Decks, Patios, Porches and Docks - Joist Spacing

Hi, I am putting a deck on one of our roofs. I looked in the ceiling and found 2x6 joists spaced 16" o.c. The joists are actually 2" x 6" and I think made of redwood (Victorian in San Francisco). The span of the joists is 12'. The decking I want to put up is about 15lb/sf. (Check out www.levelit.us- a great product.) The deck is 12' x 10'-8". And I would expect 12 people at most on the deck. Can someone tell me if this is structurally sound?

2X6's can span 12' as a ceiling joist, but NOT as a floor joist -- and that's what you are turning them into as soon as you put a deck above them. You'll need a midspan beam in the room under this deck.