Deck Over Rubber Roof

 
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Old 11-05-2005, 02:10 PM   #1
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Deck Over Rubber Roof


Hello all, I Have a potential customer that wants a deck built over a rubber roof system. The rubber roof is less than a year old . It has a high spot in the center running the full length with approx. a 3" drop an the ends. The roof is 24'x28' the high 'ridge' runs the 28' lenrth. It is supported by 2 8" I beams that are 48" oc. I am having trouble coming up with a way to support the deck , but not have to much contact with the rubber roofing membrane. under the membrane is 3/4" foam.The outside walls are 8" block.capped with 2x's. The joists need to be run across the 'ridge' 24' span end to end. I just am not sure how to support the joists on the membrane. I have a couple ideas, but I am sure some of you have had experience with this. any suggestions would be greatly apprecieated. THANK YOU for your help in advance .
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Old 11-05-2005, 03:37 PM   #2
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Re: Deck Over Rubber Roof


Quote:
Originally Posted by smokepole
under the membrane is 3/4" foam.The outside walls are 8" block.capped with 2x's. The joists need to be run across the 'ridge' 24' span end to end.
You may need to use PT LVL's with all top edges capped, $$$

 
Old 11-05-2005, 03:37 PM   #3
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Re: Deck Over Rubber Roof


incorporate the actual support blocks into the roofing system then build the deck from your support blocks. Therefore allowing drainage under the deck. Basicly making the support areas, penetrations, consult or hire roofer for this part.
I never liked the idea of a floating wood deck on a roof due to wind and walking pressure.
Hope it helps

Last edited by red_cedar; 11-05-2005 at 05:33 PM.
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Old 11-05-2005, 09:42 PM   #4
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Re: Deck Over Rubber Roof


Hey smoke, are you in colorado springs? I went and looked at something VERY VERY similar almost the exact same size too... I drew a blank and kind of said I could not do it. Let me know what you end up doing just in case they call me back.
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Old 11-08-2005, 07:24 PM   #5
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Re: Deck Over Rubber Roof


thanks guys for the help.No I am not from CO. I`m in MI. Anyways I had a vision of TGI`s spanning the 24'. But I can`t find any span tables to tell me if my vision will work or not. I am thinking of setting posts along the walls,attaching a 2x12 on the outside of them then joists hangers on the inside of the 2x12`s. then the tgi`s, then another 2x12 under the tgi`s on the inside of the posts.Basically nothing will touch the rubber roof.I am making a couple calls tomorrow to c if I can get some answers as the customer would like this done asap.Any help with finding span tables online or another idea as what to span 24' with would be awsome . thanks guys
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Old 11-08-2005, 07:44 PM   #6
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Re: Deck Over Rubber Roof


This shoudl really be in the roofing forum since after your deck damages the roof you will wonder why and be asking the roofers how to fix it and the first thing us roofers will say is to dismantle the deck and properly prep the roof to receive it.
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Old 11-08-2005, 07:54 PM   #7
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Re: Deck Over Rubber Roof


The tgi sounds like a good idea I know you can get them to span just about any length you want, just find the right class rating the TJI L/360 360 series 11 7/8 at 12" O.C should span 24' with a 40 psf live load and a 10 psf dead load. hope this helps
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Old 11-08-2005, 09:54 PM   #8
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Re: Deck Over Rubber Roof


grumpy , that is why I want to span over the entire rubber roof so that NOTHING comes in contact with it. If nothing comes in contact with it how can any damage occur? This is why I asked for suggestions from you guys.cuz I don`t want any problems by not seeing everything. Also grumpy, I have been reading these forums for some time now and your opinion means alot to me. please explain how damage can occur if I do it this way? thank you
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Old 11-08-2005, 10:18 PM   #9
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Re: Deck Over Rubber Roof


Quote:
Originally Posted by smokepole
grumpy , that is why I want to span over the entire rubber roof so that NOTHING comes in contact with it. If nothing comes in contact with it how can any damage occur? This is why I asked for suggestions from you guys.cuz I don`t want any problems by not seeing everything. Also grumpy, I have been reading these forums for some time now and your opinion means alot to me. please explain how damage can occur if I do it this way? thank you
smoke
you are on the right track, but you want PT LVL's not TGI's, big difference and they will have to be capped in copper
 
Old 11-09-2005, 09:01 AM   #10
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Re: Deck Over Rubber Roof


I can not comment on the framing of the deck. Infact pt lvl and tgi are just acronyms I have heard before in the past but have no real idea what they mean.

I also can not comment on the span of the deck joists but it would be my recommendation for your deck to sit on the parapet walls and make zero contact with the roof. Or deck hangers can be mounted to the parapet wall and the joists can span within the parapet walls instead of ontop.

If for any reason you need to sit the deck on the roof, in any location where the deck will come in contact with the roof I highly suggest some kind of barrier to protect the roof. Concrete walk pads to distribute the pressure will work. At very very least use a loose laid piece of membrane (what ever membrane the roof is) as a pad between the deck and the roof.


Why not just install a garden roof instead of a deck?
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Old 11-09-2005, 12:27 PM   #11
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Re: Deck Over Rubber Roof


Quote:
Originally Posted by Grumpy
it would be my recommendation for your deck to sit on the parapet walls and make zero contact with the roof. Or deck hangers can be mounted to the parapet wall and the joists can span within the parapet walls instead of ontop.

If for any reason you need to sit the deck on the roof, in any location where the deck will come in contact with the roof I highly suggest some kind of barrier to protect the roof. Concrete walk pads to distribute the pressure will work. At very very least use a loose laid piece of membrane (what ever membrane the roof is) as a pad between the deck and the roof.


Why not just install a garden roof instead of a deck?

Amen Tgi's or I-joists are no good for exterior applications, LVL's or Laminated vaneer lumber is, you can get Preassure treated lvl's but they WILL have to be capped in copper along the top edge at least, probably the most feasable option would be to use 12" york copper flashing and wrap the top edge $$$ at $27/20'roll, or I guess you could achieve the same results using grace IWS , but I don' t know what the long term exposure will do to it' s integrity between the gaps
 
Old 11-10-2005, 01:43 PM   #12
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Re: Deck Over Rubber Roof


WR Grace makes a product for protecting PT wood called Vycor Deck Protector. It is also used to protect hangers from corrosion.
http://www.na.graceconstruction.com/...singlepg_5.pdf
There are neoprene pads, usually used as walking pads, that can be glued to the EPDM membrane to protect it if necessary but it shouldn't be loaded heavily. If you added a drawing I might be able to offer a suggestion about support.
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Old 11-10-2005, 10:52 PM   #13
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Re: Deck Over Rubber Roof


I bet to span 24' with lvls you are going to need 14" or 16" around here the 14" are about $6.08 LF (that more then $3,000 just for joists) I have not priced out 16" lvls I know that tgi would be cheaper they might make an outdoor rated tgi I would look into that
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Old 11-11-2005, 07:23 AM   #14
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Re: Deck Over Rubber Roof


Framing for this structure MUST be sized from the building code tables or by an engineer so you really don't need any other span table.

Here is a joist span calculator if you need one to check information from elsewhere.
http://www.awc.org/calculators/span/...orizontal+Span

The live load on a deck should be at least 60 psf plus a dead load of 10 psf (check your building code for the required loading).

2x12 dimensioned lumber @ 12" o.c. will only span 19 ft. or a bit more if the wood is of an unusually high strength species. 8" o.c. will get you up to 22-6 with a LL deflection of .8" or L/333. You could span 24 ft if you were willing to accept a deflection of 1" or L/275 which of course is very bouncy.

1 3/4 x 11 7/8 LVL's @ 16" o.c. with a Mod. of Elast. of 2.0E will work with a pretty high LL deflection (1.224" or L/235) which will feel bouncy to most people. Using 12" o.c. will reduce the deflection to .92" or L/314 which is still bouncy but might be acceptable to the owner. 1 3/4 x 14 Lvl's @ 16" o.c. would have a LL deflection of L/386. At 12" o.c. it would be L/514.

If you use anything other than dimensioned lumber sized from the building code tables you MUST have the deck designed by an engineer. If there is no building code in your area you SHOULD use an engineer to protect yourself. The perimeter beams, supports and reinforcement to the foundation will also have to be sized by an engineer.

This deck is going to be very expensive and an error in the framing could destroy lives and bankrupt you. I would have thought the owner would have hired his own engineer at the beginning. If he doesn't hire an engineer I would advise walking away from the job.

Good luck with it.
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Old 11-11-2005, 08:46 AM   #15
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Re: Deck Over Rubber Roof


Not knowing your exact layout I dont know if this will work but I do belive you can span 24' with 3 1/2" x 14" glulam use these for 3 beams 1 at each end and 1 in the middle with posts down to piers then use 2x10's in hanger to span the 12' in between glulams are a lot less then lvls last time I bought some this size they were $8.48 LF. As for what mighty says do hire an engineer if required, here in cases like this I can take my plans to the building department plan check and they double check all the enginering even if it has a stamp from an engineer so I dont need to hire one most of them know me and I just say I want to do this what beams do I need and they tell me. Sure makes life easy sometimes dont have to call engineers every time I want to build a deck a little differant than the norm.
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Old 11-11-2005, 11:35 AM   #16
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Re: Deck Over Rubber Roof


A 3 1/2 x 14 gluelam might work at the ends but at the center the load is doubled so it won't work. If you use LVL's it would probably need to be a 5 1/4 x 16 center beam. This is a serious structure, not just a DIY deck. Connections at the supports and lateral bracing are critical too. You really need to get an engineer.
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Old 11-11-2005, 06:24 PM   #17
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Re: Deck Over Rubber Roof


Ahhh yes good point mighty, I forgot to double the center beam thanks for pointing that out
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Old 01-07-2006, 08:25 PM   #18
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Re: Deck Over Rubber Roof


Here is a deck system that acts like a roof
http://www.lockdry.com/ It would be the perfect answer over flat roofs.
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Old 03-27-2009, 09:40 PM   #19
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Re: Deck Over Rubber Roof


Are speaking TJI's from Truss Joist Institute the I joist, yeah you are right those arent for exterior app, but could you one a series of PT LVLs or PT parallams thru the middle and then 12' PT 2x 10 Floor joists each way.
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Old 03-28-2009, 09:52 AM   #20
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Re: Deck Over Rubber Roof


Smoke,other than the high spot in the center the fall sounds about right. The wallet wants the deck to be above the roof? or would it be ok to land stringers on the roof/fasten the decking to the strigers. J.

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