Given the critical role of roofing in facilities and the complexity of replacing or installing roofing systems, it is no surprise that owners and managers run the risk of mistakes and misconceptions when selecting and installing green roofs on their facilities.
One such issue involves understanding the rooftop’s location and surroundings.
"The first thing that you have to do is you have to make sure that your roof is in sunlight and you're not shadowed by a next door neighbor casting a shadow over half your roof for half the day,” Caldari says. “We need to make sure that we have the correct amount of daylight, or we have to alter the plan. If a quarter of your roof is in shadow all day long, we're not going to put a green roof in that section. We'll pave that section. But we'll do the rest in a green roof.”
Owners also need to understand the maintenance needs of green roofs.
“Some of the systems that are promoted promote them as being virtually maintenance free,” Juhlmann says, adding that managers hear, ‘Don't do anything. Don't worry about them. The sedums will get brown in the winter, but they're always going to come back.’
“Well, some do, some don't. I would never ever put any type of green roof system on without incorporating irrigation. You don't have to irrigate it regularly, but if you get a good sedum system and you haven't had rain in a few weeks, kick it on. That absolutely, positively makes a difference.”
Caldari also says owners need to build a project team that provides reliable information on the green roof and an overall perspective on the goals of the project.
"Definitely use a reputable architect, engineer, contractor,” he says. “You want to get good people involved in your project, and you want to keep it simple. Work to reduce the installation and maintenance costs. Are we putting the green roof on the building purely for functional reasons, or is this going to become an amenity for the tenants of the building?”
Perhaps most importantly, owners and managers need to pay close attention to the existing roof on which the green roof will be installed.
"You want to make sure that if you put your roof down on your building 20 years ago, you might consider either putting an additional layer of membrane on top of the existing roof or doing a reroof before you bury it under a couple of tons of soil,” Caldari says. “The roofing membrane, the waterproofing system, has to have integrity, and you don't want it to be too close to its warranty date.”
Says Juhlmann, “The biggest mistakes that I see are with the system as a whole because so frequently, when you see green roofs installed, they are replacing the entire roof system from the structure up. And the mistakes I see are made below the green roof. They don't pitch the membrane properly to drain, or they don't incorporate a drainage composite between the membrane and the green roof area.
“As a result, water was not getting off of the roof. You’re not adding water to the sewer system, but it can potentially cause a problem with the waterproofing membrane or a problem at the flashings. Or the drains might get blocked. The mistakes I see aren't necessarily with the green cover. It's about giving proper consideration in design to everything that goes below it.”
Juhlmann cautions owners to think carefully about the reasons behind installing a green roof on a facility and, more specifically, the results it can provide for the organization.
“To me, the value is harder to put dollars on,” he says. “I turn this ugly roof into something my employees 20 stories up get to look down on, and it's beautiful, and they're going to enjoy that more. Or I have a multi-tenant condo building, and we've turned our roof into this usable space, and it's added value to the building. It's giving us the ability to charge more rent. To me, that is harder to measure, but that's the real benefit.
“I caution you about the return on investment number and just to try to let (owners) look at it from a real standpoint. If you've got a conventional roof and you want to turn to a green roof, it's not going to be cheap. Understand why you're doing it, whether it's because you want to do something for the environment or you're trying to make your roof into a usable space. I have a tough time saying, I'm doing it because it's going to reduce my utility bills. In that case, you're probably better off just adding insulation than adding a green roof.
Dan Hounsell is senior editor for the facilities market. He has more than 30 years of experience writing about facilities maintenance, engineering and management.
Mistakes and Misconceptions Surrounding Green Roofs
