Keeping the area beneath a deck dry usually involves a separate process to attach drainage material between or under deck joists either before or after the deck boards are installed. But the newest alternative we’ve seen is Fastendry from Deckorators, which manufactures composite decking with slotted edges to accommodate its proprietary Stowaway Hidden Fastener system.
The Fastendry extrusion is engineered to fit snugly into these slots and has an integral flange that can be pneumatically nailed to serve as a hidden fastening system. The result is a dry-deck system that’s an integral part of deck board installation. Drip kerfs field cut into the ends of all deck boards keep water from wicking back into the slots, but the deck perimeter can be left as-is or picture-framed using square-edge deck material.
Butt joints can’t be fitted with the extrusion, so to avoid leaks, deck dimensions should be coordinated with the standard 12-, 16-, or 20-foot lengths of both the Fastendry extrusion and any of Deckorators’ five composite decking products. Larger decks can be divided into smaller sections that can drain into hidden gutters built into the framing.
The black Fastendry extrusion sits about 3/16 inch below the decking surface, so seen from above it looks like a regular deck. Seen from below, the nailing flange creates an evenly spaced pattern of black stripes running perpendicular to the joists. Unlike some undermounted systems that can allow leaves and debris to collect under the decking, Fastendry completely prevents anything from getting through the spaces between deck boards.