Building a floating deck on an epdm rubber roof surface

by Paul
(WA)

I have an interesting problem. I am taking a 25x25 roof over a garage that was done in decking then tile and leaked. I tore everything up, replaced the wood that needed it and built up the base and covered everything in EPDM. I now need to get it back to decking and am running short of info. Can I do floating 6ft decking sections? Any info or links would be most appreciated.

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May 29, 2011
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A floating framing structure is your best option
by: Editor - Rich Bergman

Without any slope you are going to have to entirely rely on the integrity of the epdm to protect your roof. That means water will pool somewhere over such a large surface. There is not much you can do about the slope of the roof surface. That is now set.

Waterproof deck tiles can be installed in some cases but I would not recommend you try this unless you have started from the very beginning with this in mind and you are using a reliable system like this one by Duradek.

That being said, without a proper slope you should never install deck tiles as you are asking for trouble, even with a great system like the above.

And it doesn't sound like you have done the basics that the Duradek tile system requires so I think your best option is some kind of floating deck frame structure that you can fasten the composite decking boards to. They must be secured in such a way as to provide a minimum amount of air flow for heat issues and to stair relatively dry during their service life.

Another thing to keep in mind with using composite boards that are very long in length is they do expand lengthwise in heat and this is different from wood decking. So you can not just butt joint one end of a board to the next or when they expand they will buckle at the joint.

Refer to the manufacturer's recommendations about this. That is why you often see intricate designs like herring bone and picture frame borders throughout a composite decking job. Yes, it looks very nice but there is a practical need to do this sometimes. And with 52 feet of deck yours definitely will need to consider this

May 29, 2011
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Decking on EPDM
by: Art in the Rockies

Thanks for the info. I am in the same situation with a deck over an enclosed pool. The only thing is that my deck is about 1200 square feet over epdm.

Unfortunately we don't have great slope on the surface.

From the house to the edge of the deck is about 28 feet and about 52 feet across. I'm not sure what materials to use. I did pick up some composite siding at a local building thrift store. It looks great, like a giant hardwood floor but it warps up when gets wet.

I have been trying to figure out how to attach it ( biscuits) but I don't think that will work. They need to be attached to some thing.

Also, I considered sitting tile on top of the epdm and float.

Not sure if that is a good idea either. I would appreciate any ideas you might have.

Oct 27, 2010
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Thanks for your comments
by: Paul

Thank you so much for the input - invaluable. With all the different ways that other contractors swear by, it's takes so long to discern the generally accepted from the not-up-to-code to the no-fail.

Your advice has been right on the money and is exactly how I am proceeding. I was very surprised that the 20x50 piece of EPDM only cost $350. If you wouldn't mind, I would like to keep you on my email list for the next time I scratch my head. Thanks again.

Oct 27, 2010
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A couple important suggestions
by: Editor - Rich Bergman

Great question. Now that you have properly sealed the entire deck surface with proper drainage, slope to edges, drip edge to ensure water doesn't dribble down the fascia or wall below you need to consider the safest way to set up the decking surface.

You can do a floating deck and is really your only option. You can use 2x material laid flat or 4x material also as sleepers. However I would highly recommend that you consider

a) that the epdm is lying flat on the roof subfloor without any sharp objects that can puncture the edpm once sleepers are laid over top and placed under load;

b) that you take the time to glue strips of epdm rubber underneath each sleeper where they will sit on top of the epdm surface. This will ensure no danger of damage to the epdm over time and while under load;

c) that the sleepers which replace the traditional beams of a deck run in parallel direction to the slope of the roof surface so that water is free to run its natural direction to the lower surface and keep the roof relatively dry over time. Very important!

Hope this helps.

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