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If you’ve ever searched for lumber online or walked into a local hardwood dealer, chances are you’ve seen the term S4S lumber pop up. What does S4S even mean? When should you use it in your next woodworking project? Whether you're a seasoned contractor or a DIYer shopping at an online lumber shop, understanding this term can save you time, effort, and headaches in the shop. Headaches like not having the sort of the heavy-duty tools needed to dress some of the exotic hardwoods on the market.
Let’s break it all down so you can choose the right material for your next build with confidence.
S4S stands for “Surfaced Four Sides.”. It’s also known as D4S (dressed 4 sides) or dressed lumber. This means the lumber has been planed smooth on all four faces: the top, bottom, and both edges. Unlike rough-cut lumber, which comes straight from the mill with a coarse texture, S4S boards are ready to use the moment they arrive at your shop.
To make S4S lumber, rough boards are first kiln-dried and then passed through a jointer and a planer until the wood is flat and clean on all sides. This results in a smooth surface that’s uniform in thickness and width. This eliminates the need to square your stock before building, saving valuable prep time.
A jointer to flatten one wide face of the board. This becomes your reference surface for future steps. Ensure consistent pressure and feed direction to avoid taper or snipe.
Rotate the board 90° and joint one adjacent edge. Use the previously jointed face against the jointer fence to create a square corner. This edge becomes your straight reference edge for ripping later.
Run the board through a thickness planer, placing the jointed face down. Plane the opposite face until it is parallel and smooth. Continue planing until the desired thickness is reached.
Use a table saw, placing the jointed edge against the fence. Rip the opposite edge to your desired width. This step completes the fourth dressed side
This has completed the dressing process, resulting in a square, S4S board.
Another option many suppliers may offer is “Straight-line rip one side,” often abbreviated as SLR1S. It refers to a milling process where one edge of a rough lumber board is ripped straight using a guided saw. This gives the board a clean, straight edge that can then be safely run against a table saw fence for further processing. This will ensure a clean, usable reference line for joinery or trimming.
When comparing S4S lumber and rough sawn lumber, the difference is in the finish and prep work required. Rough boards come directly from the mill with a coarse texture and unfinished. These are often preferred by traditional woodworkers who want full control over milling and sizing.
Choose rough-cut lumber when:
Choose S4S lumber when:
S4S is a go-to option for many applications due to its smooth surface and ease of use. Here are some common uses:
Because it’s already planed smooth, S4S works well where appearance and consistency matter.
When shopping for S4S lumber, keep these factors in mind:
Browse a variety of wood products to find the perfect fit for your build.
If you're new to woodworking, S4S lumber is your best friend. Here’s why:
Looking to get started? Shop from our full lineup of exotic and domestic lumber!
So, what’s the real takeaway? S4S lumber gives you a head start—smooth, square, and ready to roll. While rough board options offer flexibility for experienced builders, S4S is the go-to choice when efficiency, consistency, and simplicity matter most.
Whether you're sourcing stock for furniture, trim, or your first DIY build, working with S4S means less prep and more progress.
The Knotty Lumber Co. offers premium S4S boards in a variety of species and sizes—kiln-dried, planed smooth, and perfect for your next woodworking project.
