Intro
Storage sometimes is not considered in deck design. But there are opportunities to make space, such as boxed seating with hinged lids. And a natural space for storage is under the deck.
A space at least 2 feet high under the deck offers plenty of room for storage. Grade-level access (through a door), isn't handy with a 2-foot space, however, because you would have to crawl under the deck. Instead, build an access hatch so you can lower things into the storage space from the deck.
To create underdeck storage, attach a storage box to the joists before you install decking, and make the hatch from decking cut to fit the recess. Cut a hole in decking boards or install flush lifting handles so you can lift the hatch out.
If your deck is raised 4 or more feet off the ground, entry through a door is practical. In that case, build removable skirting sections or hinged siding panels.