April 24, 2008

CITY OF TORONTO

Toronto City Hall has a green roof with a walking path and plaques explaining the plant life to those taking breaks in the fresh air.

NATIONAL RESEARCH COUNCIL

Researchers examine readings from a reflective roof as they work on tightening definitions of the category and defining optimum maintenance procedures.

Roofing Options

Subtle nuances may distinguish new sustainable roofing systems

PETER KENTER

correspondent

New sustainable roofing systems and concepts are providing builders with more choices than ever, but a glut of information has blurred the distinction between different types of roofing.

“When people hear the term ‘green roof,’ some of them think of a rooftop garden, while others think of roofing that is environment-friendly,” says Dr. Ralph M. Paroli, director of the building envelope and structure program for the National Research Council Institute for research in construction. “When they hear about a ‘white roof,’ they may expect to see something coloured white, instead of something reflective.”

The upshot is that builders and specifiers seeking sustainable roofing systems may be confused about the best choices available to achieve the goals of their particular roofing project.

“Clarifying the terminology will help to give building owners and the construction industry the confidence to try these technologies,” says Paroli.

The first step in sorting out roofing options requires the understanding of four basic terms: sustainable roofing, high-performance roofs, green roofs, and white or reflective roofs.

Sustainable roofing

Sustainable roofing is a concept, not a system says Paroli. The idea was defined in 2001, in a document entitled Towards Sustainable Roofing, published by the International Council for Research and Innovation in Building and Construction. The guide describes 21 tenets of sustainable roofing which minimize burden on the environment, conserve energy and extend the life of a roof.

“This document suggests that buildings employ a garden roof system in urban areas, where appropriate, for example, but they don’t tell you to choose that particular style of roofing,” says Paroli. Other guidelines in the publication include the use of local labour, material and services to reduce energy use and to help the local economy, and employing the services of skilled professionals to put roofing know-how into practice.

High-Performance Roofs

High-performance roofs are durable, economical, energy efficient, environmentally-friendly and provide an extended roofing life cycle. “A high-performance roof encompasses all the elements of sustainable roofing,” says Paroli.

Green Roofs

The term green roof specifically refers to rooftop gardens and not the general approach to environmental sustainability, says Paroli. Green roofs fall into two categories: intensive and extensive.

An intensive green roof is a labour-intensive rooftop garden consisting of trees and shrubs, while an extensive green roof is virtually self-sustaining and requires little maintenance. “Green roofs help preserve the environment by reducing roof run-off and reducing the urban heat island effect.”

White or Reflective Roofs

A white roof, is also known as a reflective roof or cool roof. These roofs provide high reflectivity of solar radiation and high emissivity — the ability to emit more radiant energy into the atmosphere than darker roofs. “White roofs have been around for more than 30 years,” says Paroli. “They reduce building energy demand in summer and help mitigate the urban heat island effect. Although many such roofs are white, there are new pigments being developed that are also reflective, so they don’t need to be any particular colour.”

Ongoing research will help to further tighten up definitions and help to define optimum maintenance procedures. “Currently, ASTM (American Society for Testing and Materials) says you should wash a reflective roof, while the Cool Roof Rating Council says you shouldn’t,” says Paroli “We still need to develop hard data on the effect of power washing on the life cycle and lifespan of a reflective roof.

“We’re currently working with the Western States Roofing Association to test reflective roofs in four distinct climates — Nevada, Washington, Texas and Alaska — to see what really happens.”

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