4 Passive Solar Benefits of Metal Roofing
When you get dressed in the morning, do you consider passive solar design principles? Probably not. At least not conciously. But I’ll bet you consider the weather as you choose what to wear? I do. If it’s going to be hot and sunny, I usually choose a light colored shirt that is made from a fabric that breathes. Experience tells me to avoid black because it will soak up the sun’s heat and avoid a tightly woven fabric because it will trap air next to my skin and make me feel hotter. This is a principle of passive solar design that we use without even labeling it or thinking about it. And you can use these principles in your house design.
Metal roofs, now often referred to as “cool roofs,” can act like your light colored, open weave shirt and keep your house cooler in hot weather. They do this “passively”, that is they use no electricity in the process. Here’s why they work. In an article posted at Classic Metal Roofing Systems website, they list four energy benefits you’ll get with a metal roof.
1. Thermal Mass. Mass is the “weight” of a material. Stone has more mass than wood because a chunk of stone weighs a lot more than a the same-sized chunk of wood. Heavy asphalt roofs have a lot more mass than metal roofs. The higher the mass, the more heat a material can absorb. Although metal can get quite hot to the touch, it does not store heat in its mass and it will give up it’s heat more quickly soon as the sun goes down, or behind a cloud, or even when a breeze blows. So just like your open weave shirt, the material will cool down easily. Aluminum is even better than steel in this regard.
2. Color. Just like your light colored shirt, a light colored roof will absorb less radiant heat. I wrote a blog post about how I use passive solar principles to help clear snow and ice from my driveway. And color was the key. Here’s a link to that article, if you’re interested: http://www.designingyourperfecthouse.com/blog/2009/01/passive-solar-design-on-my-driveway/
3. Reflective Pigment. In the Classic Metal Roof Systems article, they say “Many dark-colored metal roofs now have reflective pigments so that good reflectivity is achieved even in dark colors.” This means that you are not limited to a silver or white roof to enjoy the benefits of an energy efficient, highly-reflective roof.
4. Integral Airspace. Metal roofs do not lay tightly against the roof sheathing. This means that a gap of air is created that insulates the roof sheathing from conducted heat coming from the metal. This airspace acts like a trivet or a pad you might place beneath a hot pan to keep from burning the countertop or table in your kitchen. Asphalt roofs lay tightly against the sheathing and continually conduct heat into your attic or rooms below, adding to your air-conditioning expense.
No matter what roof material you choose, be sure to provide sufficient attic ventilation. Metal roofs do not replace this essential design feature. But metal roofs will keep your attic and house much cooler and keep your air-conditioning electrical costs down significantly.
Metal roofs tend to cost more, initially, than shingle roofs. I’m researching this and looking for ways to control the added costs. I’ll report on this in future posts. If you have any experiences with metal roofing and the energy benefits, please post a comment. I would love to hear from you.
If you would like to read more articles about house and home design, please visit my other website, www.about-home-design.com.
Tags: cool metal roof, energy efficiency, metal roof, Passive solar
December 7th, 2009 at 11:28 am
Just came across your helpful blog.
I invite you to drop by ours, share ideas, leave a comment, and join our community as a Follower, by clicking on FOLLOW link on right side bar.
Our project, THE CONCORD GREEN HOME, has a metal roof for many of the reasons you articulate in this post, and more.
Keep up the great work.
Lisa
October 9th, 2010 at 5:53 pm
Mr. Hirsch,
I’ve seen several comments about “well ventilated attic” across your blog. Can you give us your take on closed attic, expanded foam insulation systems in contrast to soffit and ridge vents?
Looking forward to your response!
-Bill Meredith
October 20th, 2010 at 3:55 am
I have being researching for some new and good ideas for building from last 3- 4 months for my new house and reading your blog, I found your post very helpful in this post i read the benefits of metal roof.
February 17th, 2011 at 7:56 pm
metal roofs offers lots of benefits. great post!Residential Roofing
March 2nd, 2011 at 12:02 pm
Bill – I see that I neglected to respond to your comment. I apologize. It must have gotten lost in the shuffle.
I like closed attics. They add some cost because they require additional insulation. But they work well and clearly help the energy performance of the house. But a sealed attic must be totally sealed and not just “sort of” sealed. Otherwise you can create a moisture problem. Seal the attic completely and treat it as interior space within the building envelope.
Regarding foam insulation, I find I can not get comfortable with that material. It does off-gas, even though they say it doesn’t. It adheres to the wood and sheathing so much that if there ever was a problem discovered about it’s health effects, there would be no way to remove it entirely from the house. And it is my understanding that it still has some petroleum product in it even when they sell it as containing soy. Since the product is so new and unproven, I recommend avoiding it so you won’t end up with a problem later on. It might be the great product they say it is. But I don’t think the benefits of foam are enough to warrant taking the risk of a future discovery of problems, like so many building products have presented over the years. Seal your attic with dense pack cellulose, instead.
March 14th, 2011 at 2:30 am
I am agree with you that Metal roofing increase the Airspace. It is really a big benefit. But With the advancement and the change in living styles of people, there has been a dramatic change in people’s preferences. With the increased choices, the demands have also increased. Building a home is one of an asset which you probably will build once in a lifetime, as the choices has changed people want to go for things that are in fashion whether they are regarding clothes, cars, furniture, home, shower doors etc.
May 31st, 2011 at 9:36 pm
i wonder if the extra cost for the metal roof will be made up for future buyers. Will the 2nd or third buyer down the road pay more for a home with a metal roof verses other material.
July 13th, 2011 at 10:40 pm
Metal roof really does have its benefits as compared to other materials that are normally used for roofing. That was a really good article, thanks for taking the time to put it together! You have managed to point out some very good points.