Roof deck over synthetic membrane: water intrusion?

Oops, so I posted this in Outdoors before I found Home. Double posting is irritating but it's kind of relevant to both... I'm new to the forums here (long time reader, infrequent poster), if I just committed a major faux pas, gimme a heads up and I'll take one of these down! Anyway, so the back door of my 3rd floor apartment opens on to what amounts to a raised back yard; the only problem is that this "back yard" is the roof of a 2 story addition to the brownstone I live in, and I'd rather not put my foot through a very expensive roof. I've been looking into decking, and right now my plan is a contact-only solid frame all the way around the perimeter of the roof, with a lip extending over the edge of the roof (to supply stability without puncturing the membrane) connecting to the actual frame of the deck which would of course be placed over the top of the brick walls of the building. From there I was going to face the deck with synthetics, probably with struts placed along the horizontal struts of the roof connected to both the upper deck and sub-deck cross bracing (depending on what materials I use/can afford and their relative strength). My hope is to find a way to make the deck in modular pieces that can be removed for when the roof inevitably needs to be resurfaced. So basically it would be large squares (or irregular shapes, whatever) that would sit on top of the struts/cross bracing with the help of a few screws and provide the deck surface. What I'm worried about is water intrusion at the contact points, such as around the edge of the roof and on top of the studs in the middle of the roof. I know synthetics are much more resistant to this type of failure than older materials, but are they impervious? Where do the pros put contacts so water doesn't leak into the floor below? Even if you minimalize it, the deck will have to come into contact with the roof at some point, or you've found some fancy new way of building I'd love to hear about. A few other thoughts are footprint: the building is an 1890 Richmond row house, could this be done with a small enough profile to increase the value of the property without damaging the "drive by" value? (I was picturing an iron railing to keep the project semi period, and this roof actually connects to the big hulking wooden fire escape, so it wouldn't be marring a virgin landscape) Also, do you think any building codes in the country would allow L bracing and big old bolts to hold the structure of the deck together instead of end-nailing the boards? It would make removal for roof work a lot easier. For the corners, would it be better to miter the ends at 45 and run a bolt through the two of them, end nail an L joint or use a thick metal l bracket and a few bolts to hold the joint together? That was kind of an intense post, I'm just looking to shoot the breeze a little bit with anyone who has any thoughts. Everybody always has their perfect way of doing things, on such a big, high pressure job (if this goes south I'd be poor AND homeless!) I want to really chew on the idea a little bit first. Thanks to anyone who actually read this far!

Picture of Roof deck over synthetic membrane: water intrusion?
Rishnai8 years ago
Well, first of all, if you were in Denver, I'd have the name of a roofer for you. Since you're not, if you decide that any part of this job is too much to tackle on your own, make sure you talk to several roofers about your specific plans. Make sure they're on board, seem capable, and take pride in their work. Big crews tend to mean bad work... it took two weeks to lay an awful roof on my house with a crew of about 14, most of whom didn't actually plan on doing anything but making out with their girlfriends in my driveway. When the next hailstorm came through, the insurance company let me choose a roofer myself, and one man did the job right in three days, for a lower price. For your modular sections, you could try and drain out to the side with channels (sliding door track?) placed underneath the joints. Besides that, the simpler way is probably to put copper flashing across the joints, same as with matching a garage roof with a higher house roof, if you know what I mean. Tar a little around the edge, and you're golden. Come daylight I could have photos if you like.
i.am.flink8 years ago
If you are a decent, experienced carpenter you might tackle that. Penetrations are safe enough as long as they aren't depressing the area around them. Water is your enemy. Doing a membrane roof is tricky and probably best left to a pro. I've seen a few roof decks that were not much more that a frame with railings and a ledger to hold a floating deck. Take an careful look at the roof slope. If there is ever any standing water, that must be corrected before you attempt a deck up there. The composite is a good idea. You'll need check out a serious reference on the subject. This is absolutely a "building permit required" job. You'll need plans to verify the structural integrity of the roof and it's load bearing capability. Since it is going over an addition, try and locate the company that built it. They may have plans on file, as might your local building inspection office.