Green Roof planter boxes, feedback requested - Page 3 - Router Forums
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post #21 of 29 (permalink) Old 05-05-2020, 08:13 AM
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Don't overthink it. I built a small entrance shed going into the yard with a living roof on the bottom I used 100 year old 1" flooring and for the sides, I used regular 2x4" nailed together. I lined the roof with rubber leftover from a koi pond. For your project use pressure treated lumber, decking would be ideal. It's cheap and will outlast cedar by years if not decades. Nail them together with 16 penny nails and you'll be long gone before they fall apart. If you want to be extra safe use galvanized nails. The biggest thing that you should be concerned about is the pitch of the roof. If it's more than 22 degrees the soil will wash away. Once the plants take hold the roots will help hold everything together. You didn't mention what you will be putting under the boxes but with drain holes in the boxes the roof will rot out if it's not completely protected. EPDM roofing is what I would put down.
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post #22 of 29 (permalink) Old 05-05-2020, 09:50 AM Thread Starter
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Default Since there is some interest in this green roof part...

The roof was designed by an architect and a structural engineer. It is slightly pitched in places for drainage but basically flat. Specifically designed for plantings. It has a thick membrane coating - don't know if it's EPDM but it's thick, well sealed and drains quite well. See the photo.

Originally, we hired a company to put in the green roof materials and plants but they flaked on us so we get to do it ourselves. I've done a lot of research and am pretty sure this is the right way to go. We will lay down a 6 mil plastic sheet on that (aka slip sheet), then a JDrain drainage composite layer (think plastic sheet with small cups and fabric on top to create a .4" drainage layer), granular pumice infill on top of that to level the planting surface, then landscape fabric followed by the planter boxes. I may put a fabric layer on top the JDrain to prevent pumice incursion because I will have to piecemeal the JDrain in places. Special attention will be paid to the upper roof drain to make a channel it can run in.

We will finish it off with a row of pavers between the major rows of boxes (for weeding access and such) and small river rock around the edges to hide the fabric. Mostly sedums in the boxes though my wife is talking about some ornamental grasses in pots at the corners by the windows. Will have drip irrigation to the boxes though it will be used infrequently once the plants are established.

I've also spent some time thinking about the logistics of staging box placement. Will lay down plywood sheets to walk on so we can carry the boxes to their locations. Will lay the boxes down starting in the far left corner in the photo and work our way back. The railing you see in the lower right of the picture actually pops out giving easy access and the small "panhandle" section has access from the other side.
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post #23 of 29 (permalink) Old 05-05-2020, 09:56 AM Thread Starter
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Originally Posted by mgmine View Post
Don't overthink it. I built a small entrance shed going into the yard with a living roof on the bottom I used 100 year old 1" flooring and for the sides, I used regular 2x4" nailed together. I lined the roof with rubber leftover from a koi pond. For your project use pressure treated lumber, decking would be ideal. It's cheap and will outlast cedar by years if not decades. Nail them together with 16 penny nails and you'll be long gone before they fall apart. If you want to be extra safe use galvanized nails. The biggest thing that you should be concerned about is the pitch of the roof. If it's more than 22 degrees the soil will wash away. Once the plants take hold the roots will help hold everything together. You didn't mention what you will be putting under the boxes but with drain holes in the boxes the roof will rot out if it's not completely protected. EPDM roofing is what I would put down.
I've been thinking about using PT wood. Though, I've seen it rot just as bad as untreated in places. 16 penny is vast overkill. Also, my unskilled labor doesn't know how to swing a hammer for beans. Nail/staple gun is the way to go, imo.

Out of curiosity, what over thinking do you see?

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post #24 of 29 (permalink) Old 05-05-2020, 10:55 AM Thread Starter
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Re your drawing, Phil; I like that you've got the bottom boards literally on the bottom, but I'd build it so that all four side bottoms are in full contact with the bottom edges of the side boards. Nailing/screwing up into them all the way around will add tremendous strength where it needs it most. It'll prevent the sides and ends from blowing out; most of the force is at the bottom~sides.
Hopefully that made sense...
Yeah, I've been thinking about that - would make the sides stronger/less prone to bowing. Need good drainage so that's why the slots on the edge. Maybe landscape fabric would hold the dirt in.

Another approach is to turn the bottom boards sideways. Here's a picture of the bottom. It would add some more work because I'd have to rip a bunch of the wood and make more cross cuts.
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post #25 of 29 (permalink) Old 05-05-2020, 10:59 AM
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Now, having seen the 'big picture' I'm wondering why you don't simply frame up some areas with PT 4x4's and line the timber areas with high quality landscape fabric (on top of your prepped roof).
Personally, I'd have the material moved up onto the roof by a Hiab crane. Two trips; one for the building material and the second for moving the soil up in a skip.
That's a lot of soil required you have in that latest picture!
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post #26 of 29 (permalink) Old 05-05-2020, 11:44 AM Thread Starter
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The way were are doing it is pretty much the standard way that green roofs are built. Moving loose soil makes for a huge mess. Also, one needs to have fairly minimal activities on the roof itself as that disturbs the drainage layers which are critical to making the whole thing work. We will probably hire a couple of day laborers to move the boxes up and other things.

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post #27 of 29 (permalink) Old 05-05-2020, 11:56 AM
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I've been reading this for a couple of days and have a few thoughts. First. red cedar shrinks when it dries out, so shiplap is a possibility since the gaps will leak soil all over the roofing material. Furtilizers will leak some nasty acidic or base stuff as well, amplifying the problem

Laying the boxes down onto the roof sounds like a recipe for rot, particularly on a flat roof. Controlled watering will help, but rain will flood unless you work out a way to drain it quickly, or cover it when it rains. I don't think I'd like climbing up onto the roof every time it might rain.

Oh my aching back. Bending down to tend to plants, especially edible plants, will get old, in, say, 6 months. And have you thought about carrying the soil back down or transfereing it to replacement boxes in a few years when your spine is that much older? I'd consider building some sort of framework to elevate the boxes, which will allow you to suspend some sort of water collection and drainage underneath the boxes. Run some heavy plastic roofing material underneath and attach to some pipe to carry the water down and away from the roof and foundation.

Minimize the wet contact with the roof since the wet framework will wick moisture to the end pieces. Perhaps a heavy coat of some sort of waterproofing rubber on the ends would limit this source of mischief. What about wrapping a couple pieces around the sides of each box and connecting them to relieve outward pressure, which I bet will bow the sides and pull out the connectors at the ends, no matter what kind.

I've used cedar extensively for water valve control box covers in the back yard, and just the wet/dry cycle will destroy the tightest of joints quickly. Personally, I'd make narrower boxes, longer with reinforced sides every 18-24 inches.

If you raise the boxes, consider attaching taller 2x4 redwood pieces centered on the boxes with a wire strung between them with clear plastic on rings so you can simply pull them over the plants when you need to control moisture. If plants are edible, leave ends open for pollinating insects. Wasps will probably love this thing, although the cedar will help with that while it's still aromatic.

This structure, no matter how you set it up, is going to be fairly high maintenance. Will the architects and engineers be available to help with fixes? Will they help pay for those fixes?

Do you have a way to set up a stairway up from the inside. If you have edible plants that would be nice. Change out one of those windows maybe? Just speculating.

Or at least a fixed outside ladder and motorized/hand cranked lift next to it? You'll be grateful you did it for decades, so will the next buyer.

Not meaning to be a negative nellie, but having made stuff, including planters, out of red cedar meant for fences, I suggest you think this through a bit more. I've made a lot of my outdoor projects out of redwood. Very forgiving stuff that turns gray but just doesn't rot.

My solution would include a 2x2 or 2x3 redwood floor set across the roof, set fairly close with a rubber drainage set underneath. I'd set it on a framework perched on top of, but above the roof, next to the point where the flat roof is affixed to the wall. Start the drainage there and continue it to the other side. I'd attach the other side of the 2xs to the top edge of the outside wall so no weight was carried by the roof, and no water would settle on the the flat roof. Run one or two drain pipes or troughs off to the side into a drain that runs 4-6 feet away from the foundation on a downhill run into a french drain, if it isn't already there.

Setting the trough bottons width wise across the boxes sounds like a better idea to me than setting them lengthwise. I also found lining with shade cloth helped, but if the soil is left wet, will only add to the wet/dry cycle. Or rather, make that the wet/dry/crack and cry cycle. I'd line the bottom with fine galvanized 1/8th mesh, a layer of pebbles and a layer of rocks. Total about 2 inches. That's what lasts longest for me.

As usual, there's my $.250 worth.
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Last edited by DesertRatTom; 05-05-2020 at 12:04 PM.
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post #28 of 29 (permalink) Old 05-05-2020, 12:03 PM
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Yeah, I've been thinking about that - would make the sides stronger/less prone to bowing. Need good drainage so that's why the slots on the edge. Maybe landscape fabric would hold the dirt in.

Another approach is to turn the bottom boards sideways. Here's a picture of the bottom. It would add some more work because I'd have to rip a bunch of the wood and make more cross cuts.
Use full width boards, working from each end, and fill in the last piece with a ripped to width one. If the boxes are all the same size, that final narrower piece will be the same for all the boxes.
The bottom boards are fully supported from below and if you don't carry them fully loaded there's no issue with the narrower board bowing/breaking.
Absolutely yes on lining them with landscape fabric, but if you weren't already aware, all landscape fabric is not created equal. Look for the longevity warranty.
Permanent but easily moved 'duckboards' to protect the roof in the walkway areas (PT 1x4's on 2x4 sleepers). 18" x 8' sound about right?
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post #29 of 29 (permalink) Old 05-05-2020, 12:22 PM
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"My solution would include a 2x2 or 2x3 redwood floor set across the roof, set fairly close with a rubber drainage set underneath. I'd set it on a framework perched on top of, but above the roof, next to the point where the flat roof is affixed to the wall. Start the drainage there and continue it to the other side. I'd attach the other side of the 2xs to the top edge of the outside wall so no weight was carried by the roof, and no water would settle on the the flat roof. Run one or two drain pipes or troughs off to the side into a drain that runs 4-6 feet away from the foundation on a downhill run into a french drain, if it isn't already there."
-Tom

There's no problem in laying movable duckboard walkways directly on his prepped roof drainage. No need to anchor them to anything, in fact it's a bad idea. They need to be easily movable for maintenance, and the psi applied to the roof when walked on is negligible. Up here, most condos/apartments have flat roofs, and duckborad walkways are used to allow access to the HVAC equipment on the roof without the trades people actually having to walk on the roof membrane.
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