For what I’ve learned in this green roof project, I would like to start with my summer school’s experience. I will talk about the design of this green roof and compare it with the green roofs in Houston which I visited in summer. Then I will start from the beginning of the constrcution in fall, and what I’ve learned from this project.
Initially, I participated in this green roof project during the summer school. Unfortunately, we weren’t able to start the construction, but I was lucky to visit some of Houstion’s green roofs with Kirk and Johanna from horticulture. Those roofs are more of semi-intensive green roofs. There was one green roof that they planted some plants for cooking!
They use volcanic rock as drainage layer which is a lightweight material for green roofs, and more complex irrigation system to maintain the plants.
In our project, we have 800 s.f. of 4.5” thick green roof, it’s weight is 34 lbs per square feet. Therefore, it is an extensive green roof. In our project, we use expanded clay as drainage layer which is similar with volcanic rock, they are all currently good drainage materials. Houston’s green roofs have more larger groundcovers and shrubs. When we collected the soil sample, I could dip into the soil about 10″ to 12″ deep, while our soil is 3-4″, therefore they are semi-intensive green roofs. Houston’s green roofs are very expensive from what I have seen. In our project, we will use more plants that could be good survivers, so that we can find the plants for Texas’ green roofs with low mainatenance cost.
Professors had selected 28 plant species for the roof to test their abilities to survive on green roof in Texas, in the climate which we describle it as hot, hot, and hotter. In the design, we have modules planted with different combinations of plant species. We have 162 modules planted with sedums, herbaceous, or their mix. We plant five types of plants in each module, in the way of 5*5 plants at 4″ spacing. The plant species are randomly assigned. I guess this way of combination could help us to see the how plants influence each others. Some of them are taller, some need more sun, and some are more drought tolerant. They could compete with each other, so I think more combination types could reflect more information of plants’ behaviors. The modules are separated into two big groups, and one with irrigation while the other without. Professor Dvorak told me that he wanted to see that which group works well. Also some of the plants professor Dvorak has used before in his first green roof research program, and he has found some that are usable in this harsh environment in Texas. In this project, we will have more plants and hopefully we can find more plants that can be used in Texas.
I am making a poster of plants we use on the roof, and I will post it later after professor Dvorak checks it.