• Moisture-Plagued Southeast HUD Code Homes

A significant number of new manufactured houses built to HUD code and located in the hot, humid Southeast are experiencing moisture problems.  Soft wallboards, buckled floors, damaged wood molding, and extensive mold growth are the most common symptoms.  These problems do  not respond to the standard service and repair strategies for water intrusion.  (Please see Appendix D for sample problem home inspection trip reports.)

At the request of six manufacturers, 69 such moisture damaged homes were investigated from 1999 to the end of reporting year four (through March 31, 2003) to determine likely causes.  In Year 4 alone, 18 homes were investigated.  One-time blower door, duct tightness, and pressure differential measurements were performed on all homes.  Field data on ambient, crawlspace, belly and house temperatures, plus relative humidity levels were collected on a few of the homes.  Recommendations and reports were prepared for the manufacturers service, production, and design staff.  Field repairs were performed in most of these homes.  A general theme was found in the houses investigated.

• Air conditioner thermostat settings (typically 68° to73° F) set below the ambient dew point.
• Negative pressures across the envelope from high supply duct leakage (CFM @25Pa >10 per 100 square feet of conditioned floor area), inadequate return air paths, interior door closures, exhaust fans, or a combination thereof.
• Inadequate moisture removal from disconnected return ducts, continuous fan operation (air handler or ventilation), inadequate condensate drainage, oversized air conditioners, or a combination thereof.
• Moisture diffusion from the ground into the house because of poor site drainage, inadequate crawl space ventilation, tears in the belly board, or a combination thereof.
• Vapor-retardant in the wrong location (i.e., vinyl or other impermeable wall or floor coverings located on the colder surfaces).
• Recommended solutions provided to the manufacturers to eliminate moisture problems included:
• Maintain air conditioning thermostat settings above the ambient dew point (at least 75°F).
• Eliminate long-term negative pressures created by air handler fans or ventilation equipment.
• Tightly seal all ductwork and provide adequate return air pathways.
• Enhance moisture removal from the conditioned space by correct equipment sizing and maintenance.
• Eliminate ground source water and provide an adequate moisture barrier for the floor assembly.
• If possible, remove vapor barriers located on the wrong surfaces.

Research continues to determine if these steps will be sufficient to prevent problems even when  vapor barriers are incorrectly located in homes in the hot, humid climate.  Preliminary results are encouraging. One manufacturer has not reported a single new moisture problem in any of the homes produced since 2000 in a factory that previously had a significant number of problem homes.  Steps taken by the factory were inclusion of airtight duct systems (a zero net-cost increase), right-sized cooling systems (a negative cost), return air ducts from all bedrooms (a cost of about $15), installation of a ground vapor barrier (no change from previous practice).

Figure 54.  Wall cross section.

Homes of Merit: In 2002, researchers performed multiple diagnostic tests on a home located in Marathon, Florida that was experiencing "mold problems."  Researchers determined that the mechanical system was significantly oversized and that the home was operating under negative pressure when the system was operational.  The home's owner exacerbated humidity problems by leaving the fan in the "on" mode.  On-site relative humidity readings showed that indoor and outdoor relative humidity were the same, approximately 70%.

Palm Harbor Homes:  Palm Harbor Homes, James Hardie^®, and FSEC performed two separate drywall assembly tests to determine the cause of some moisture damage occurring in homes sheathed with Hardipanel. Hobo dataloggers recorded temperature and relative humidity measurements inside the assembled panels on eight different wall panel configurations. (Please see Figure 54).

Results determined that the unprimed, unwrapped sheathing performed best.  The painted drywall assemblies allowed the greatest moisture movement - or wall assembly drying.  (Please see Table 14.)  The vinyl-covered drywall held moisture longest, recording the slowest drying time.  Adding perforations to the vinyl reduced the drying time.  Though more perforations than the amount used in this test would be necessary to make this an effective option.

In 2002, two Palm Harbor homes with comfort problems were tested in Ocala and Okahumpka, Florida and one high bill complaint was investigated in Odessa, Florida.  Duct leakage testing and infrared imaging revealed a duct disconnect near the attic crossover in the Ocala home.  Inspections with the IR camera found no insulation problems in the Odessa home.  Ductblaster and blower door tests revealed airtight duct and envelope systems. Other than an oversized air conditioning system, there were no obvious reasons for the high bills.

Fleetwood Homes: In 2002, four Fleetwood factories in Southern Georgia were visited to investigate possible causes of moisture related building failures found in homes installed in hot, humid climates.  The factories were located in Douglas, Alma, Pearson, and Willacootche. (Please see Figure 55.)

Six Fleetwood homes, all in Florida, were tested for moisture and mold damage from April 2002 through March 2003.  All of the homes had damaged flooring due in part to a lack of ground cover and poor crawlspace ventilation. Damage to the floor in one home was exacerbated by a plumbing leak. Only one home had moisture damage to the wallboard material, and this home showed a history of thermostat settings below 72° F.  A report for each home was submitted to Fleetwood for corrective measures.  One additional high bill complaint in Cobb, Georgia was investigated during this reporting period.

Southern Energy Homes: During Year 2001, 12 homes were field tested in the Houma, Louisiana area.  Some of the homes had new moisture damage.  Others were rechecks of previous moisture problems already repaired by SEH personnel. FSEC inspectors reported improper repairs and recommended additional dealer and staff training.  An additional five homes were field tested in Houma during this reporting period, with another home in Mississippi and one in Alabama also field tested.

Figure 55.  Testing Results from Fleetwood Homes Plant in Alma, Georgia illustrate that tape sealed ducts can result in total (initial) duct leakage under Qn=<6% and that implementing mastic sealing without duct assembly improvements does not necessarily improve duct tightness.

Floor Decking Material Lab Tests: FSEC conducted initial investigations on manufacturers' floor decking materials, looking for ways to enhance the material's performance by eliminating moisture diffusion, floor warping, and mold/mildew. Over a dozen materials were tested without finding an effective product.

Blue Sky Foundation:  Blue Sky Foundation, in coordination with FSEC, conducted an evaluation of energy efficiency and the moisture damage potential in 16 North Carolina homes in the summer of 2001.  Blue Sky foundation proposed that the energy and moisture evaluation focus on the building envelope integrity, HVAC duct systems, and the moisture impact of unvented space heaters.  All of the homes in the study were manufactured models located in Carteret and Craven counties, each located on the North Carolina coast. Field teams gathered additional energy and moisture information from homeowners.

Only three of the 15 tested homes recorded moisture and/or mildew problems. Because of the small sample size, the results are mostly anecdotal and would need to be evaluated within a larger data set.  Planning for this is underway.   Data from the summer field program as well as the final report is now on the Internet at bluesky.inetogether.com/cgi-bin/show_page.cgi?mhousing.