Crazy roofing question

[df909]

Hey Guys-

This might sound a bit crazy, but here goes. We have a fairly flat roof on our house and we want to use some of it for garden space. I'd like to put some short planter boxes on the roof for a small vegetable garden. The roof is comprised of full 2"x6" t & g over 6"x12" beams- so the roof is very strong. The actual roofing material is torch down rolled roofing and it's about three years old.

My questions is: is it ok to walk on the rolled roofing without damaging it? We'd have to walk on it maybe once or twice a week. I know if you walk on a tile roof you can break the tile or if you walk on a hot mopped tar roof you can hurt it. Also, I will elevate everything a bit to get airflow around the planter boxes so there's no water standing on the roof for prolonged periods.

Thanks for the help.

 

[veritas honus]

Re: Crazy roofing question

If the temperature is 70's-80's, you should be fine. If the temperature is 90's-100+, stay off the roof. when it's hot, the asphalt is very soft, and you'll damage it by rubbing the granular off it's tar/asphalt base. early morning and at night are good times because it's cooler.

...And by the way, there's nothing crazy about it. Good thinking, not having the planters directly on the asphalt.

 

[rickryder]

Re: Crazy roofing question

You'll be fine but like veritas said watch out when it hot out....the tar may become soft and sticky.

 

[foodfisher]

Re: Crazy roofing question

You're going to loosen the granules anyway. Just avoid the edges so the flashing stays intact and try rolling a strip of old carpet down to walk on. Easy roll up when not in use.

 

[df909]

Re: Crazy roofing question

Thanks for the replies. It gets pretty hot where I am, at least 100 for a few weeks every summer and the roof is in full sun all day long. I won't walk in it until it's much cooler, I'll wear soft rubber shoes, and that's a good idea about a roll of carpet.

I'll make a frame to hold the planter boxes and obviously the frame will be in contact with the roof. I'll also make it with a fairly wide base to even the load out. Will that cause a problem when it gets hot or will it be ok since it's stationary and was built when the roof was cool?

By the way, I'm thinking watermelon, pumpkin, and honeydew since they'll have all the room they need to grow and will have all the sun they want. Thanks again.

 

[lncoop]

Re: Crazy roofing question

No maters? You crazy Californians!

 

[badkins50]

Re: Crazy roofing question

it will be ok like stated before. alot of high rise buildings are going with what they call "green roofs" that have irrigation systems with grass and plants and trees. pretty cool. google search green roofs.

 

[wifisher]

Re: Crazy roofing question

Sounds like a bad idea. Repeated traffic will damage the roof. So will the "table legs" that you use to elevate your boxes. I would also think about what you are going to plant that would survive in those conditions. If it is 100 degrees outside, it is a lot hotter than that on the roof.

 

[lncoop]

Re: Crazy roofing question

it will be ok like stated before. alot of high rise buildings are going with what they call "green roofs" that have irrigation systems with grass and plants and trees. pretty cool. google search green roofs.

True, but the roofs on high rise buildings aren't tongue and groove supported by wooden beams. If you went ahead with your project it would be prudent to first determine the weight of a planter full of wet soil (if you haven't already). I suspect it's significant. Just sayin'..........

 

[drice379]

Re: Crazy roofing question

In Michigan we use an ice and water shield. It comes in a roll like tar papeer and has a sticky side. You dould lay that down for a walkway and save the tear on your original roof.

 

[dockwrecker]

Re: Crazy roofing question

Walking on a built up roll roof is a bad idea. If you look at a typical HDPE, rubber membrane or Trocal ballasted roof system, you will always see traffic mats between things like roof fans, condensers, etc for service work. You need something similar to that for your purpose that won't blow away. I'd recommend the 16" square pavers from the big box store. They will distribute point load for your box support frame (NOT legs!) and will also distrubute foot traffic. Me not being much of a gardner couldn't tell you what will grow in that kind of heat. Just be careful that whatever it is won't attract the Feds. (you Californians are so obvious sometimes...) Now as far as the weight of your soil. In my business we use some pretty basic guidlines. Dry concrete per cu. ft is guess-timated at 160 lbs. Saturated soil is 145 lbs. compacted dry soil is 135 lbs. Light weight concrete (high vermiculite) 130 lbs. Loaded soil (uncompacted) 130 lbs. Gravel 125 for 3/4 crushed. A sensible plan would be to keep the box shallow, some sort of liner, bottom half crushed gravel, top half soil. Water will definitely percolate out of this thing, I wouldn't worry too much about drainage unless a monsoon fills it full of water, then the loads above for saturated soil would apply. Now back to the leg thing. NO STINKIN' LEGS! Think sled with additional center runners. The name of the game is to distribute load SPANNING the roof joists. Sounds like you've got a pretty sturdy roof underneath, but this info is to be used at your own risk! Good Luck! :facepalm:

 

[df909]

Re: Crazy roofing question

Hmm...sounds like good advice- thanks to all. I'll incorporate ideas from everyone into this and see what I come up with. We converted 1/2 of our front yard to grow veggies and I'm installing a garden on the side of the house too. I have 4x4 posts with 2x4s across with a rain gutter attached to each 2x4. This will be just enough soil to grow lettuces, herbs, and stuff like that. We're the crazy people on our block that tries to grow a bunch of food- we have chickens in the back for eggs and we're raising meat chickens for the BBQ.

 

[lncoop]

Re: Crazy roofing question

It's cool that you're trying to make a connection to the land. Let us know how it turns out.

 

[mommicked]

Re: Crazy roofing question

Put the planters at the edge of the house and plant blue lake green beans! they could then cascade down the side of the house and they produce well w good soil,you would need to pick w a ladder though.The ground hugging melons and pumpkin vines would have to be supported feet off the roof or I think they would die from the heat.horizontal grid of somekind?plants that grow vertically would probably be easyer.Like tomatoes!.If you covered the roof w green leafy vegees it would have to cut down on the cooling bill too!!

 

[hrdwrkingacguy]

Re: Crazy roofing question

If I were going to do something like this in AZ where it gets to the 120's in the summer...I would build a box with 2x6's put a plywood bottom, line it with rubber membrane like a shower pan...build 6 legs down and run them to a 4x4 redwood on each side and under that put a 8" wide x length of the 4x4 piece of rolled roofing...and fill with dirt/soil/whatever...We set 2000# air conditioners on roofs all the time, just run the 4x4 across the truss's to distribute the weight...

 

[df909]

Re: Crazy roofing question

Good point about the a/c units on the roof. Our house is the only one in the neighborhood that has a concrete slab foundation and such a sturdy roof. From what I've heard this was the builder's house and he was going to make a two story but for some reason changed his mind, but still made a strong roof.

I'll have to see what we can grow that would cascade down rather than grow across a hot roof. I'll also put some pics here when we figure it out.

 

[ajgraz]

Re: Crazy roofing question

df909, maybe you have a greener thumb than me, but the only items that I've found to grow well in S. California in the home garden AND that were worth the effort vs. just going to the Farmer's Market are: pole beans (green beans), tomatoes (though they need some DEEP soil), and various herbs. Everything else either gets too much sun, not enough water (forget one watering and they're done!), require just too danged much water (like melons), or just wasn't any better than the Farmer's Market could provide. Oh, and Everbearing strawberries. Hey, put strawberries on the roof; they can take some massive heat, don't root all that deep, and you don't have to worry about their invasive runners taking over your whole yard up there!

 

[Auxie]

Re: Crazy roofing question

Here's a crazy idea: If the roofing membrane is intact, how about spreading some topsoil and planting grass? Extra cooling insulation and you could walk on it.

 

[dockwrecker]

Re: Crazy roofing question

Yup that's crazy all right. Never hold moisture on a roof if you can avoid it. Grass will root rot without drainage, even I know that one, and good luck packing the Toro up there to mow it.

 

[df909]

Re: Crazy roofing question

That would he pretty funny to be driving along and see some guy mowing his roof. Even though it'd be 10' up, I'm sure there's a dog somewhere that'll manage to poop on my roof grass.

Here's a pic of the rain gutter garden I did on the front of the house.