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flat walkable roof

paulack's picture

I am looking for some details on the design of a flat walkable roof on one of my projects. I am thinking possibly lightweight concrete on top of open web joist. Any thoughts?

(post #97840, reply #1 of 31)

What I've seen is corrugated steel decking (the kind with sort of squared off corrugations) on the steel joists, then the concrete on top of the steel decking. But you have to waterproof it really well because concrete will let water through it.

(post #97840, reply #2 of 31)

i seen the same thing with a membrane between 2 layers of concrete. i dunno what the membrane was though.

(post #97840, reply #5 of 31)

now that has potential. we need to find out what membrane. rubber?

(post #97840, reply #6 of 31)

Frame the deck in wood, add shims to create drainage slope, install drains and a Sarnafil membrane, install pavers on adjustable pedestals. The pavers are removable if you need to repair the membrane.

(post #97840, reply #9 of 31)

wasnt rubber. i didnt ask since it seemed like a long term maintainance nightmare. i cored the first layer of concrete dropped the roof bowls in and walked away.

if i were ever going to actually do it i like the idea of pavers as ballast. so u can remove them to make repairs. but ultimatly would rather have a deck completely suspended above the roof. also removeable to reroof.

in the end a flat roof on residential property in wisconsin is kind of askin for it. imo. but thats wi. if i were to build winter home in say az i would want a flat roof cause u get a whole other set of design possibilities.

(post #97840, reply #10 of 31)

thanks Brian
been in snow country 53 years but now we're in FL trying to thaw out. All I have to here is run the water downhill and off.
Again thanks for your input.
Stay tuned pics will follow


(post #97840, reply #11 of 31)

Check out it's made for this & looks good

"this dog may be old but he ain't cold. And he still knows how to bury a bone."


(post #97840, reply #12 of 31)

checking rob

(post #97840, reply #14 of 31)

Not sure what your original post means by "walkable". Is this to create an outdoor living space on your roof?

Or are you asking about the best flat roof systems in general?

Piffin should chime in about that. He good.

(post #97840, reply #15 of 31)

I've been staying out of it because I don't understand the question or situation or whatever.

Depending on the person a walkable roof might be a 3/12 or an 8/12



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(post #97840, reply #16 of 31)

I think he wants a flat roof that he can use like for a patio, at least that is how I read it.

(post #97840, reply #18 of 31)

Flat means just enough pitch to run water. Walkable means yes an extension of lining space. I hope that clearifies things for everyone. So let's all chime in now. a one a and and a two a .....
thank you all for your thoughts

(post #97840, reply #19 of 31)

Were you a cheerleader?

I WOULD DO EPDM - have done several times

Then sleepers and wood deck.

Use advanced search on those terms for past discussions and photos.

anna three anna four...



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(post #97840, reply #20 of 31)

I suppose there are several options if creative & unconventional interests you.

If you're open to conventional solutions though, I would agree with Piffin and add that the deck on sleepers could be constructed in removable sections for ease of repair/replacement.

Conventional materials. No unusual weight issues.

Take the sections idea a step further and you can rearrange them periodically for amusement. A different deck each week!

Good Luck!

(post #97840, reply #21 of 31)

and the unconventional????

(post #97840, reply #22 of 31)

no rah rah here piffin. Just trying to get the job done to the best of our collective ability.

(post #97840, reply #23 of 31)

There are walking "pads" available that cement directly to a EPDM roof.

they are ahe same material but about three times thicker and have treads that face up.

any competant rubber roof installer/supplier will be able to get them.


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(post #97840, reply #24 of 31)

T, you thinking of or something different?

(post #97840, reply #25 of 31)

The ones I have seen were only about 3/16 to 1/4 inch thick.

but those ones would be better for a living area with constant traffic.

1/2 or 3/4 thick!!!

you couldn't put holes in those with golf shoes!!!


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(post #97840, reply #7 of 31)

Roof of a highrise apartment building I worked in had precast, pre-tensioned hollow concrete planks as floor/ceilings and as roof deck. It was covered with something pronounced something like "Trelkeld" (or "Threlkeld"?), [edit: Trocal?] a grey membrane that was then ballasted with river rock. Worked well, where they didn't run short and just put the ballast on, hoping we wouldn't notice (like we wouldn't notice a waterfall running down five flights of stairs from roof to ground floor every time it rained!).

That system of precast planks would work for this application, but would need a crane (I know I didn't address this to original poster--assume he's following what everyone is saying).

Edited 3/31/2005 1:01 pm ET by Danno

(post #97840, reply #13 of 31)

What your refering to is pandecking.

(post #97840, reply #3 of 31)

What do you mean by walkable?  Rubber roofs are "walkable" for occasional traffic.  Not ok for a deck surface.  How big a roof?  Do you care what it looks like?  Are you building the entire roof system?  The best roof system I've seen is a rubber roof with foam panels to insulate and protect the rubber.  Topped with cocreate blocks that are about 4" thick to hold down the foam.  It's fireproof.  You can drag furniture around on it.  And you have easy access to the roof if a repair is needed.  Just lift out the blocks and foam.  The only drawback is the system is very heavy and the roof has to be designed for it.

(post #97840, reply #4 of 31)

ok joe one at a time. Is not for occasional traffic. about 1800 sq ft. I do care what it looks like. I am building the whole, new construction. Your proposal is a good system but too heavy. let's put our thinking caps back on.
thanks Joe

(post #97840, reply #8 of 31)

So, you'll have a pretty deep parapet as a railing anyway, right?  Then, why not seperate roof and deck? 

Maybe thats an EPDM or a modified torchdown roof, or even a metal roof--that's more a question of what's best for your locale.  Then "float" the walking surface over it.

Why go to that much trouble?  Depends on where you are.  Where I am in central Texas, we get between 2 and 3 inches of rain per month.  I'd likely use an APP roof over whatever structure seemed most efficient, and mount the deck over the finished roof using a standard equipment base detail.  But, that would be so the walking surface of the deck would not have ponds on it until the water eventually ran off.

In Midland, I might go with a membrane roof and pavers, closer to the Sabine, I'd be inclined to a 1.5/3 in 12 R-panel metal roof with a nice flat walking deck over that.

But, that's me.

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)

(post #97840, reply #17 of 31)

Resource conservation technology inc They can help to determin the right material.  They have roll ons that can go right over ply wood to epdm.

(post #97840, reply #26 of 31)

I've done several of these, and I'm in the process of another.

My first was a deck built over a metal roof....PITA and a task to maintain.

I did another with a product called Gaco Deck which is a walkable coating over taped seams on plywood.  It works and is fairly easy, but the seams tend to telegraph through, in spite of what the product literature may look like.  Gaco is available at most yards and big boxes.

I did a couple with Dura Deck.  It works well, but requires a factory qualified installer and requires a durable walking surface layed over it.

The method I now use is a plywood deck overlayed with 1/2" Durock thinsetted down with a careful job of taping and thinsetting the joints, a trowled on (2 coats give you 80 mils) polyurethane membrane called Tremco (made by the folks who make Vulcum polyurethane caulking), with a UV resistant walkable  sanded topcoat.

I slope the deck 1/8" to 1/4" per foot.

On my current effort, the 12' X 30' deck is supported by 4 structural fiberglass columns with downspouts in the columns fed by a formed SS gutter below a flush-surface 4" wide grating that runs just inside of the outer perimeter of the deck.

The topcoating is available in a range of colors.

My supplier for the membrane and topcoat is Allied Building Products.

Rain is currently holding up the process from the durock on up, but I'll post pictures  when the time comes....hopefully within the next 30 days, weather permitting.

(post #97840, reply #27 of 31)

Would this be the specific Tremco product?

Thanks for the reference. I'm always on the lookout for good products for that purpose.

(post #97840, reply #28 of 31)

That's the one. 

I recently lost all my picture files, including one of these finished decks, but what I like about the results using the Durock is, with careful prep of the seams, the deck turns out as smooth as a good concrete job without the weight issues.  And the Tremco membrane is really tough.

This whole process kind of evolved after having done one small outdoor tiled deck over Durock, but, IMO, tile decks can be a bit of a hazard around here if they aren't kept clean and free of the slickness that develops from accumulations of tree pollen, and Oregon Winter slime.

I actually use a belt sander to get the seams nice and flat so they don't telegraph through.

The Tremco is put on with a notched trowel or a notched squeegee....each coat is 40 mils.  They say one coat is sufficient, but 2 coats is good and here in the PNW where is rains occasionally, I tend to opt for the extra weatherization.  I use 3/4" pt plywood screwed down on 16" joist centers for the substructure.

On these kinds of projects, flashing details are important, especially at doorways;  I always use sill pans under the doors to serve as counterflashing and wall flashings are run up pretty high....I usually go 10" or so.


Edited 4/1/2005 9:44 am ET by Wormdrive

(post #97840, reply #29 of 31)

>The Tremco is put on with a notched trowel or a notched squeegee....each coat is 40 mils.

Does it then self-level?

I have an area that would be a perfect application, but it's only about 30 sf. Don't know that I wanna go searching for a distributor just for that small amt.

Have a few designs that can make use of it, though. Gotta go search out their specs.


(post #97840, reply #30 of 31)

Yes, it is self leveling; sets up very smooth.  The sanded topcoat is necessary for traction.

Allied Bldg. products is nationwide.  They should be able to supply you.  They deliver over 120 miles to me...roofing, F/C siding, charge, including stocking a roof is about $20 and their material prices beat the big boxes.  Great outfit.

Good luck!