The secret garden, a vegetative roof

  • Published
  • By Senior Master Sgt. Elizabeth Gilbert
  • 136th Airlift Wing Public Affairs
NAS FORT WORTH JRB, TX. - The 136th Civil Engineering Squadron is the first to take advantage of an extensive vegetative roof system here. The roof was constructed under Executive Order 13514/13423, a strategic plan to reduce energy usage for the newly constructed maintenance add-on buildings.

"The hotter the rooftop the more energy it takes to cool the building" said Capt. John Hall, 136 CES deputy base civil engineer in charge of new construction. "The vegetative roof system prevents the rooftop from getting hot, therefore requiring less energy to cool the air-conditioned space."

According to the National Institute of Building Sciences a vegetative roof, also known as a green roof, consists of thin layers of living vegetation installed on top of conventional flat or sloping roofs.

There are two categories for vegetative roofs: 1) extensive vegetative roofs, which are six inches or shallower and designed to satisfy specific engineering and performance goals such as energy conservation, and 2) intensive vegetative roofs for deeper rooted plants such as large perennial plants and trees.

Extensive planning with building contractors took place prior to installation of the roof. The building design had to meet or exceed the Leadership Energy Environmental Design (LEED) rating of silver and the infrastructure had to be re-enforced for the added weight.

The LEED Green Building Rating SystemTM designed by the U.S. Green Building Council advances energy and material efficiency and sustainability.

"The LEED has four ratings: 1) platinum, 2) gold, 3) silver and 4) LEED certified," said Hall. "It cost money to have LEED requirements. Since it is tax payer money, DOD will not authorize above a silver rating."

The entire building-construction project cost was $1.7 million to include the 5000 sq. ft. solar panels, 16 geothermal wells and the 2700 sq. ft. vegetative roof. The vegetative roof cost was more than $145,000 by itself. With all the energy initiatives installed the construction attained a LEED rating of platinum.

"We have the only facility on base to achieve this rating with the budgetary constraints in DOD," said Hall. "Only a few buildings in the DFW area have achieved this high of a rating."

The vegetative roof system is designed to be self-contained. Currently, yucca and buffalo grass is planted on the vegetative-roof trays. Other plants are under consideration.

The roof was also tested for water tightness by filling the rooftop with more than six inches of standing water to ensure no leakage will occur. There are overflow measures in case the water exceeds the required depth. The water will drain down the downspouts onto the ground, removing excess water.

Future measures have already been planned for the upkeep and maintenance of the vegetative roof. A periodic trimming, once the vegetation grows will keep the system manageable and could last as long as standard roofing materials.

"The secret garden is no longer a secret and hopefully future building constructions will follow suit and take advantage of several energy initiatives," concluded Hall.