Pressure Treated Lumber – Don’t Panic!


I was recently asked a question by a Realtor friend if using pressure treated lumber in a basement would give rise to off-gassing of Arsenic.  If this had been any other Realtor who I was dealing with for the first time I would have immediately thought this was one of those pet questions asked by realtors to establish the credibility of the inspector.   This one was so far fetched, and from a Realtor I know to be both reliable, professional and trustworthy I thought “where did that one come from?”

On questioning further I found out that a fellow inspector, had put in their report that using pressure-treated wood for framing in a basement would off-gas arsenic and suggested it had the potential to cause serious illness to anyone exposed to it.

I have fought long and hard against the term “Deal Killer” when used against Home Inspectors, as it is not the inspector that generally kills a deal, but the condition of a home.  However in this case, I’m wondering if the term is apt.

So a bit of background.

telegraph polesWood preservative did in fact at one time contain Arsenic.   It was held in a compound called Chromated copper arsenate  or CCA for short.   This wood preservative was invented by an Indian Scientist in 1933 and first patented in 1934.   This treatment was used worldwide extensively until the 1990’s when research into Chromium and Arsenic provided an alternative to CCA.

The problem with CCA treated wood was that, over time, exposed to the elements, and water, the CCA compounds would leach out of the wood and into the soils.   This would release the Chromium and Arsenic which were seen as contaminants.   Following a public outcry, multiple studies were done across the work, and in North America the Environmental Protection Agency (EPA) commissioned several studies which concluded that while no validate evidence showed a high risk to poisoning from CCA treated wood existed when proper treatment and handling was used,  it accepted the lumber manufacturers request to cancel the approval of using CCA for residential products.  Although a ban on CCA treated wood was never imposed, the voluntary cancellations prohibited CCA treatment on wood intended for outdoor residential structures such as decks and playgrounds.   Wood intended for outdoor use, but used indoors is considered unlikely to leach sufficient quantities of the CCA compounds because of the lack of moisture.

Since 1992 a Chromium/Arsenic free timber treatment for wood has been available, first introduced into the U.K. and Canada  by the Hickson Chemical Company (under the brand of Tanalith E).

Modern treatments use ACQ or Alkaline Copper Quaternary compounds, which are free from Chromium and Arsenic.    These too have been available since 1992 undergoing a series of modifications that in north America were labelled ACQ-A through ACQ-D.   ACQ-A was discontinued in 2000 due to lack of use.  ACQ-B, available since 1992 has a dark greenish brown colour that fades to a lighter brown as it dries.  It is known to off-gas ammonia until it is dry.   Wetting is not believed to re-introduce off gassing.   ACQ-D was standardised in 1995 has a lighter greenish brown colour and little to no odour.    ACQ-C was standard in 2002.  Again, a little off-gassing of ammonia until dry can be detected.

What’s the danger of CCA?

CCA-LabelThe real danger using CCA is in inhalation of the compounds.   CCA does not off gas when wet.   CCA does not off-gas when dry. So if there’s no off-gassing how can one inhale it?  Well it’s certainly difficult to inhale a piece of 2×4 wood, but if it’s cut, fine particles of dust can be inhaled.  These particles can contain the CCA compounds and then inhalation is possible.   So the risk is:

  • if you managed to find some CCA treated wood, and
  • you cut it using a high speed saw, without wearing a mask
    (Note: you should always use a mask when cutting ANY wood with a power saw) and
  • you inhale the wood particles, and
  • the particles contain CCA compounds

You may be at risk.  Alternatively:

  • if you managed to find some CCA treated wood, and
  • you burn it, and
  • you inhale the wood smoke

You are definitely at risk.

Newer construction

Newer treated lumber for residential use, has since 2003 been ACQ treated.   If you purchased wood from a supplier, for residential use, since then, it will not have CCA compounds in it.  If it does, then the wood supplier is probably breaking the law somewhere along the line.   Major box stores such as Home Depot, Home Hardware and Lowes certainly have ACQ treated lumber for residential use.   CCA treatment is not available for use as a treatment to the public, so you won’t get wood that’s been treated by someone after market.   If you do have older CCA treated wood, it’s likely to be used outside for decking, and any leaching of the toxic compounds has probably already taken place.

treated-woodsHow to identify CCA treated wood

CCA treated wood has a particular green tinge.  It can still be found but is only for heavy duty industrial or farm use.   Things such as Railway ties, Telegraph Poles and wooden barn posts might still have CCA treated wood.   All of these should be avoided if they are on fire!

For consumers reading this, I hope this put’s your minds at rest, for Inspectors reading this, I hope this put’s the risks into perspective so I don’t hear reports of other “Deal Killers” out there, and for those in home Depot, Lowes and home Hardware that are selling treated lumber for internal residential use, stop doing it!

Putting a damp proof membrane below the bottom sill plate is all that’s needed to protect the wood from damp coming up from the floor.  It’s cheaper than treated lumber and it’s the right way to do it.  If the basement is so damp that it needs treated lumber for framing, I suggest there are other things that need to be addressed in the basement long before a decision to frame and finish it should come to mind.

The original concern

Going back to the original concern at the top of this post.  The other inspector who suggested people might die from the off-gassing of Arsenic from the wood was, how can I put this nicely?   Over exaggerating somewhat.

If the home had CCA treated wood in the basement, and the basement was dry, it is highly unlikely that any CCA would leach from the wood, as it would not be subject to moisture.   If it was subject to moisture the CCA compounds would leach out of the wood and form salt deposits on the floor staining the floor green.  It certainly wouldn’t off-gas arsenic into the atmosphere.

There is a possible concern, and this is how i put it to the Realtor.

“I would suggest that the risk to anyone using CCA lumber in a basement for framing would be if the basement caught fire, and the occupant stayed in the home to breath in the Chromium and Arsenic gases that were given off by the burning wood.   They would them likely be exposed to high levels of toxicity that would have to be treated to stop them from succumbing to these gases.

The problem is, that they would more likely be killed by the fire.   So medication for the toxic effects of CCA high temperature off gassing would be pointless.”