How to build a roof deck?

May 12, 2007 12:29 AM

Anyone have a roof deck or build roof decks? I'd like to invest in one - what should I do, and what am I missing?

My girlfriend and I just moved into a brownstone apartment on the west side of Manhattan, with access to a fantastic outdoor roof space. The only problem is that the roof surface itself is kind of old and spongy, made from a material that the previous occupant told us tends to melt in the summer heat if furniture or really anything is resting on it. Naturally.

The solution seems to be a roof deck; the building next door has a pretty nice one built on top of what seems to be a fairly similar if not identical surface, so my guess is the roof can accommodate the construction, just nobody's bothered to make the investment.

Has anyone out there taken on a project like this? Did you do it yourself or hire a contractor? In either case, how much did the project cost - as measured in money or labor, or even frustration, if that's the dominant emotion you now associate with the project?

Hive mind, if you have a roof deck story to share, roof deck advice to give or referrals to make, or any general roof deck wisdom to dispense, it would be very much appreciated. I'll put more specific information below.

- The dimensions of the roof are roughly 22x50 feet, though in all likelihood we'd only be building on half of that area. The roof surface also has a mild downward slope. It's not too crazy -- i'd say somewhere in the neighborhood of 10 degrees, noticeable but not so steep that a ball would roll down it.

- Wherever possible, we'd like to make this a green construction that uses recycled materials. As far as I've been able to gather, these are the three major brands of weather-proof recycled plastic wood substitutes:
o Trex - http://www.trex.com/Universal/DealerLocator.asp
o ForeverDeck - http://plasticlumberyard.com/foreverdeck.htm
o LP WeatherBest - http://www.lpcorp.com/deckingrailing/deckingrailing.aspx
Anyone have any experience with any of these?

- Any recommendations on a good outdoor furniture source? We're on a budget but don't mind spending for quality pieces that will last. Ideally, we'd like to use it for everything from grilling, to hosting company, to having a nice place to read or work during the day.

- Super-ideally, we'd like to install a small solar array on the roof to provide power for roof lights, a stereo, possibly even a small computer. Anyone delved into DIY or small-output solar systems?

- In my head, this can be done (well, maybe not the solar power) for somewhere in the neighborhood of $5000. Am I crazy?

- What are the inevitable things I'm forgetting or have failed to consider? There can't be fewer than a dozen.

All's to say, I feel like we have a pretty neat opportunity and I don't want to mess it up. Thanks in advance for your help and collective expertise.

posted by waterbottle to home & garden (9 comments total)

I worked as a front office/computer guy for a roofing contractor for a couple of years. So while I don't have actual physical knowledge of roofs, I have a fairly good overview of the process.

It sounds like you have a flat roof. Flat roofs are a real pain in the ass. There are two major roof flat roof types; tar and gravel and modified bitumen. (when I left the business about 10 years ago, membrane roofs were just starting to happen.) Since you didn't mention gravel, but you do mention sticky and melty, I'd assume you have a modified bitumen roof.

The problem with these roof types is that they just don't last very long. Modified bit is better than T&G, but you'll rarely get much more than 12 or 13 years out of a "15 year" roof. If I remember correctly, the longest possible rating for a flat roof when I left the business was about 20 years, of which you'd get 18 or so. I know NYC gets a lot colder than California and I assume it doesn't get as hot, so I think a flat roof might last a little longer up there.... I believe it's heat that ages those roofs the most.

If you put a deck up there, you're going to make roofing a real pain in the ass, and it's likely to be a problem sooner than you might think. Before you do anything, I'd suggest finding out:

A) What kind of roof you have up there;
B) what its rated lifetime is, and;
C) when it was installed.

Plan your deck installation accordingly. Remember that you will have to put something up that can be disassembled again and stored somewhere, and that this will add to the cost of any roofing projects if you can't do it yourself. If you put a new roof on it (you say it's old), and build the deck on that, chances are pretty good you won't have to mess with it again personally, but do the job right so that the next people won't get bitten.

As far as the actual decking goes, I have no idea at all. Hopefully someone else will chime in. I just wanted to point out that this project could be a lot more expensive than you'd think because of the impact on roof installation.
posted by Malor at 4:01 AM on May 12, 2007

Always one more thing after hitting post..... don't put the deck up right away after you put up a new roof, if you go that way. Leak-test the heck out of that thing before you add the deck, because fixing leaks after you add all that stuff on top could be a real problem.
posted by Malor at 4:02 AM on May 12, 2007

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.

Furthermore, whatever you'd want to build would need to meet building codes, so as not impede fire department access in case of fire, or become flying debris in a wind storm. You might also need to provide safety railings and access control, to assure that the space does not become a hazard for kids. There are reasons why building codes exist, and why there is a permitting process for building and improving property in Manhattan, and your project would have to respect that.

A budget of $5,000 is inadequate to do the job properly (forgetting solar power entirely), but you might offer that to the building ownership as seed money for such a project, although I think it would be, by itself, such a small fraction of the cost of doing the job properly, as to not be too persuasive. You might first talk to people at GSAPP about low cost planning resources to help you think this through, or put together an intitial plan, with which you could approach the building owners. You'd learn a lot, doing that, and start off on the right foot, whether you ultimately get what you envision, or not. And such knowledge could prove useful and valuable later in life, if you get to the point of buying a coop or condo, with similar "possibilities."
posted by paulsc at 4:55 AM on May 12, 2007

All Malor had to say was good, adding to that try to put as much of the weight of the roof on to the actual beams underneath the roofing and where the weight hits the roof try to spread it out with wide platforms for each suppourt.

Also I would recommend against the plastic decking materials, that stuff gets hot in the sun and you won't want your skin to touch it, meaning no bare-feet and no laying down.

I don't know how much construction experience or tools you have, but this would definitely be a good beginners project and would make hitting you cost goal much much easier. The main tools you will need are a chop saw, an air compressor, a framing nail gun, a level, and a tape measure. Also if Malor is right and accessing the roof will be important you will want to use a screw gun to attach the decking boards. The actual construction is fairly easy and will go quick because you can work with large pieces of wood.

The other thing is this is the kind of project you will need city approval for, meaning getting someone to draw up plans for you so that your railings and support meet code, and then submiting them to the city. This will make getting started take a little longer, but in the long run it will make the whole process much easier. Also an architect will get someone to asses the roof and figure out what needs to be done to address the issues Malor stated.
posted by CaptMcalister at 5:03 AM on May 12, 2007

I have friends who built a roof deck in South Philadelphia and it is fabulous. I know it cost a bunch, but I don't know how much. They built a platform a few feet above the roof surface with kind of a beach house style.

One thing they said worked out for them was running a water line up there to a sink for cleaning up after dinner.

And Trex is great. I had a Trex deck and had no problems.
posted by MtDewd at 6:16 AM on May 12, 2007

Maybe this is just the trauma of sopping water off the windowsills for months after a bad roof install talking, but I'm going to go way out on a limb here and suggest that CaptMcalister is wrong as wrong can be; this would not be a "good beginners project." Screwing together lumber into something that looks like a deck is pretty simple, sure. Putting together a deck that can be attached to a roof without destroying it in the process, not so much.

We recently built an addition to our house which has a flat roof with a deck above it, roughly the same size of what you're talking about. (This wasn't the leaky one, that was a different job. I've been spending altogether too much time with contractors lately. :)

I can't give you a good estimate of how much it would cost in your case, since ours was all wrapped up with all sorts of other construction work, and because it was a new structure instead of an existing roof that needs retrofit -- though I'm pretty sure that $5000 is indeed crazy low, especially in manhattan. In our case the structure consists of
* building the roof out with a slight pitch, so water won't pool anywhere -- you've already got this, so you've a major head start there.
* The entire roof area is covered with a single large waterproof membrane -- no intrusions means (hopefully) no opportunity for leaks. I'm not sure if you'd be able to just slap this down onto an existing roof or if there'd be more work involved.
* The deck itself just floats on top of the membrane; it's not actually attached anywhere. (Driving nails or screws through that membrane would defeat the purpose.) In our case the deck has a 'lip' extending down over the edge on all sides, so it can't shift around... also we're in the middle of nowhere so in the unlikely event of a tornado there's nobody for it to fall on if it flies away. I imagine that regulations in Manhattan would be somewhat less relaxed than around here; you might need something a little sturdier.

All that said: we love having the extra outdoor space; don't let the construction horror stories throw you off :)

Definitely do use the recycled plastic decking material. Ours is wood, and I have to re-stain it every couple years, which is turning out to be quite a hassle; really wish I'd gone with the plastic. (Friend of ours has some, so I've been able to compare. It does not get any hotter in the sun than wood does -- rather the opposite, if anything -- and never needs painting.) If you do go with wood, use semitransparent, oil-based stain instead of solid stain or paint; it lasts much longer. Do the painting on a cool, cloudy day or don't bother at all; otherwise it'll just cook before it has a chance to soak in, and it'll start flaking off within a month.
posted by ook at 6:59 AM on May 12, 2007

Suggestion about the deck itself: Years ago I was treasurer of a small self-managed co-op apartment building where I lived in DC. We had to repair/replace the flat roof, and also decided to build a roof deck.

We chose to build the deck in sections that were removable so that we could more easily perform maintenance and repairs on the roof in the future. Basically, it had wooden sections of about 3' or 4' square, bolted together, with the railing bolted around the outside. Check your local building codes, of course. Our railings had gaps between the vertical balusters that were probably wider than would be allowed now.
posted by Robert Angelo at 7:15 AM on May 12, 2007

If a deck is too much of an investment when you just want to be able to hang out up there, you could try deck tiles.
posted by oneirodynia at 8:52 AM on May 12, 2007

Thanks to everyone who answered. This will help enormously when I talk to contractors, especially knowing what kind of roof I have (not to mention learning that there are different kinds of flat roofs in the first place).

Talking to architecture grad students is also a fantastic idea, one that I'll definitely follow up on. You're all awesome.
posted by waterbottle at 2:53 PM on May 12, 2007