The Living Roof
BRIT's living roof is a one of a kind example in green roof technology. Rather than a roof with plants adapted to hot environments, the roof is a recreation of an existing Texas habit.
The urban environment is an ecosystem in itself. With this living roof, BRIT is bringing a functional, native Texas ecosystem back into the built environment. Rather than just looking for plants that can survive in hot environments, BRIT asked the question, “What are the environmental parameters of a roof and what are its analog and native environs?
Biomimicry after a geology formation known as the Goodland/Walnut Barrens, BRIT's roof represents possibly the largest Texas barrens habitat of its type and is one of the only living roofs in Texas modeled after a true native ecosystem. Prairie barrens ecosystems are characterized by extremely shallow, limestone soils and low water throughout most of the year, perfect conditions for a roof in Fort Worth.
Most importantly, our living roof creates a useable ecosystem in space that would otherwise go unused by the biological community. When it's hot, the living roof also maintains a lower daytime temperature than the non-living roof, reducing heat island effect and insulating the inside of the building. During the winter, the roof insulates the building from the cold. The rainfall collection system from the living roof allows for clean usable water to be used for irrigation on the campus and helps to mitigate storm water surges during rain events.
Design and Construction
This ecosystem was not described until 2007, when several of BRIT's researchers began work on the project. As the compositions of these ecosystems were described, planting ideas were drawn up for the living roof, as well as design specifications for the planting medium. Similar to the prairie soil, the characteristics of the soil to be used on the roof needed to be defined and matched to topsoil with specific soil microbes and the seed bank. A matching topsoil was found and transplanted to the roof from Little Bear Aggregate site in Cresson, TX.
BRIT's roof sits at a 9.5 degree angle to the south, mostly to facilitate viewing from ground-level but also to promote drainage. Biodegradable planting trays were used to prevent erosion during establishment and allowed for a modular design and easy installment. Each 2’ x 2’ tray was planted with six native Texas species (from a list of 38 total test species) within 7.5 cm of mixed native and engineered soil. The trays were initially grown in a sheltered spot under the tree canopy on the east side of the parking lot and delivered onto the roof using a conveyor belt.
A weather station was installed on the roof in 2011 to collect data on rainfall, temperature, humidity, wind speed and direction, UV, solar radiation, evapotranspiration, and air pressure. In order to compare temperature and humidity, two more satellite stations were set up, one in the middle of the prairie and one on the northeast corner of the solar roof above the herbarium building. Data are collected every five minutes from all weather stations. Visit bdi.brit.org/weather for real-time weather conditions on BRIT's campus. For historical weather data back to 2011 (living roof only), visit BRIT's page at Weather Underground.
After the initial roof installation, observational vegetation surveys were done on a monthly schedule. Attention was paid to any invasive species or weeds that were coming up on the roof, as well as species of plants that were not on the original planting list. Formal vegetation surveys were started in the second year, analyzing species diversity relative to initial planting scheme (i.e., one of three vegetation assemblages) and slope position on the roof (high versus low). Overall success of the original planting palette was reported in a paper published in 2013 in Journal of Living Architecture and in a chapter within the 2015 book Green Roof Ecosystems.
Arthropod surveys of the roof were conducted from July through Novemeber of 2012 under the direction of Dr. Brooke Byerley Best and BRIT intern Adam Ulissey, a student at El Centro College. These surveys utilized pitfall traps to document and inventory ground-dwelling insects on both the living roof and the ground-level prairie. A side-project performed by TCU students Haley Rylander and Devon Spencer involved collecting and identifying insects from a reference prairie site at Dutch Branch Park. These data are still being processed but should inform BRIT researchers as to the soil health of the roof in comparison to an intact prairie as well as help guide other living roof researchers on the merits of native soil inoculation with respect to soil biota establishment.
Arthropod Diversity of a Biomimicry-Based Extensive Green Roof -- poster presentation by Adam Ulissey on preliminary findings
Arthropod Diversity: In situ prairie versus prairie-style green roof -- poster presentation by Haley Rylander on preliminary findings