06 July 2007

advice needed: pressure treated lumber?




Okay, so I've learned how it work, and it sounds nasty.

Wood is a great building material. It is strong, lightweight, easily worked with tools and relatively inexpensive. The only problem with wood is that many varieties of bacteria, fungi and insects find it appetizing. When wood is in contact with the ground or moisture for any period of time, these organisms attack the wood. Untreated wood like pine will only last a year or two if it is touching moist ground.
Pressure-treated lumber is wood that has been immersed in a liquid preservative and placed in a pressure chamber. The chamber forces the chemical into the wood fibers. The pressurized approach makes sure that the chemical makes it to the core of each piece of wood -- it is much more effective than simply soaking the wood in the chemical.
The most common chemical used to treat lumber used to be chromated copper arsenate, or CCA. In 2003, however, the Environmental Protection Agency restricted the use of CCA in residential settings due to health and environmental concerns about arsenic leaching out of the wood. The most widely used alternative to CCA is alkaline copper quat, or ACQ. Copper is toxic to various insects and fungi that might cause decay. ACQ binds to wood fibers very well and allows wood to last decades even when it is in contact with the ground.
The protection provided by the chemical depends on the amount of chemical that the wood absorbs. In the United States, the amount of chemical is measured in pounds of chemical per cubic foot of wood. For ground contact, 0.40 pounds per cubic foot is needed. For foundations, 0.60 pounds per cubic foot is the standard.
The chemicals in treated wood are generally not good for humans. This is why you see warnings advising you to wear gloves, avoid breathing the sawdust, and refrain from burning treated wood. Keeping small children away from treated wood is also a good idea.
(Okay, I think that pretty much falls WAY outside of the Green scheme at play here)

But there is:
Borates may be better
Not all pressure-treated lumber is copper-based. Borate-based treatments are also effective at stopping bugs, mold, and rot. Borate lumber treatments have low toxicity levels for people and pets. Borate taken into the body doesn't build up like heavy metals do; our bodies excrete what they don't need.
Borate pressure-treated wood has excellent to outstanding corrosion resistance to common metals, according to standards established by the AWPA. No special fasteners or flashings are required.
Lumber treated with disodium octaborate tetrahydrate (DOT) historically has been used in protected, not exposed, locations because borate leaches from wood when the wood gets wet.
But studies show that borate-treated lumber doesn't leach as much as its reputation suggests.
And borate treatments are getting better. Wood Treatment Products Inc. (http://www.eswoodtreatment.com/) has developed a way to fix borate into lumber better. EnviroSafe Plus is the brand name of this turbo-borate, and it has tested well for borate retention, noncorrosiveness, fire suppression, and nontoxicity of smoke.
I hope not to need much new wood, but for framing the house, as well as the deck materials, I'm sort of wondering what to do here.

Your advice is welcome!!

1 comment:

Alex said...

If you love wood, you'll love Roger Deakin's latest (and sadly last) book, Wildwood, which has just come out over here in the UK. Nothing to do with pressure treated lumber though.