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

Never Stop Learning

This year as I watch my friends and family send their little ones off to school, I, too, am starting a new educational journey. I’m taking piano lessons. I’ve wanted to play since I was a child but never had the opportunity. My husband heard me talk about wanting to play a few times, so he suggested giving me lessons and a piano as a gift for our first wedding anniversary.

I literally thought about it for a full day. I was completely touched that my husband wanted to help me accomplish a lifelong dream. However, did I really want to commit myself to something completely out of the ordinary? I learned to play the trumpet in middle school and played through high school, so I can read music—treble clef. I’ve never had to learn bass clef or how to make my left hand and right hand play different music at the same time. Could I do it? What if I’m the worst adult student my teacher has ever had?

I came to the realization that the accomplishments of which I’m most proud pushed me out of my comfort zone. Plus, how could I possibly say no to my husband when his gesture was so sweet? I’ve had one lesson so far and the idea of being able to coordinate my hands still seems a little like being able to rub my stomach while patting my head. However, I’m excited about the future and am hoping I’ll be playing well by the holidays!

Every issue of Roofing has an educational bent, but this issue may push you out of your comfort zone. For example, cool roofs have been a hot topic for many years. Conventional wisdom states cool roofs are not appropriate for northern climates. Kurt Shickman, executive director of the Washington, D.C.-based Global Cool Cities Alliance, will challenge that notion in “Cool Roofing”. He presents new evidence from several scientific studies that demonstrate cool roofs provide benefits to buildings in Climate Zones 4 through 8.

Meanwhile, Thomas W. Hutchinson, AIA, FRCI, RRC, CSI, RRP, principal of Hutchinson Design Group Ltd., Barrington, Ill., and a member of Roofing’s editorial advisory board, shares his in-the-field experiences regularly. He notes in “From the Hutchinson Files” that code-mandated insulation thicknesses are forcing designers to take roof access door and clerestory sill details seriously. Hutch’s goal with his article is to give designers some confidence to create appropriate design and detailing solutions.

These articles may challenge what you’ve always done but they’re worth considering and discussing. In fact, I’d really like to hear what you think about them. In return, I’ll keep you updated on whether I’m becoming the next Chopin!