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Prevent Ponding On Flat Roofs

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When the Justice Court Mutual Housing co-op had a self-adhesive roof installed, the contractors made sure that the roof membrane had proper slope to avoid ponding.


Justice Court Mutual Housing, a cooperative apartment building in Elmhurst, NY, possessed a 13,000-sq.-ft., built-up roof that was in dire need of repair. Though exposed to just more than a decade of environmental stress, the building experienced water damage in critical areas, such as in the vertical and horizontal transitions and in the roof field.

The numerous mechanical units on this roof were not properly considered when the original roof was installed in the early 1990s. The new, self-adhesive system includes sloping toward the roof’s three drains to avoid ponding.

The existing roof was a torch-down system that had settled and became susceptible to water intrusion. It was built without any slope and suffered from severe ponding. “When there is no slope to the drains, the water has nowhere to go. The water stays on the roof and causes major damage,” said Chris Kelly, principal of CK Engineer PC, New York.

Water pooled around a concrete block water tower and a 30-ft. bulkhead structure that topped the Justice Court Mutual Housing cooperative. The art-deco building, constructed in the early 1960s, featured alternating horizontal blocks, which required a roof system specific to meet the needs of the building.

The original roof was not properly sloped in relation to the building’s multitude of mechanical units. Only a short 10 yr. later, the roof deteriorated and began to leak. “Many times, with commercial buildings, people focus on the interior of the building such as the carpet, wall paper, and interior decorating, when the exterior of the building is the most important. The quality of the exterior will affect the whole building,” Kelly said.

With the roof as a major component of the renovation, the co-op board and the engineer focused on the long-term needs of the building envelope. In addition to extensive masonry work, the engineer recommended a four-ply, self-adhesive system with tapered insulation that would provide an adequate positive slope for water drainage.

Tapered insulation and durable roofing membranes are two essential elements that can prevent a roof from settling, while also reducing the threat of ponding. To meet the needs of the Justice Court building, Elastoflex SA V and SA P membranes, as well as tapered insulation and crickets, were installed to prevent ponding from occurring once again. The Elastoflex membranes are manufactured by Polyglass, Fernley, NV. “Establishing proper pitch is important. All roof components must work together,” Kelly said.

The first steps to constructing the self-adhered system involved priming the concrete deck and applying two-plies of the Elastoflex SA V base sheet. “We used two plies of base sheet as a temporary roof,” said Tony Lado of Bulado General Contractors Corp., Elmhurst, NY. “The roof was so large that we couldn’t remove the original roof and install the new system all at once. The integrity of the system allowed us to do one section of the roof at a time.”

“There’s definitely something to be said about the beefiness of the Polyglass membrane. When you compare it to other membranes, it’s substantially thicker,” Kelly said. The thickness of Elastoflex is attributed to its composition of a “true” SBS compound on the top layer and an aggressive self-adhesive compound on the bottom layer. Unlike other SBS membranes, Elastoflex SA V is manufactured using Adeso technology and is built with a reinforced fiberglass mat to guarantee dimensional stability and provide pliability at low temperature conditions.

Following the base-sheet, tapered insulation and crickets were installed to develop slope and channel the water toward drains. The tapered insulation was laid at between 1 1/2 in. and 8 in. thick as needed to shift water to three drains.

The process was so simple that it only took Bulado’s crew four weeks to install the entire roof system, with minor weather complications here and there. A quick application of another two plies of the Elastoflex base sheet and the Elastoflex SA P granular cap sheet, as well as repair to the flashings, aluminum panels, and copings, and the roof renovation was complete. “We had twice the production rate using the Polyglass self-adhered membranes,” Kelly said.

“The whole process was fast and clean,” Bulado stated. The self-adhered system uses the manufacturer’s SealLap and FastLap features. These features enhance bonding at laps. “There was no waste with the self-adhered system so it went faster and the roof and surrounding area stayed cleaner.”

New York has outlawed torch-down systems on wood roof decks and, although Justice Court’s roof was concrete, self-adhered is becoming the preferred application method over torch-down roofs. “The concern for a safe flat roof system has already affected wood-deck roofs,” Kelly said. “Self-adhesive is important for concrete decks because it avoids hazardous application methods and the roof is expected to last 30 years or more.”