Treated timber is used for decks, fences, garden beds, playground frames and outdoor furniture because it resists rot and insects far longer than untreated wood. But the chemicals that protect it have long raised a question: is treated timber safe for you, your children and your garden?
The short answer: modern treated timber is considered safe for most everyday uses if you handle it sensibly. Older timber treated with arsenic-based preservatives needs more care.
What is treated timber?
Treated timber is wood that has been soaked in preservatives, usually under high pressure in a factory, so the chemicals penetrate deep into the wood. This protects it against fungi, termites and other insects. The preservative used makes a big difference to safety.
The older treatment: CCA (chromated copper arsenate)
For decades the most common preservative was CCA, which contains chromium, copper and arsenic. It is very effective, but arsenic is a known toxin, and studies found small amounts could leach from the wood surface and into nearby soil.
- In the United States, manufacturers voluntarily stopped producing CCA-treated wood for homeowner uses such as decks and playsets at the end of December 2003.
- The US Environmental Protection Agency did not ban CCA outright, and it is still used for some industrial and commercial products such as foundation poles and shakes.
- The EPA does not require existing CCA decks or play equipment to be removed.
- Rules elsewhere vary, so check with your local supplier if you are buying in India, the UK, the EU or Australia.
If your deck, fence or play set is older than about 2004, it may well be CCA-treated.
Modern treatments
Most timber sold for home use today is treated with copper-based preservatives that do not contain arsenic, such as:
- ACQ (alkaline copper quaternary)
- Copper azole
- Micronised copper treatments
These are considered much lower risk for people. The higher copper content can corrode some metal fixings, so use fasteners recommended for treated timber.
When can treated timber be a health risk?
- Burning it. This is the biggest danger. Never burn treated wood in a fireplace, stove, barbecue or bonfire. The smoke and ash can release toxic chemicals.
- Sawdust. Cutting and sanding create fine dust you can breathe in or swallow.
- Hand-to-mouth contact. Small children playing on older CCA decks or play sets may pick up residue on their hands.
- Food contact. Treated timber should not be used for chopping boards, food storage or anything that touches food directly.
How to handle treated timber safely
- Wear gloves, safety goggles and a dust mask when cutting or sanding.
- Work outdoors where possible, and sweep up and dispose of sawdust and offcuts.
- Wash your hands before eating, drinking or smoking.
- Wash work clothes separately from other laundry.
- Coat older CCA structures regularly with a penetrating oil- or water-based stain to reduce leaching.
- Encourage children to wash their hands after playing on older wooden play equipment.
Is treated timber safe for vegetable gardens?
Many gardeners use modern copper-treated timber for raised beds without problems. If you are concerned, line the inside of the bed with heavy-duty plastic, or choose naturally durable wood such as cedar or larch, or stone, brick or composite boards. Avoid old CCA timber for growing food.
How to dispose of treated timber
Never burn it, and do not turn it into mulch or compost. In many areas, small amounts from home projects can go in ordinary household waste, but check your local council’s rules first.
Safer alternatives
- Naturally rot-resistant woods such as cedar, larch and teak
- Thermally modified timber, which is heat-treated rather than chemically treated
- Composite decking made from wood fibre and plastic
- Metal, stone or brick for structural elements
Frequently asked questions
Is treated timber toxic to touch?
Touching modern treated timber is generally considered low risk. Wash your hands afterwards, especially before eating.
Can I burn treated wood?
No. Burning treated wood can release toxic chemicals into the smoke and ash.
How do I know if my old deck is CCA-treated?
CCA timber often has a green tint and was common in homes built before 2004. If in doubt, assume an older deck is CCA-treated and seal it regularly.
This article is general information, not medical or professional advice. Follow the supplier’s guidance and your local regulations.
Sources: US EPA – Chromated Arsenicals (CCA)
