July 17, 2009 | Filed under: Roofing Help Podcasts
One the things I often talk about is the Energy Efficiency of metal roofing. The biggest Energy Efficiency for metal roofing occurs during the summer. There’s a number of ways through which a metal roof keeps in attic naturally cooler. If you keep that attic cooler… you’re going to keep the home cooler… which is going to reduce your need for air conditioning… which is going to save you money. And no one’s going to complain about that!
How much savings can you expect? Well, that’s a good question.
It’s not unusual for us to hear after someone has had a metal roof installed that they will have air-conditioning savings (electrical savings) during the summer months of up to 20%…or sometimes even more…so the Energy Efficiency can be significant. The big question is… how can you make your new roof be as energy efficient as possible? What are the ways in which a metal roof can be energy-efficient?
One of the big ways is the metal roofing has a very low thermal mass. Now if you think of a product like asphalt shingles, or if you think about clay tile, you realize you got a product there has a lot of thermal mass. That means that during the daytime it absorbs a lot of heat, and it continues to hold that heat and continues to radiate that heat into the home even after the sun goes down. That’s not good! Metal roofing on the other hand has very low thermal mass, meaning that any heat it does absorb during the day quickly dissipates (actually it dissipates not only when the Sun goes down, but it dissipates when the Sun goes behind a cloud, and it can even be carried off the roof just by a gentle breeze). So you’ve got this low thermal mass that helps keep a metal roof energy efficient.
Now one of the big advances in recent years though has also been the onset of coatings on metal roofs that have reflective pigment in them. This is available in most of the Kynar 500® and Hylar 5000® PVDF resin-based finishes today. Most of them are available with reflective pigment, which with old paint systems before reflective pigment was available you may have reflected maybe 3 or 4 percent of the sun’s rays. Well, with these reflective pigment finishes, we’re often reflecting 25 to 30, even 35 or 40 percent of the sun’s Rays. And that’s why I many metal roofs are actually EnergyStar rated for their reflection of radiant heat. Again keeping that attic naturally cooler during the summer months.
Now the other big thing that happens with many metal roofs (look at different styles that are formed to look like Cedar Shake, or Tile, or something that gives them some formation), if you really study those systems you realize that the metal itself is not laying against the roof deck. It’s not touching anything… you’ve got this dead air space between the metal and your roof deck. Well that dead air space is also incredibly effective at not allowing heat to be transferred down into the attic, because it blocks heat transfer by conduction. We all know what conduction is… one material gets hot… it touches something else, and it passes that heat along to that other material. Well the metal roofs that don’t have a lot of contact between the metal on the roof deck do not transfer that heat by conduction.
So, some things to think about as you’re looking at a metal roof …
- Make sure it has a reflective coating on it for maximum efficiency.
- Think about the systems that actually have an integral air space between the metal and the roof deck (because that also blocks heat transfer by conduction).
Kynar 500® is a registered trademark belonging to Arkema Inc.
Hylar 5000® is a registered trademark belonging to Solvay