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Replacing Roofing, Siding, an Opportunity to Lower Energy Bills

05.08.2008
Are you planning to add a new roof or new siding to your home before winter?

Paul Fisette of the University of Massachusetts Amherst says that these home improvement jobs can be the perfect opportunity to boost your home’s energy efficiency and lower your heating bills, especially if you own an older home.

“Often a catastrophic event like water dripping from the ceiling can launch home improvement projects into high gear, but there is a lot you can do beyond fixing leaks and replacing worn exterior siding,” says Fisette, head of the department of natural resources conservation and an expert on green building. “A well-designed exterior retrofit will lower energy bills and improve the comfort of your home by eliminating drafts.”

According to Fisette, roof shingles need to be replaced every 20 years, and if your home needs a new roof, it is safe to assume that it also needs new, or at least better, insulation. “Homes built 20 years ago are under-insulated by today’s standards, since fuel was cheap then,” says Fisette. “Builders of that time didn’t devote much attention to insulation and air-tightness. High energy bills, drafty indoor climates and ice dams on the roof are all costly symptoms of these subpar designs.”

For most homes, an energy retrofit of the ceiling is fairly easy. Just climb into the attic, block all air leaks connecting the living space to the attic with foam insulation from a can, and increase the thickness of the insulation on the attic floor. You will need 12 inches of fiberglass or cellulose insulation to deliver the R-38 values recommended for much of the country. A good plan is one that provides a continuous insulation barrier between the attic and the living space below.

The situation gets more difficult in cape style homes and homes with cathedral ceilings, where sloped ceilings mean that areas between roof rafters are sealed by finished surfaces. Shallow roof pitches can also be problematic, since there may not be enough space between the rafter ends and the attic floor to install enough insulation. In these cases, insulation needs to be added after the lower edge of the roof has been removed, exposing areas that were inaccessible from the inside. Insulation products with a high R-value per inch, such as rigid foam, may also be required due to space constraints.

If your siding has also seen better days, replacing it can not only dress up your home, but can also be a way of addressing places where air leaks, holes and lack of insulation reduce your homes energy efficiency.

“At first, this process may seem simple; just strip off the old siding from the walls, replace any failing trim, and put up new siding,” says Fisette. “But this limited vision can lead to lost opportunities to increase the insulation in the walls.”

Fisette says he is constantly surprised by the number of old houses that don’t have enough, or any, insulation in the wall cavities. Many owners of older homes replace or add to the insulation in the attic, where it is fairly easy to reach, but avoid the more complicated enclosed-wall insulation. Filling these cavities with blown-in cellulose, fiberglass and foam when old siding is removed becomes much easier, since the insulation can be placed in the wall cavities through holes in the exposed outer sheathing.

This is also the time to repair loose sheathing, replace any rotten wood and patch all gaps, holes and seams with foam insulation from a can. Sealing around window and door openings should also be done at this time.

For maximum energy benefits, Fisette recommends wrapping the exterior walls with rigid foam insulation, which is available in sheets. The rigid foam can be attached to the sheathing with glue or nails, and seams should be taped. Since siding should not be nailed directly to the rigid foam, this process can get a bit tricky, requiring the use of vertical wooden strips attached to the foam sheets to serve as anchors for the siding. This creates an air space between the siding and the insulation. While it may seem like a lot of work, this method will provide a tight, dry and warm structure for many years.

Fisette says that payback times are the most common question posed by homeowners, who wonder whether the cost of extra insulation will transfer into savings. “Payback can be very hard to calculate, since it depends on how much money is spent on improvements and a host of other factors, including climate, existing levels of insulation and fuel costs,” says Fisette. “Calculations on savings for adding insulation to the walls of a standard ranch house predict a five to 10 year payback.”

Paul Fisette | Newswise Science News
Further information:
http://www.nrc.umass.edu

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