As part of its new low-income weatherization program for manufactured housing, the Bonneville Power Administration (BPA) is requiring mechanical ventilation in dwellings that receive other standard measures despite the fact that there's no mechanical venting requirement for retrofits of low-income, site-built housing.

The venting requirement was put into the new program to satisfy federal regulations (from the 1992 National Environmental Policy Act) on indoor air quality. The BPA retrofit specifications are the same as those required for new manufactured houses in the Super Good Cents program. Using prescriptive specifications, a three-bedroom manufactured home must have equipment that provides a minimum air flow rate of 100 cubic feet per minute (cfm), has a sone (noise level) rating of 1.5 or less, and operates for a minimum of 8 hours per day. Performance-based ratings are somewhat lower; a minimum of 75 cfm for a three-bedroom house is required.

While the location of the fans is not specified by BPA rules, installers typically put them in bathrooms. Crews must also add an air-inlet port--a passive vent through a window or wall--to the main living area and to each bedroom. In real life, if a house already has a fan (in the bathroom), it's cheaper to use existing duct work than installing new ducting, roof jacks and wiring, said Roy Reinhart, a BPA engineer in the residential technologies section who helped write the new specifications. Crews almost never install added mechanical ventilation in the kitchen because the fans are louder and people are more likely to disable them.

Mason County Public Utility District (PUD) is managing a pilot program using the new BPA specifications. So far, 21 manufactured homes have been weatherized. About half had post-retrofit natural infiltration rates of 0.35 air changes per hour (ACH) or lower, according to program manager Kevin Nelson. These houses do not have a lot of insulation (compared to site-built houses), but they got down to a low rate of infiltration because of air sealing. The low infiltration rates can put people in danger if proper ventilation is not installed in the house, especially if the people use a wood stove.

Venting is needed to remove stale air and moisture caused by cooking, smoking, and pollutants such as formaldehyde, which are brought into the home with new furniture, carpeting, or plastics. Many low-income households also use secondary fuels or cooking stoves to heat their homes, burning unvented natural gas, propane, or kerosene, and making mechanical venting vital.

In site-built homes, insulating attics and floors has little infiltration effect; air sealing must be done as well to achieve lower infiltration rates. In manufactured houses, insulation alone will cut down significantly on infiltration, because ceilings and floors are cavities that can be packed densely. Insulation will have a greater impact than in typical site-built homes, according to Reinhart. This is especially true in many older mobile homes, which have ventilated wall cavities which are open at the bottom, allowing air to blow up and into the interior space. Packing the wall cuts down on the home's built-in ventilation system.

Mechanical ventilation is added to compensate for the loss of natural ventilation. Inspectors are being trained to look for the most common problems associated with degraded performance in ventilation systems, such as blocked exterior registers, reversed interior dampers, ventilation air pulled from the attic through fan housings, and small flex duct diameter. (A 3 in. duct can cut flow rates by 40% or more compared to a 4 in. duct.)

An even greater challenge in the new program will be getting the occupants to use the venting. Recent research in BPA's Residential Construction Demonstration Program has found that the most important variable affecting ventilation system performance is occupant control. The best ventilation system performance was found in homes where occupants understood how the system worked, believed it was worthwhile and operated it as it was designed, according to Mike Lubliner of the Washington State Energy Office. In the Mason County PUD pilot, installers programmed the fans initially, and inspectors reviewed the purpose and operation of the fans with the occupants.

Program Status

The BPA program began in October, 1992, but most utilities are still training auditors and inspectors about the program specifications, and haven't actually started retrofitting manufactured homes. Most utilities are moving ahead with the manufactured house program cautiously. They want to make sure they have a well-trained work force when they go out into the field, said Sharon Doggett, BPA Weatherwise program manager. Doggett also cited substantial backlogs of low-income site-built houses waiting for weatherization as a reason that the region has not actively pursued existing manufactured housing in its low-income weatherization programs.

From a regional perspective, retrofitting manufactured housing looks more cost-effective as a resource than in the past, for several reasons. Most manufactured houses are not mobile homes anymore--typically they do not move once they have been sited, and so efficiency investments in the sector are likely to remain in the region. Manufactured home residents are also a customer group we haven't been able to serve, said Doggett. New, longer lasting, and more cost-effective techniques are now being applied to retrofitting manufactured homes.

Besides the mechanical ventilation requirement, the low-income manufactured housing program differs from the site-built program in other ways. The program will not pay for window replacement, unless the original windows are jalousies. Some measures are installed differently, such as insulating under floors instead of crawl spaces. BPA is also paying a lower incentive to utilities for weatherizing manufactured homes. The power distributor will pay 80% of the measure costs, compared to 90% for site-built homes.

BPA is uncertain how many manufactured homes may eventually be served by the program. In 1992, BPA spent $21.7 million on residential weatherization programs for existing housing, and of that, $7.2 million was spent on low-income housing, according to Doggett. BPA estimates that almost one-third of the privately owned housing stock in its service territory is manufactured housing. Potentially, more than $2 million per year could eventually be spent retrofitting low-income manufactured housing in the region.

-- Maureen Quaid

Maureen Quaid is a partner in the Olympia Network, an energy and environmental consulting firm.