Solutions for Wood Treatment Toxins

Back in February 2014, we discussed the need for adequate R-values to meet current building and energy codes. Buildings in the mid-continent United States with all above-deck thermal insulation require an R-factor of 20 – dramatically more than during the pre-oil embargo years of perhaps R-2.8 for 1 inch of wood fiber or perlite boards.

A combination of polyisocyanurate and cover board is much more typical today, with a half-inch cover board contributing an R of 0.56 and the isoboard contributing the rest. With the recently revised R of 5.6 per inch of isoboard’s thickness, we now need roughly 3.5 inches of isoboard to meet code.

I also reminded you that low slope roofs need wood nailers at roof edges and penetrations that match up to the above thickness of 3.5 inches of isoboard, plus the half-inch of the recover gypsum board.

Ironically, a 2-by-4 is really only about 1.5 inches thick, so we need two 2-bys plus a 1.25-by to match up to the nominal roof thickness.

To understand where we seem to be heading, it may be helpful to see where we are coming from.

The Early Years
Creosote was originally used as a wood preservative. Derived from coal tar pitch, creosote is the most widely used wood preservative in the U.S. but is falling out of favor, as the EPA now considers it a probable human carcinogen.

The next generation of preservatives was based on chromated copper arsenate (CCA), which is now being phased out to reduce potential exposure to arsenic, also now considered a potentially toxic substance.

However, recent years have seen the development of several water-based alternatives to CCA treatments:

• ACQ: A class of preservatives containing copper oxide and a quaternary ammonium compound.
• Borates: These low-toxicity alternatives have been used for more than 70 years. Borates naturally occur in trace amounts and are non-volatile when formulated for use as wood preservatives, so no off-gassing occurs.
• Copper azole: Typically used to treat softwood lumber from sources such as southern pine, red pine, ponderosa pine, hem fir, and Douglas fir.
• Cyproconazole: Specifically for above-ground applications, cyproconazole is not intended to protect wood that comes in contact with the ground.
• Propiconazole: Like cyproconazole, propiconazole prevents wood decay in above-ground applications only.