it.
Constraining wood movement means gluing a panel rigid, attaching a tabletop with no float, or drawboring a breadboard end tight across its whole width. Constrained wood eventually breaks something: a joint, a glue line or the panel itself.
Accommodating wood movement means building each joint so the wood can move without loading the structure. Floating panels, breadboard ends with slotted fasteners, and tabletop clips that ride in the apron are all accommodating joints.
Traditional frame-and-panel construction is a movement management system. The panel floats unglued inside a groove in the frame, moves with the humidity, and the frame holds the piece together.
When quartersawn stops being a preference
Below 8 inches wide, the choice between flat-sawn and quartersawn stock is mainly an appearance choice, because the movement difference is manageable in most species [2].
Above 18 to 20 inches wide, quartersawn stock is the structural recommendation for hard maple panels, not a preference [2].
Wide flat-sawn panels need larger float clearances than narrow panels, and the variation in movement between flat-sawn boards makes grain-matched glue-ups harder to predict.
A wide panel glued up from flat-sawn hard maple needs larger gaps, more float clearance and a plan for its finished width to change through the year.
Sources
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients, valid 6 to 14% moisture content (as listed in Hewn's notes, entries HEU-R735 and HEU-R739).
- Hewn heuristic entry HEU-R737, flat-sawn vs. quartersawn structural threshold, 2026-03-15, Hewn internal, unreviewed.