Living Roofs

Does anyone have experience with a flat or slightly sloped living roof?  I'm building my first one on a flat surface connecting the top of a greenhouse to the underfloor of the main house (winter sub-floor air heating).  I've worked out all the structural issues.

What I'm most concerned about is drainage and how many inches and type of soil to put down for sedums and native grasses.  Also will the sedums thirstiness preclude or reduce drainage needs? 

Living Roofs info:
http://en.wikipedia.org/wiki/Green_roof
http://www.greenroofs.com/

sample picture:

      Rob Roy covers green roof's fairly well in one of his cordwood books. Google him.

thanks... read him years ago... the 'modern' living roofs use single ply EPDM type membranes, etc.  so that's what i'm trying... i've found other sources... curious that living roofs got 1 reply.

I read one of the green roof books recommended elsewhere on the list. They were suggesting PVC over EPDM because it is a waterproofing and root barrier in one.

this  link might give you some suggestions..seems as though they have most of the different permutations on one site or another
http://www.greenroofs.com/content/Various%20Types-of-Green-Roof-Systems-Come-Together-at-NYC%27s-5-Boro-Complex.htm

That's a "guest blog" on a site dedicated to green roof stuff

Pam wrote:
this  link might give you some suggestions..seems as though they have most of the different permutations on one site or another
http://www.greenroofs.com/content/Various%20Types-of-Green-Roof-Systems-Come-Together-at-NYC%27s-5-Boro-Complex.htm

That's a "guest blog" on a site dedicated to green roof stuff

That's a great link - thanks Pam! 

They said a couple things like 19-29 psf saturated soil weight, 0.65 gallons/sqft or water retention, etc... can go as low as 4" soil depth, extensive (shallow soil) living roof has minimal maintenance.  I also like reading about a roof diverting 424,000 gallons from the storm drain.

I still have not seen anyone talk about the maintenance headaches of living roofs.  one big issue for me is: are they impervious to leaks for 30+ years?  and are there any lessons learned on how to discover/repair leaks... digging up an entire roof section to find a leak would be pain.

Sedums and native grasses just require a height of 1 foot soil to grow on. And talking about drainage system for your roof..just give a little slope to your roof so that water can easily drain on to another end.

We're putting on a green roof right now.  I put really thin, really cheap from the guy down the road, blue board on the plywood.  The plywood is over 12" centered 2x12's.  On top of the insulation is the EPDM.  I've put in one sun tube and have one to go.  The EPDM is currently laying on the roof with no glue or nails at all.  The seems have 2x12's with concrete blocks on them holding them  down.  The EPDM is in 10 foot widths.  We've got 3 37' lengths up there.  So far, after several rains with wind, there are no leaks at all.  I'm impressed with the EPDM.  Its stout!  We've got Enkadrain to go on next.  On the Enkadrain we're gonna put down flakes of straw bales.  4" thick flakes maybe.  We'll keep adding straw and manure and whatnot for a while until it gets to be around 3-4 inches of growing medium.  Hope it works.