Timberline Lumber Company · Published November 14, 2026
Rough Douglas Fir has a sawn texture. S4S has been surfaced on all four sides for a smoother finish. Either can be used for exposed beams and posts, depending on the appearance and grade the project needs. The dimensions deserve a separate look: an 8×8 label doesn’t necessarily mean the timber measures eight inches square.
Choosing between rough and S4S
If you want to see saw marks on the finished beam, rough is the surface to start with. S4S gives you smooth faces and edges. It still shows the wood’s grain and knots; surfacing doesn’t turn a knotty piece into clear lumber.
The word “rustic” can mean a lot of things. You might like the deep saw marks in a photo, or it might be the knots and uneven edges that caught your eye. Send us the photo and point out what you like. That helps us understand the appearance you’re after before we quote material.
Think about which sides you’ll see once the wood is installed. A freestanding porch post may show all four sides. A beam against a ceiling may show three. Tell us which faces matter, especially if you want a particular appearance on every exposed side.
S4S describes the machining: both faces and both edges are surfaced. It doesn’t include sanding, stain, or sealer unless those are part of the order. The person doing the finishing should plan for any preparation the surface needs. When comparing rough and S4S quotes, include that work in the comparison.
What size is an 8×8 Douglas Fir timber?
An 8×8 is a nominal size, the name used to order the timber. Its actual dimensions depend on how it was manufactured and its moisture condition. For example, the standard minimum dressed size for a green 8×8 is 7-1/2 inches square; for a dry 8×8, it is 7-1/4 inches square.
Rough doesn’t automatically mean full size, either. Lumber can retain a sawn texture while being cut to dressed dimensions. If you need a full eight inches, make that requirement explicit, including whether it must be met after surfacing or at delivery.
| Nominal size | Reference condition | Minimum dressed section |
|---|---|---|
| 1×6 | Dry board | 3/4 × 5-1/2 in. |
| 2×8 | Dry dimension lumber | 1-1/2 × 7-1/4 in. |
| 6×6 | Green timber | 5-1/2 × 5-1/2 in. |
| 8×8 | Green timber | 7-1/2 × 7-1/2 in. |
| 8×8 | Dry timber | 7-1/4 × 7-1/4 in. |
These are minimum dressed sizes at manufacture from PS 20-25, Table 3. They aren’t a Timberline stock list or guaranteed delivery measurements. The definition of dry timber follows the applicable grading rules, and the green and dry rows don’t predict how much a particular piece will shrink. [1]
For a replacement post, measure the existing wood and the connection it fits into. Two pieces sold as 8×8 can leave you with a different fit. Send those measurements with a photo or sketch so we can quote to the required size. The custom millwork ordering guide explains what to include when matching existing work.
For exposed beams and posts
A beam that carries a load needs the structural grade specified for the job, even when its appearance is the reason you chose Douglas Fir. A smooth or clear-looking face doesn’t establish that grade. “Select Structural” is a structural grade name; “Select” used to describe appearance means something different. Our lumber grading guide covers the terminology. [2] [3]
Include the species, grade, dimensions, and any required grading documentation from your plans. Your designer or engineer handles member sizing and connections, including any change to a structural piece’s dimensions.
If you’re thinking of buying rough stock and having it surfaced later, work backward from the finished size. Surfacing removes wood, so the starting piece needs enough material to reach that size. Settle the milling allowance before buying the rough timber.
Moisture matters for either surface. Wood changes size as it gains or loses moisture, mainly across the grain. A timber going into a heated room may dry differently from one on a covered porch. Include where it will be used and any moisture requirement from the plans. [4]
As a timber dries, cracks called checks can open along the grain. Thick timbers can still hold moisture inside when their surfaces are drier, and kiln drying doesn’t guarantee a check-free piece. If checks would bother you on an exposed beam, discuss that appearance before ordering. A structural concern about a check needs review against the grade and project design. [5]
Getting a Douglas Fir quote
We quote Douglas Fir lumber, beams, and posts for pickup in Black Mountain, North Carolina, or regional delivery. Send us:
- Sizes, lengths, and quantities, with any exact dimensions flagged.
- What you’re building, along with plans or a material list.
- Rough or S4S, which faces will show, and a photo if you have a particular look in mind.
- Grade and moisture requirements shown on the plans.
- The jobsite town and ZIP if you need delivery.
You don’t need to have every choice settled to get in touch. Send what you have and tell us what you’re unsure about. We can quote rough and S4S as separate options, with dimensions and availability confirmed for your project.
Sources
- NIST. American Softwood Lumber Standard PS 20-25, sections 2.7, 2.16, 3.3, and 5.2; Table 3. Surface definitions and standard dimensions.
- Western Wood Products Association. Appearance lumber.
- Western Wood Products Association. Timbers. Structural grades and classifications.
- Western Wood Products Association. Dimensional stability.
- USDA Forest Products Laboratory. Wood Handbook, 2021, chapter 13. Moisture in thick timbers and drying defects.