Decking can be installed over flat built up or EPDM roofing material if done right. The finished product is great usable space, and since it's on a roof it usually has a view.
Before building a rooftop deck, consider the following. The roof structure must be able to support the additional weight of the framing, decking material and the people who will be standing on it. In Coloraodo, as with may states that have snowey winters, all our buildings are engineered to support an incredible amount of weight just in case we get that once in a lifetime blizzard. In your area, this may not be the case so always make sure to figure out if your structure can handle the increased loads. Consider hiring an engineer to inspect the area you wish to use and have a letter written stating that the project is safe. This will help speed up the process when you go to pull a permit.
For the deck itself, there are no real codes currently addressing this sort of installation. The actual construcion of the deck will be based more on standards being adopted by your local building department and on commonly used techniques. This is many times referred to as "best practices" and referes to the way contractors and manufactures have agreed to do projects of this sort to date. This is many times the basis for codes that are later written about new techniques. Before biginning your project or even purchasing materials, talk to your building inspectors to find out if they have standards they would like you to abide by. If not, then submit a drawing of what you would like to do. A simple sketch shoing materials and spacing goes a long way in this process.
Regardless of your exact installation, you will have a few things to consider.
1. The decking must be attached to a wood or metal frame work. You can throw a bunch of material on a pile and call it a deck but you will be wrong. This generally means dimentional lumber placed on side, but not always. The framing is usually treated 2x4 or 2x6, but again this can vary depending on the regulations in yoru area and the physical work area you are dealing with. These members are referred to as "sleepers". Before laying our sleepers out, we drew markes on the roof using a perminant marker then used a high visability chaulk to snap lines every 16". The sleepers are just set against the marks whiel deck boards are attached. Just keep an eye on your boards as you go so that you odn't push them out of line.
2. The sleepers must not be allowed to directly touch roofing material. Over time, small movements in the deck from walking or even wind can cause the framing to rub through the roofing materials and cause leaks. "How do I impliment such magic" you ask - I'll tell you. The raming should be seperated by the use of a materail approved by the roofing installer. This is usually strips of roofing rubber that are glued to the bottoms of the sleepers before they are placed on the roof. The sleepers are not attached to the roof, as the entire deck is actually floating. In the case of the deck shown here, the roofer prefered that we use rubber feet that were cut from walking pads and glued to the sleepers using construction adhesive.
3. The decking should not be allowed to rub on the side walls of the roof. In cases such as the deck shown, the roofing membrane runs up the side walls and is then covered by the siding. When installing the deck boards, leave at least a 1/4" space around the edge. As a contractor, I make sure not to allowe the gap to be to large as a womens high-heel shoe could get caught in the gap and cause an injury. Until women stop wearing party shoes to rooftop parties, we need to take this into consideration.
4. The fasteners used for the deck boards must not penitrate all the way through the sleepers. For some reason, roofing contractors get cranky when you nail the sleepers into their roof. Until these guys learn to deal with adversity better, it's up to us to keep them happy. Measure and then double check by trying a small sample deck board instalation to make absolutely sure that the fasteners will not penitrate deep enough to come through the bottom of the sleeper. In cases where the sleeprs are installed on side, this is not usually an issue, but in our case this was a major concern. We did a lot of practice before building the real thing.
5. Nail look better when they are in a strait line. When you place each deck board, just install 2 or 3 screws to hold it in place with the propper spacing. When you have all the boards down, snap a line using a non-staining chalk line and the ninstall all the remaining fasteners along these lines. The finished product will look awesome, which is exactly what we are after.
6. Many of you have noticed the use of a nail gun in the photos and have concluded that since nails are not screws, we must not be using screws on these decks. You would be correct, and incorrect - get ready to have your pardine shifted. For these decks we are using a balistic screw. This is a hibrid screw with smaller threads that is fired from a framing nail gun. Once in, the screw can be removed or re-set with a drill. This is the first time we have ever used these on a project like this. You can click here for a review of UFO's balistic deck screws.