disassembling the green roof Dagwood sandwich
Green roofs: raise your hand if you’ve done `em. I want to talk about absolute-minimal approach.
I’m about to get one set up on this outbuilding, and on reviewing the necessary layers, I’m wondering if I can strip the layers down to as few as possible.
Generally, the layers necessary are:
waterproofing layer
root barrier
insulation
drainage
growing medium
plants
Since we will probably be installing by putting trays of sedum in lightweight growing medium down, here’s what I see:
1) spacers occurring between trays of sedum = drainage assistance. Add some rough aggregate and your drainage is set.
2) if you’ve grown sedum, you know the roots are not aggressive. Root barrier = skip.
3) waterproofing layer: I could put down Ice/Water shield, and the sedum would probably survive freeze/thaw cycles without optional insulation board on the deck (compare this environment to their normal habitat, where with their shallow roots they’re hit with every cycle anyway) but instead, I’m thinking–
Without aggressive roots to worry about, why don’t I just make this assembly consist of seam-taped XPS, adhered to the decking, and edge flash it, place my trays, and give it a shot?
FWIW, I’d call the particular application I’m doing “noncritical” if a small leak eventually appears. The roof is a clear span over a foam-wrapped box that’s all taped up with ample rainscreen drainage.
Start shooting! Curious to hear your thoughts.
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You are bound to have problems sooner rather than later with this system. First off IWS is not going to be a good membrane, you need something that will create a monolithic layer, remember, water is just going to be sitting there all the time, I would use EPDM for a flat roof like that. Secondly I wouldn't skimp on the root barrier unless you know you have a membrane that is root resistant, some EPDM's are, some aren't, I would spend the money for one that is. Generally speaking you still need a protection fabric to keep sharp edges of the drainage off the membrane. You could use the insulation as a protection but I would be more inclined to put the insulation below the water proofing. You may need to add another layer of fabric as well to protect your drainage plane from the growing medium, the silt can clog up the drainage very quickly. I kinda get that you want quick and dirty, but if you have significant enough problems after a year or two then the cost/time saving wasn't worth it.
You forgot your shovel barrier.
It;s not just roots but also gardeners who trash roof gardens, and falling branches. You also need to be thoughtful of the damage that can be caused by uplift of nails from the plywood through the water barrier from below. my neighbor has an amazing polka-dot issue on his EPDM roof.
From the bottom, cheapest cost.
Plywood deck glued and screwed to joists, pitched to drain twice what you think you need.
rebond board with big washer screws over that, offset joints (from the same folks, ABC, where you get the EPDM)
EPDM roof membrane, glue down, no fasteners except on adjacent walls and fascia well above or below the roof plane.
Drip edge to throw run-off away from fascia and walls below.
Light rain collection plus hurricane mega rain release scuppers w/ plan for leaves and snow.
Drainage Gap, Ameridrain or eq. dimple/filter mat to create 1/2" drainage space between EPDM and wear layer.
Wear layer, some hard, light, easily removable and cheap material (tile backer, fiber cement or 18" x 18' x 1 1/4" concrete pavers to float over the drainage layer. I use galvanized flashing between the drainage layer and the wear layer run up the wall to cover and protect the EPDM running up the wall.
Then your planting trays soil etc.
Unnecessary words of caution
The Ford Indian River Plant is allegedly the poster child for why you don't put the water proofing over the foam. Rumor has it that shovels punctured that roof by digging through the soil and rubber into foam and damaged a large amount of very expensive machinery. I've not heard any collaboration there but no matter if it's true or not you need to think about ice, neglect, UV degradation, leave accumulation, falling tree branches, and drunks falling off the edge of the roof because you didn't think that safety railing was attractive. I even visited one project, where we had built a koi pond on a roof, and discovered that someone had managed to get to the EPDM with a cigarette butt. (easy repair). Safety railings that are flashed through the rubber are a pain. Floating them on the drainage mat is best or anchor them outboard of the fascia.
Images, out board railing from above showing bottle rocket launcher (and one of James Morgan's designs across the meadow)
Same railing from below showing drainage gap running down soffitt and post attachment.
Floating railing, don't really have any better photos, just finished it recently, but it has steel corner plates and hidden rope lights and is only attached to the side wall of the house in four pionts and not at all to the roof.
Ha, thanks for the great answers. Root-resistant EPDM it is, for starters, and effective fastening and drip edges all mandatory, agreed.
And nice pics. Your bottle rocket launcher is way too steep to hit the neighbors' window. Try to plan better next time.
I would quibble that with lightweight medium in trays, no one will ever be using a shovel. Trays are maybe 3" deep. Having worked in a nursery 8 or 10 years ago, planting and shuffling trays, I feel pretty confident this is a hand planting/weeding environment. If someone wants to go up there and stomp on a shovel, they've got bigger judgement problems.
While I acknowledge and agree with your points about protection and truly adequate drainage, I still can't help but think there could be, for as lightweight of an application as I'm intending, a redundancy that can be designed out of this sandwich. For example, within the trays themselves, which due to spacing when you butt `em together already assists drainage, why not a bottom internal (inside the tray) layer of crushed aggregate topped with light growing medium topped with sedum? The tray bottom is protection from aggregate placement, and both tray shape and aggregate are drainage assistance. Designing out the dimple mat? Glued and double-screwed plywood on joists, EPDM, insulation-and-protection layer, drainage within trays, Bob's your uncle?
Slope is 1/12, by the way. Minimum slope for adequate drainage I've read is 1/2 / 12 so whew, apparently I'm already double.
Thanks again for weighing in--great stuff.
MD,
Looking good. Almost wish you could keep it as is ; )
I would second Micheal's suggestion to use fiberboard screwed down with big screw washers.
If you decide to go to EPDM I have some leftover adhesive, primer, screws and washers you can have.
I think there might be a difference between a typical commercial built up system and a tray system that is not being captured here. Potentially some trays can be designed as a self containing units that allow drainage below them that you could place on a protective fabric right on top of an EPDM roof.
Could you get by with Ice/Water Shield? I don't know how well that would bond to the fiberboard and I don't think you want to skip that layer per Michael's suggestion. Installing the EPDM roof is not that much more effort. Trick is detailing your edge/ eave conditions.
Is that your roof structure on the ground? A nice piece of fabrication but I am concerning that your structural members will be oriented the wrong way (horizontal flat as opposed to vertical upright).
J,
I wish I could keep it that way too.
Those are the end braces, lying flat in wait. It's (3) 2x12s oriented vertically coming across the ends of the beams at the bottom. Come by on Sunday at 11am and you can supervise and/or pitch in as a team of humans moves them into place. They're heavy. A guy I play music with sometimes is a state dead lifting champion and thank god he's one of the people chipping in.
Bonus that I owe you a lunch by now. Come collect it.
Hi again, all. We were working on the roof a couple of weeks ago and I got spooked. So we're probably hiring it out.
One roofer's counterproposal is that we use heat-welded GAF--probably this: http://www.gaf.com/Roofing/Commercial/Products/Modified-Bitumen-Roofing/Ruberoid-Modified-Bitumen-SBS-Membranes/Ruberoid-SBS-HW-Smooth.aspx
Will that be incompatible with this application?
The question I have with the heat welded stuff is why have seams at all when you can just buy a piece of EPDM big enough to cover the whole roof and lap down over the fascia?
The link is for modified bitumen, I would doubt it is rated for wet all the time applications. A seam every 3 feet.
I am a big fan of EPDM, and it is available 20 feet wide. Hell, it is used as pond liner.
Thanks, Keith, and agreed, Michael.
Yeah, that's what I'm thinking too, J--have somebody get the framing finished in a few hours and put a tarp on it.
Hey--so how long can I leave my foil-faced polyiso uncovered on my walls before I have to hang my siding?
Mr Disaster:Hey--so how long can I leave my foil-faced polyiso uncovered on my walls before I have to hang my siding?
Long enough to really annoy your next door neighbor ;---)
You can do EPDM went if is fairly cool. A good sunny day in the 40's is ok, but be done well before the sun weakens. What happens is that the contact cement cools the air as it evaporates and pulls it down through the dewpoint. That is a bad thing, it spoils the surface and it doesn't stick. If you know it has happened just go have a beer and let it wait till tomorrow. So you need to wait long enough in the morning for the dew to dry off[or keep it tarped well] and finish long before the sun goes down.
So, yeah, it is a PITA when it is cold.
Not that it is fun when it is hot.....
Actually now that I think of it, you are going to have ohh, ten thousand pounds of dirt and stuff on top of it. Proper flashing and seam detailing are much more important to you
Thanks, Keith. It has really warmed up here today, to a balmy 27F. So, it'll have to wait.
Dr. Joe had a good screed on Green Roofs recently: http://www.buildingscience.com/documents/insights/bsi-052-seeing-red-over-green-roofs
He's a big believer in protected membranes under insulation.
"Let’s go back to the water stuff and green roofs. Folks also like green roofs because you can store water in them; you can control the rain run-off from your building. You’re kidding, right? Storing rainwater on top of your building? Are you on crack? The whole point is to get the rain off of your roof, which is why we slope them."
Good read from Dr. Joe. Yeah, we're doing it for the reason he validates: its beauty compared to looking down on a regular roof. We have to look down on this thing every day, and we like sedum. I've maybe put this up in the other thread already--our view from inside the house every day:
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/s720x720/384803_10150361530791331_525716330_8631580_445937419_n.jpg
Update and apology -- the roofer who had the counterproposal was in fact proposing TPO.
http://www.gaf.com/Roofing/Commercial/Products/Single-Ply-Roofing/EverGuard-TPO-Single-Ply-Membranes/EverGuard-TPO-60-Membrane.aspx
I can't find my reference document (an Environmental Building News feature) but I do recall that the TPO type plastic is considered more environmentally benign than the EPDM. TPO isn't typically used for small scale work because smaller contractors typically don't have the equipment or source of smaller square footage of product so I'm surprised a contractor is actually suggesting it as an alternative. I think TPO has been around long enough to have some confidence in the materials durability (comparable to EPDM I think but again I'm no expert).
MD,
I'm guessing here but it's probably too cold to install the typical EPDM roof via gluing to a mechanically fastened fiberboard. I'm not the expert but this still seems like the most cost effective and durable option.
One thing you can consider, given the small size of the roof, you can have a contractor frame the roof, sheath it with plywood and tarp it until the Spring. You might find working on the sheathed roof structure is something you can again do yourself.
When I worked as a carpenter I can admit now that I didn't do my best work in the winter ; )