I want to build a room addition with a cathedral ceiling. What is the best way to insulate that type of ceiling since there isn't an attic above it? T.J.
A - A cathedral ceiling is very attractive, but it requires careful design and construction to be energy efficient. Often, there are moisture problems in the winter and overheating in the summer.The key to building a room with an energy-efficient cathedral ceiling is providing adequate ventilation between the insulation and the roof sheathing. This allows for cooling and moisture control. It can also prolong the life of the shingles.
One effective method is to use 2x12 roof rafters (actually 11 1/4 inches high.) If you lay R-30, 9-inch-thick fiberglass batt insulation in between the rafters, this leaves a 2-inch air gap above it for ventilation.
Another option is to nail 1-inch thick rigid foam board insulation under the rafters. For the same R-30 roof insulation, you can use smaller lumber and thinner fiberglass batts, still leaving the necessary ventilation air gap above it. Using foil-faced insulation provides a good vapor barrier to block moisture.
With only one inch of rigid foam insulation, you can usually screw the drywall directly through the foam insulation into the rafters. If you use two inches of foam insulation, you should strap it with furring strips, or it may not look smooth enough.
For high levels of insulation, fill the rafters totally full of insulation.
Cover them with an air barrier film and nail 1x2 furring strips over it to provide ventilation clearance. Then nail the roof sheathing to the furring strips.
There are some new types of "ventilated roof" insulation panels that are ideal for insulating a cathedral ceiling. In addition being very energy efficient, they are simple to install. The panel itself has a R-value ranging up to R-26. This yields a total roof R-value of R-31.
These panels are designed with an air gap between the top roof sheathing and the rigid foam insulation attached to the underside. Cool air is naturally drawn in the bottom edge inlets and the hot air is exhausted out the roof ridge vent at the peak.
You can write to me for UTILITY BILLS UPDATE No. 383 showing diagrams of several cathedral ceiling insulation methods and a list of manufacturers and specifications on the ventilated roof insulation panels. Write to James Dulley, The Deseret News, 6906 Royal Green Dr., Cincinnati, Ohio 45244. Please include $1.00 and a self-addressed business-sized envelope.
Q - What is meant by time-of-use electric rates? I heard them being discussed on Earth Day. F.P.
A - Many electric utility companies offer lower electric rates during offpeak-usage times of the days. This is often at night when much industry and business is shut down. Contact your local electric company about time-of-use rate options in your area.
The electric company offers this discounted rate to discourage usage during the peak times. Therefore, it doesn't have to invest as much capital in excess generating equipment which is only occasionally used. In areas of the country that burn inexpensive coal, the extra generating capacity often uses more expensive diesel fuel-powered units.