Most building timber is treated with preservatives to stop the wood from rotting and to protect it from burrowing insects. Treated timber is used to build homes, decking and garden furniture, and you will find it in some playgrounds.
Last updated: February 2020
Some of the chemicals used to treat timber are toxic. Although it’s unlikely that you or your whānau will be exposed to high levels of these chemicals by touching treated timber, there are a few precautions you can take, particularly if you are working with treated timber at home.
Working with treated timber at home
If you are working with treated timber for DIY projects around the home and garden:
- store the timber in a well-ventilated, covered area away from children and pets
- wear gloves when handling treated timber
- if you are sawing, using power tools or sanding treated wood: wear gloves and safety glasses, and use a filter mask to prevent breathing in dust – if the timber is CCA-treated (chromated copper arsenate treatment), take it outside when you are working with it
- don’t work with treatment-damp timber – allow it to dry first in a well-ventilated area
- clean up scraps, shavings and sawdust thoroughly afterwards, and brush off the wood before use
- if you get sawdust on your clothing, wash the clothes before using them again – and in a separate load from other household clothing
- wash your hands, face and any other exposed skin before eating and drinking, rubbing your eyes, smoking, or going to the toilet.
Treated timber and food
- Don’t prepare or serve food directly on treated wood.
- Don’t use treated timber to make food platters, or serving or eating implements (manufactured wooden utensils bought from a store should not be made from treated timber, but if you have any concerns, check with the retailer).
- Never use treated timber in beehives.
- The risks from using treated timber to make planters and raised vegetable beds in your garden are negligible, but some treatment chemicals, such as CCA (chromated copper arsenate), can leach poisonous compounds like arsenic from the wood into the soil over a long time. Leaching should be insignificant because modern timber treatment processes - and the current timber treatment standards - require preservatives to be fixed to the cells inside the wood before the timber is sold.
- To reduce the likelihood of exposure in planters, plant a few centimetres away from the timber, or line the planters with sheets of plastic.
- You could also consider using a harder, untreated wood for raised beds to grow vegetables, like macrocarpa, Douglas fir or Lawson cypress, or use alternative building products.
- Never burn treated (or painted) wood - for example, in bonfires, barbeques, wood-burners or open fireplaces.
- Never use the sawdust or shavings from treated timber for animal litter, in compost heaps or as a mulch in your garden.
- Take treated timber offcuts to your local council landfill or transfer station for disposal.
- It is extremely unlikely that the health of children would be damaged by playing on treated timber, for example at playgrounds, but there is sometimes a chemical residue left on the surface of some treated timbers when they are newly installed. This residue is tiny and likely to be negligible, but it’s best to wash your kids’ hands afterwards and before they eat or drink.
- Never make toys for children out of CCA-treated treated timber (the toys you buy from a store should not be made from treated timber, but if you have any concerns, check with the retailer).
- Don’t let young children play with CCA-treated timber offcuts.
For more information, see the section below on our extensive research into the safety of CCA-treated timber.
Applying decking and fence stains, oils or paints
You could choose to coat CCA-treated timber with paint or a polyurethane coating to reduce your exposure, and refresh this coating on a regular basis. Some studies suggest that this can reduce the amount of CCA that leaches from treated timber.
In general, if you are applying any timber coating product, such as a wood preservative, stain, coating or paint:
- Read the label and packaging carefully and follow the instructions.
- Store all unused products in a dry, well-ventilated and secure place, away from children and pets.
- Dispose of any unused product carefully – follow the instructions on the label.
The chemicals in treated timber
When you buy timber for building, if it is treated timber you’ll see it is labelled with a code starting with an ‘H’ (such as H1.2, H3.1, H3.2 or H4). These show what uses the timber is suitable for, for example, internal framing timber or below-ground uses such as piles, and give an indication of the type and extent of chemical treatment. The higher the number, the higher the treatment level.
For more information about the different hazard classes for treated timber, where the timber can be used, and the type of chemical treatment involved:
- see the Treated Timber Hazard Class guide - New Zealand Timber Industry Federation website
- read more about timber treatment - BRANZ Weathertight website
Our research into the safety of treated timber
Research commissioned by our predecessor, ERMA, and further work we funded later, looked into the safety of children and adults around treated timber (particularly wood treated with CCA). The investigations considered safety at home and outdoor settings, such as, in playgrounds, on decks, garden furniture and picnic tables, and landscaping features like retaining walls, fences and gazebos.
The research found that it is extremely unlikely that the health of adults and children would be affected by coming into contact with treated timber around the home and in playgrounds.
You can download the 2005, 2006 and 2009 reviews of CCA use in timber treatment chemicals from the related content at the end of this page.