C16 – Structural timber suitable for general construction and non-critical load-bearing use.

C24 – Higher strength structural timber used for load-bearing applications such as joists and roofs.

KD – Kiln dried timber, dried to a lower moisture content for improved stability.

AD – Air dried timber, dried naturally over time rather than in a kiln.

HT – Heat treated timber used to kill insects and meet transport regulations (not preservative treated).

PT – Pressure treated timber, treated with preservatives for improved durability.

UC2 / UC3 / UC4 – Use Class ratings defining suitability for internal, external, or ground contact use.

BTR – British Thermally Refined timber, thermally modified for improved stability and appearance.

CLS – Canadian Lumber Standard; planed, eased-edge structural timber commonly used for studwork.

PSE – Planed Square Edge timber, machined smooth on all faces.

PAR – Planed All Round; similar to PSE, often used interchangeably.

Sawn – Timber supplied rough-sawn, not planed or finished.

FJ – Finger-jointed timber, made from shorter lengths joined together for stability.

GL – Glulam (glued laminated timber), engineered structural timber.

LVL – Laminated Veneer Lumber, high-strength engineered timber product.

T&G / TGV – Tongue & Groove (V-jointed where specified), used for cladding, flooring, or panelling.

FSC® – Forest Stewardship Council certified timber from responsibly managed forests.

PEFC™ – Programme for the Endorsement of Forest Certification, another recognised sustainability scheme.