Keeping a Mobile Home Cool

Do you know any source of information for placing a light-colored tarp over a mobile home, several inches above the metal (so as to create an air barrier) in order to keep the home cooler in the summer?

R. Taylor

Ron Judkoff, director of the buildings and thermal systems program at the National Renewable Energy Laboratory, responds:

The tarp does not create an air barrier. The purpose of such a tarp would be to shade the home from direct-beam sunlight. Any method of shading the home, and especially the windows, in summer would be of value. If the home is already shaded, the tarp will not help, and may actually make the home hotter by impeding natural ventilation. Different devices for shading windows include solar-shade screens, awnings, trellises, and well-placed trees and shrubs. Devices that shade from the outside are more effective than those that shade from the inside. The tarp you mention would be fairly expensive because you would need a wind-resistant structure. Fabric garages, carports, and semipermanent tents fall into the category of structure you would need. Most state energy offices have a weatherization program with experience on what works best in your particular climate.

Cool Roofs Too Hard to Find

We believe in home energy efficiency and are willing to lead the way for others, even if that means having to pay more or risk using "unpopular" building materials on our home. Our next big project is reroofing. We've read everything we could find written by Paul Berdahl of LBNL (including a section in No Regrets Remodeling) and sent requests for information to our local utility company, the League of Homeowners, and the EPA. We've searched more than a dozen Web sites of efficient product manufacturers, visited a local library and do-it-yourself superstores, and met with four roofing contractors. No one has been able to answer two basic questions:

1. Which specific manufacturers and contractors are building energy-efficient roofs in southern California?
2. Where can we see examples of such homes?

Please help us work through this maze. It should not be so difficult for willing consumers to become more energy self-sufficient.

Joe and Audrey Risser
San Diego, California

Dr. Lisa Gartland, principal of Positiv-Energy, a consulting firm based in Oakland, California, responds:

Thanks for your efforts to try to find cool roofing materials for your house. I'm sorry it's been so difficult for you, but I'm glad to hear that you're so interested in environmentally friendly building materials. Since you say you're not afraid to pay more for roofing materials, I've been told that Monier Lifetile has some new light colored tile products that will soon be (or maybe already are) certified as Energy Star Roofing products for sloped residential roofs. The sloped-roof Energy Star standard is not very rigorous--the product must have 25% reflectivity initially and maintain at least 15% after three years of use, versus 65% and 50%, respectively, for low-slope roofs. But I've been told the new Monier Lifetile products have reflectivities of around 40%, which is pretty good for this product type. These tiles are more expensive than shingles would be, but they will last much longer. One downside of tile for re-roofing is that you have to be sure the structure is strong enough to support the added weight. Some of the upsides are durability, fire safety, and a cooler roof.

Unfortunately, these products are currently being supplied to the Florida market only. The roofing marketers seem to believe only certain colors work in certain regions, so chances are these colors are not available in California--yet! The person to talk to is Donna Baldwin, Senior Marketing Manager at Monier Lifetile, at Tel:(800)432-2715 Ext. 142; E-mail: dbaldwin@monierlifetile.com. It would be great if you could express your interest--as a Californian--in getting these products to the West Coast! Now if we can only get the shingle manufacturers to start selling cool colored roofing products. The only other thing I've seen on the market for residential construction is some paint sold by Home Depot: Henry's fibered aluminum coating and a white paint called Henry's Solar-Flex White Roof Coating (see "Green Products Brighten Multifamily Rehabs," p. 34).

Btu Miscalculation

Another great edition (July/Aug '00), but I wanted to point out a possible large error in Larry and Suzanne's response about domestic hot water costs. They seem to have their calculations wrong. They have a therm being equal to 1,000 Btu when it should be 100,000. Also, for the numbers provided it should cost about $4.75 per delivered therm for propane and $3.91 per delivered therm for electric.

Chris Burns
Burlington Electric Department
Burlington, Vermont

Larry Weingarten replies:

We have egg on our faces. Your calculations are correct. However, the basic method for determining which is the least-cost form of heat still holds.

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