Publication date: 08/24/2012

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Roof insulation options cover hot, cold theories

his summer's heat has put extra emphasis on the importance of proper attic insulation and its ability to help keep your home cooler.

But we have come a long way from the days of rolling out fiberglass insulation in our attic, and one of the topics of discussion these days in insulating the attic is the hot roof versus the cold roof theories.

Most homes in our area feature the cold roof version, which calls for proper insulation and ventilation to protect homes from heat loss in the winter and keep it cooler in the summer.

The theory is that the insulation provides a thermal barrier, while the stream of air coming in through the attic's soffit vents and going out through roof or ridge vents keeps the roof deck cool year round.

So when you hear me talking about upgrading your attic insulation to R-49 level and making sure you have the proper ventilation, I'm talking about the cold roof theory.

But over the past decade, another type of attic insulation process, the hot roof theory, has become popular. With the hot roof, the attic is completely sealed and is unvented. The soffit areas are packed with insulation and the attic walls and roof deck (ceiling) are coated with sprayed on foam insulation.

Besides the obvious difference of a vented versus unvented attic and roof deck, there are some other things you need to consider before deciding which insulation method is best for your home.

The Oak Ridge National Laboratory, www.ornl.org, in Tennessee tested properly vented versus total sealed attics and found some interesting results. The tests showed that a properly vented cold roof only reduced the roof deck temperature by 3-5 degrees Fahrenheit.

In comparison, the hot roof had an attic temperature that adjusted to within 10 degrees of the ambient temperature of the house. That compares to the vented attic that typically reached 130-140 degrees.

While we are focused on the temperature of a roof deck in the summer months, it is also important in the winter when there is snow on the roof that could lead to ice dams. In most cases, a properly insulated and ventilated cold roof shouldn't have ice dams or icicles along its eaves.

However, a hot roof causes accumulated snow to melt gradually, and when the water reaches the eaves it can refreeze and build up as an ice dam.

Gary Kearns of Kearns Brothers, (888) 355-6700, www.kearnsbrothers.com, said that hot roofs are more common in homes with cathedral ceilings or in older homes that have floors in the attic and are used for storage, and having layers of insulation is not an option.

However, there are some potential issues that can arise with the hot roof.

"If there isn't 100 percent fill in a hot roof, it can lead to air pockets developing and causing condensation and delamination of the OSB boards or plywood that make up the roof deck," he said. "That could cause issues with the roof shingles."

Obviously, anything that impacts your roof shingles leads to talk of the shingle warranty. According to Martin Grohman, director of sustainability for GAF, (973) 628-3000, www.gaf.com, one of the leading makers of roof shingles, having a hot roof doesn't void the shingle warranty.

"If a homeowner has a hot roof with foaming that is done properly, our shingle limited warranty against manufacturing defects will remain in effect," Grohman said. "However, any damage to the shingles attributable to using sprayed-in-place insulation directly applied to the roof deck or due to lack of ventilation is excluded from GAF's responsibility under the terms of our limited warranty."

The same is true for some metal roofs. Frank Farmer of American Metal Roofs, (866) 763-9117, www.americanmetalroofs.com, said that a hot roof won't void the metal roof's warranty, unless the hot roof causes additional roof-deck issues.

"If the foam is not sealed perfectly, the seal could break and it could shrink and lead to moisture and delamination," Farmer said. "That could cause the roof nails to loosen, which could lead to an issue with the warranty."

So before you decide whether the hot or cold theory is best for your home, do your homework to find out about your shingle warranty and consider the space constraints in your attic. Then get some advice and estimates from attic insulation contractors.

If you would like to suggest a question for this column, email askglenn@masterhandyman.com. If you want to talk to Glenn Haege personally, call his “Handyman Show” on WJR-AM (760) at (866) ASK GLENN, (866) 275-4536 between noon and 2 p.m. Saturday and Sunday.

Note: This article was accurate at the date of publication. However, information contained in it may have changed. If you plan to use the information contained herein for any purpose, verification of its continued accuracy is your responsibility.

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