What's more energy efficient for warmer climates: shingles or a metal roof?

Asphalt shingles tend to absorb a lot of heat, which often seeps into the structure below.
Asphalt shingles tend to absorb a lot of heat, which often seeps into the structure below.
©iStockphoto.com/BanksPhotos

If someone dared you to walk across hot asphalt or hot metal -- barefoot -- you'd probably have a hard time deciding which would be worse. Well what if they were talking about climbing up on a tar-shingled or hot-tin roof? It's still a close call. When it comes to which material can keep your home the coolest from the top down, though, one is definitely a hotter pick for keeping cool.

Asphalt shingles are the traditional choice for roofing in North America. In the Southwestern United States and in Florida, as well as Spain, Mexico and Greece, terra cotta and white tile roofing cover much of the housing landscape, but in most parts of the West, shingle roofing made of asphalt and fiberglass is still most common [source: InterNACHI]. These shingles are thin, flat rectangles that cover a roof in layers, with overlap areas to prevent any gaps. Nails and tacky backing secure pieces of shingling onto a roofing surface of plywood covered in roofing felt, or tar paper.

When it comes to metal roofing, we're talking about more than just the corrugated tin roofs that might come to mind. Today's metal roofing is available in various shapes, sizes and textures that resemble traditional roofing materials -- from asphalt to slate to wood -- and it also comes in large, pre-formed panels. Steel, aluminum, copper and even stainless steel roofing systems are available. Installation involves matching the seams of panels and snapping or locking them together. Shaped tiles resembling the rectangular asphalt type are also available.

Both metal and asphalt roofing get the job done when it comes to sheltering a building, but they really part ways when it comes to durability, energy efficiency and cost. Asphalt shingles absorb a lot of heat, and that heat doesn't stop at the roofline; it streams into the structure and increases the indoor temperature by 20 to 25 degrees [source: Florida Solar Energy Center]. Metal roofs, on the other hand, reflect the sun's heat away from a building, leading to energy savings of about 50 percent, and they can be about 100 degrees cooler on the surface than traditional asphalt roofs [source: MRCA]. A shingle roof also weakens and curls over time, making it less of a full-proof barrier for the effects of rain, wind and other environmental forces, and necessitating roof maintenance and earlier replacement. A metal roof doesn't take in all of the heat, it is very resistant to the elements when installed correctly, and it lasts much longer, needing little if any maintenance.

So which roof is more energy efficient in warmer climates? By far, it's metal roofing, but how does it work?

Hot Tin Roof?

Chickens and cows have long roosted and roasted under corrugated tin roofing. As an inexpensive and long-lasting material, metal covers agricultural out buildings, factory and industrial sheds, and makeshift housing. But plunking a big expanse of tin or other sheet metal over support walls isn't likely to yield energy savings, or much comfort for that matter. Metal has a high conductivity -- it holds a lot of heat -- and if it's dull and angled without taking advantage of reflectivity, heat will simply settle in and the space beneath will become like an oven.

Many scout groups and science classes experiment with reflectivity. Holding a mirror at an angle where it reflects the sun downward onto a flammable surface, such as a patch of dry grass, can start a fire if you wait long enough. That's how powerful the sun's reflective energy is. Holding a magnifying glass over dry grass on a sunny day magnifies the rays and can also start a blaze from the heat energy.

Modern, energy-efficient metal roofing acts as a giant mirror of sorts by reflecting the heat and energy up into the air. A white or light-colored metal surface reflects best under testing, at about 67 percent reflectivity, and even some newly developed "cool colors" send the rays away [source: Florida Solar Energy Center]. And while asphalt tiles don't have the power of a magnifying glass, they do intensify the heat from the sun by holding it long after the sun itself has called it a day. Dark shingles, with a lower reflectivity of about 22 percent, tend to release the heat into the structure's surrounding air below and make it warmer [source: Florida Solar Energy Center].

Of course, not many people would want a giant mirrored surface on the top of their lovely home, but most do want the energy savings or a break from the white noise hum of constant air conditioning, and that's more than achievable with today's metal roofing. With fitted whole-panel to single shingle-like designs, metal roof systems have come a long way from the backyard coop. Whether formed from the most popular steel and aluminum or the most expensive copper and stainless steel, metal roofs fit all housing and commercial architectural types.

But at what cost? Next we'll look at the green and "how much green?" aspects.

Precious Metal

Metal roofing costs more than shingle roofing, but the investment pays for itself with more savings in the long run.
Metal roofing costs more than shingle roofing, but the investment pays for itself with more savings in the long run.
©iStockphoto.com/Terry J Alcorn

Metal roofing costs at least two to three times more than shingle roofing. It costs less than slate or some premium woods, but it is initially a larger materials and installation investment than traditional shingles [source: Metal Roofing Alliance]. Long term, however, the savings add up with some tax credit options, widespread insurance breaks and longer warranties [source: MRCA and Metal Roofing Alliance]. Additionally, a metal roof is fireproof, requires little maintenance and is better for the environment because it decreases the need for running air conditioning and cooling systems.

If all of this sounds really great, there are some points to consider before you let just anyone start slinging hammers, including the following:

  • Installation is important: Moving forward with metal means hiring the right people for the job. Poorly installed metal roofing is less efficient metal roofing.
  • Value and time: Cost-savings won't be apparent immediately. Long-term savings and the possibility of a lifetime roof are appreciable, but only if you plan on staying in a property for many years.
  • Most places are moving in a green direction: Many regions have requirements for energy efficiency in new construction, and metal roofing has a wide range of options and ENERGY STAR ratings for meeting building codes.
  • Conscience and cost: Many individuals choose to pay more for the betterment of the environment, and metal roofing is one way to decrease the negative effects of dark roofing and energy overuse.
  • Waste not, want not: Metal roofing cuts down on waste in landfills because it is most often installed over the existing roofing, eliminating the need to dispose of the traditional tar-laden shingles.

Replacing or repairing a roof in warm climates will probably always be a hot job for the people doing the work, but metal roofing has some pretty cool payoffs. Check out the resources on the next page to find out more.

Related Articles

Sources

  • California Energy Commission, Consumer Energy Center. "Frequently Asked Questions about Cool Roofs." 2011. (Jan. 7, 2011)http://www.consumerenergycenter.org/coolroof/faq.html
  • Cool Roof Rating Council. "What's So Cool About Cool Roofs?" McGraw-Hill Construction Continuing Education Center. March 2009. (Jan. 7, 2011)http://continuingeducation.construction.com/article.php?L=68&C=488&P=1
  • Distinguished Contracting Group. "Metal Roofing." 2008. (Jan. 5, 2011)http://www.dcgflorida.com/roofing-basics.html
  • Encyclopaedia Britannica. "Roof." Encyclopaedia Britannica Online. 2011. (Jan. 2, 2011)http://www.britannica.com/EBchecked/topic/509178/roof
  • Florida Solar Energy Center (FSEC). "Energy-Efficient Design for Florida Educational Facilities." 2007. (Jan. 9, 2011)http://www.fsec.ucf.edu/en/publications/html/FSEC-CR-1682-00/images/e-dsn-3.htm
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  • Metal Roofing Alliance. "Frequently Asked Questions." 2011. (Jan. 7, 2011)http://www.metalroofing.com/v2/content/about/faq.cfm
  • Midwest Roofing Contractors Association (MRCA). "Beating the Elements: Metal Roof Sales Are Through the Ceiling." 2011. (Jan. 8, 2011)http://www.mrca.org/i4a/headlines/headlinedetails.cfm?id=277&pageid=3627&archive=0
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