Weathering the Storm

Feb 1, 2000 12:00 PM, By Mike Kennedy

Arizona must endure the unrelenting intense heat of the desert sun. Colorado has to contend with the volatile temperature swings that go hand in hand with its scenic mountains. Florida must cope with the high winds and torrents of rain that tropical storms and hurricanes bring.

Wherever your school is, the particular climate of the region will play a key role in determining what kinds of roof construction and maintenance will work best.

The goal is to make sure that your roofs are doing what they are designed to do: keep the outside elements on the outside.

"You want to correct problems before they occur," says Jerry Teitsma, technical director of the Roofing Industry Educational Institute (RIEI), Englewood, Colo. "You don't want to wait for the problem to land in buckets at the bottom."

To keep moisture out of the building, roofs need to be resistant to cracking, tearing, blistering, warping and shifting. Materials have to withstand the punishment they inevitably will receive from heat, cold, wind and rain.

Taking the heat Excessively hot temperatures can cause some roofing materials to soften and stretch, or bake and crack.

"Organic materials oxidize more quickly at higher temperatures," says Teitsma. "It's advantageous to keep temperatures down."

That's easier said than done in areas such as Tucson, Ariz., where temperatures on roof surfaces often reach three digits.

"The biggest issue here is the excessive amount of heat," says Jerry Sidio, facilities management director for Tucson (Ariz.) Unified School District. "We have intense sunlight for nine months out of the year."

The sun bakes millions of square feet of roofing surfaces on the district's more than 100 school buildings. The heat crystallizes the roofing material and the cracks it leaves behind make the roof susceptible to leaks when the rainy season comes.

"It's 110 degrees, and then the storm comes in," says Angel Llamas, the district's building inspector.

Most of Tucson's schools have built-up roofs that are flat or low-sloping. To lessen the effect of the heat, Tucson most often uses reflective coatings on its roofing surfaces-either an oil-based silver coating or a water-based white coating.

Sidio says the oil-based coating forms a better bond with the roofing material, while the water-based coating is easier to clean up without damaging the environment.

Heat damage to school roofs isn't limited to desert climates like Arizona. Many cities exhibit characteristics known as an "urban heat island." Lots of dark-surfaced roofs and roads absorb heat, while fewer trees and vegetation are present to provide cooling shade.

White or light-colored roof surfaces made of reflective materials are effective in lessening roof damage, says Teitsma, as well as in reducing the costs of cooling a building.

A shock to the system The cycle of freezing and thawing in colder climates also can play havoc with a roof. That is especially true in an area such as Colorado, where the temperatures can vary widely.

"In this climate, thermal shock is the number one factor," says Bob Matschulat, facilities and planning specialist for Jefferson County, Colo., Schools. "The temperature can change as much as 80 degrees in 24 hours."

The extreme temperature changes lead to thermal shock-the damage to a roof stemming from sudden and frequent expansion and contraction.

To protect itself from the damage of thermal shock, Jefferson County most frequently uses a four-ply built-up roof system on most of its school buildings.

"It's redundant-four membranes instead of one," says Matschulat. "You can compensate for any errors in building. The fewer layers you have, the more perfect the work has to be."

Blowing in the wind In places like Florida, where storms often pack high-velocity winds, roofs can be vulnerable to blowoffs.

High winds can lead to uplift, in which the forces of higher air pressure inside a building and lower air pressure on the surface of a roof can cause roof material to lift off the building. If a roof has inadequate or not enough fastenings, the entire roof can be shorn from a building. The perimeter of a roof is especially susceptible to uplift and blowoff.

"You have to really, really bolt the edges off," says Bill Smith, program director with the facilities department of Okaloosa County School District in Florida's Panhandle. "If the leading edge of the roof comes off, the whole thing comes off."

Smith says his district tries to avoid foam roofs. "The material is so light, the wind blows it off," he says.

Okaloosa County typically uses metal roofs or built-up roofs, depending on the size of school and type of construction.

"With a 3,000-student high school, you can't design a metal roof," says Smith. "If a school is 200 feet wide, you would have to have a pitch that is 60 feet high."

Because of hurricane damage in recent years, the roofing industry has strengthened its standards for combating wind uplift. Roofs had been tested to withstand uplift of up to 90 pounds per square foot. Now, they are tested to withstand uplift of 120, 150, or even 200 pounds per square foot.

Besides the gale-force winds, storms in a hurricane region can dump so much precipitation so quickly that roofs must be designed to drain water adequately. One of Okaloosa County's schools that couldn't drain water fast enough fell victim last year to Hurricane Georges.

The parapet walls on the district's Northwood Elementary School didn't allow for adequate drainage, so stormwater accumulated atop the school until the weight of the liquid collapsed the roof above the auditorium.

"We had a horrendous amount of rain, and the roof couldn't drain," says Smith.

Better practices Regardless of climate, school districts can improve their efforts by maintaining roofs and monitoring their conditions.

"Schools traditionally have not done a good job maintaining roofs," says Teitsma. "A lot of schools can get money for major reroofing, but are strapped when it comes to ongoing operating funds for maintenance."

Inspecting a roof regularly is much cheaper than replacing a roof that has been neglected. Ideally, a district should establish a regular inspection schedule and supplement that with checks after a storm or major construction work.

"Roofs should have a thorough inspection twice a year to maintain them in a ready state," says Teitsma. "Schools often ignore this."

In many cases, school systems with limited resources and competing needs can't afford to devote sufficient resources to roofing inspections.

"We are lucky to get an annual inspection," says Sidio. "We have one inspector and three roofers and somewhere around 8 million square feet of roof."

In cases where schools find themselves unable to keep up with roof maintenance, districts should consider low-maintenance systems, such as a metal roof.

Still, cautions Teitsma, a low-maintenance roof needs regular attention.

"You don't have blistering, ridges or splits, but metal roofs still need maintenance," says Teitsma. "You have to monitor the screws so they aren't backing out, you have to look for corrosion and use coatings to stop it. You have to check the seal joints. Caulking wears out and you have to check that."

The RIEI recommends that districts establish an asset management system to better monitor the conditions of school roofs.

Acceptable Use Policy blog comments powered by Disqus