# Deck on Flat Roof



## Guttersmiths (Aug 7, 2012)

I don't know how the pricing compares, but I've heard good things about Duradek. Find a certified installer that also does roofing and have them price out Duradek vs. EPDM with a wood deck. 

I've never heard of not being able to install over a heated space, but if I were you I would call the manufacturer and get their recommendation.


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## roofnron (Dec 7, 2011)

You can use DuraDek or DecTec. These systems must be put down perfectly. The plywood decking must not be exposed to the weather prior to installing the membrane. Insulate the heated space properly and you won't have a problem. 

I would do everything I could in talking you out of using these systems. The membrane is expensive. No room for any error in installation. Typical membrane warranty 10 years. It will get dirty, same with coated metal you use for flashings. There is a danger of poking holes by dragging furniture, dropping utensils, etc. 

I would consider the option of using fully adhered 0.060 EPDM over a 1/4" dens-deck insulation board. (I would not use modified or coatings.) The EPDM can be applied with NO seams. There will be nothing to leak. (Install the EPDM walls behind the Tyvek, and flash the door sills with roof membrane before setting the doors)

Now you have an option of installing the deck with the sleepers. Sleepers running in the direction of waterflow. Place the sleepers on leftover scrap EPDM pieces. You could also install roof pavers instead of decking, or even a tile on a mud bed. 

The EPDM option would last decades, upwards of 50 years.


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## Michael Thomas (Jan 27, 2008)

There are many possible problems with roof-top decks retrofit to existing roof designs, and I see the results on a regular basis.

These include, but are _far_ from limited to:

1) Emergency egress: Is there a way off the roof if there is a fire at the primary access?
2) Structural: Is the existing roof structure strong / rigid enough to support the additional weight?
3) Roof drainage: For example, will there be readily available access to clean / inspect / maintain roof drains and scuppers? Is there a provision for controlled secondary overflow if a primary drain clogs?
4) Roof penetrations: Will there be readily available access to clean / inspect / maintain the flashings at vent stacks, AC power and refrigerant lines, skylights, etc.
5) Door installation issues: For example, in snow areas, is the door sill at a adequate height above the new "roof" height? (I see many, many door leaks resulting from such problems).
6) Roof membrane issues: In addition to issues caused by the direct contact of sleepers with roof membranes, decks can impose new stresses at locations such the upturns to termination bars, and details such as omitted cant strips are now more likely to cause problems.
7) There are a whole raft of miscellaneous code and practical problems: Do electrical service drops still meet clearance requirements? Are (if you want them) electrical, water (supply and DWV) and natural gas/propane supplies code compliant? Are vent stacks the minimum height required by the new usage?
8) And, the list goes on and on.

Many of these potential problems can be difficult and expensive to fix, and it is _very_ hard to find people who know how to do _everything_ right the first time: here in Chicago, where there are tens (hundreds?) of thousands of rooftop decks, there are only a handful of contractors who can do it all right... and they make _most_ of their money fixing the problems created by everyone else, because it is quite expensive to do it _all_ right the first time.

So the bottom line, to me, is that residential rooftop decks are a very problematic way to spend your money.


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## modusvivendi (Aug 6, 2012)

thanks roofnron

Why would you not use modified bitumen?

Are you saying we could lay the pavers or the tiles/mud directly on the edpm membrane?


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## roofnron (Dec 7, 2011)

With modified roofs, there are seams everywhere. They are fine roofs in the right situation. I would be looking for a system that is proven to last a very long time and with little to no seams or flashings that can leak. Anything you lay on the modified will also dig into the membrane. Modified material will not last as long as EPDM. The EPDM sheet will last twice as long or more. Modified roofs must have positive slope so water will drain. 

Yes, paver systems and tile systems are done all the time. There are all kinds of paver systems made of concrete and rubber. Tile is done as well. Pavers can be laid directly on the EPDM or on pedestals. It wouldn't hurt to lay them on some kind of sacrificial sheet though. 

I am working on a job right now where I have laid the EPDM membrane, (no seams, 60 mil), then tile guys are coming behind me and installing a tile system by http://www.schluter.com/5357.aspx.

I would have to agree with Michael Thomas for the most part, especially no 2 and no 5. There are a lot of things that get screwed up and cause damage. But when done right it can be a great use of the space.


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## modusvivendi (Aug 6, 2012)

Ronnroof

Yes, I would like a system that lasts a long time, but I thought EDPM only has a 10 year warranty and we have been offered a 25 year warranty with modified bitumen (that was before we discussed putting a deck up there)? Also Wouldn't PVC last longer than edpm?

OUr roof does slope for drainage. 

Thanks for the tips on pavers


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## roofnron (Dec 7, 2011)

You are really dealing with commercial products on residential applications. You are dealing with a warranty on 280 sqft. No manufacturer wants to warranty something that small, even though I know some do. If you are getting a 25 year warranty then great, make sure you read and understand all the fine print. Possibly building a deck over the roof would void it anyway. 

There are cases I would suggest modified over EPDM on a residential application. A modified roof system can be 5 times or more thicker than EPDM. Because of this, when exposed they will likely take more abuse from things like falling tree branches. Under a deck this is not a concern. 

Let's compare the material. Lay a sheet of EPDM and modified outside on the ground and let it sit there for 10 years. It doesn't matter if you are in Alaska or Florida. The EPDM you can pick up and install on a roof and confidently say it will last another 20+years. The modified you would throw in the trash. There is no other roof material like EPDM. (Also let me clarify I am talking about Black EPDM, white EPDM is limited to only 10 year life, and you may be lucky if you get that.) All systems are limited by qualifications of the installers. 

On residential work, you most likely will have a two warranties. One from the installer and one from the manufacturer. You may be able to get a total system warranty from the manufacturer but you will pay big for it. I would look for a 5 year labor warranty from the installer. If there is a workmanship issue you will likely find it in the first year. The second warranty would be the material. These warranty's are often limited in many ways. Get a copy and read it well. They are often limited by application methods, size, are heavily prorated, and more. 

As far as PVC lasting longer, I say it is not possible. You have a 50 mil thick membrane. Lets say 25 mils is above the scrim. Depending on location, solar exposure, the membrane will deteriorate a 1,2, or 3 mils a year. Once the membrane gets near the scrim it is done. This is why a manufacturer will advertise as "56% more above the scrim then competitors". This is what causes the chalking and makes welding, cleaning difficult on an aged TPO, or PVC roof.


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