Firestone Guidelines Regarding Treated Lumber
Why Is Treated Lumber An Issue?
Lumber or plywood that has been treated with copper compounds is sometimes specified for use in roofing projects. Typical copper compounds used for treatments are ACQ (alkaline copper quaternary), CCA (chromate copper arsonate), or CA-C (copper azole). Copper corrodes steel components due to the galvanic reaction caused by the interaction of dissimilar metals. The presence of any moisture will accelerate this natural galvanic corrosion, and creates an electrical current that degrades the steel, which is the “lesser” of the two metals.
What Happens If Treated Lumber Is Used In Roofing Projects?
The corrosion of steel fasteners in copper-compound treated lumber compromises the integrity of the steel and significantly raises the possibility of performance failure. Corroded fasteners cannot be expected to perform. Copper-compound wood treatments can also discolor and/or compromise the integrity of roofing membrane materials. The typical result is brown tinted areas where the membrane has contacted the wood, or where a galvanic reaction has occurred. There have been reported instances of membrane failure, especially in wetter environments where the reaction is accelerated.
What Firestone Fasteners Should I Use If Treated Lumber Is Present?
These Firestone fasteners are manufactured with an electrolytic PMS485 corrosion resistant barrier coating process to make them highly resistant to corrosion from copper-based wood treatments:
- Firestone All Purpose Fasteners
- Firestone Heavy Duty Fasteners
- Firestone HD Plus Fasteners
- Firestone HD HailGard Fasteners
- Firestone UNA-CLAD #10 and UNA-CLAD #12 Fasteners (metal roofing applications)
- Firestone Stainless Steel Fasteners are likewise highly resistant to corrosion. No other fastener types should be used in CCA, CA-C, or ACQ-treated lumber. Firestone is not liable for claims related to the use of non-approved fasteners in treated lumber.
What If The Roofing Membrane Is In Contact With Treated Wood?
To reduce the possibility of membrane discoloring, install a sacrificial sheet of membrane material over the treated wood before installing the roofing membrane.
Are There Any Non-Copper Wood Preservative Treatments?
A common non-copper wood treatment is SBX (borate). In addition to electrolytically-coated fasteners, galvanized fasteners may also be used in SBX lumber.
Posted on Thu, February 17, 2011
by CSR filed under