Maple Grove Elementary

It Rains Every Night: EPS Rigid Insulation Specified on Commercial Re-Roof To Tackle Ponding Challenges

In 1968, when construction started on the Maple Grove Elementary School in Boise, Idaho, the Boise School District had not anticipated the rapid residential development that would soon flood the neighborhood with school-age children. Originally designed as a single-story brick building with a flat roof, a boom in the area’s residential population forced the District to expand the school before the originally designed building was even complete. A few years later, the school had to be expanded a second time to meet growing demand. Today, the 22-classroom facility serves an estimated 500 students in grades K – 6th and is one of the District’s largest Schools.

After nearly 50 years of service, by 2015, the school was beginning to show the wear and tear of time. Local designers, Hutchinson Smith Architects conducted a facility assessment and determined that the flat roof was in borderline failure condition. Due largely to its lack of slope, a significant amount of rainwater was accumulating in several low spots across the roof leading to the deteriorating condition. Adding slope to a flat roof is a common and relatively simple solution to a problem with potentially complex consequences if left unchecked.

Atlas Molded Products manufactures molded polystyrene roofing materials to be used as both insulation and a solution to drainage issues where the profile of a flat roof needs to be increased to achieve positive drainage. In addition to roofing insulation, molded polystyrene products manufactured by Atlas include in-wall and cavity insulations, perimeter foundation insulations, and underslab and below-grade insulations all of which combine to significantly contribute to a high-performance building envelope.

The Challenge

For Maple Grove Elementary, the primary problem to be resolved was the threat of a failed roof due to water infiltration. As a result of the overall flatness of the school’s roofing system, the lack of positive drainage was causing rainwater to pond in the roof’s low points. Over time, the weight of standing water can slowly increase the size of a collection depression making it to become ever more significant. With no way other than evaporation for the water or, in the case of a Boise winter, snow and ice, to get off the roof, the structural integrity of the building begins to become compromised at these depression points. As the water sits, the surfaces beneath it are susceptible to possible infiltration. Water seeping into the building can deteriorate structural members, corrode mechanical and electrical equipment, damage interior surfaces, and cause safety hazards of all sorts from wet spot slips to potentially lethal electrical conditions – all of which are significant concerns in a building populated by young children. Unmitigated, the long-term consequences of a failed roof are eventual collapse, which in the case of an occupied elementary school is a situation that had to be rectified without delay.

In general, the conditions on a commercial roof are significantly more complex than most residential roofs. While a residential roof is typically sloped, commercial roofs are designed to conform to a much greater range of architectural influences. Further, while most residential roofs can be removed and replaced in a single day’s work by a skilled, efficient crew, commercial reroofing projects can take quite a bit longer, sometimes stretching weeks or months. An old adage in the roofing industry suggests that it rains every night, meaning that no matter how much remains to be done on a roofing project, the entire roof must be completely water-tight before the crew can leave for the day.

The Solution

In the case of Maple Grove Elementary, the challenge was to essentially eliminate the roof’s flatness without substantially altering the architectural appearance of the building by changing the roofline. Doing so meant adding a slope to the roof’s surface extending from a high point in the center to the edges of the building, while also keeping the slope hidden from external view. The solution devised by Hutchinson Smith Architects was to use molded polystyrene foam insulation to build up enough slope to get rainwater and snow to move to perimeter drainage spouts by gravity.

On a flat roof like the one at Maple Grove Elementary, this often involves using triangular-shaped pieces of foam, known as crickets to build up the center of the roof enough to allow gravity to force water to perimeter drainage. Creating a consistent directionally controlled roof slop required working around the building’s rooftop mechanical units, skylights, and other protrusions using an easily customizable material. Molded polystyrene insulation from Atlas is easily trimmed or shaped by workers in the field using only a hand-held hot wire cutter to make custom pieces. Though lightweight and easily moved into place by hand, the material is extremely durable, comes in a wide range of compressive resistances, offers lifetime R-values, and exceptional moisture resistance.

In total, approximately 250,000 board feet of molded polystyrene insulation was used at Maple Grove to create the compound slope. Whereas many architects appreciate Atlas’ molded polystyrene insulation products for being a great value relative to thermal efficiency, contractors like Signature Roofing, who rebuilt the Maple Grove reroof, appreciate it for its ease of installation and ability to be quickly customized on-site. While some other rigid foam insulations are manufactured in sheets that are only a few inches thick, a single piece of molded polystyrene can be up to a few feet thick. While creating the compound slope needed on Maple Grove may have required other types of rigid foam insulation sheets to be stacked on top of one another, using molded polystyrene allowed the entire slope to be placed in a single layer of material. Not having to build up layer after layer saves both time and money for the installation contractor. On large commercial roofs with a significant slope build-up, the savings in time, materials, and labor can add up significantly.

Solving a significant deficiency like standing water on a flat roof proved to be a little more than a minor challenge for designers at Hutchins Smith Architects on the Maple Grove Elementary school in Boise, ID. Saving both time and money by using tapered foam crickets manufactured by Atlas Molded Products made it a win-win for builders at Signature Roofing. Atlas is dedicated to customer- and building- focused solutions that span a wide range of commercial architecture and civil infrastructure challenges, big and small from 15 manufacturing facilities spread across the United States and Mexico.

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