green roof s - ping Mr Andy Dingley?

pondering a green roof for me garage/store extravaganza....
any pointers anyone to design/construction/ issues/ Bldg Regs issues etc all gratefully received...
Andy - from a quick google on here I believe you recently did one? using perlite/vermiculite etc - care to share?
Cheers JimK
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I've one that's currently an almost completed brown mud roof, waiting for an afternoon's trim work and for the "green" bit to start growing properly. If I have time, I'll do a proper write up.
Over Easter (In my Copious Free Time) I'm planning another ultra- budget green roof on a concrete sectional garage, just to make it look less ugly from a distance. Writeup likewise.
More later...
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Andy Dingley wrote:

There's a sedum mat round the corner here (actually just a roof for a wheelie bin house) that seems to be thriving. I guess the plant must be virtually drought and frost proof.
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Information sources are hard to find. There are some nice books out there at the architectural scale, but little about constructional details for DIY. However the big-scale books can be useful for justifying the roof at all (Look dear, It's not just hippies, look real architects are doing them!) and the plant guidance is useful. Planting Green Roofs and Living Walls Nigel Dunnett and Noёl Kingsbury <(Amazon.com product link shortened)>
Most UK-based information of small-scale projects seems to come from Sheffield Uni. CAT at Macynlleth were depressingly clueless.
The Living Roofs website has a downloadable PDF for a tenner(ish) that is worth getting, as it's dealing with the sort of project scale we're interested in. Free sample pages too. <http://www.livingroofs.org/diy-guide-green-roofs.html Be warned, I had a lot of email trouble dealing with them and actually getting hold of my copy. Nice people, but it was an uphill struggle and their webbery isn't working right.
There's a lot of commercial project information out there too, from people like Oldroyd who make sophisticated membranes <http://www.safeguardeurope.com/products/oldroyd-green-range.php Don't let the pricetag put you off immediately. This stuff has major advantages for convenience and speed of working. You can do better with zero-charged DIY, but if you're building a lightweight (i.e. thin layer) roof with employed labour, these membranes would have a lot going for them, especially for steeper pitches.
You need some careful design, i.e. spreadsheets. Estimate your thicknesses, your weights, and your materials costs - including planting costs. There are several ways to build a roof and they do vary by cost / workload / pitch angle / weight / soil demand / plant compatibility. Your choice, but understand what these compromises are before starting and choose something that suits your needs, budget, looks and plants before starting to build it.
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My small workshop roof is 8' x 24' and began as flat corrugated iron. The green roof was to make it look nicer, fix its obvious plan to fall down imminently, and to get some insulation in there. It's now almost flat, with 3" of soil over 1" of vermiculite, over 1" of polystyrene insulation.
Construction began by discarding the old roof and the top foot of wall, owing to original poor construction. A course of cement blocks and a course of bricks on one long wall, tapered at the end walls. Joists were 4"x2" on 400mm spacings, laid on top of this new wall and held up by noggins between at the ends. They stopped an inch short of the outer wall edge. Roof deck on top of this was 3/4" OSB screwed down - fortunately my shed is a convenient 6-sheet multiple, so everything fell out of standard lengths quite nicely, helping with the budget. A surrounding upstand wall of 3/4" OSB was made, screwed into the edge of the OSB, with long screws through the foam (see below) and into the noggins, then against the outer masonry edge - no overhanging eaves. The entire external woodwork was then coated with black bitumen paint (runny stuff - real fibre-reinforced exterior grade is impractical to apply over OSB) . 1" of polystyrene foam went down on top, to make an insulated warm roof. This same foam was used around the edges of the joist, between the noggins and the upstand wall to avoid a cold bridge there.
Around this time, I still needed a ladder to the roof, but no longer needed to move the ladder around as I worked. So I rawlbolted the wall and tied my strongest and steadiest ladder down to it. This was a _very_ good move.
The first waterproof layer went down on top of the polystyrene foam. As it was polystyrene, not yellow PIR, and was a green roof anyway, I didn't bother with a moisture barrier beneath. This layer was geotextile around the edges (didn't bother over the polystyrene foam) and then a double layer of 1200 gauge polythene DPM. This was then carefully tucked into a "swimming pool" around the edges and stapled down to the outside of the upstand. Triangular firrings of polystyrene were used to smooth out all the internal corners before the liner.
I now tested the liner by placing 2" of rain into it over the next couple of days. Not ideal, but it's why I'd been working in the dark to get the liner laid beforehand...
An 18"' strip of geotextile along the lower edge started the formation of the 4" square shingle drainage gulley, as described in the livingroofs guide. Their drain is a vertical outlet commercially moulded into the liner (and outside the building plan, through the eaves). Mine (as I had no eaves and didn't want an indoor drainpipe) was PVC drainpipe, cut in through the side of the upstand. I sealed this to the liner itself with bitumen mastic and hope. With the liner in place, and the gulley liner held in place with masking tape, I half- filled the shingle load to hold it in place.
The drainage layer of the main roof (a crucial aspect) was 1" vermiculite (600 litres). This sits waterlogged beneath the soil layer, so adds no insulation, but it's lighter than an equivalent volume of soil and _far_ lighter than an equivalent water retention layer of soil. This vermiculite was loose laid to about 1" depth (at this point the rain switched to wind - being lashed with flurries of damp vermiculite is delightful) and then a layer of geotextile over that.
Next step was to begin soil loading. This was lifted bucket by bucket (rope lift is easier than ladder carry, but a gibbet or gin pole would be even easier) and first dumped around the edges to anchor the liners down. A shallow sprinkle stopped me walking directly on the geotextile, especially as I was now back to my digging boots, rather than roofing slippers. As filling went on, I filled and shaped the shingle gulley to match.
Total soil load was 3", which was 21 barrows (I was using a small barrow), maybe 150 buckets. This took three partial days, spread over months, to complete! The first day shifted the most, enough to anchor, fill the edges and cover the liner from damage. After that, and in the depths of winter, I became lazy.
To neaten and weatherproof the outsides, I attached 10" vertical fascia board of Versapanel - a cement fibre board like concrete MDF. This is weatherproof when painted. There was also a narrow capping strip of the same, glued down crudely with mastic.
Planting has been done on the cheap - I have about 20 of assorted sedum and sempervirens up there, which I hope will spread in time. There are also a few handfuls of cheap crocus or similar small bulbs. Then there's a boxful of mixed wild flower seed and also some basic lawn grass seed. Patches within the roof are full-depth plain sand (no soil), also some stacked broken bricks, stacked short bamboo tubes and lumps of branchwood to give a variety of bug habitats.
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Now the mistakes:
* OSB should be OSB3 (quality grade) to qualify for category 2 (usage grade), such as roofing. I shopped local, wanting to support the local merchant, and was instead sold OSB2 for use in roofing - it's not up to it. My attempted remediation was to apply the bitumen paint.
* I've a (doubled) polyethylene DPM on top of polystyrene foam, rather than a geotextile interleaf (as I used over the timber). Maybe this will be a future issue with plasticiser leachout, as for PVC cables?
* The Verspanel fascia boards are purely decorative, but still too thin. This stuff is always brittle - 6mm is unusable without extreme care, 10mm is dodgy for anything outdoors. Livingroofs use 3/4" thick!
* October isn't a good time to build one, unless you have time available to build it all in one blast. Otherwise you're off into November, which then really isn't a good time to be doing it. My combination of November worktimes being limited to weekends, and unpredictable weather that I had to just work through anyway, meant that I was laying liners in a gale. Although this was an excuse to wear my copper hat and shout "All Gods are Bastards!" while standing on a roof in a thunderstorm.
* I ordered Perlite, but was delivered Vermiculite. There's not much between them, but Perlite grains are less crumbly and a lot less wind- blown. See above about working in storms.
* The fall (1 brick in 8') was insufficent, and I think the soil is going to remain too damp over Winter. Should have used a whole block height instead.
* My outfall pipe outlet through the liner is a bit of a hack and I should have been more careful with it. Bitumen mastic hides a great many sins.
* The outfall pipe was initially too high, so I dropped it by half an inch later on. In combination with the shallow pitch, it just can't drain the roof adequately and it leaves too much standing water behind afterwards. I should probably have sunk it locally into the insulation, to get another 1/2" below the majority of the liner.
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Lessons:
* It works. Green roofs are a good thing. They're buildable, they're buildable with simple materials and to a budget. You can do this, and the results are rewarding.
* It looks a lot better than corrugated iron - even in winter.
* My meagre insulation transformed the usability of the workshop.
* They're more complicated than you realise. Mine has something like 13 distinct layers in there, some of those have measurable thickness, and just that can be enough to push you very close to height limits for planning. Draw out sectioned views beforehand.
* For a "flat" roof, too much fall is better than too little.
* You need to build right first time. The idea of partial dismantling to fix something afterwards is terrifying.
* Materials sourcing is a problem. Builders' merchants are clueless and will sell you what they have, not what will last.
* It's a _lot_ of soil!
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