Cedar 1x8 Lumber

Cedar 1x8 is a workhorse board for exterior trim, fascia, siding, fencing, and outdoor projects like planters and pergolas. It’s typically Western Red Cedar (Thuja plicata), measuring about 3/4-inch thick by 7-1/4 inches wide by various lengths. Here’s the thing buyers trip over first: that “1x8” is a nominal call, not what you measure on the board.

The single most important decision isn’t length or even species. It’s grade. For small-scale woodworkers, selecting the right one cuts material costs by 20-30% right off the bat. Match the grade to the job and you stop paying for clear faces that’ll never be seen — or worse, you stop fighting loose knots on a finish surface.

Why cedar in the first place? Cedar is renowned for its appearance, stability, durability and weather resistance. It’s ideal for outdoor projects where lumber is exposed to the elements. Cedar’s natural oils and preservatives fight off weather, bugs, fungi and algae and, if desired, allow excellent absorption of stains and paint. That rot and insect resistance is the whole reason it earns its keep on Montana exteriors that take freeze-thaw cycling and moisture year after year.

Sizes, Grades, and Profiles

Standard solid cedar 1x8 lands at an actual size of 3/4 x 7-1/4 inches against a nominal 1 x 8. Engineered, finger-jointed versions run slightly different: the nominal size is 1x8, the actual finished size is 1 inch x 7-1/2 inches, with a tolerance of ±1/16 inch. That engineered product is built for a reason — manufactured using finger-jointed and laminated Western Red Cedar, it provides enhanced stability, reduced warping, and long lengths that maintain consistent appearance.

Western Building Center carries solid cedar 1x8 in S1S2E profile across 8, 10, 12, and 16-foot lengths. Engineered and other-supplier products show up in longer runs too — lengths are typically available in 4’, 8’, 10’, 12’, 16’, or 20’.

Grade drives appearance, yield, and price. Here’s how the common grades stack up:

Grade	Knot Allowance	Usable Yield	Best Use
Clear / Clear Heart	None	~98%	Visible furniture faces, premium millwork
C & Better (C&BTR)	Few tight knots, mostly clear	High	High-end siding, paneling, fascia, soffits
Select Knotty (STK)	Sound knots under 1”	~90%	Siding, benches, exterior trim
Std & Btr NPS Tight Knot	All knots sound and secure	—	Trim, fascia, siding
Common	Knots under 2”	~75%	Hidden framing

Clear grades ensure premium looks, reducing sanding time. Skip the right grade and you face visible flaws that devalue finished pieces. On the top end, C & Better is a top-tier grade of Western Red Cedar, prized for its clean appearance and natural durability. With minimal knots and consistent grain, it’s ideal for high-end siding, paneling, trim, and custom woodworking. The Std & Btr tight knot grade earns its place where you want the cedar look without the clear-grade premium — surfaced smooth on one side and two edges, while the opposite side remains rough-sawn to accommodate diverse design preferences.

That surfacing call matters more than most buyers realize. S1S2E cedar boards are smooth on 1 side and 2 edges with a rough back side, making them an ideal reversible trim board. Flip it for a planed face or a rustic one — your choice on the wall. S4S is the other option: surfaced four sides, smooth all around, which saves plane time when you want a finished look on every face.

Cedar takes finish well because of what it lacks. Western red cedar is pitch and resin-free, which means it’s ideal for accepting and holding a wide range of finishes including dark stains, bleaches, solid colors and semi-transparents. Left bare, it goes its own way — a subtle red-brown color that weathers to silver-gray. Worth knowing before you set unfinished fence boards or siding in full Montana sun.

Moisture, Acclimation, and Install

This is where cedar jobs go sideways. Skip acclimation in a dry climate and you’ll watch joints open up after install.

Target moisture content depends on where the board lives. Ideally 6-12% for indoor use. Below 8% it’s too dry and brittle; 12-14% is right for outdoors. The reason matters: high MC over 15% causes shrinkage up to 7% tangentially, leading to gaps or cracks.

Let the wood settle before you fasten anything. For proper installation, allow lumber to acclimate on site 1-2 weeks prior to installation. The rule of thumb is straightforward — acclimate boards 1 week per 1 inch of thickness in your shop. That step is non-negotiable in a dry Montana climate where wood gives up moisture fast and moves while it does.

Inspect every board before it goes up. Check for straightness — no bow over 1/8 inch per foot. And cedar’s soft, but it still splits — drill pilot holes near ends and edges to keep boards from cracking when you fasten.

Cedar’s a pleasure to work for a reason. With low density around 23 lbs/ft³ when dry, saws glide through with about 30% less blade wear than hardwoods. Light to handle, easy to nail and cut.

Frequently Asked Questions

What does a 1x8 cedar board actually measure? A nominal 1x8 in solid cedar measures 3/4 inch thick by 7-1/4 inches wide. Engineered finger-jointed cedar runs a touch different at 1 inch by 7-1/2 inches, with a tolerance of ±1/16 inch. The nominal number is taken before surfacing, so always measure if a tight fit matters.

Which grade should I buy for exterior siding and fascia? For siding and benches, Select Knotty with sound knots under 1 inch delivers around 90% usable yield. If you want a cleaner, higher-end look on siding, paneling, or fascia, C & Better offers minimal knots and consistent grain. Reserve clear grades for visible furniture faces where every knot shows.

Does cedar need a finish, or can I leave it bare? You can leave it bare — Western Red Cedar is naturally resistant to rot, decay, and insect attacks. Untreated, it weathers to silver-gray. For engineered boards, note that a field-applied topcoat is required after installation to protect the board and maintain the manufacturer’s warranty.

How long does cedar last outdoors? Untreated cedar 1x8 lasts 15-25 years outdoors, versus pine’s 5-10. Regular finishing extends that further.

What’s the difference between S1S2E and S4S? S1S2E is smooth on one side and two edges with a rough back side — a reversible trim board. S4S is surfaced four sides, smooth all around, so you don’t have to choose a face.

Why do my cedar joints open up after installation? Almost always moisture. High MC over 15% causes shrinkage up to 7% tangentially, leading to gaps or cracks. Acclimate the boards on site — 1-2 weeks before installation — so they reach equilibrium with local conditions before you fasten them down.