Metal Roof On Pressure Treated Wood

I would be concerned that galvanic corrosion could degrade the metal roofing or fasteners.

Metal roof on pressure treated wood.

From the manufacturer s website. Consumers and regulators of building construction involving wood components often require pressure treated wood to help protect the components from attack by termites other insects and fungal decay. In the nrca roofing and waterproofing manual fifth edition the national roofing contractors association nrca specifically recommends the use of decay resistant treated wood for blocking and nailers at roof perimeters and penetrations for fastening membrane and sheet metal flashings. High copper content in the preserved wood was in contact with galvanized fasteners and hardware dissimilar metals.

The chemicals used to treat this wood have been revised in 2003 to remove some of the potential harmful elements in the pressure treatment. Pressure treated wood is often used for construction areas that will be exposed to the weather or in high moisture areas. Copper is the culprit since most pressure treated lumber is used where moisture is present outdoors crawl spaces and basements the perfect storm for galvanic corrosion was created. Pressure treated lumber is often treated with one of two chemicals.

Treated wood commonly is used in the u s. Hot dip galvanized steel in contact with treated wood. The asphalt in the felt paper is waterproof and does a great job of protecting the. Copper azole ca c or alkaline copper quaternary acq both of which contain copper a harder metal.

Most metal roof companies recommend installing felt paper on roof sheathing before you install the metal roofing. The metal present in the treatment chemical copper is dissimilar to the metal roofing steel. If the treated wood is situated next to flashing or fasteners made out of a metal softer than copper like aluminum the copper in the treated wood will attack the softer metal. Most pressure treated wood is treated with chromated copper arsenate.

Galvanic corrosion occurs when electrons move away from an anode toward a cathode. Steel framed buildings often include wood components such as sill plates top plates door or window bucks and sheathing for floors walls and roofs. Construction industry as a component in roof assemblies.