i have been tossing around the idea of building a small wood deck over an existing single story flat roof. the section of flat roof that would support the deck is roughly 20′ x 12′. the walls are 2×4 wood framing on a concrete slab with 4×6 ceiling joists 16″ oc. the home is located in the san francisco bay area, so snow would not be an issue.
my search of the archives didn’t come up with a relative thread. i was told there was an article in a past issue of FHB on the topic. after searching through the back issues index, the only article i found that might be of help was
Fine Homebuilding – December 1982/January 1983 – #12
THE DECK UPSTAIRS
by Dan Rockhill
How to combine a deck with a roof that won’t leak
i would appreciate any tips/ideas/pros/cons of putting a deck over a flat roof. i realize there are the issues of supporting the added weight, and if the roof ever leaks, it will be a PITA to fix.
also, if anyone happens to have issue #12, could you let me know if the above article is relevant my idea.
thanks in advance
oak
Edited 4/25/2002 1:51:26 PM ET by oak
Replies
I had to replace a deck on the third floor on the flat roof at the rear of the second story couple of years ago because the roof was leaking and the deck was rotting. I did it the same way as it was done before except I used PT sleepers and cedar decking. The deck is about 10X10. The sleepers were laid floating on the gravel, above the ceiling joists and decking screwed perpendicular to the sleepers. Make sure the screws are not too long to puncture the roof. You can also buy some prefab 2X2 interlocking decking made for that purpose. That way if the roof even leaks, it would be a cinch to lift up the decking to get to the roof. By the way your 2X6 joists would probably need to be beefed up a bit.
You don't mention what your roofing material is.
EPDM is a forty year material so if you did it new before putting the deck palette down, you wouldn't need to worry about leaks.
You need slip runners under the stringers you put down. Your roof will flex with traffic over it and the friction between surfaces can rub the roofing thin. The slip runners are just scraps of the same material tacked in place under the sleepers with appropriate caulk (ie for EPDM so the wrong kind won't react and disolve it)
Check with your codes dept because if a high wind area, you may need to design against wind uplift.
thanks tom and piff for your thoughts...