Can pressure-treated wood be used in contact with bare and prepainted GALVALUME sheet?
Contact with pressure-treated wood or, for that matter, any wet lumber is not recommended for either bare or prepainted GALVALUME sheet. Treated lumber contains chemicals that protect the wood when buried in soil. Direct contact between wet treated lumber and GALVALUME sheet creates a corrosion cell and the corrosive chemicals leaching out from the wood accelerates this process. All rooftop ancillaries, such as air conditioners, should be mounted with factory-made mounting accessories compatible with GALVALUME sheet (roof curbs, for example). Some HVAC contractors commonly mount rooftop air conditioners on pressure treated landscape ties. Direct contact of these ties with the GALVALUME roof causes corrosion of the aluminum-zinc coating. Even drainage from pressure treated lumber onto GALVALUME sheet should be avoided.