In last week’s column, we discussed a number of ways to keep your roof cool, helping to keep your home cool and comfortable without air conditioning. Some of the measures, such as selecting light-colored roofing material or designing sufficient ventilation, are most appropriate when you’re re-roofing or building a new home.
What can you do to your home’s existing roof that is effective and easy?
Both insulation and radiant barriers can be installed in existing homes’ attics. Nearly everyone is familiar with insulation—fiberglass, foam boards, blown-in foam and other insulating materials are all available in Hawai‘i.
Insulation effectiveness is measured by its “R-value.” The higher the R-value, the thicker and more effective the insulation will be. For your roof, you want at least R-19. This would be about six inches of fiberglass, five inches of blown-in foam, or two inches of foam board. Insulation can be placed just under the roofing material, or on the “floor” of the attic, between the ceiling joists.
Besides insulation, you can add a radiant barrier in your attic. Radiant barriers are shiny materials that reflect the sun’s heat and keep it from entering your home. They can work in conjunction with insulation and can also do a pretty good job by themselves, especially if the roof is light colored and you have a well-ventilated attic. Some radiant barriers look like foil attached to a board. Others are simply a foil-like material that can be stapled to the roof framing. Another popular kind is two layers of foil sandwiching something that looks like bubble wrap—this kind provides some insulation as well as radiant barrier protection.
Radiant barriers are measured by their “emissivity,” or ability to keep heat from radiating down to your ceiling. A radiant barrier with an emissivity rate of 0.05 or less is recommended. Be sure to follow the manufacturer’s instructions; radiant barriers should have an air gap of at least three-quarter of an inch on the shiny side, and if you can have an air gap on both sides, that’s even better.
In partnership with the state’s energy office, the Maui Weekly provides this feature to help Valley Isle homeowners reduce their utility bills and increase their environmental awareness. For more information, visit www.hawaii.gov/dbedt/info/energy.