| Term | Description |
| Seasoning stresses | Stresses in timber caused by variation in shrinkage as it dries. |
| Select | A high grade of lumber that allows few defects. |
| Selects | In softwood, lumber which has been graded strictly for its appearance. In hardwood, lumber which is one grade below first and second. |
| Shade tolerance | The capacity of a tree or plant species to develop and grow in the shade of and in competition with other trees or plants. |
| Shake | lumber defect referring to a separation of wood fiber through the annual growth rings. |
| Shake | Separation or breakage of the wood fibres caused by stresses in the standing tree or by felling and handling of the log. It is not caused by shrinkage during drying. |
| Shake | A separation of the wood along an annual ring (ring shake)or cracks radiating from the heart (heart shake) caused by frost, wind, or felling of the tree. |
| Shear | A condition of stress or strain where parallel planes slide relative to each other. |
| Shear connector | Usually metal connectors fitted inside a timber joint to transfer shear across a wide area of grain. |
| Shear Stress | Result from forces which tend to cause one portion of a body to move with respect to another in a direction parallel to their plane of contact. |
| Sheet metal connector | A shaped connector made of sheet metal and perforated so that nails can be driven through. |
| Shelterbelt | A wind barrier of living trees and/or shrubs maintained to protect farm fields or homesteads. |
| Shelterwood cutting | Any harvest cutting of a more or less regular and mature crop, designed to establish a new crop under protection of the old. |
| Shipment time | The time indicated for a shipment of lumber to leave a sawmill or reload center. |
| Shipper | The party paying the freight bill. |
| Short (position) | A speculative position in which one sells lumber before it is bought. |
| Shrinkage | The reduction in dimension or volume which takes place in timber when the moisture content is reduced below fibre saturation point, expressed as a percentage of the original dimensions or volume. Linear shrinkage occurs in three directions radial, tangential and longitudinal. |
| Shrinkage | The percentage change in the dimension of wood with respect to the swollen size as a basis. |
| Sidecuts | Boards usually 1×3, 1×4 or 1×6 produced in a dimension mill from the thin slabs taken from the outside of logs; slabs not thick enough to make dimension lumber. |
| Sill | 1) A sill plate. 2) The structural member forming the bottom of a rough opening for a door or window. Also, the bottom member of a door or window frame. |
| Silviculture | The art and science of growing and tending a forest. It includes assessing sites before they are harvested to determine what is growing there now, evaluating soil conditions to determine moisture and nutrient levels as well as assessing the types of plants that are growing on the site. |
| Skidder | A wheeled or tracked vehicle used for sliding/dragging logs from the stump to the landing. |
| Slab | A broad flat piece of wood cut directly from the log, often with bark on both edges. |
| Slab | The exterior portion of a log removed in sawing timber. |
| Slash | Tree tops, branches, bark, and other debris left after a forest operation. |
| Sliced veneer | Veneer that is sliced off a log or flitch with a knife. |
| Sliding Dovetail Joints | A sliding dovetail joint is similar to a tongue and groove joint except the tongue and grove are matching dovetails. |
| Softwood | Wood from trees commonly referred to as conifers or evergreens. |
| Softwood | A general term for timber of trees classified botanically as Gymnosperm. Commercial timbers of this group are nearly all conifers. The term has no reference to the relative hardness of the wood. |
| Softwood | Evergreen trees, conifers, cone-bearing trees or wood cut from these trees. Softwood lumber has long been the mainstay of the residential construction industry where it is used in relatively large-sized pieces. Though some of this wood, such as that used for siding, must be of good appearance, most requires only adequate strength. Because of these factors, and because construction requires material of uniform size which can be stockpiled economically (meaning a relatively small number of standard sizes), softwood lumber is manufactured to standard sizes and is measured accordingly. |
| Softwoods | Generally lumber from a conifer such as pine or cedar. The name softwood does not refer to the density of the wood. There are some hardwoods, such as Balsa, which are softer than some softwoods, like Southern Yellow Pine. |
| Sound | A term referring to a board which has no or very few defects which will effect its strength. |
| Sound knot | A knot that is solid across its face, at least as hard as the surrounding wood, and shows no indication of decay. |
| Spar | A pole, tower or tree used in cable logging to raise the mainline off the ground. |
| Specific Gravity | The decimal ratio of the ovendry weight of a piece of wood to the weight of a volume of water equal to the volume of the piece at a given moisture content (green, air-dry, or ovendry). |
| Specific Gravity | The ratio of the weight of wood to an equal volume of water. The higher the specific gravity, the heavier the wood. |
| Spermatophyte | Plants that reproduce by seeds. This includes almost all plant species. |
| Spike top | A tree with a dead top, usually a mark of declining vigor. |
| Spindle | The threaded arbor on a shaper that holds the cutters. |
| Splice | To join the ends of timber elements together. |
| Spline | A thin piece of wood that fits in the mating grooves cut into two pieces of wood. |
| Split | A defect that occurs when tensile stresses cause the wood fibres to separate and form cracks. Splits are cracks that extend through a piece. |
| Spring | A longitudinal curvature of the edge of a piece of timber, not affecting the face. |
| Springing | Support point or origin. |
| Springwood | The less dense, larger wood cells of an annual growth ring. Also called earlywood to refer to the fact that it is the wood formed early in the growing season. See also summerwood. |
| Squeeze-out | A bead or drops of glue that are forced out of a joint when pressure is applied. |
| Stain | 1) A discoloration in wood caused by a fungus or chemicals. 2) A die or pigment used to color wood. |
| Stand | A community of trees sufficiently uniform in species, age, arrangement or condition to be distinguishable as a group from the forest or other growth on the area. |
| Starved Joint | A poorly bonded joint caused by lack of glue. |
| Steam bending | The curvature to which a 1 inch (25mm) thick sample may be steam bent with an expectation of a 5% failure rate. |
| Steaming treatment | A treatment sometimes carried out before commencing a drying schedule. The timber is subjected to live steam. See also reconditioning. |
| Stem Wood | See Bole Wood. |
| Sticker � | A thin wood strip that is inserted between stacks of green wood to allow air to flow through the stack to ensure proper drying.. |
| Stickers | Strips or boards used to separate the layers of lumber in a pile and thus improve air circulation. |
| Stickers | When kiln or air-dryin wood, stickers are pieces of wood placed perpendicularly between layers of boards to allow for airflow through the stack. Stickers are usually placed 12 to 18 inches apart and directly over any support beams under the stack. Placing stickers as close as possible to the end of the boards helps to llimit end checking and reduce warp. |
| Stiffener | All elements used to support or stiffen the slender webs of box and I-shaped beams and to enhance compressive capability of webs at support points or points of high transverse loads. |
| Stile | The vertical part of a raised panel door. |
| Stitch bolt | A long bolt through laminated timber that holds the laminations together. |
| Straight grained | Timber in which the fibres run parallel to the axis of a piece. |
| Strength | The ability of a member to sustain stress without failure. |
| Strength group | Species of timber are classified into groups according to mechanical properties of the wood of that species and AS 2878, Timbers – Classification into Strength Group. There are seven strength groups for unseasoned timber (S1 the strongest to S7 the weakest) and eight for seasoned timber (SD 1 the strongest to SD 8 the weakest). |
| Stress | Applied force per unit of volume or area. It is expressed as primary stresses, i.e., compression (with forces acting toward each other), tensile (with forces acting away from each other), or shear (with forces sliding on each other). A combination of the three results in bending stresses. |
| Stringer | 1. A beam that joins the top of columns and supports the cross members in floors and ceilings. 2. An inclined member that supports the treads of a stair. 3. A deck element in timber bridges that supports transverse deck planks and runs parallel to the beam span. |
| Structural I-Beams | Structural I-Beams were developed to take advantage of the fact that compression and tension stresses are greatest at the top and bottom edges of a beam as it is subjected to a load. By concentrating the amount of wood at the the top and bottom edges and by paying close attention to the quality of wood used at these locations, beams are made that have high strength but which use far less wood than solid lumber. Such products are widely used today and were used in 19% of the homes built in the United States during 1996. Structural I-beams are used for the most part as floor joists, replacing 2 � 12, 2 � 10, and 2 � 8 solid-sawn lumber that has traditionally been used for joists. |
| Structural timber | Timber to be used in construction where its strength is the controlling element in its selection and use. |
| Strut | A structural timber resisting compressive forces along the grain. |
| Stud | One of a series of vertical framing timbers used as a supporting element in a wall or partition. |
| Stumpage | The value of timber as it stands uncut in the woods. The price charged for the right to harvest timber from publically or privately-owned forest land. The University of Massachusetts publishes a local stumpage fee report quarterly based on responses to a survey of local landowners and loggers. |
| Summerwood | The denser, later-formed wood of an annual growth ring. Also known as “latewood” relating to the time in the growing season that these cells are produced. |
| Sunscald | Death of cambial tissue on one side of a tree, caused by exposure to direct sunlight. |
| Surfaced | Lumber that has gone through a planer so that its sides are smooth and uniform in size. |
| Surfaced Lumber � | A piece of wood that has been planed smooth on one or more surfaces. |
| Surfacing | The way a piece of lumber has been prepared at the lumber mill. |
| Sustainable Forestry Initiative (SFI) | The program and polices formed by the American Forest and Paper Association (AFandPA). SFI was developed in response to criticism from environmentalists aimed at logging practices that did not promote forest sustainability. SFI is the industrial counterpart to programs promoted by Smartwood (non-profit)and Scientific Certification Systems (for profit) which promote and certify landowners engaged in proactive and sustainable forest management. AFandPA requires all its members to comply with SFI principles among which is the requirement that forest management be “certified” by an independent third party. SFI certification can be easily confused with “green certification” promoted by the Forest Stewardship Council (FSC). |
| Sustained harvest | A level of harvest that does not exceed annual growth, so that at least as much is available for harvest in 50 years as today. |
| Sway bracing | Bracing members required to resists the transverse movement of a structural element. |