I am in the process of doing a major refresh of my home's exterior. I need some help with one area that has me stumped. I have round attic vents that were originally installed with the exterior siding. I replaced the siding with Hardy shingles. Because of the layering of the shingles, the vent is no longer flush. It is too late to replace the vents so I decided to put a frame around them. What kind of lumber product would be suitable to build the frame? Outdoor plywood would work but is there a better alternative?
Your issue is not only getting the face of the vent flush with, or proud of, the shingles, but also to make sure you'll be able to seal or flash it to make it water tight. You don't want water running down behind the new shingles.
Beachguy has a very good point.They need to be flashed or weathproofed first.I would use pvc lumber.Something like Azek for the trim.The big box stores carry it in white but Certanteed and some others make it in many colors which can be bought at a lumber dealer.