Was this web flat and round, with a spiral on it, or tangled, messy, and three dimensional?
The black hourglass reminds me of certain species of Orb Weavers (family Araneidae). Like this:
http://bugguide.net/node/view/357128/bgpageHowever, orbweavers don't build webs so low to the ground, and build them out in the open. Cobweb spiders that build the three dimentional webs are more likely to build a web in the dark area under your deck.
