cool roofs

Cool Roofs for a Hot Planet

Monday, October 3, 2016

Today’s cool roofing systems are a significant platform for urban building sustainability

We have always lived in a greenhouse of sorts. Our atmosphere traps the heat of the sun, which allows living things to thrive. Scientists maintain the expansion of that greenhouse effect is causing the planet to heat up at a rate too quick for nature to adapt, an issue that is widely believed to have been worsened in large part by human activity. As the planet warms, the world’s population continues to move into urban areas that are heating up at twice the rate due to human activity, lack of vegetation and the use of dark roofing and paving materials.

For many decades, traditional asphalt roofing construction was the norm, as it experiences little expansion or contraction, causing no thermal shock issues. At the time, there was little concern for insulation and heat loss.

Single-ply membrane products appeared in the early 1970s. Over the past few decades, scientists and product manufacturers developed better knowledge of chemical interactions and methods to prolong material life. At this point, the single-ply roofing industry has a proven performance record of more than 30 years.

While most people don’t think about roofs, they can be 25 to 30 per cent of total city area, making them a significant platform for urban sustainability that most people may not notice. But roofs can help solve the problem of hot cities. Cool, reflective roofing, especially PVC roofing, helps decrease energy use, thereby lowering emissions. PVC single-ply roofing deflects heat from buildings, decreases energy use, mitigates urban heat islands and serves as a durable platform for photovoltaic systems and vegetative roofs.

Roofs tend to be replaced more frequently than a building is retrofitted, so the rate of change (and rate of results) can be relatively quick. In short, smart roof usage is a climate strategy because it is immediately effective across a broad spectrum of benefits, and can be rolled out relatively quickly with good policy and good business decisions.

What are cool roofs?

Among the solutions to decrease energy use and thus decrease emissions from burning fossil fuels are cool roofing systems. Cool roofs use a highly reflective surface to direct a significant portion of solar heat away from a building. Unlike a dark or non-reflective roof surface that absorbs solar heat into the building and the surrounding neighborhood, a light-colored, reflective roof surface reflects and sends solar heat away from the building and into the atmosphere or beyond. Cool roofs have been widely available in the marketplace for more than 25 years.

Cool roofs can be achieved using a wide variety of roofing technologies, including single-ply membranes, cool-surfaced modified asphalt systems and metal roofing panels. For any of these roofing products to be labeled a “cool roof” by today’s standards, the minimum percentage of solar heat reflected away from the building must typically fall within a range of 50 to 70 per cent.

What are the benefits of cool roofs?

The cheapest solution is rarely the least expensive. While the upfront cost of the cheapest roof possible may appeal to an owner, you’re sacrificing any long-term benefits. The primary goal should be to design and construct a watertight roofing system that will not only create a healthier and more comfortable environment for occupants, but will save the owner or operator money and trouble in the long run.

They also reduce peak demand charges when installed on air-conditioned buildings. Although a share of this peak may be attributed to equipment use in the building, a significant portion is caused by increased demand for air-conditioning in the heat of the afternoon. One of the best approaches to shrink peak demand is to reduce the heat load on a building, especially the solar load that drives the need for air conditioning.

Heat islands are urban areas where temperatures are hotter than the surrounding areas. On average, the difference in afternoon temperatures between rural and urban land is seven degrees Fahrenheit, but can increase during extended heat waves. Some possible solutions include adding vegetation, which is a long-term improvement that may require up to 50 years to reap the full benefits or replacing dark pavement with lighter-coloured paving, which could help but requires significant capital outlays for somewhat minimal benefit. HHowever, replacing dark roofing with light, reflective cool roofing provides the biggest bang for your buck. By raising reflectivity, you can offset the warming impact. Relative to other possible measures, it is easy to accomplish, relatively inexpensive and provides immediate benefits to lessen the impacts of heat islands on a heating planet.

In many cases, educating the owner is necessary so that the best decision for long-term benefits can be made. Cool roofs make insulation about 25 to 50 per cent more effective; improve HVAC efficiency; reduce heat flux; and cause ambient indoor temperatures to drop by up to 15 to 20 degrees. In short, cool roofs can contribute to lowering the interior temperature and maintaining comfort levels for the occupants.

Cool roofs are also generally safe. Despite lingering misperception and long-debunked misinformation, PVC roof systems are safe for building occupants and the environment. During installation, no danger exists from flames, kettles or hazardous fumes that could cause disruptions to business or result in irritation to building occupants, which is especially important when discussing projects in schools, daycare centres and hospitals, to name a few.

Finally, cool roofs are sustainable. One of the major sustainability benefits of PVC roofing is that it is recyclable. Vinyl materials can be reprocessed and recycled repeatedly into useful products. In addition, PVC cool roofing systems can help architects reach their LEED goals.

Considerations before selecting a cool roof

Although you may have other considerations unique to certain projects, these are just some of the key questions you should ask when deciding on the best system for your needs:

  • To offset a shortage of skilled labour, find out whether the membrane and roofing accessories for penetrations can be prefabricated.
  • Determine the fabrication of the base material. Some materials have a lower carbon footprint, last longer and provide more benefits. Find out if temperature, moisture and dirt will affect the roof’s integrity.
  • Investigate whether there are any code considerations. What is the impact of the weight of the roofing? Are there structural concerns? Are there any aesthetic issues?
  • For the highest performance and lowest chance for error and incompatibility, a single supplier should supply all parts.
  • Ask if the flashings are prefabricated in a controlled factory setting, which is the preferred method. Or, are they fabricated in the field, where errors can be more likely? Are the flashings integrated with the system? Are the flashings included in the warranty?
  • Look over exclusions in the warranty. In particular, watch for fine print, which will suggest the weaknesses of the system. Make sure the warranty can be transferred with ownership. Be sure to request a copy to review before making a purchase, because some manufacturers require extensive care and maintenance for their warranties to remain valid.

Architects have long been leaders in reducing the heating and air-conditioning burdens caused by buildings. Installing a cool, reflective roof deflects solar heat from reaching into the building, thus reducing cooling needs. The use of PVC adds to the sustainability of the roof by providing a material that will not only last about 20 years or longer, but can be recycled at the end of that use. Using a PVC membrane for a cool roof system can go a long way in meeting the goals of a sustainability-minded architect or specifier.

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