The Envelope, Please
- By Michael Fickes
- October 1st, 2012
The envelope of a pre-K-12 school building encloses and maintains the learning environment created by heating, ventilating and air-conditioning systems, lighting systems and interior aesthetics and finishes.
Not only that, the envelope, through the skillful design and construction of walls, windows, clerestories, skylights, ceilings and other components, can contribute heat, coolness, natural light, acoustical performance and aesthetics to the learning environment.
What constitutes a good learning environment and how does a building envelope maintain and contribute to it?
The Learning Environment
Research conducted over the past 20 years has defined a high-quality learning environment in terms of temperature, humidity, ventilation, acoustics and lighting.
As long ago as 2002, Mark Schneider, a political science professor at the State University of New York, Stony Brook, reviewed research studies about optimal temperature and humidity levels for schools in a highly regarded white paper entitled “Do School Facilities Affect Academic Outcomes?”
According to Schneider, research suggested that moderate temperatures from 68 to 74 degrees and humidity levels ranging from 40 to 70 percent elicited the best student performances. These levels remain today’s benchmarks.
Designers and heating, ventilation and air-conditioning (HVAC) engineers have always known that ventilation removes contaminants and carbon dioxide from the indoor air and prevents people from getting sick or tired. Until about 10 years ago, however, the standard number of air changes was set at a level far below what is now thought to be adequate for schools.
“Prior to 1999, a ventilation rate of 5-cfm-per-person was the standard,” says Ian T. Hadden, PE, LEED-AP BD+C, energy and sustainability services manager with the Celina, Ohio-based architectural firm of Fanning Howey. “For about 10 years now, ASHRAE 62.1 has recommended approximately 15-cfm-per-person for schools.”
According to Schneider, a consensus of lighting studies indicate “appropriate lighting improves test scores, reduces off-task behavior and plays a significant role in students’ achievement.”
Perhaps surprisingly, the connection between performance and natural daylight isn’t a recent discovery. Schneider cites a 1999 study that examined 2,000 classrooms and found that “students with the most classroom daylight progressed 20 percent faster in one year on math tests and 26 percent faster on reading tests than those students who learned in environments that received the least amount of natural light.”
Finally, Schneider links poor acoustics — noise and vibration — to significantly reduced student performance.
In short, get the temperature, humidity, ventilation, lighting and acoustics right, and students will perform better.
That’s when the building envelope becomes important. Walls, windows, doors, ceilings and floors must combine to create an envelope that protects, maintains and sometimes contributes to a finely tuned learning environment.
Sealing New Envelopes
“New building codes and organizations like the U.S. Green Building Council are helping to establish new and improved guidelines for better envelopes,” says Dennis Hacker, AIA, CSI, CCS, CCCA, LEED-AP BD+C, specification writer and manager with Fanning Howey.
Today’s guidelines make it easier and more economical to build envelopes that limit problems such as mold while promoting thermal comfort, continues Hacker.
Consider the new Milkovich Middle School in the Maple Heights City Schools district in Maple Heights, Ohio. Designed by Fanning Howey, the two-story, 130,000 square foot facility is LEED registered and aiming for Silver certification.
“The school is designed with a variety of strategies meant to balance the relative strengths of various building envelope systems,” Hacker says. “The exterior walls are cavity wall construction with spray foam insulation, which provides high insulation value and high thermal mass. This helps to maintain desired temperatures with less energy.”
Energy Shield, Inc., a small, family-owned company based in Pontiac, Mich., worked with construction manager, Heery International-Cleveland and Crowe Masonry of Ravenna, Ohio, to install spray polyurethane foam onto the building’s 60,000 square feet of perimeter masonry walls. Once applied, the foam formed a seamless insulated R-14 air barrier.
“The school district got a finished product that will ultimately save them considerable money in operating costs,” says Dave Fritzinger, president of Energy Shield. “Plus, the indoor air quality of the new school will be much healthier for the students, teachers and staff.”
According to the Air Barrier Association of America (ABAA), failure of building air and vapor barrier systems causes buildings to deteriorate prematurely and costs owners approximately $500 million per year.
Milkovich Middle School will likely avoid that problem. “The spray foam provides high insulating performance while allowing overall wall thickness to be at a minimum,” says Hacker. “In addition, the strength of the bond between the spray foam insulation and the concrete masonry backup wall is extremely strong and provides an excellent composite of insulation and air barrier to minimize thermal transmission and air leakage.”
Fanning Howey selected energy-efficient window systems that keep heating or cooling inside the building while providing natural daylight to all of the school’s educational spaces. “In addition, the classroom wings are oriented for the most efficient natural lighting,” Hacker says.
Insulated, low-slope roof systems minimize the enclosed volume and support solar panels to provide pre-heating of domestic water, Hacker continues.
“If the envelope isn’t well designed and constructed, you will have uncontrolled infiltration of air and moisture, and you will be lucky if the HVAC system will be able to handle it,” adds Hadden. “Whether it can or can’t, utility costs will be high.”
Renovating Old Envelopes
Built in 1921, the 288,000-square-foot Eastern High School in Washington, D.C. has undergone several renovations over the years.
“The most recent was completed in 2010,” says Hacker. It was a $67-million project that provided the building with 21st-century energy-efficient systems and a tight, modern envelope, while respecting and restoring the Collegiate Gothic architecture of this landmark structure,” says Hacker.
Fanning Howey carried out the design, and the Washington, D.C., office of Turner Construction Company handled the construction work.
It was a complex project. “Our assignment was to restore the historical façade and replicate the original windows, while adding today’s tight energy efficiency,” says Joseph Swanson, Turner’s project superintendent on the project.
No easy task. The windows were 10-feet tall, double hung with an operable sash and made of wood. To open the window, you could push out from the bottom and let the unit swing out from a hinge at the top. You could also open the window by pulling up on the bottom unit or pulling down from the top.
“We studied the original 1921 drawings,” Swanson says. “Instead of wood, we used aluminum and insulated glass, but they functioned like the originals.”
Now a division of the Norcross, Ga.-based Kawneer Company, Traco, fabricated the windows — all 1,900 of them.
While Traco was making the windows, Turner carried out a $7-million abatement package that involved removing asbestos plaster from all of the interior walls. “Underneath the plaster was the building’s original brick walls,” says Swanson. “We left the brick exposed on walls that we didn’t have to insulate — interior walls.”
On the inside of the brick exterior walls, Turner installed a high efficiency insulated wall made from a layer of R-19 insulation, a layer of drywall, a thermal barrier made of foil faced insulation and another layer of drywall.
In addition to energy efficiency values, both the windows and the insulation selected for the walls carry an acoustical rating to keep the city noise out of the school.
“We replaced the roof with white TPO membrane — white so it won’t absorb heat,” continues Swanson. “Under the membrane, we installed a layer of R-30 insulation.
“We wanted to make the roofing continuous by flashing up the parapet wall. To do that, we had to repair failing brick and mortar joints between the parapet and the walls. Over the years, the freeze-thaw cycle had done a lot of damage.”
A major part of the project involved transforming two light wells in the center of the structure into tall useable atriums. Classrooms on the interior side of the corridor had windows looking into the light wells, but three of the structure’s five floors were cut off from natural light by roof structures. “We removed the roof structures and installed large skylights across the top of the building, bringing natural light into those three floors,” Swanson says.
In addition, Turner opened up the school’s circulation corridors to the atriums so that students could gather there in their spare time.
“Both of these projects illustrate the value of treating buildings as systems,” says Hadden. “What you do with the envelope affects the specifications of the HVAC system. Glazing affects the electric lighting. The envelope and interior finishes also affect acoustics. All of these systems together create a high-performance learning environment.
“And one more thing: you can have a great envelope design that works seamlessly with the HVAC, lighting and acoustics, but if you don’t understand how to take care of the building and doesn’t do it properly, the learning environment won’t last. Owners and maintenance people must be engaged and understand the reasoning behind the materials selected for the building.
“If you replace a ceiling tile with the wrong kind of tile, you can hurt the acoustics. The same is true with light bulbs, ballasts and the flashing on the roof — if you fail to keep up with that, moisture can get into the system.”
A school building system — any building system — is a three-legged stool, says Hadden by way of summary. The legs are design, construction and operations management. If one leg gets broken, the school breaks.