Cedar species and joinery for outdoor work.
Eastern white cedar vs. western red cedar, how to size structural posts and beams, why mortise-and-tenon is the right choice for outdoor cedar work, and what hardware survives 25 Vermont winters.
— Why this matters
Cedar Species & Joinery: A Working Reference — and why it matters in Vermont.
Cedar is the most rot-resistant softwood available in our region — but cedar work is only as good as the joinery, the hardware, and the foundation detail. Here’s what we’ve learned over a decade of building cedar pergolas, pavilions, and fences in Vermont.
— Quick reference
— The detail
What to know.
The working detail — what we apply on every Cairn & Cedar project.
Eastern white cedar (Thuja occidentalis)
Native to Vermont. Tighter grain than Western red cedar. More rot-resistant in cold climates because it grew in cold climates. Lighter color, ages to silver-gray. Sourced from Vermont mills. Our default for everything.
Western red cedar (Thuja plicata)
Pacific Northwest native. Softer, more aromatic, larger boards available. Better for some applications (siding, large-section beams). More expensive shipped to Vermont. We use occasionally for specific design needs.
Sizing: structural posts
6×6 milled cedar for standard residential pergola posts (up to 9-ft height). 8×8 for spans over 12 ft, taller posts, or pavilion structures. 10×10 for major pavilions or wind-exposed sites. Always milled, not ‘rough’ cedar — kiln-dried for stability.
Mortise-and-tenon joinery
Tenon (rectangular projection) on the beam, mortise (matching slot) in the post. Glued and pinned with a white-oak peg through the joint. Strong, beautiful, traditional. Doesn’t rust, doesn’t introduce a different material at the connection, doesn’t fail under thermal cycling.
Hardware that survives
Stainless steel for everything in contact with the wood. Hot-dip galvanized as second choice. Never electroplated (fails in 5 years). Bronze hinges and traditional latches age beautifully. Stand-off post bases keep wood out of standing water.
What we don’t use
Pressure-treated lumber (toxic chemicals, doesn’t age well, wrong aesthetic). Big-box ‘cedar’ (often pine stained brown). Pocket screws (fail with thermal cycling). Galvanized strap hinges (rust streaks within 5 years). Sealants and stains (trap moisture, accelerate rot).
— Frequently asked
What clients want to know.
Should I stain my cedar to keep the warm color?
We don’t recommend it. Cedar wants to silver — it’s the natural protective response to UV. Stains seal moisture in at the joints, which is exactly where rot starts. The silver patina is beautiful, structurally protective, and zero-maintenance. If you really want to preserve the warm color, a UV-blocking clear oil (Penofin, Cabot Australian Timber Oil) can work but needs reapplication every 18 months.
What’s wrong with deck screws?
Three things: they introduce a different material (steel) at every connection, which weathers differently than the wood; they concentrate load at the screw heads, which can split the wood under thermal cycling; and they’re visually loud. M&T joinery distributes load along the joint surface and is invisible from a distance.
What about pre-fab cedar kits from big-box stores?
Different product. The ‘cedar’ is often pine or fir stained to look like cedar. The joinery is pocket screws. The hardware is electroplated. Pre-fab kits last 5-10 years before they look bad and 10-15 before they fall apart. Real cedar work lasts 25-30 years and looks better at year 20 than year 1.
How big does the pergola post need to be?
6×6 is standard for free-standing residential pergolas under 9 ft tall. 8×8 for pergolas over 9 ft, attached pergolas, or those subject to significant wind load (lakefront, hilltop). 10×10 for major pavilions and gazebos. ‘It’s just a pergola’ is a great way to undersize a post.
Will the cedar split or check?
Some surface checking is normal — small cracks that develop as the wood seasons. Doesn’t affect structural integrity. Major cracks (full-depth, running with the grain) indicate moisture imbalance or improperly seasoned stock. Cedar from Vermont mills, kiln-dried before milling, doesn’t typically check beyond surface level.
Is cedar good for raised beds in vegetable gardens?
Yes — Eastern white cedar is the right choice. Naturally rot-resistant, no preservative leaching, lasts 15+ years in direct soil contact. Don’t use pressure-treated for vegetable gardens; the preservatives leach into the soil.