Renovations taking place at Horticulture Hall will feature more plants than it will hold in its greenhouses.

The building will feature a greenroof, a roof that has vegetation.

Jen Bousselot, lecturer in horticulture, received a grant from the Iowa Nursery and Landscape Association to implement the vegetated roof.

“In most cases you have rocks on top of the roof; that’s used to help hold the roof down and help prevent the sun’s rays from hitting it because the most damaging things to any flat roof are UV rays,” said Kerry Dixon-Fox, manager of the King Pavilion, which featured the first greenroof on campus.

“Instead of putting rock on top of the roof, you put a growing media on top of the roof.”

Greenroofs are nothing more than a roof with vegetation, Bousselot said.

“The installation process is actually just the same as any other roof,” Bousselot said. “You have to make sure the membrane is water proof, and then we apply a series of layers. We usually go for very shallow systems because most buildings can withstand that amount of weight and not any deeper.”

Sedums, more commonly known as stonecrop, a plant extremely tolerant to heat and drought, will be planted on top of the new greenroof.

Other LEED Certified Buildings such as the King Pavilion and Biorenewables Research Laboratory both have greenroofs that benefit both Iowa State and its students.

One benefit Mark Huss, engineer in facilities, planning and management, emphasizes is the stormwater management a greenroof supplies.

“It captures rainwater, so it uses the stormwater rather than just falling down from the storm sewer.”

Bousselot and Fox both stress the importance of this benefit, which prevents a significant amount of water from washing down into Ames’ storm systems.

“If we don’t manage that stormwater upstream, we’ll have to tear up our streets and change the stormwater system,” Bousselot said.

Another concern Fox points out is the contamination of Iowa’s water quality from the runoff of water into the storm systems.

“When [rainwater] goes into the storm system, you have to deal with runoff, contaminants, by keeping [rainwater] on the roof, the plants use it and then aspirate it.”

The plants on the roof operate like a filter, absorbing any molecular contaminants that can be found in rain.

“Some of those molecule-sized contaminants are found in raindrops, and so the water by the time it goes into the storm system is cleaner, then you’re not dealing with contaminated rain water that then effects the water quality of Iowa’s rivers and lakes,” Fox said.

Greenroofs are also useful for reducing temperatures. Otherwise known as the “heat island effect,” greenroofs function well to manage high temperatures.

“Most roofs are about 170 degrees in the middle of the day during the summer, if you put a plant up there, it has to cool it because it can’t live,” Bousselot said. “It transpires or loses water and that acts as a little evaporative cooler for that area, [reducing] the temperature.”

Compared to roofs without the vegetation, Bousselot stresses the benefits of a greenroof from a cost perspective.

“Greenroofs protect [the membrane] and most roof membranes last two to three times longer than they would without a greenroof,” she said. “Most of these systems cost about twice what a typical roof would be, but if they last two or three times as long, then you got major benefits.”

Once the greenroof is installed, Bousselot plans to have the Horticulture Club involved to help plant the plants.

The lecturer wants to use this opportunity to teach her students about the benefits of greenroofs.

Like the King Pavilion, which absorbs up to 80 percent of the average rainfall or the Biorenewables building, which has both shallows plants and prairie grasses, Iowa State hopes to continue implementing green roofs around campus.

“We’ve started to look at trying to retrofit some of our existing buildings, but we really haven’t had enough money in the last couple of years set aside to do major roofing repair projects,” Fox said.

“[Iowa State] takes the opportunity to include a green roof in newer existing projects whenever possible,” Huss said.

“It is always on the table when we start building. In new buildings we start looking very early at what kind of sustainable features we want in that building,” Fox said.