Surfaced Lumber (Dressed Lumber)
Surfaced lumber, also called dressed lumber, has been planed to a smooth finish and specific dimension after sawing. The surfacing removes saw marks and reduces the board to its final dressed size. Surfacing can be done on two sides (S2S), one side and one edge (S1S1E), or all four sides (S4S).
In-Depth Explanation
Surfacing lumber involves passing the board through a planer (and optionally a jointer for edges) to create smooth, flat, parallel surfaces at a precise thickness. The process typically removes 1/8 to 3/16 inch from each face, which is why dressed lumber is always thinner and narrower than its nominal sawn dimensions. In the softwood trade, virtually all retail lumber is sold fully surfaced (S4S), with the well-known nominal-to-actual size difference (2x4 = 1.5 x 3.5 inches) being a direct result of surfacing. In the hardwood trade, surfacing options include S1S (one face), S2S (both faces), S1S1E (one face and one edge), S1S2E (one face and both edges), and S4S (all surfaces). Each additional surfacing step adds cost but saves the buyer from needing their own equipment to do the work. Surfaced lumber should have a uniform thickness with no snipe (deeper cuts at the board ends), skip (areas the planer missed), or chatter marks (ripples from dull or improperly set knives).
Usage Example
The trim carpenter ordered S4S clear pine from the mill, ready to install as baseboard without any additional planing or sanding.