Roof Rot: Ignorance Is an Easy Way to Damage Low-slope Residential Roofs

Change often brings with it unintended consequences, and the issue of reflective roof surfaces in North America is no exception. In the late 1990s, U.S. cities in northern climates started to mandate the use of reflective roof—more for politics, feel-good, pseudo-environmental reasons than sustainable, resilient and durable reasons. In my estimation, cool roofs often did more to lower the quality of buildings than enhance them. Furthermore, code and standard changes were made with no understanding of the result and no education to the architects of America.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Although the resulting unintended consequences affected commercial and residential buildings, it was the often-catastrophic results on low-slope residential buildings that went untold and left homeowners with tens of thousands of dollars of corrective work on basically new residences.

Following is a summary of how these concerns evolved in wood-framed residential construction. I’ve included case studies of failures, potential solutions and lessons learned.

HISTORY

During the industrialization of America’s large cities throughout the 1800s, the need for labor caused populations to explode. To house the labor migration, row houses (3- to 4-story structures, often with a garden level and four or more narrow units) were constructed approximately 3-feet apart, block after block, creating medium-sized apartment blocks. Most of these row houses were wood-framed, masonry veneer with low-slope roof structures. The interior walls and ceilings were finished in cementitious plaster, which provided a durable, fire-resistive finish. The plaster also performed as an effective air and vapor barrier, preventing interior conditioned air from penetrating into the non-insulated walls and ceilings where it could condense within the walls and roof on cold days.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Heating costs were low, so little—if any—insulation was installed in the walls and roof. Roofs were composed of built-up asphalt and coal tar, both smooth and aggregate surfaced. Attic spaces often 4 to 6 feet in height were vented via static vents. Any conditioned air that passed to the attic was able to dissipate through these static vents. This method of construction performed without significant attic condensation, and the roof systems and roof structure served these buildings for decades.

In the mid 1990s, researchers (theoretical researchers with no architectural, engineering, roofing, construction or practical building technology experience or knowledge) at research institutes conducted studies into the effects of minimizing solar gain through the roof via a reflective surface. Based on the researchers’ algorithmic findings and recommendations (regardless of their validity), environmental groups used the concept to promote change. Large cities started introducing new energy codes with reflective roofing requirements and prescribed reflectance values. These new codes contained greater insulation requirements, which was a benefit. However, in this one code adoption, roof systems, such as coal-tar pitch, that had performed for centuries were no longer permitted. Consequently, roofing contractors went out of business and so did some roofing material manufacturers because of unproven and suspect research.

Photos and Details: Hutchinson Design Group Ltd.

Pages: 1 2 3 4

The Cool-roof Bandwagon: Is It Headed To Your City?

Spring is here, and summer is on the horizon. But for millions of Americans, it will take more than a few days of sunshine to thaw the memories of the winter of 2013-14. The National Weather Service is still compiling the statistics to let us know just how bad the winter really was. In the meantime, most of us have a more immediate way to measure the impact of the polar vortex on our lives: One look at our heating bills and we know that this past winter deserves its reputation as one of the most brutal on record.

On the West Coast, as 2014 dawned, very different climate issues were front and center. The city of Los Angeles was being praised for its mandate requiring all new and renovated domestic housing to install “cool”, or reflective, roofing. The L.A. City Council passed the requirement as one of its last acts of 2013, and the new ordinance became part of California’s Title 24, which already required “cool” roofs in new and remodeled commercial construction.

THE NEWS media hailed Los Angeles as the “first major city to require cool roofs”, implying other urban areas will inevitably follow its lead. However, the winter of 2013-14 did a good job of reminding us that the climatic conditions of Southern California are dramatically different from the Midwest, Northeast and Mid-Atlantic regions of the U.S. This simple fact needs to be underscored as the bandwagon to require cool roofs travels somewhat erratically to major Eastern cities.

Last June, the mayor of Pittsburgh initiated a lukewarm cool roofs program by calling for volunteers to help paint the roofs of 10 city buildings white. Two-thirds of the Pittsburgh effort—$56,000—was funded by the Bloomberg Philanthropies, a project of former New York City Mayor Michael Bloomberg. The tagline of Bloomberg Philanthropies is “Good Intentions, Great Results.” I applaud the mayor’s good intentions in supporting projects that are designed to save energy. As for achieving “great results” by painting the roofs of 10 Pittsburgh buildings white? Don’t bet your next heating bill on it.

While Bloomberg was mayor of New York, the city launched the “NYC °Cool-Roofs” initiative, encouraging building owners to cool their rooftops by applying a reflective white coating as part of the city’s overall plan to reduce greenhouse- gas emissions 30 percent by 2030.

In Baltimore, the talk about cool roofs was fueled by a report issued last October by the Abell Foundation, a non-profit dedicated to enhancing quality of life in Baltimore and Maryland. The report, which is primarily an overview of previously published research, recommended increased use of cool roofs in Baltimore.

While these cities institute varied programs to support cool roofs, several major facts are ignored:

    ▪▪ Energy costs are closely related to climate. A solution that works in a warm and temperate climate to curb energy costs will not necessarily work in a colder climate.
    ▪▪ It’s vitally important to consider the source of information about cool roofing. Unbiased, up-to-date scientific studies can provide the data you need to make an independent judgment. Likewise, the manufacturers of roofing membranes have a vested interest in ensuring their products are used correctly and have in-depth knowledge of how roofing systems will perform in a wide variety of conditions.
    ▪▪ Choosing and installing a roof that will contain energy costs is a complex business. It requires understanding the interaction between building design, climate, insulation and all the other factors that impact the efficiency of a roofing system. A one-size-fits-all approach will only delay the discovery of workable, cost-effective, energy-efficient solutions.

IN FACT, a study conducted by Arizona State University published this past winter in the Proceedings of the National Academy of Sciences underscores the pitfalls of disregarding climate differences in roofing decisions. “What works over one geographical area may not be optimal for another,” says sustainability scientist Matei Georgescu, who led the research.

Although the headlines are touting Los Angeles’ cool roof requirements, I’d like to see headlines that read, “Energy Savings Achieved by Roofs Designed to meet Midwest and Northeast Climate Challenges”. Before anyone thinks about driving that cool-roofing bandwagon from Los Angeles to New York, you might want to equip it with snow tires.