Oil-Canning Deck Fascia
When fascia boards are set flush to the deck boards, debris and moisture can get caught in the joint and warp the composite material.
I’ve seen composite fascia boards set flush to the top of the deck boards several times. At least twice, that fascia had become wavy and pushed away from the framing. This seems like it’s more a fault of the construction method than the material. I live in the Hudson Valley of New York, where we have an abundance of falling plant matter from spring through fall. I think this debris works its way between the fascia and framing and gets saturated with water, making for a nearly constant amount of moisture between the fascia and the framing member. Either that moisture alone or a couple of freeze/thaw cycles creates this wavy effect. Am I just seeing a lowball application by substandard contractors, or is this actually a recommended method of installation?
—Mark via email
Bruce Verblaauw, of NJ Decks and Railings by C. Verblaauw & Sons, LLC, replies: What you have seen and diagnosed correctly is what the industry calls “oil canning.” As a contractor who builds only decks, I would never allow my crews to install the fascia like this. I see it done a lot by others, though. It is a quick way to hide the ends of composite decking boards, but it comes at the expense of the customer. At least one manufacturer, Trex, now excludes warranty claims on their fascia when it’s been installed flush with the top of the decking.
My crews install a border of decking that runs perpendicular to the main deck boards. This hides the ends of the boards and overhangs the fascia by 3/4 in. all around the deck to keep water and debris from getting behind the fascia board. It takes a little more time, and we have to install blocking between the joists at the sides of the deck to support the border, but that work pays dividends in looks and longevity.
Oil canning can still happen due to expansion and contraction from temperature changes if you are not careful. We install fascia boards with three screws spaced every 12 in. to avoid this problem. Several companies (FasterMaster, Starborn Industries, and TimberTech, among others) offer special fascia screws that come with a countersinking bit. These bits drill a hole in the fascia that’s larger than the screw. The screws keep the fascia flat while allowing for expansion and contraction along its length.
Photo: courtesy of Mark Eis
From Fine Homebuilding #298