Past comments from the forum…
What I mean byroofdecksis woodendecks*(2 x 4 joists with planking) laying, directly, upon a modified bitumenroofcovering. Sometimes, they put another layer of membrane under some points of the joists.
Putting aside the questions about proper structure and loading, it has been my experience that the deck will a) move, rub and tear theroof covering and b) increase the cost of replacing theroof*(you have the added cost of having to remove the deck first).
Does anyone have any reference, code or authority to cite when calling this out?
I also understand that there is a membraneroofcovering that allows this?
Any help would be appreciated.
I looked quickly to find you something, but did not find much other than what I have seen and known over the years.*
Modified bitumen or built-uproofsystems always had strategically spaced blocking pre-planned for the deck and incorporated in theroofsystem at the initial install.*
If done after the fact, blocks of wood or sleepers were adhered to theroofmembrane and water proofed and became part of theroofsystem.*
On rubber membranes, an addittional layer of rubber is adhere to the membrane where sleepers will be for the deck framing. Usually, this is .060 rubber, whether it is Carlile, Firestone, or Goodyear product.*
I have seen at times where walking pads were installed to protect the membrane of theroofsystem, regardless of the type ofroof.
As far as finding some back up for what I am saying, I can’t find any at the moment.*
I did find this if it helps.*
Building a FlatRoofDeck
Occasionally a project is presented where a deck will be built over a flatroofof a house or a garage. First you must make sure theroofis strong enough to support 55 lbs per square foot. Next you will want to install a watertight EPMD rubber membrane over the top of theroofdeck for protection against water infiltration in place of roofing materials. You will then install “sleepers” or flat 2x6’s laid on their profile every 16” on top of theroofsurface. This will provide the surface for you to attach the decking. In most cases your “sleepers” will float on the surface of theroofwith only the weight of the deck to hold it in place.*
Make sure the deck slopes slightly to promote drainage towards gutters or at least away from the house. Always check with the local building inspectors and obtain a permit before building a rooftop deck.*
Hope this helps a little.*
It sounds like your building has a standard bitumen built up roof, as malor describes. Building a roof deck over that surface, that would meet building codes, and not damage the roof, or cause premature failures and water leaks is not a simple matter of building directly on the existing roofing system. Problems with water intrusion from something as simple as laying wooden pallets out on such a roof, where differential expansion and contraction under a constant load as light as the weight of a pallet, can cause failure of the top most membrane in as little as a single season. Once water intrusion starts, a felt and tar roof deteriorates fairly rapidly, particularly in climates like NYC, where alternate freeze/thaw cycles let minor amounts of water do major damage quickly. So, a pedestrian deck system is usually built as a series of bridge segments, over such a roof, connected to the building’s underlying frame by structural elements that penetrate the roof, and are flashed to prevent water intrusion. Every one of these points is an additional point of potential leaks and roof failure, so they are engineered to be as few, and in as advantageous locations as possible to support the deck loads, and provide the means for removing the deck when roofing work is required. Whole systems of walkable integrated membrane structures have been developed to meet demands for roof decks that try to overcome these problems.