# Install a deck on top of a EPDM flat roof.



## Dale Chomechko (Mar 11, 2008)

Do it in torch on , its much tougher.
Dale Chomechko
DC Roofing Inc


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## Slyfox (Jun 13, 2008)

You can purchase a thick rubber slip that you will tact glue in place and set your runners on them.

Go too ABC Supply and you'll find the material I'm talking about.


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## -Pjackso (Jul 21, 2010)

Dale,
This house is 25 years old, and it's had at least 3 roof applications on the garage (not including the EPDM). Given the past performance, that leads me to believe that torch down only lasts between 8-9 years in this situation. I'm looking for a solution that will last longer. 
The EPDM was installed (2-3 years ago). The EPDM may not last near as long, but I'm already committed. I think if I were to replace the roof again - I'd go with a thick guage 3" standing standing seam metal roof.


Slyfox,
I called the local ABC, and the only thing they had was the rubber walkway pads. (30"x30"x3/8" @ $15.65) That's $2.51 per sq ft - not including the deck. The hardibacker is about $1.00 per sq ft. (BTW, The ABC website is terrible.)
How much is your rubber slip pad? Any references?


Back to my hair-brained idea - Is my logic wrong about the hardibacker?
Is there some background details that makes this a bad idea, or is it because it's not a proven approach?
Freeze/thaw cycles? Cracking?

I haven't bought supplies yet, so I'm still open to ideas.

Thanks.


Edit:
Good reference websites:
http://www.conservationtechnology.com/waterproofing_epdm_coverings.html

http://www.roofing.com/forum/sutra19413.html&highlight=&sid=acc6400b101e06ebb0d81c5718c61e89


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## seeyou (Dec 12, 2008)

-Pjackso said:


> Hello all,
> I've been a long time lurker and I finally signed up.
> Between this site (and the other), I've searched and found a lot of really good advice.
> 
> ...



We run into this situation often. Forget the hardi-backer. Glue strips of EPDM to the bottom of the runners/sleepers so you have rubber to rubber. If you really want to be anal about it, lay another strip of EPDM under the sleeper.


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## -Pjackso (Jul 21, 2010)

Thanks Seeyou,
I had read about the approach on a few websites, but I was looking for someone with first hand experience. So Thanks!
Any call-backs? expected service-life? Typical damage after x years?


I will need to butt-up a few runners along the down-hill slope (35 ft long).
Other than the bottom rubber layer, do I need to do anything special at the butt-joint? I'm concerned about some of the runners trying to warp/cup in the future.

Also, I can get some cheap hardibacker locally. 
Although the hardibacker is not required, would it be cheap(ish) insurance from damage? (from acorns, sticks, cigarettes, etc...)


I do appreciate the help. You've certainly given me plan A.


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## seeyou (Dec 12, 2008)

-Pjackso said:


> Thanks Seeyou,
> I had read about the approach on a few websites, but I was looking for someone with first hand experience. So Thanks!
> Any call-backs? expected service-life? Typical damage after x years?
> 
> ...


The only call back I've ever had on one of these is where a carpenter cut the rubber with his circ saw when framing the deck. I would try to panelize the deck to be able to access any debris that might get under it or in the off chance any damage might occur. 

The life of the rubber is extended under a deck since few if any UV rays get to it. 

I don't understand the 1st question highlighted above. 

Forget the hardie backer. It's not designed to be used as you're intending.


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## kwikfishron (Mar 11, 2010)

What makes you think your garage roof will support a deck?

You said the garage was “worthless” and had “major leaks” and “HOLES too”.

You said you replaced the sheathing but what kind of shape are the rafter and the rest of the structure in?

It’s hard for me to believe if the roof was rotted to the point of having holes in the sheathing and that there wasn’t any other rot issues.

Any deck coming off a second story bedroom would require a permit. Have you considered that?

Going through the permit process will ensure you that your deck will be structurally sound and safe.

It’s a important step you should not skip.


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## -Pjackso (Jul 21, 2010)

Seeyou,
Thanks for the ideas. I was planning on making the deck modular for easier installation/removal. (3x3 or 4x4)
Based on your recommendation, I will forget the hardibacker. I have a bad habit of making projects harder and more complicated than they really need to be. (My wife calls me "King-Make-Work", ...and she's usually right). I appreciate your help.


kwikfishron,
I think you misunderstood my posts. To clarify your questions:

The garage was originally built with the deck on top. My concern was about adding concrete paving blocks at 15-25 lbs per square foot. (Deck is 875 sq ft, so extra weight would be 13125-21875 lbs) I don't know the structural design limit, and I'm concerned about the extra dead weight. Therefore I ruled out conventional thick paving blocks as a option.

The garage ***ROOF*** was worthless. The garage itself is fine. When I replaced the roof decking, I inspected the rafters (2x12's) and they were in good condition. Drywall was the only other damage.

The deck sits on the garage roof. I did not change any structural configuration of the garage or the rafters. I removed the deck (off the garage) to replace the roof. I am now ready to re-install the same deck as before - and was looking for ways to protect the new flat roof.
I'm returning the house back to the original condition as when built.



Thanks everyone for your help!


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## Grumpy (Dec 12, 2003)

This may help you in making a decision on what to do with the roof. http://www.reliableamerican.us/articles/chicago_roof_decks-what_you_need_to_know.html

The roofing system that the deck is built upon is more important thant he deck and must be built in such a way that the deck won't damage the roof. a regular ol' epdm roof won't cut it unless the roofing system was designed to receive a deck. In short repalce the roof before you put a deck on it or you'll be very very sorry when you are ripping up your brand new deck in 2 years.


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## firehawkmph (Dec 12, 2009)

Pjack,
Check out these adjustable pedestal deck supports. They were featured in an article in the June 2010 issue of Journal of Light Construction. They also offer wood panels.

http://www.bisonip.com/home.asp?pid=2

Mike Hawkins


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## Grumpy (Dec 12, 2003)

Mike I installed those once in the past. On areas with walls on 4 sides they aren't bad, but on areas open on the sides, they are not suggested. Furthermore you'd still need to design the roof to receive the load as well as protect the roof membrane.


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## firehawkmph (Dec 12, 2009)

Gotcha Grumpy,
I wasn't thinking of the open roof vs. one with a wall around it. I just remember reading the article and thinking it seemed like a neat setup. 
Mike Hawkins


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## -Pjackso (Jul 21, 2010)

Thanks for the input guys.

Grumpy,
You said: "a regular ol' epdm roof won't cut it unless the roofing system was designed to receive a deck. In short repalce the roof before you put a deck on it..."

Now I can read your statement in a couple different ways, so I'd like some clarification... Are you saying?
A) You can't install a deck on a roof unless the roof structure (walls and truss-work) was designed for the additional loading.
or B) EPDM can't support a deck sitting on it.
I think you were talking about "A", and I agree. If you were actually talking about "B", then please clarify why (and what to do).


To clarify my situation, 
The house was originally built with the deck on top of the garage. The garage is more than strong enough to support the deck. (Structurally speaking) 
I have already replaced the roof - I installed a 0.060" EPDM roof. (It's new)


Thanks!


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## Grumpy (Dec 12, 2003)

I am saying A and B are both true. Read the link I posted in my above reply it should explain.

I won't speak of structure since I am not a structural engineer. Just because it had a deck before doesn't mean the structure was intended to support the load. Around here very few people actually secure permits and will slap up what ever the customer is willing to pay for. But let's assume the structure is fine.

You say you just did a new roof, but how was the roof done? Can you explain step by step what you did to repalce the roof? Was there a tear off? was insulation installed? How was the insulation secured? How was the membrane secured?

Like I said the roofing system must be designed in such a way that it can receive the deck. If the deck spans wall to wall and doesn't come in contact with the roof, you have nothing to worry about. If the roof comes in contact with the deck in any way shape or form, you may be in big trouble.

The way I would design it would be as follows...
Tear off.
Some kind of coverboard perhaps fiberboard over the substrate secured with insulation adhesive.
If insulation is a requirement the insulation would be installed first and then a high density fiberboard or cement board installed over the insulation to protect the insulation from being crushed by the weight of the deck. Again no fasteners would be used for the top layer of fiberboard/cement board.
A fully adhered roofing system, 60 mil EPDM is fine. Again no fasteners.
Then a sacrifical layer of roof membrane or preferrably some rubber walk way pads would be installed in strategic locations so that in no place would the deck contact the roof.

You see, protecting the insulation (if any) is important, this requires an extra step. This is why I say the roof must be designed to receive the deck. Polyisocyanurate insulation has a high R value but is very weak when it comes to compression. A deck sitting on the roof would compress the insulation which would tear the roof membrane over time and thus leak.

Fasteners should not be used or kept to a minimum. Let's say a joist rests directly atop a screw and plate. The dead load of the decks' weight would eventually tear through the roof membrane from the bottom side. Again, if the roofing system is not designed to receive the deck you'll have problems.

Finally the roof membrane must be protected from everything else. A deck sitting directly on top of a roofing membrane will no doubt eventually tear through the roofing membrane. 

All of these extra steps adds upfront cost to the roofing system, which is why peopel tend to cheap out. They would rather spend the money on the bling of the deck with exotic South American hard woods that they can show off to their friends and complain about how crappy their roofer is because they cheaped out on the roof and bought a regular ol' roof that was never intended to receive a roof deck. 


Does that explain it?


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## -Pjackso (Jul 21, 2010)

Hi Grumpy,
Thanks for the write-up. That really helped clarified things right up.
I agree on the concern about fasteners tearing thru the EPDM, and the proper installation method for the job.

Ok, just to wrap up the story...
Step by step process:
1) Complete tear-off: check. All old roofing was removed down to the plywood sheathing. All plywood damage was removed and replaced. (NO other damage found, other than drywall).
2) Insulation: Not a requirement - No insulation installed.
3) Black fiberboard was installed over the plywood. (Celotex blackboard, it was a compressed fiber/cardboard like material) 
The fiberboard was attached with NO nails - I used liquid nails to secure it in place. (ha ha, does LIQUID nails count?)
4) EPDM was applied over blackboard and draped (down) over the sides and secured to the wall with metal attaching strips screwed to the wall. 
The EPDM is installed per the ballast method - no adhesive. (The deck will be the ballast). 

The deck will be sitting directly on the roof.
5) I will use left-over EPDM (strips) as a sacrificial layer between the EPDM (roof) and the deck runners.

My original idea was to use concrete fiberboard as an additional wear/chaffing surface between the sacrificial EPDM strips and the runners. 
The material layering would be like: EPDM (roof) -> EPDM (sacrificial strip) -> Concrete fiberboard -> Runner -> deck. 
But seeyou recommended forgetting the concrete fiberboard, so I tossed the idea.



Thanks all for the help and clarification.
-Paul!


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## Grumpy (Dec 12, 2003)

In addition to the sacrifical layer it wouldn't hurt to procure some neoprene/rubber walk way pads. A little extra cushion never hurts.


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