Post Bases vs. Anchor Bolts
ComparisonPost bases elevate and connect wood posts to concrete; anchor bolts fasten sill plates and ledgers. Understanding when to use each prevents structural failures at the wood-to-concrete interface.
Quick Comparison
| Criterion | Post Bases | Anchor Bolts |
|---|---|---|
| Primary Function | Connect wood posts to concrete piers/footings | Fasten sill plates and ledgers to concrete |
| Typical Application | Deck posts, pergola posts, carport columns | Mudsills, foundation walls, ledger boards |
| Moisture Protection | Elevates post above concrete — critical for decay prevention | No elevation — requires sill gasket for moisture break |
| Load Transfer | Gravity (downward) + lateral (shear) + uplift | Primarily shear (lateral) + some uplift |
| Installation Timing | After concrete cures (retrofit models) or wet-set | Set in wet concrete or drilled and epoxied after curing |
| Common Sizes | 4×4, 4×6, 6×6 post models | 1/2" and 5/8" diameter × 10" or 12" long |
| Code Reference | IRC R507.8 (deck posts) | IRC R403.1.6 (foundation anchorage) |
| Cost Per Unit | $8–$25 per base | $1–$4 per bolt |
Our Recommendation
Use post bases for any vertical wood post connecting to a concrete footing or pier. The elevation gap is essential — wood posts set directly on or in concrete wick moisture and rot within 5-10 years, even when pressure-treated.
Use anchor bolts for horizontal wood-to-concrete connections: sill plates on foundations, ledger boards for decks, and hold-down straps. For ledger connections, combine anchor bolts with structural screws and proper flashing for a complete load path.
Detailed Analysis
Post bases and anchor bolts are both wood-to-concrete connectors, but they serve fundamentally different structural roles. Confusing the two leads to code violations and potential structural failures.
Post bases provide a standoff connection that holds the bottom of a wood post above the concrete surface while transferring gravity loads downward and resisting lateral and uplift forces. Adjustable post bases allow fine-tuning the post position after the concrete has cured — invaluable when anchor bolt placement isn't perfect.
Anchor bolts, by contrast, are embedded in concrete (cast-in-place or post-installed) to fasten horizontal members. The standard residential foundation uses 1/2" anchor bolts at 6 feet on center, within 12 inches of each corner and plate splice, per IRC R403.1.6.