Why Older Pressure-Treated Fence Posts Are More Durable Than New Ones
Fence posts manufactured before 2004 were treated with chromated copper arsenate (CCA), a preservative significantly more effective at preventing rot and decay than the compounds used in modern pressure-treated lumber — meaning older fences are often structurally superior and worth repairing rather than replacing.
Lean On Me
May 24, 2026 · 4 min read
Most homeowners assume that a new fence post is always better than an old one. It is newer, cleaner, and made from fresh lumber — so it must be more durable, right?
Not necessarily. There is a little-known shift in the wood treatment industry that took place in the early 2000s that changed the chemistry of pressure-treated lumber in ways that have reduced its resistance to decay. If your fence is 20 years old or older, the posts may actually outlast a brand-new replacement — and understanding why can significantly change how you think about repair versus replacement.
H2: What Changed in 2004
Until 2004, pressure-treated lumber in Canada and the United States was treated with chromated copper arsenate, commonly known as CCA. CCA is a highly effective wood preservative that penetrates deeply into the wood fibres and creates a chemical bond that resists fungal decay, insect damage, and moisture absorption for decades. Studies have documented CCA-treated wood lasting 40 to 60 years in ground contact applications under the right conditions.
In 2004, CCA was phased out for residential use due to concerns about arsenic leaching into soil near children's play areas. It was replaced by alternative preservatives: ACQ (alkaline copper quaternary), copper azole, and micronized copper compounds.
H2: Are the New Treatments as Effective?
The newer treatments are effective for above-ground applications, but field evidence and independent research suggest they do not match CCA's performance in ground contact situations — particularly in the wet, freeze-thaw conditions common across Canada. ACQ and copper azole treatments also contain higher concentrations of copper, which accelerates corrosion of steel fasteners and hardware in contact with modern pressure-treated wood.
H2: What This Means for Your Repair Decision
If your fence was built in the late 1990s or early 2000s, the posts may be more structurally sound — even with surface weathering — than a new replacement post would be in 20 years. Repairing a post with CCA-era lumber means preserving material that will likely outlast modern alternatives. This is one of the reasons Lean On Me consistently recommends repair over replacement for older fences, particularly those built before 2004.
Frequently Asked Questions
How do I know if my fence posts are CCA-treated?
If your fence was installed before 2004, it almost certainly uses CCA-treated lumber. Visual indicators include a slight greenish tint to the wood (though weathering often removes this), and older stamps or tags on the post may reference "CCA" or "0.40" (the retention level for ground contact). Any fence post from 2004 or later uses one of the newer treatment systems.
Is CCA-treated wood safe to have in my yard?
According to Health Canada, CCA-treated wood already installed in fences, decks, and structures poses no significant risk to homeowners in normal use. The arsenic compound in CCA is chemically bonded to the wood fibres and does not readily leach in typical outdoor conditions. The phase-out applied to new production, not existing installations.
Does this mean I should never replace an old fence?
Not exactly. If the fence structure — rails, boards, panels — is failing significantly, replacement may make sense. But if the posts themselves are structurally sound and simply leaning due to ground movement, repairing those posts and preserving the original CCA lumber is almost always the better long-term investment.
sources
- Health Canada: Chromated Copper Arsenate in Wood Preservatives (canada.ca)
- Forest Products Laboratory (USDA): Comparative Performance of Wood Preservatives in Ground Contact
- Canadian Wood Council: Preservative-Treated Wood Standards and Applications