Help my pups poop in the clouds!
March 24, 2009 10:30 AM   Subscribe

I want to build a dog run on a flat (well, 1% or so) modified bitumen (I think) roof. What materials should I use?

(The roof has high parapets, and there will be an enclosure around the run, so don't worry about dog or person safety.)

I definitely want to keep moisture away from the roof as much as possible and allow for air to circulate under the plywood/cedar chips. What materials should I use, and in what order? I want the top to be wood chips, probably cedar. What should I put immediately under the cedar? And what should be the base of the whole structure?

I was thinking, from the roof up, some sort of moisture-sealing sheet, then frame of pressure-treated 2x4s, another moisture barrier, then plywood base resting on that (the plywood will be about 2 inches off the surface of the roof), then landscaping fabric, then cedar chips. I feel like the plywood and 2X4s will rot pretty fast, though. Should I try to use something synthetic instead?

I have also thought about using some sort of patio-type bricks, but I don't want to use any heavy material, and I'm having trouble finding non-stone patio materials. Something like this might be useful as a base, although I want the top surface of the run to be wood or cedar chips.

I've googled extensively, but none of the links address dog runs AND modified bitumen roofs.
posted by iknowizbirfmark to Home & Garden (8 answers total)
I can't give you any specific advice for modified bitumen roofs, but have you considered using a green roof approach? There is a lot of information about constructing green roofs, but it seems like you could substitute cedar chips for soil. You'll want to be careful of the weight load.

If you're looking for a true DIY approach, you could construct a deck on top of old wooden pallets to keep everything elevated and allow for drainage. Pallets are usually available for free on craigslist.
posted by Andy's Gross Wart at 11:13 AM on March 24, 2009

Best answer: Fine Homebuilding has several (subscriber only) roof deck plans that could be adapted for something like this. I think online registration will cost $30 or so.
posted by electroboy at 11:16 AM on March 24, 2009

Best answer: Redwood or cedar 2x4's won't rot, at least not for a dog's age. Probably pine won't either, if it can dry in the sun.

I'd be concerned about water pooling on the plywood. Plywood doesn't like to get wet because of the glue.

If you build a deck of 2x4's or 2x8's, and lay astroturf over that, I would think you'd keep your dogs happy for years to come.
posted by musofire at 11:16 AM on March 24, 2009

Also, pressure treated wood is fine for your purposes. Pressure treated plywood is also suitable for outdoor use.
posted by electroboy at 11:49 AM on March 24, 2009

Response by poster: Andy's Gross Wart, I may be doing other "green roof" approaches, but I'm not sure what it would mean in this context. There still has to be a moisture barrier and I don't want things growing in the dog run, nor do I want to mix runoff from it with other water and soil that may be up there. Even with an overall "green" approach, I want to keep the dog waste and related cedar chips isolated from the rest of the roof.

As for pallets, I want to DIY, but still approximate professional results. Around here, pallets aren't free and don't really seem like the right long-term approach.
posted by iknowizbirfmark at 2:20 PM on March 24, 2009

Before you do anything, find out exactly what's up there on the surface and when it was installed. If it is bitumen and it's been there a while, it'll probably need patching--maybe replacing--in the next few years. It would be a huge drag to build the whole thing and then have to take it apart for roof access.
posted by dogrose at 4:03 PM on March 24, 2009

Response by poster: Thanks, dogrose. Roof is relatively new (6 years) and has been recently patched and inspected in connection with some ice floe-related leaks around exhaust pipes.
posted by iknowizbirfmark at 4:08 PM on March 24, 2009

Best answer: Consider using open grid plastic tiles such as from Turtle Plastics. They are easy to install, already include drainage and are lightweight. Several different styles are available. With the tight grid style, you may be able to install the cedar right on top without worrying about dog traffic pulling up the landscape fabric.
posted by mightshould at 5:43 AM on March 25, 2009

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