| Term |
Definition |
| Reaction wood | Eccentric growth that forms to withstand stress forces in the growing tree caused by a learning trunk, continual strong winds, etc. Prone to distortion as the timber dries, due to uneven shrinkage. |
| Reconditioning | Technique used to reduce problems that can occur during kiln drying – such as abnormal shrinkage, warping and collapse – by steaming the timber to help equalise the stresses in the wood cells. |
| Resin pocket | Cavity in a softwood board that contains (or has contained) resin, generally associated with a wound in the growing tree. Note that ‘gum’ performs the same function in hardwoods. |
| Resin streak | Visible resin deposit in wood cells of conifers that appears as a streak along the grain. |
| Ring shake | Shake that follows a growth ring (see ‘shake’). Also called a ‘shell shake’ or ‘cup shake’ – with the timber sometimes described as ‘shelly’. |
| Rot | Another term for ‘fungal decay’, but generally used to describe more advanced decay, or a particular type of decay (such as brown rot, white rot, etc). |
| Rough sawn (R/S) | Fibrous surface finish of wood that has been sawn with a circular saw or bandsaw. |
| Rougher headed | Surface finish of framing timber that has been sized in a planer, with small grooves running along the surfaces. |
| Sapwood | Outer layers of wood in the growing tree containing living cells that are used to transport water and minerals from the roots to the leaves. |
| Scantling | Timber used in the construction of wall frames, roof trusses and other types of building framing. |
| Seasoned | Timber that has been dried to a certain moisture content range – generally 10% to 15% unless otherwise specified. |
| Seasoning | Process of drying timber to a specified moisture range, either though air drying or kiln drying. |
| Shake | Separation of wood fibres caused by stresses in the standing tree or during the felling or processing stages – but not caused by drying stresses. |
| Shatter | Structural defect caused by several long splits or shakes. |
| Shelling | Separation of fibres along a line of weakness following a growth ring – generally caused by a ring shake (also known as ‘shell shake’). |
| Shook | Short length of timber that can be joined lengthwise with other shooks to make a long piece (such as through finger jointing). |
| Shrinkage | Reduction in the width and thickness of a piece when the cell walls lose moisture. |
| Softwood | Timber from ‘gymnosperm’ trees, where the seeds are held in cones. Commercial softwood species are generally conifers or pines. |
| Split | Separation of wood fibres that form a crack running from one surface to another surface in a piece (not to be confused with a ‘check’). |
| Spring | Lengthwise curve of the edge of a piece of timber, not affecting the face. |
| Stain | Discolouration in the surface of a board from any cause, such as glue, micro-organisms or chemicals. |
| Strength groups | Classification system that groups different timber species according to their bending strength. Green timber strength groups range from S1 (strongest) to S7. Dry timber strength groups range from SD1 to SD8. |
| Stress grade | Classification system that rates individual pieces in terms of the load they can safely support, taking into account the defects in the piece. The most common stress grading systems are ‘F grades’ and ‘MGP grades’. |
| Super foot | One twelfth of a cubic foot – that is, one square foot one inch thick. Used to quantify volume (instead of cubic metres) in countries that measure timber in feet and inches, particularly USA and Asia. Sometimes referred to as a ‘board foot’. |
| Surface check | Shallow check (separation of fibres along the grain caused by drying stresses) occurring on one surface only |