Deck on Flat Roof help

[Jeffrey R. Jonas]

Hey guys/gals...

Anyone have a great graphic or pic of the proper method of constructing a wooden deck on a flat roof? This home had a "floating" deck with ponding water beneath. I see flat roofs often, but not with decks installed on them in this manner. I know many of you "big city" guys see this alot. All help is appreciated.

[David A. Andersen]

It looks like crap, but at least it's not in contact with the top of the roof which will cause failure. I question the structural integrity of the deck and all the trip hazards.

I have an entire complex of condos downtown (1yr old) that are getting new roofs as we speak because of massive leaks. Decks are on top of the EPDM.

[Bruce R. Grant]

Given that there is no such thing as a flat roof, all must slope to drainage, ponding is a concern with regard to the proper drainage of the roof. It is likely that there may be some settlement of the roof sheathing around a drain that is causing the ponding. Or, if the roof structure was never meant to have a deck, the deck may be built within the exterior framing perimeter and not full size thus incorrectly loading the roof rafters and causing subsidence. Designing and building a roof deck must take into acount the structure below and how the load of the deck is transferred through it to the footings.
Decks are not usually built to obstruct drainage but anything can happen.

On a nearly new condo I inspected last year all the decks were being ripped off as the contractor did not shim off the sleepers to level the rooftop decks. When I was driving up to the building I could see all the railings looked wonky to the structure and to the adjoining deck railings.

Most smaller decks up in this area of central Ontario where we have moderate snow fall are built on frames in sections so the decking can be lifted for repair. I do find that larger decks are often built on framework set on sleepers that follow the drainage slope of the roof.
Looks like that all applies here and what is to stop a child from getting around unsecured ends? Me, I don't give a damm if its off the childless owners master bedroom the next owner may have young children I would call the railings too.

Incidentally, railings around roof decks are often a concern up here. I find many contractors rely on corners to achieve the strength for the railing and on smaller decks this works but on decks with uprights every five feet a fifteen foot or larger deck often has very weak anchoring to prevent the top rail from giving out. Most I find are just using post brackets to secure the uprights. Many contractors do not build the joists and railings as one unit on these decks. Often the framework is only 2x4 as the sleepers transfer the deck weight to the roof. I often find the railings are not secured to the home at the upper ends making the end that dead ends against the structure very weak. On the last one I inspected in early June the end running to the building moved four inches or more, Photo opp . This is very common on condos where the railings of one unit butt into the railings of the next or the building itself. The end is often not attached at the upper railing level. Speaking with contractors there seems to be some concern about keeping the units separated, and about tying the floating deck structure to a fixed portion of the building. I just call it out, provide photos and let the owners settle it.

[William J. Decker]

I call them out, around here, all the time. Any direct contact deck on modified bitumen roofing membrane (with one exception) voids the manufacturer's warranty, in any case.

Simply put, if you have a wooden roof deck, you have just decreased the life of the roof by about 1/2 and increased the cost to replace the roof by three times (added labor cost to remove deck, replace roof and put roof back, which is never done well).

Hope this helps;

[David A. Andersen]

It looks loike this one is not in contact with the roof Will...

[William J. Decker]

Picture 3. Looks like a 2 x 4, laying flat, directly on the roof. Obviously, someone lifted the deck for the picture.

I may be mistaken, but don't think so, but welcome any correction.

[David A. Andersen]

Your probably right.
It didn't make much sense to me.

[Jeffrey R. Jonas]

Thanks for the comments guys.

Yes, Will is correct. Two 2x4's laid flat with the decking attached to the 2x4's. Approx 3' x 3' square. I lifted two of them to look for damage. The home is a Dutch Colonial. The old shingles were replaced a few months ago. See all the loose, washed off granules acting like sand paper under the wood deck? All the wood was warped and rocked when walked upon. Also lots of leaves, debris. Two scuppers in outer corners blocked by the debris.

Anyone note the NM under the decking?

[Marvin Maizel]

We normally see designs that start with a fully adhered membrane on concrete. Rails embedded in pitch pockets and counterflashed. The decks are panellized for access and roof drains galore. Basically a swimming pool with an accessable deck on manual levelling stand-offs above it
Anything less then that would require structural engineering for the load and a method of fully adhering a suitable membrane with protection board above it. Drains, flashings and rails to match.
Well engineered commercial kitchen floors are similarly engineered but with different substrates and finish above the membrane, Also double (top and bottom) floor drains.
Sorry for the shorthanded story...there is a lot to this issue and I am only touching the surface.

Hopes this helps Jeff,

Marvin M

[Bob Elliott]

Past comments from the forum.....


What I mean by*roof*decks*is wooden*decks*(2 x 4 joists with planking) laying, directly, upon a modified bitumen*roof*covering. 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 the*roof covering and b) increase the cost of replacing the*roof*(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 membrane*roof*covering 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-up*roof*systems always had strategically spaced blocking pre-planned for the deck and incorporated in the*roof*system at the initial install.*
If done after the fact, blocks of wood or sleepers were adhered to the*roof*membrane and water proofed and became part of the*roof*system.*

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 the*roof*system, regardless of the type of*roof.*

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 Flat*Roof*Deck
Occasionally a project is presented where a deck will be built over a flat*roof*of a house or a garage. First you must make sure the*roof*is strong enough to support 55 lbs per square foot. Next you will want to install a watertight EPMD rubber membrane over the top of the*roof*deck 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 the*roof*surface. This will provide the surface for you to attach the decking. In most cases your “sleepers” will float on the surface of the*roof*with 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.*

Marcel*

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.

[Jeffrey R. Jonas]

I don't care what others say about this MB... you guys are AWESOME!!!

Thanks for all the comments. In a nutshell, everything posted is what I basically told my client. He asked if I had a graphic or pic that he could see, to know what it should look like, given he purchases the home, and has the corrections made.

I recommended a complete tear-off, a plan review by an SE, and a phase inspection (2 or 3 visits) as his best course of action.

[David A. Andersen]

Yes, Will is correct.

Then it is absolutely a deficiency under any circumstances.

[Sean Fogarty]

Your'e a deal killer Jonas!!! Whats wrong with it? Its not leaking now..

[ROBERT V. YOUNG]

Sleepers in contact with a bur roof is acceptable when installed correctly. Proper sized placed and materials for the sleepers Jeffery.
Not at home.
I will come back later.
Also levered on the parapets is sometimes allowed.
It all depends on the stricture and placements .

[Linas Dapkus]

Originally Posted by ryoung7

Sleepers in contact with a bur roof is acceptable when installed correctly. Proper sized placed and materials for the sleepers Jeffery.
Not at home.
I will come back later.
Also levered on the parapets is sometimes allowed.
It all depends on the stricture and placements .

Take your time Robert, you're 2 weeks too late. Get any good meds lately?