Timber Posts (6×6 & 8×8)
Solid-sawn timber posts in 6×6 (5.5" × 5.5") and 8×8 (7.5" × 7.5") sizes serve as vertical structural columns for decks, porches, timber frames, and post-and-beam construction. Available in pressure-treated, Douglas Fir, and cedar.
Fast Facts
- What Is It?
- Large-dimension solid-sawn lumber used as vertical load-bearing columns. Common species: Douglas Fir, Southern Yellow Pine (PT), Western Red Cedar.
- Common Uses
- Deck posts, porch columns, post-and-beam construction, pergola uprights, fence posts, basement lally column replacements.
- Cost Range
- 6×6 PT: $2.50–$5.00/LF; 6×6 DF: $4–$8/LF; 8×8 PT: $5–$10/LF.
- Durability
- PT posts rated for ground contact (UC4A/UC4B) last 20–40 years. Untreated above-grade posts with proper protection last indefinitely.
Specifications
| Property | Value |
|---|---|
| Actual Dimensions | 6×6 = 5.5" × 5.5"; 8×8 = 7.5" × 7.5" |
| Common Lengths | 8', 10', 12', 16', 20' |
| Species | SYP (PT), Douglas Fir, Western Red Cedar, Hem-Fir |
| Grade | No. 1 or No. 2 per NELMA/WCLIB/SPIB |
| Treatment Retention | Ground contact: 0.40 pcf (UC4A) or 0.60 pcf (UC4B) |
| Axial Load Capacity | 6×6 No. 2 SYP: ~25,000–30,000 lbs at 8' height (varies by species/grade) |
Choosing the Right Post Size
6×6 posts are standard for most residential deck, porch, and pergola applications. They support typical tributary loads of 500–1,500 square feet at heights up to 10 feet. Upgrade to 8×8 posts when heights exceed 10 feet, tributary areas exceed 1,500 sq ft, or for timber-frame aesthetics.
Post-to-Beam Connections
The traditional notched-post connection is being replaced by engineered post caps that maintain full cross-section strength. Simpson Strong-Tie CC/AC series post caps, through-bolted saddle brackets, and knife-plate connections all provide code-compliant load paths without weakening the post.
Foundation Options
Posts can bear on concrete piers (Sonotubes), precast pier blocks, helical piles, or continuous footings. The post base must provide positive connection to the foundation (Simpson ABU/ABA post bases) and stand off from concrete to prevent moisture wicking. Posts set directly in concrete without hardware fail prematurely.
Frequently Asked Questions
Do deck posts need to be pressure-treated?
Posts in ground contact or within 6 inches of the ground must be pressure-treated per IRC R317.1. Posts on post bases above concrete piers can be untreated if the base provides 1" clearance from concrete. Most codes require ground-contact rated (UC4A minimum) for any post near soil.
What is the maximum height for a 6×6 deck post?
IRC Table R507.8 limits 6×6 deck posts to 14 feet for single-level decks (no lateral bracing) with typical loads. For multi-level decks or heights over 8 feet, lateral bracing is required. Always check your local code — many jurisdictions limit unbraced height to 8–10 feet.
Can I notch a timber post?
Notching reduces the effective cross section and should be minimized. IRC allows notching up to 1/3 of the post depth on any face for non-structural connections. Structural notches (like for beams) must be engineered. Use a post cap or saddle connector instead of notching whenever possible.
Also Consider
Pressure-Treated Lumber
Pressure-treated lumber is dimensional softwood (typically Southern Yellow Pine) infused with preservative chemicals under pressure to resist rot, decay, and insect damage. The most common decking and structural lumber for outdoor applications.
Post Bases
Post bases are steel connectors that anchor wood posts to concrete while elevating the post above standing water and transferring compression, uplift, and lateral loads into the foundation.
Anchor Bolts
Anchor bolts secure sill plates, post bases, holdowns, and steel connectors to concrete or masonry and are a core part of the structural load path between wood framing and the foundation.