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I've got a roof that looks like this:

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We just had the roof redone with what I think you'd call rolled roofing. It needs a deck!

Here in San Francisco a lot of restaurants have outdoor eating for the pandemic, and many of them look like they'd work perfectly on our roof. This one for example:

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I'd like to make a lighter weight version of that, loosely.

The main priority is being low impact on the roof. Another priority is longevity. And we don't want to spend too much money if we can avoid it.

My current plan is some pressure treated 2x6's flat against the roof, with plywood decking over that. The 2x6's would dissipate the load and provide ventillation. And the plywood would be the deck top.

I'm wondering if people have a suggestion for what plywood to use? We have to haul everything up the side of the building, so I'm thinking 1.25" inch plywood would be too hard.

And any suggestions for what to use to seal it?

One post I found very interesting is this one from moderator @firehawkmph:


this thread brings to mind something I built when I had a camping trailer parked at a campgrounds for the summer. I built a deck out of treated 2 x 6's and 5/8 cdx plywood. I made it in 4' x 8' sections so it could be transported and moved. I had 5 of these sections. I put a concrete block under each outside corner and at each intersection where two sections butted together. When I was done I had a deck that was 8' x 20'. Once they were in place and leveled, I covered the top with that green outdoor carpeting that comes in 6' wide rolls. I stapled it down and overlapped the edges so the treated 2 x 6 was covered. I didn't do anything to the plywood waterproof it. Three years later when we pulled the camper out I took off the carpeting and kept it. I gave the wooden sections to another camper there. They looked like the day I put them together. The carpet had a rubber backing to it, which probably helped keep the cdx dry. Didn't cost much money, worked fine and I still have the carpet. The kids were babies then, so this was about 17 or 18 years ago.
Thoughts on simply doing some basic sealing of the plywood and then covering it with astroturf?

Eventually I'd like to add walls and a roof. The loose plan is to have 4x4 columns leading to a 2x4 frame for the roof, covered by thin plastic. Basically a lighter weight version of what's in that pic.

- how to attach the 4x4's to the floor? I'm thinking I should have the 2x6's protrude out from the plywood for that?

- and should I connect the 2x6 floor pieces to the 4x4 roof columns with joists? Or should I simply toenail them?

The entire structure will be about 20 feet by 12 feet.
 

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Great place for a deck, I've never done that but 2 big issues come to mind.

Wind, basically you need to handle a once a century wind, 100mph etc. Consult a construction engineer etc about how to strongly attach it to the building in a way that won't leak. Even if it is just a flat floor a strong wind could take it off the roof and then it'd be a missile.

Zoning, codes etc, don't be surprised that you've done something wrong after it is already up.
 

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I would be careful about what you do (codes, permits).

Initial thoughts - use decking not plywood. Avoids water being trapped on top of ply. Composite decking would be the way to go, no worries about anything pressure treated leeching into roof.

A retractable roof would be really nice!
 

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I almost hate mentioning it on a wood working site, but if weight on the roof is an issue, don't build a wooden deck.
You can use metal framing and make it stronger and lighter than a wooden structure.
 

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We just had the roof redone with what I think you'd call rolled roofing.
Not only does one need to know how much weight the roof structure is designed to hold, the same applies to the roofing materials just installed. Did you or are you planning to discuss this with the contractor who installed your new roof?
 

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Here's something I came across. My younger brother is a union commercial roofer and he was telling me about this type of product for flat roofs. The adjustable pedestals make for an easy installation. Different types of material seem to be available, so you can get something that is light weight. Like the others have mentioned, you really need to evaluate your roof structure to see if it can support an additional weight load.
Mike Hawkins
 
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