Everyday things / room to move
A door, a frame,
a little room to move.
Imagine a timber door in an old stone building. A few millimetres separate its edge from the frame. If the timber gets wetter, how quickly could that little reserve disappear?
Explore a simple clearance budget. The numbers are illustrative assumptions, not measurements of a particular door.
Loading the experiment… If the controls stay unavailable, reload this page.
01 / Change the assumptions
How much room remains?
Use the arrow keys on a slider for small changes. Home and End reach its limits.
Calculated clearance
2.70mm
A gap remains in this model
A positive number describes this one edge. It does not establish that a real door opens freely.
| Contribution to the gap | mm |
|---|---|
| Reference clearance | +3.00 |
| Door moisture change | 0.00 |
| Jamb moisture change | 0.00 |
| Wall / frame shift | −0.30 |
| Remaining clearance | +2.70 |
Positive contributions open the gap; negative contributions close it. Display precision is arithmetic precision, not measurement accuracy.
02 / Follow one variable
If only the door gets wetter…
The line holds your jamb moisture, frame movement and reference clearance fixed. The dot marks your current door setting.
At these settings, the model reaches contact at 22.8% door moisture.
03 / Read the model
A small equation, with large assumptions.
Gap = reference clearance − door change − jamb change − frame shift
The arithmetic
Door change = 0.25 × (door MC − 12) mm.
Jamb change = 0.20 × (jamb MC − 12) mm.
Frame shift = 1.50 × movement factor mm.
The timber coefficients are millimetres per percentage point of moisture content. A move from 12% to 16% is four percentage points. Below 12%, the assumed timber movement reverses and opens the gap.
These are assumed changes at the gap edge. Their values already stand in for the missing timber dimensions, grain direction and restraint. The jamb is assumed to move inward as it swells; a real frame’s geometry may behave differently.
The boundary
The 12% reference and all three coefficients come from the original experiment. They have not been calibrated to a building, species, sandstone type, climate or historic period.
The original title imagined a seventeenth-century Cumbrian door. That remains a motivating scene, not evidence for these numbers. The wall factor is simply an independent inward-displacement assumption.
A negative answer is an overlap in the unconstrained arithmetic. A real contact problem would require deformation and force calculations. Hinges, warping, uneven moisture, friction and the rest of the opening are outside this model.
Moisture terminology and the source
Moisture content (MC) is water mass as a percentage of oven-dry wood mass. Equilibrium moisture content (EMC) describes the condition at which wood neither gains nor loses moisture; it depends on the surrounding conditions. These sliders set assumed MC directly, without modelling humidity or drying time.
Wood movement varies with grain direction and species. Swelling and shrinkage mainly occur below fibre saturation, whose moisture level varies. Keeping the original 6–28% slider range does not validate a linear law throughout it for a particular timber.
Background: Glass & Zelinka, Wood Handbook, Chapter 4 (2021), pp. 4–1, 4–3, 4–7 and 4–10. Read the chapter (PDF). This source supports the terminology and limits, not this toy’s coefficients.