Decks, Patios, Porches and Docks - roof/deck materials

I am planning a 650 sf addition to my home. A section of the second floor addition will be used as a deck over ground floor living space. I want to install decking material (composite or other material) to walk on to match a new deck area off the addition. I need to seal the "roof" below the second story deck to prevent leaks due to rain/snow/ice. I have been advised to use either fiberglass (expensive) or a tar type material, however either one will have an approximate life of about 10 years (I live in the northeast US near the shore). I want to find an alternative material for sealing the surface below the deck, one with a greater life expectancy where I will not have to pull up sleepers and deck boards to re-seal the "roof." Suggestions are welcome along with specific product/manufacturer names. Thank you for your help.

A Goodyear 60mil EPDM sheet may be a possibility.
The life expectancy may be extended by covering, esp. with gravel as on commercial flat roofs. The gravel, or any covering, will keep out the sun's UV rays which shortens life.
fred

EPDM membrane. Try Resource Conservation Technology in Baltimore, MD. There may be a local company, but I have used RCT. You want a factory seamed EPDM membrane roof. The roof will be made up to a drawing to fit. They have a very long life and are easy to put down. Unfold and screw through the back flaps. The only holes exposed are at the edges, and the screws are run through uncured EPDM that seals.

I recommend that you build your deck in about 4' or 6' square sections so you can easily pick them up if you have any leaks. Be sure to order enough extra EPDM that you can tack to your sleepers to avoid direct contact between the sleepers and the roof membrane. Also, EPDM can be prematurely broken down by grease, so just be aware of that if you have a BBQ grille that likes to drip. IMHO, EPDM is the best choice, 60 mil (don't use the 45 mil).

Bruce

Thank you all for your suggestions.