This is a stretch, but has anyone had any luck specifying a turfgrass blend on a greenroof? The catch is that it will have (at best) 3" of soil.
This is not ideal in any situation as it is, a-monoculture and b-irrigation hog, however it is only a small portion of the extensive roof so we may be able to create a micro climate of sorts for it to exist in.
Anyone have any thoughts?
You haven't yet stated (did I miss it?) whether the site is full sun all day or part day and which part, whether it is exposed to noticeable winds, whether the building extends above this floor casting shade. In NYC a rooftop can have any of a wide range of conditions and with the growing parameters already so limited you need to get all the specifics out in order to focus on the right choice (IF there is one. Not everything is possible with plants). Look carefully at the possibility of some structural support system. It may help or in fact it may make matters even worse.
You might also consider soliciting the aid of a horticulture or turf consultant (I am not plugging for myself: I am way too busy), or even contact the turf folks at SUNY, Rutgers or Cornell. They are ofter thrilled to give opinions. But you'll need to give them a thorough understanding of the site if they are to help.
To take RH's comment "Not everything is possible with plants" further, are you preparing anything to show the client that this design element is in fact not possible.
Who's going to get sued when it fails ?
You said it there. The conditions vary on this project between the north and south side so exposure to the elements has driven the majority of our design decisions. I have two calls into Cornell (no response), I am going to contact Rutgers today as they developed a mix named Predator that may be feasible.
I will let you know how that goes.
Did you find anything further about the thin soil with turf?
I spoke with a professor at Rutgers - and ended up adjusting the layout - to provide an
even 6" of soil depth. I havent finalized the species of Turf Grass though but I did narrow it down to a fescue mix (hard, fine, creeping and red).
I did happen to speak with the rep at Liveroof about the Bella Bluegrass - they offer it in their build-up. While it appears is everything they claim (low growing, self repairing, beautiful color, etc.) it is not necessarily meant to be utilized as an active lawn. That was essentially what I got out of the conversation. It looks like a great product though.
In case anyone is interested, LiveRoof's green roof modules have been wind tested and rated with 2 of them being acceptable under the ANSI RP14 for ballast.
We have used the Live Roof Trays before and are quite happy with them. Have not tried turf however. The live roof trays work really well on smaller roofs where you just want an easy system installed and are more for looks. On bigger roofs with more active use it is nice to have a little more flexibility that you can get with an intensive green roof system.