Moisture problems aren’t just from water seeping down from roof leaks. Moist air rises up from the ground and comes in through any openings in the floor, walls, and ceiling of a mobile home. When the wet air hits a cool surface, it condenses into water droplets. If the surface is absorbent—like insulation and drywall—the water collects and builds up over time. Moisture is also created by indoor activities like cooking and showering.

   When you wait until you see speckles of mold below a window sill or feel a soft spot in the floor from wood rot, the fix can get expensive, because you have to both repair the damage and stop the water intrusion problem causing it. There are two ways to take preventative action: 1) improvement projects that make the home more moisture resistant and/or, 2) everyday lifestyle adjustments to decrease the amount of moist air generated inside the home.

   Here’s our “Top 10” list of ways to control humidity in your home, starting with a few improvement projects:

1) Install a ground cover. While HUD requires adequate openings in the skirting around a mobile home to ventilate the moist air rising up from the ground, the best preventative measure to keep moist air from accumulating under the home is a ground cover. The recommended product is a 6-mil thick polyethylene sheet (often referred to by the most popular brand name, “Visqueen”), rolled out in the area inside the skirting. The ground cover does not have to seal every square inch of soil. Cover the area the best that you can, and a 12-inch overlap is an acceptable alternative to sealing the joints. 

2) Seal any openings in the belly board. Think of it as an upside-down roof. The plastic sheet that wraps the bottom of a mobile home, called a belly board, provides a moisture barrier for the bottom of the home. We believe you should take it just as seriously as the roof. Tears in the belly board can happen while the home is being transported to the site, during installation, or as a result of being cut open to get access to the under-floor plumbing for repairs.

   Both mechanical fastening and a flexible sealant or tape should be used to secure the repair area. The best repair technique is to install a sheet of lightweight sheathing within the belly opening above the hole, mechanically fasten (staple or nail) the torn area to the sheathing, apply a sealant to the edges (mastic, caulk or adhesive tape), then cover the whole area of the tear with a scrap piece of belly board that is also mechanically secured and sealed.

3) Make sure the dryer exhaust duct is well supported and extends out from under the home. It should slope downhill without any sags (where occasional water condensation could accumulate), so you may want to add additional support along the run. Also, the duct should end at a rigid exhaust collar on the outside of the skirting, with a hinged closure flap. Check the duct occasionally for lint buildup, especially behind the termination collar and at any bends in the duct. A dryer duct that terminates under the home, as at right, also cannot be checked for lint clogs, which starts hundreds on house fires in the U.S. each year.

4) Seal openings in the floor, walls and ceiling. Caulk works best for smaller cracks around windows, doors, and ceiling light fixtures. An insulating foam sealant (“GreatStuff” is one popular brand) is better for larger openings and where a neat seam is not important. Pay special attention to sealing around the base of bathtubs and showers, where spilled water might leak through the floor and be trapped under the floor by the belly board. 

   Also, the Manufactured Housing Research Alliance recommends the following measures to decrease the amount of moisture generated inside the home:

5) Eliminate moisture problems at the source. Many moisture problems begin with excess amounts of water dumped into the air by common household activities, such as cooking and bathing. Ventilation fans should be turned on during such activities. They should be left on for a short time after the moisture producing activity ceases.

6) Do not use unvented propane, kerosene, or other unvented combustion heaters. About a gallon of water vapor is released into he air for every gallon of fuel consumed. This is a significant source of water vapor that can quickly cause damage. Some unvented heaters can also increase pollutant levels and contribute to health problems.

7) Do not cover or close off floor or ceiling vents (registers). In many homes, air from the heater or air conditioner is distributed through registers in the floor. Covering these registers with furniture or rugs can imbalance the system and create cold spots on room surfaces, increasing the potential for moisture condensation. Closing ceiling registers will cause the same problem. Also, closed or obstructed floor registers corrode from moisture condensation.

8) Check your cooling equipment filter monthly. Clogged filters can interfere with an air conditioner’s ability to removed moisture from the air, and in some cases interfere with condensate drainage. Dirty filters should be cleaned or replaced. Consider using pleated filters for better dust control and better dehumidification.

9) Keep the thermostat set above 75º F in hot, humid climates. Keep the thermostat setting at or above 75º F in the summer. In high humidity climates, a lower setting could cause water to condense inside wall cavities.

10) Recognize signs of moisture problems. Big moisture problems start as small ones, and any moisture problem is more easily cured if discovered early on. The following are warning signs of possible moisture problems: persistent, musty smells; discoloration on walls or ceilings; swelling of floor, wall, or ceiling finishes; condensation on window glass; or standing water under your home.

    If you think you smell mold and need to find it, see our blog post How do I look for and find mold in my mobile home?

   To learn more about controlling moisture in your mobile home, click on the link below to download the complete manual Moisture Problems in Mobile Homes - Understanding Their Causes and Finding Solutions.

                                         MHmoisture.pdf 

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Want to learn more about inspecting
manufactured/mobile homes? 
Get our  Handbook for 
Manufactured Home Inspectors 
at amazon.com for $19.95

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Here’s links to a collection of our blog posts about MOBILE/MANUFACTURED HOMES:

• Where can I file a complaint if I have problems with my new or used manufactured/mobile home in Florida?

• What are the most common defects in mobile/manufactured home foundation piers?

• How do I determine the age of a very old mobile home?

• What is a "HUD label verification letter" for a mobile/manufactured home?  

• When did a ground cover vapor barrier (plastic sheet) become required under a mobile/manufactured home? 

• Is it safe to go under a mobile home? 

• Are older mobile homes unsafe? 

• What do I need to know about buying a foreclosed mobile home? 

• Does it make sense to buy an older mobile home and remodel it? 

• Where do I find the vehicle identification number (VIN) on a mobile home? 

• How do I find out how old a mobile home is and who manufactured it?

• What is the right price for a used mobile home?

• How energy efficient is a mobile home?

• When were the first double-wide mobile homes manufactured?

• How do I upgrade my old (pre-1976) mobile home to meet HUD standards?

• What size air conditioner is right for my mobile home? 

• Can you move an older mobile home in Florida? 

• What does the HUD tag look like and where do I find it on a mobile home? 

• Can you put a zone 1 mobile home in Florida?

• How can I remove water under my mobile home?

• What's the differences between a trailer, a mobile home, a manufactured home, and a modular home? 

• What is a D-sticker mobile home? 

• What are the tie-down requirements for a mobile home?

• How fireproof is a mobile home?  

• Can I install a mobile home myself?

• What is a Park Model mobile home?  

• Does an addition to a mobile home have to comply with the HUD Code? 

• What walls can I remove in a mobile home?

• What can I do to prevent dampness and mold in my mobile home? 

• How can I tell if a mobile home is well constructed?

• How can I tell the difference between a manufactured home and a modular home?

       Visit our MOBILE/MANUFACTURED HOMES  page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.