Going to a Green Roof - Where to Get Started

[jeb6294]

I just started my new job at the VA back home in Cincinnati. One of the issues they have here is that there is absolutely no green whatsoever. I noticed the first day I was here for orientation. At the same time, I also noticed there looks like there would be potential to add some green roofing that could be visible from many different areas (lots of roof lines at varying levels). Since everyone took off today for opening day I ended up doing the weekly walk through this morning with the Director and the Chief of Engineering. The lack of green came up and I mentioned what I had observed and the Director was all for it.

After a quick Google search, it doesn't look like any other VA's have done this so I'm betting it could be quite a feather in my cap if I could make something happen (disclaimer: if anyone else from the VA happens to be on this site, I already called dibs).

Where is a good place to start when looking in to retrofitting a green roof to an existing building? The VA is a pretty typical hospital structure, i.e. flat roof. couple inches of stone, scuppers, etc. so I'm thinking we've already got flat spaces with drainage built in. Can you lose the stone when you go to green? Can we assume the roof can handle a light weight green roof if it is already holding stone?

 

[Ble_PE]

What do you consider a light-weight green roof? Are you talking about some planters or are you going to be adding soil and extensive landscaping? I would be concerned about the additional load that you are imposing on the structure and you would need to get a structural engineer involved to determine if the structure is capable of carrying the load. It's not only the weight of the green roof, but also the additional seismic load due to the new load. Also, is this just for aesthetics from the ground or are you looking to make it sort of a courtyard allowing people up there? If so, that would possibly mean additional live load to account for assuming that the roof wasn't initially designed for that type of use.

I think you've got a good idea and it's definitely doable, but you just have to make sure it's possible structurally.

 

[Mike in Gastonia]

sorry - this is all I got....... :wave2:

 

[Capt Worley PE]

What Ble said. You're not going to be able to do the sod and grass thing, more than likely. It is a pretty significant load.

 

[Supe]

Would it be possible to intermix artificial with real plants, thereby reducing the static load through reduction in sod/soil?

 

[pbrme]

I would also look at some of the LEEDTM criteria. I studied some of this back in my earlier career but it was all for new construction. I believe now there is a category of quals for existing structure. The LEED stuff will also give some credits that I believe can be used for tax purposes. Let me know if you need more.

 

[jeb6294]

While a lot of these green areas would be visible from patient rooms, they would not be readily accessible so we're talking about purely aesthetic and any of the other "perks" that are supposed to go along with a green roof (lower energy costs, better water quality, longer roof life, blah, blah, blah). I started doing some searching on-line and there are a number of places offering "light weight" media now so I was hoping (very likely foolishly) that we could take up the stone, throw down a root barrier, throw out some hardy wild flowers and have a quick and easy starting point to give people an idea of what we're going for. The only places where there would be people is if we did something where there is already an air handling unit that would need access for maintenance.

We don't do very much of the design work here so we would likely farm this out to a local firm who could determine what kinds of loads we could support, but I don't have access to the network drives yet which is where any of the drawings for the building would be.

 

[Dexman PE PMP]

Have you considered artificial grass? The stuff looks damn close to the real thing and you literally don't have to touch it for 10-15 years (at which point it's a complete replacement).

The only aestetic issus with the fake grass is that it looks very obviously fake during the fall/winter months (at least in places were sod turns brown and goes dormant for the winter)...

 

[cement]

the stone protects the rubber from the UV, so I would be hesitant about removing it. If you have to remove it for weight, you have to ensure no light gets through what you replace it with. That roof is designed to take a sinificant snow load, so you probably have some room to work with there. call the code official for what the requirements are locally, or maybe check the building plans?

I would think that you could get the desired effect with small clusters of containers planted with xeriscape plants.

this looks like a good resource for plant suggestions: http://flourishcincinnati.blogspot.com/2010/08/midwest-xeriscapingwhat-is-xeriscaping.html#!/2010/08/midwest-xeriscapingwhat-is-xeriscaping.html

 

[Ble_PE]

Another thing to take into account is Chapter 34 of IBC, Existing Structures. It gives you limits on the amount of additional load that can be added to members without having to bring them up to the standards of the new code. I'm sure that you have probably got a lot of reserve capacity in the building, but Section 3403.3 of IBC 09 only allows for an increase in gravity load of 5% on any member.

That roof is designed to take a sinificant snow load, so you probably have some room to work with there. c

I don't think this would help you out because you still have to have the capacity to carry the design snow load plus the additional load from the green roof. You couldn't substitute the new load for the snow load.

 

[kevo_55]

Green roof or not, you'll still actually have your snow load.

:2cents:

 

[cement]

I'm just saying that a couple of potted plants is insignificant in comparison. But go ahead and count your beans...

 

[MA_PE]

the green roof addition could change the drifting snow pattern and potentially reduce the snow load (OTOH it might reatin more drifting snow and then.....

 

[pbrme]

Don't the building's structural drawings state the available dead load?

 

[Capt Worley PE]

And how are you going to mow/maintain all this?

 

[Ble_PE]

And how are you going to mow/maintain all this?

Goats.

 

[wilheldp_PE]

And how are you going to mow/maintain all this?

Goats.

Then you have to worry about "goat loads."

 

[Judowolf PE]

And how are you going to mow/maintain all this?

Goats.

Then you have to worry about "goat loads."

What about residual Goat loads?

 

[Capt Worley PE]

And how are you going to mow/maintain all this?

Goats.

With such a view, what would the goat see?

 

[pbrme]

And how are you going to mow/maintain all this?

Goats.

With such a view, what would the goat see?

Probably an expanseive manscape