Greetings:
I have a client who wants an 850 square foot deck on a rubber roof. The existing design uses a series of 4x4s for support resting on 2x12x12 PT pads that make direct contact with the roof. I would like to put some kind of waterproof bond between the pad and the existing rubber membrane. Some have responded to my earlier query with pictures of sleepers, but that is not practical given the gradual slope and size of the structure.
My arrangement with the customer is to give a two warranty on damage to the rubber and 4 years on the deck. That is generous of him given the size of the structure, and I don’t want to hear from him or anyone else up there for the next ten years.
thanks in advance for anyone who has succeeded in building decks on flat rubber roofs and can offer guidance.
I will try to upload some referance photos of the existing site.
Handy Dan
Replies
If you are going to lift that mucch above the rubber, you will need to incorporate a tiedown against twinnd uplift somehow
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
thanks PiffinYou didn't like my idea of building the deck high enough to provide a crawlspace for repairs, but my client likes that idea. My question is how to get at the rubber for cleaning and such if you can't get under the deckthanks Dan
why assume that you need to clean it? see above and do not use modbit for padds
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Edited 3/7/2009 9:37 am ET by Piffin
I slip a 14 x 14 peice of torch down under 2x12x12 pads no need to bond to the roof.
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.
- Fyodor Dostoyevski
Excellent. Please tell me more (source, vendor) about that product choice thanks Dan
You can buy Modified Bitumen torch down from a roofing supply house. Most often we built decks after a new roof install and just ask the roof co. to leave us a roll. The stuff is about a 1/4" thickI've only built 10 roof decks, and agree with Piffin... build it as low as you can to still allow for drainage and ventilation. IMHO, the longer levers of a raised deck can increase micro-motion that can lead to increased loading and wear on the roof below.In my experience, no one is crawling under the deck to clean or do repairs. We often build in 4x8 modules (2x6 framing) if materials are being boomed on to the roof. We build smaller if materials need to be carried up or there are a lot of trees and the client says they plan to clean underneath. If you screw down the decking and run your framing parallel to the drainage planes the deck should last as long as the roof.YMMV
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.- Fyodor Dostoyevski
Dear FN:
That is really helpful. Thanks for your detailed input. Let make sure I got it:
You can buy Modified Bitumen torch down from a roofing supply house. Most often we built decks after a new roof install and just ask the roof co. to leave us a roll. The stuff is about a 1/4" thick
My client wants to reinforce what is there with something heavier. 1/4" sounds thick enough to withstand the pressure of my 2x12x12 post pads. Do I need a torch to put it down? There are other products that have a sticky back that melts tight to the substrate when the sun is on it for a while.
I've only built 10 roof decks, and agree with Piffin... build it as low as you can to still allow for drainage and ventilation. IMHO, the longer levers of a raised deck can increase micro-motion that can lead to increased loading and wear on the roof below.
Yes I am liking the raised deck idea less and less and in this area (Brookline MA) there may be a problem building something in a historical district that is visable from the street. And of course, if anyone tries to get on the outside of the deck, they have to climb over the rail and jump that 3 feet to the fragile surface of the existing rubber membrane. How about 18" high. With the 70 or so posts we have, I don't imagine it shifting that much side to side.
In my experience, no one is crawling under the deck to clean or do repairs. We often build in 4x8 modules (2x6 framing) if materials are being boomed on to the roof. We build smaller if materials need to be carried up or there are a lot of trees and the client says they plan to clean underneath. If you screw down the decking and run your framing parallel to the drainage planes the deck should last as long as the roof.
I am intrigued by the idea of building modules on the ground, and have considered prefab modules like the Bigfoot System (4x4 squares of IPE mounted on framing). Can those 4x8 modules really be lifted? We have no trees at all at this location, so cleaning is more of what ever falls through the cracks, or if there is a need to make a repair. In the long run, does your deck need to be dismantled somehow to replace the roof?
thanks again Dan
YMMV
First: If indeed the 'rubber roof' your client has put down is EPDM (the most common type used today), you need to listen to Piffin about the intolerance it has for modified bitumen (torch-down) membrane. One will dissolve the other and you'll be SOL with a very unhappy client in short order, Dan.
Second: Pads and posts to support a rooftop deck are problematic for the long term. There will not be enough friction--because the pads won't provide enough surface contact area--to keep the deck from moving and having your pads chafe through. You need sleepers laid parallel to the drainage plane. Each sleeper should have a strip of the same membrane that is laid on the roof glued to the bottom of it.
Sleepers should be cedar or hemlock or some other naturally rot-resistant species; do not use PT. There may be as-yet unknown chemical interactions between copper quat and EPDM over the short- and medium-term: Copper quat's only been on the market for about 7 years or so, IIRC.
Third: I have never heard of anyone building a rooftop deck with a crawl space for cleaning access. If dead leaf accumulation under the deck is a concern, the best way to clean that out is with a leaf blower. Build the deck so that a few sections of decking can be easily lifted out to enable the HO to shove his blower in there.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I foresee vermin and birds nesting in a raised deck space. They are not kind to the rubber when they get to digging and scratching around in the nest.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
thanks for the input guys.
By mutual agreement my clients and I have given up the idea of a raised deck and will instead support the deck by short 4x4s resting every 3 feet on 2x12x12s. The stamped drawings calls for 75 of these little posts, so I am going to go back to the engineer and try to reduce the jungle of posts.
I include again the drawing as it exists now. You can see two decks, one 20x20 the other 20x15 connected by a 6' wide walkway.
How to rest the 2x12x12s on the rubber? I have no intention of torching anything
Dan
75 does not sound like too many bearing points at all for that much deck. I would be expecting 85-90 of them. Keep in mind that the fewer bearing points you have, the more load is on each of them and the more vibrations transmitted to the job of wearing out the EPDM roofing
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
"How to rest the 2x12x12s on the rubber? "I think that was explained 2-3 times here already. maybe it was disquised language...Cut a piece of EPDM a few inches larger than the pad to glue down to the deck with EPDM caulk and glue to pad to it with the same.
Some guys would use contact cement instead
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Pifin:
Thanks for the clarification. That was what I had in mind. Glue the extra layer of EPDM to the existing membrane and glue the post to it. Right.
I spoke to the building department in the town where we are building and they were okay with the design, provided we anchor the whole structure. I don't imagine the wind picking up a 850 square foot deck but stranger things have happened. My goal is to attach the mimimum amount of anchors allowable by the engineer, provided we can find the beams. Any suggestions?
Dan
straps down over the edge to avoid penetrating the rubber. if you have to penetrate the rubber, call a roofer experienced with EPDM to flash it for you, or expect a leak.I could sketch a piece up, but I can't open your plans attachment it is so large.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Holy contact cement Batman! That thing has more ruffles than a petticoat! Must have missed the fact the deck is not covering all the roof. Gotta sleep on it.G'nite Senior Rez!And Gracias
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Why not plunge several posts from the railings into the roof deck and attach to rafters with 1/2 lags and blocking then apply copper pitch pans around the posts and fill with 2 part sealer made by rubber roofing manuf. Now you can thru bolt framing with carriage bolts so it can be removed to fix leaks, if need be.
then apply copper pitch pans around the posts and fill with 2 part sealer made by rubber roofing manuf.
The problem I've seen with that procedure is the wood can shrink away from the sealer over time. We typically cut a kerf into the post and counterflash that detail.http://www.quittintime.com/ View Image
Pitch pans are ancient technology by comparison to other methods, but they were never intended for this kind of suggestion anyways. They were for install over a roof surface that was NOT penetrated, but had mountings placed in them on top of the roof. Penetrating the existing is always a bad idea. This whole thing would have been easier to do right if planned before the roof was installed too.One thing about this plan that has been percolating in back of my head and just now boils to the surface, is that these 2x12x12 pieces are shorter than the spacing between joists in the existing invisible framing below. So about a fourth of them - or more - will be seated on the ply sheathing only and can cause a lot of flex right there along with the point loading. That will increase odds for wear and tear at those individual placements.so I'm thinking he wants to spread that load, by using skis ( bottom plates) of full length 2x12s laid on the wear strips of EPDM with the axis of drainage. By gluing them down, he gets some protection against uplift, and can use short lags to fasten his 4x4 peglegs for the rest of the deck. I have idea for the mechanical hold down too. Can't draw it up now and still noodling the idea some more. Gotta run.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
That ancient technology has worked on 6 different jobs that have an average of 7 years in direct southern sun exposure. You wont find a stronger way to attach railing posts. This also allows everthing to move with condition changes. The pourable sealer works great in my experience.
How many times have you been on a deck thats built on a rubber roof and the posts are fastened to rim only and feel like loose teeth after a year? I have seen quite a few.
I won't argue that it is the best way to attach a railing to a deck, but that is not what we are talking about here if you have looked at his plans.What I argue is that as a roofer, the pitchpan is NOT the way to seal a penetration like that. I can't think of a roofer that will gaurantee it that way. you've been lucky to not be having any water intrusion.
Fact is, you probably do have water following the wod post into the shell, but is such a small amt that it is not being noticed.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I foresee vermin and birds nesting in a raised deck space.
Another good reason to put it on 2x sleepers. Highest I've even built a deck over a flat roof is 3" tapering down to 2" at the high end of the roof. That makes life uncomfortable for all but mice and pygmy red squirrels.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Edited 3/9/2009 6:35 pm ET by Dinosaur
Ditto everything that Dinosaur said. That's the way we've always built them. Only difference is that we did use PT for the sleepers. I'll have to keep my eyes and ears open now to see if that turns out to be a problem.
Have you observed non-PT sleepers in this type of situation that have been in place long enough to get a feel for their life expectancy? What you're saying about the potential problems with ACQ and EPDM makes me wary enough to want to avoid putting the two together for the time being. I'm wondering what how long other materials will hold up in this application.
Piffin suggested using a section of the same EPDM as a pad between the sleeper and the existing roof. I am thinking the same approach can be used for insulating my 2x12x12 pads from the existing roof.
Again here is the existing plan. I didn't post it last time.
Dan
As Dinosaur suggested, I too would advise against supporting the deck on posts. I've never built a roof-top deck on anything higher than 2x4 sleepers. The best plan is to keep it low for stability. Determine how much pitch the roof has and size your sleepers accordingly. For example, if it runs out 2", use a 2x4 ripped at a taper from 1½" to 3½" for your sleeper. If the difference is greater than 2" go up to a 2x6.
Have you observed non-PT sleepers in this type of situation that have been in place long enough to get a feel for their life expectancy?
I use red or white cedar for sleepers, as do most of the older guys in the business up here. I have seen several installations using cedar sleepers that range from 10 years old on down, and have not heard of a problem.
The oldest deck-over-EPDM I've done personally is about 5 years old; I don't have much call for that kind of thing as few people are brave/stubborn enough to construct a flat roof in this area. For one thing, it's expensive and you can only use such a deck a few months a year; for another, the snow loads are quite high (2.5 and up). 'Long about mid winter when there's 3-5 feet of snow on that deck and the January Thaw comes in and soaks it all with rain, most owners of a flat roof start looking for somebody to shovel it off.
Every few years, a big commercial flat roof in the area collapses, in spite of having been engineer-designed and framed with steel trusses. One year there were three in the same winter: A hotel lobby, a golf-course cart-garage, and a supermarket.
Makes you think....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
You don't use torch down in conjunction with EPDM. It is intolerant of bituminous products. If he wants to pad it, he wants more EPDM
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Like I said, we get the material from the roofers who lay the roof. MoBit is most common in NYC. I didn't see the words EDPM in the OP.
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.- Fyodor Dostoyevski
He said rubber roof. Mod bit gets called rubber sometimes, but it is not.
What confirmed it is the photo of you saw it, it was definitely EPDM, so if he uses torchdown, he will ruin the roof
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Thank You!!! I was certified in rubber roofing 20 years ago and that was drilled into my head, asphalt and rubber dont mix yet I see shingles run over rubber all the time at tie ins WRONG.
Must robber roofing manuf. make a walkway pad or protection pad made for what he is trying to do. They look like a 3'x3' pad of sneaker tread that protects the roof yet allows minimal drainage . Ive used it for years with great sucess
Yeah, there were some of those pictured in photos I linked to in another thread for this OP.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!