Posted in Efficiency
What's Up With Attics Today?
In an effort to obtain efficiency and sustainability, some builders are sealing attics with spray foam. Turning the attic into a conditioned space for a home’s HVAC equipment can be an effective way to achieve efficiency, but it can also be costly. There are a number of alternative roofing sheathing systems that provide efficiency at varying price points.
“There are so many types of products you can put together to achieve energy efficiency. Spray foam is just one of them, and it’s not always the most cost effective,” said David Drew, OSB Technical Sales Manager at LP Building Products.
The use of a radiant barrier laminated to an OSB structural panel offers the inherent sustainable attributes of wood and cooler attic temperatures. A product like LP® TechShield® Radiant Barrier Sheathing can lower the temperature in the attic by as much as 30 degrees and reduce monthly cooling costs by up to 17 percent. With LP TechShield Sheathing’s patented post-lamination incising process, the panels can dry more quickly than other radiant barrier sheathing products.
The Oak Ridge National Laboratory has conducted tests that show the effect of a radiant barrier on the R-value of attic insulation in California’s climate zone 9, which is located in DOE climate zone 3. When combined with R-30 insulation, a radiant barrier increases the performance R-value of the attic insulation to a value of R-43, a 13-point shift. To achieve such an increase by upgrading the insulation itself in a 1,400-square-foot attic would cost the builder nearly $700 versus adding a radiant barrier like LP TechShield Sheathing at around $300 to $400.
A recent study by Oak Ridge provides yet another alternative to sealing the attic with spray foam: the combination of a radiant barrier and cool roof shingles.
“The Oak Ridge study shows that using a radiant barrier in conjunction with reflective composition shingles can provide the same efficiency as a foam-sealed attic at a much lower cost,” Drew said. “This is an excellent system in all but the colder climate zones. But even in the cooler months, tests have shown that radiant barrier roof sheathing helps the attic retain heat.”
Damon Roby, the winner of the 2010 APA Carbon Challenge, also found another method to achieve efficiency in the attic. Instead of sealing the space with spray foam, Roby utilized a radiant barrier in conjunction with R-30 blown cellulose as a part of his award-winning design. He then used 20-inch-deep floor trusses, allowing for the installation of all the ductwork in the floor system and further reducing the load on the cooling system.
“With this design I wanted to dispel the idea that you have to use spray foam to be sustainable,” Roby said. “You can’t look at spray foam as a fix all.”
And Roby’s right, there are other options. From a building science perspective, there are a number of ways to achieve efficiency in the attic, and people across the industry are at work developing alternative systems every day.
You can read a summary of the Oak Ridge study here.
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