Timber differs in structural characteristics. Any woodworker should have an understanding of timber to make sure that he can choose the right material for his projects. Timber is divided into three classes – structural material, shop and factory lumber and yard lumber. It is subdivided into common lumber and select lumber.
Common lumber is used for utility purposes and general construction. It is identified from different grade names.
- 1 – Also known as watertight lumber, No. 1 is tight knotted and durable. It can be used without waste.
- 2 – No. 2 common lumber is usually used for sheathing, framing and other structural forms where the strain or stress isn’t too much. Its general quality is similar to No. 1.
- 3 – No. 3 common lumber is ideal for rough work like rough flooring, footing and guardrails. It allows some waste.
- 4 – It has coarse features such as holes and decay. No. 4 is used for roof boards, sheathing and subfloors in cheaper construction. It is often used for crates and boxes.
- 5 – No. 5 is used for crates, dunnage and boxes with low quality requirements. It’s not manufactured in some timber varieties.
Select lumber has an excellent finish and physical appearance.
- Grade A – practically clear and ideal for natural finishes
- Grade B – generally clear and perfect for natural finishes like Grade A
- Grade C – ideal for high quality paint finish
- Grade D – perfect for paint finishes between common grades and high-finishing grades
Timber is usually sawn into average dimensions, providing uniformity in ordering materials and planning structures. Standards have been set for dimension differences regarding the quoted dimensions of timber and its average sizes when dressed. Quoted size indicates dimensions before surfacing. The common dimension difference is 2″ x 4″. It will be the nominal dimension, but the real dressed size is 1 ½” x 3 ½”. The exact size of dressed timber is less than the sawn dimensions due to finishing and drying.
Uses of Timber
Timber is used in frame construction. It used mainly for the walls and frame. For frames, it is used to support the finished parts of a structure such as the joists, beams and girders, posts, top plates, rafters, subfloors, knee braces and sole plates. Softwoods are also used for wood framing. No.2 common lumber is often used for framing. Girders, beams and other heavy frame parts are made by combining various components of the framing material.
The outside walls of a frame structure usually have three layers – the siding, sheathing and building paper. Grade No. 2 common softwood is typically used for the siding and sheathing. This grade has solid knots and doesn’t have spaces. Siding is either horizontally or vertically applied. There are various types of bevel and drop siding that can be applied horizontally.
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