What is Treated Wood?

WHAT IS TREATED WOOD?

WHAT IS TREATED WOOD?

Wood that had been appropriately treated with preservative chemicals with the intent of prolonging its intended usefulness lifecycle compared to untreated wood.

Depending on the type of application and preservative used, they help to protect wood fibers from structural degradation, decay fungi, termites, marine organisms and flames. All chemical preservatives are registered pesticides and as such they are regulated by the US EPA. The American Wood Protection Association (AWPA) writes various standards that determine use levels for wood preservative formulations as well as their suitability for the intended end-use. Third party inspection agencies regularly perform audits to ensure that quality products are produced in accordance with the standards.

treated wood
treated wood

Depending on the type of application and preservative used, they help to protect wood fibers from structural degradation, decay fungi, termites, marine organisms and flames. All chemical preservatives are registered pesticides and as such they are regulated by the US EPA. The American Wood Protection Association (AWPA) writes various standards that determine use levels for wood preservative formulations as well as their suitability for the intended end-use. Third party inspection agencies regularly perform audits to ensure that quality products are produced in accordance with the standards.

Advantages of treated wood
(life cycle of untreated vs. treated)

Unprotected wood can…

  • begin to rot within 1-2 years, depending on the environment
  • have its structural integrity greatly reduced within weeks due to termites and certain marine organisms
  • be consumed quickly when exposed to flames Because it’s intended to extend the usefulness, fewer trees are needed to perform a function over time
  • Wood that has been appropriately treated can significantly reduce the number of trees that would otherwise need to be harvested
  • If untreated wood lasted 5 years and treated only lasted 25 years, it would take roughly 5 times as many trees over the same timeframe, as well as incremental labor to continually harvest, manufacture, replace and dispose of all of that wood

Common preservative
protection categories

  • Fungal rot/decay and termite protection
  • Outdoor, exposed applications
  • Interior framing
  • Marine organisms
  • Dock/pier pilings
  • Fire Retardant Treated Wood (FRTW)

Types of preservative
treatments

  • Topical/surface
  • Usually limits protection to surface area as it is applied by brushing, spraying or dipping
  • Although regularly coating a surface with a paint or sealer may help protect wood from the elements, it won’t necessary prevent it from rotting or being attacked by insects
  • Pressure-impregnated
  • Preservatives are infused into the wood, beyond just the surface

Pressure Treatment (PT) is the general term to describe the process for infusing/impregnating the wood fibers with preservative chemicals, removing any excesses, and leaving behind only enough chemical in the wood fibers (retention) to protect the wood. The AWPA sets appropriate chemical retentions depending on their intended use/requirements, based on performance data derived from long term scientific tests. The AWPA wood preserving standards are reviewed by their technical committees every five years to ensure that retention levels are appropriate and that a given preservative formulation is performing as expected.

There are three categories of pressure treatments available:

  1. Waterborne treated lumber is generally used in building structures that are residential, commercial and industrial.
  2. Creosote treated lumber is mostly used for treating guardrail posts, railroad ties and timbers used in marine structures.
  3. Oilborne treated lumber is used when treating utility poles and cross arms.

There are naturally-occurring fungi in the ground that attack lumber, so lumber destined to be used in the ground must be treated to a higher standard, or retention level, of fungi-resistant preservatives in the wood. The end tags on treated lumber will provide you with proper use designations. Look for Above Ground or Ground Contact on the end tag.

What treating wood with a preservative does/does not do (splitting, weathering, mold etc.)

Treating wood with preservatives won’t necessarily…

  • Prevent or eliminate naturally occurring defects in wood (e.g. splits/cracks)
  • Stop wood from weathering (non-coated wood is subject to turning gray and potentially developing environmental surface molds)
  • Eliminate natural characteristics (e.g. knots) or make wood stronger

Treating wood will…

  • Prolong the usable life of the wood in specific circumstances compared to untreated wood

A wide variety of fungi and insects can attack wood. In addition there are different levels of exposures, ranging from protected/covered, to fully exposed, to immersed in water. It’s important to match the appropriately PT product to its intended use. PT lumber products are available with a variety of preservative chemical options and at varying retention levels, all intended to meet targeted performance expectations without utilizing excessive levels of chemical. Understanding the general differences in retention types and matching them appropriately to how the products are used, should ensure successful performance for an extended period of time. Check end tags on PT lumber products for appropriate use and retentions.

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