Identifying TWW

What is Treated Wood Waste (TWW)?

Wood products that are used in outdoor exposures where they are subjected to weather are often preservative treated to protect the wood against deterioration from insects and decay fungi. This protection is provided by preservatives integrated into the wood.

DTSCWhen outdoor structures built with preservative treated wood – such as decks, gazebos, fences and retaining walls – are demolished and discarded, the wood is considered TWW.

How to identify TWW

All wood when exposed to weather and ultraviolet light over time will change color, often to a dark or light gray color. So it may be difficult to differentiate preservative treated wood and untreated wood, particularly as natural cedar and redwood are often used outdoors because these species have a natural durability. Here are some potential ways to identify preservative treated wood:

  • End tags – All preservative treated wood products sold in retail locations have a tag on the end that details the use conditions and preservative used. If any wood in the structure still has an end tag, it is likely the rest of the wood in similar applications is preservative treated.
  • Incising marks – Preservative treated wood used for ground contact applications often has incisions, or small slits in the wood to allow the preservative to penetrate deeper into the fiber. If the wood has these slits, it is most likely preservative treated.
  • Outdoor use – Preservative treated wood is designed specifically for outdoor applications, so any wood used in such applications is possibly treated. Preservative treated wood can be visually identified by: a greenish exterior color, interior rot with a solid outer shell or visible color penetration just under the edge surface of the wood where it is cut.