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Roof Rehab Project Challenged by Hurricanes

Friday, August 24, 2018

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Case Study by Jeff Younger Kemper System America Inc.

 

Historic roof rehabilitation projects are not always easy. The historic Charleston Library Society completed a major roof rehabilitation project last year during what became a hyperactive U.S. hurricane season.

Charleston, South Carolina, is no stranger to high winds and heavy rains, so roof waterproofing is critical for protection. In this case, the library, built in 1914, is home to a slice of American history. It is owned by the Charleston Library Society, the third oldest private library organization in the U.S., whose archives encompass an extensive array of southern colonial newspapers; more than 14,500 rare books; 470 maps and plats; and 400 manuscript collections including letters from George Washington, Robert E. Lee, Charles Pinckney and John C. Calhoun.

Images courtesy of the author

The historic Charleston Library Society completed a major roof rehabilitation project last year during what became a hyperactive U.S. hurricane season.

The design phase of the rehab project began in 2016 after the Society retained Applied Building Sciences Inc., of Charleston, to assess the structure and the building envelope. ABS offers cross-disciplinary expertise spanning engineering, architecture, materials and the building envelope, and provides comprehensive services in the southeast. The roof was identified as the priority for Phase 1 of the rehabilitation. The full 10-month project was completed in February of this year, but work needed to temporarily halt last fall after Hurricane Irma flooded downtown Charleston and Hurricane Maria threatened a repeat.

One of the most pressing issues for the design team was a low-slope roof at the back of the library, covered with an acrylic single-ply membrane on top of many decades worth of archaic built-up roofing. Water had become entrapped in the built-up layers and was beginning to damage interior finishes after wet weather.

The main roof at the front of the building includes a parapet surrounding a slate hip roof with a skylight along the ridge. The parapets required rehabilitation and waterproofing protection especially at the roof transition and on top. The copings were terracotta covered with a piecemeal conglomerate of aged coatings and reinforced membranes. A built-in gutter, a trough that extends from the face of the parapets to the eaves of the hip roof, was also a concern. It contained layers of copper flashings and liquid-applied coatings installed over many decades.

MONOLITHIC WATERPROOFING

The ABS design team included architect Lauren Ulmer, AIA; registered roof consultant Eddie Polk; and structural engineer Jason Gregorie, PE, CFM, senior structural engineer and partner at ABS.

One of the most pressing issues for the design team was a low-slope roof at the back of the library, covered with an acrylic single-ply membrane on top of many decades worth of archaic built-up roofing. Water had become entrapped in the built-up layers and was beginning to damage interior finishes after wet weather.

“For the gutter, we first looked at relining it with metal, either stainless steel or copper, but we ultimately chose the liquid-applied membrane from Kemper System because of its monolithic nature,” Gregorie said.

“For the low-sloped roof at the rear, we considered TPO (thermoplastic polyolefin sheet), but again decided to go with the cold liquid-applied membrane. Eventually, it became a no-brainer because we wanted every area to have seamless monolithic protection.”

After initial research on waterproofing materials, Gregorie preferred reinforced polyurethane resins over acrylics and silicones, for durability and perforation resistance. With assistance from Kemper System, he specified the Kemperol Reflect 2K FR, a cool-roof system with a solar reflectance index of 110 that is also Class A fire-rated.

Kemper System educated the ABS design team about a similar project with the Philadelphia Museum of Art and that became an inspiration, Gregorie said.

“The driving force for the library was that we needed a versatile solution to address the varied substrates and surface profiles, the many contours and the intersecting planes. The roof also had tight working spaces and difficult details for the contractor to work through.”

Another important characteristic was that unlike sheet products, which use termination bars, the Kemperol membrane could self-terminate at the top outer edge of the parapet copings.

An insulated Kemperol Reflect 2K FR membrane assembly was applied to the lower roof. For most other areas, including the built-in gutter, the parapet coping and the lower part of the parapet wall, Kemperol 2K FR was applied over native masonry, terracotta and concrete substrates without insulation or cement board.

“Since the library is architecturally significant in Charleston, we weren’t allowed to make any aesthetic changes that could be visible from the street,” he explained.

Roofing installer Cahill Contracting (North Charleston, South Carolina) had worked with the Society on other projects through its general contractor, Palmetto Craftsmen Inc., and became a Kemper System-certified applicator for the roof rehab project, trained by technical service representative Joel Voss. The work began with tear-off on the low-slope roof, which held a surprise. Below the BUR there was a cinder ash topping slab, a cement mixture with a loose aggregate that just broomed away. ABS deemed the underlying 12-inch thick concrete deck structurally sound once the cinder ash topping was removed.

 

WIND UPLIFT TESTING

Before the Kemperol Reflect 2K FR assembly could be installed on the low-slope roof, it needed to pass field tests for wind uplift to a design pressure of minus-100 psf. ABS constructed test mockups for preliminary field-pull tests, and the insulated roof assembly, testing to 125 psf using a wind uplift chamber, per FM 1-52. Both tests passed. The full assembly consisted of a repair mortar topping slab on the original concrete deck, two layers of insulation board for slope, cement board and then the liquid-applied membrane system, which includes Kemperol 165 reinforcement between two layers of waterproofing resin.

For most other areas, including the built-in gutter, the parapet coping and the lower part of the parapet wall, Kemperol 2K FR was applied over native masonry, terracotta and concrete substrates without insulation or cement board. ABS field tested those areas in accordance with standard ASTM D-7234 for pull-off adhesion strength.

ABS tested the insulated waterproofing assembly to 125 psf on a section of the roof using a chamber uplift apparatus.

For Cahill Contracting, there were at least two major challenges to finishing the project—surface preparation and the threat of hurricanes. Cahill was using a scaffold tent to keep work areas dry, but with the potential of tropical storm-force winds in the forecast from Hurricane Irma the following week in mid-September, they needed another plan.

Project crews were generally five or six people, but sometimes as high as 20 in a crunch. Crews had already completed the tear-off on the lower roof and most of the repairs on the rest of the roof.

The solution was to finish or close any open repairs, and apply a temporary single-ply on the unprotected lower roof, and primers to other surfaces ahead of the storm. Owner Chris Cahill made the call.

“This is a historic building and some of those books are irreplaceable. So, our crews worked over the weekend and put in a lot of overtime to get it done,” Cahill said.

“The Kempertec EP5 (a rapid-curing epoxy) and Kempertec D (polyurethane) primers did an exceptional job of making everything watertight. I lost some sleep on the first go ‘round, but then I felt comfortable. On the built-in gutters, we didn’t need to install scupper sleeves, we just used primer to waterproof everything ahead of the storm. So that was a plus.”

A vapor permeable coating was applied to the wall on the lower roof area and to the face of the parapet on the hip roof to allow for moisture drive. The parapet walls required several passes with a needle-punch wire brush to remove layers of paint and to grind the bricks to a structural substrate.

About 10 days later, weather threatened again as Hurricane Maria barreled north about 300 miles off the South Carolina coast. Fortunately, it took a hard right east of Cape Hatteras, North Carolina, and fizzled into a tropic storm. Charleston experienced some wind, but less rain and no flooding.

In early October, when surfaces were thoroughly dry and with no rain in the forecast, the crew applied the Kemperol Reflect 2K FR system, which has an open time of about 30 minutes. The reinforced membrane system is applied a section at a time, and dries to a monolithic surface that is water-resistant after about two hours.

 

ABOUT THE AUTHOR

Jeff Younger, Southeast Account Executive for Kemper System America Inc., offers more than 30 years of experience in the commercial roofing and waterproofing industry. Over his career, Younger has been involved in specifying waterproofing for major projects including the Philadelphia Museum of Art, Ocean Resort Casino in Atlantic City, and the Trenton Cultural Center. After 18 years as an independent representative, he joined Kemper System in 2013.

   

Tagged categories: Kemper; Waterproofing

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