If your nose keeps catching a whiff of a musty smell around your manufactured home but you can’t track it down, the way to find out what’s causing the odor is to think like a mold spore. There are literally millions of spores floating in the air inside and outside your home—and everybody else’s home, for that matter—all the time, and they are always looking for good place to land, settle down and raise a big family. 

    But a mold spore needs three things in order to take hold and grow: 1) organic material, 2) high moisture, and 3) warmth. If any one of those three things are missing, mold will not grow; so, conversely, to look for mold you want to search for places that meet all three criteria.

    Unfortunately, mold thrives at the same temperature range that humans also like. It will even grow slowly in the near-freezing air inside a refrigerator, as anyone knows that has opened a forgotten bowl of cold leftovers. So, pretty much any temperature around the house will support fungal growth, and that narrows it down to organic material and high moisture.

    Organic material such as plywood and composite wood in floors and cabinets, the paper in drywall, and the wood structural framing is everywhere around a mobile home. Also, mold will grow on a thin layer of dust or soap residue on an inorganic material like metal or glass. This means the real focus of your search should be simply looking for moisture and areas of mold in places that are mostly likely to be wet. And it will probably be a location that is at least partially concealed, otherwise you would have seen it already.

    Here’s our Top 10 Places To Look for what’s causing that moldy smell:

1) Under sinks - Sinks can leak at the collar under the drain, the slip joints around the P-trap, the water supply fittings, or at the shut-off valve. A continuous small leak may not have any visible signs on the surface of the pipes. But, if you move away the stored bottles and boxes directly under the sink, you might discover a wet mess. It can get ugly fast when there is a continuous slow leak.

2) Base of toilets - When the wax seal at the base of a toilet begins leaking, it wets the plywood or OSB wood flooring surrounding it. But, if there is a non-porous floor covering like sheet vinyl, the wetness will not be visible. Feel around where the toilet contacts the floor and also look for any softness in the floor around the toilet that would indicate some wood rot.

3) Bathtubs and showers - The tub or shower does not have to leak in order for you to have moisture problem. Kids splashing water over the side of the tub or repeatedly showering with the shower curtain or door not completely closed can allow moisture to accumulate in the flooring.

4) Water heater - All water heaters leak eventually, and many manufacturers even tell you that in one of the warnings listed on the side of the tank. But the water heater in a mobile home is unique because it is usually in a sealed compartment that requires removal of multiple screws and several trim pieces in order to examine it. So it gets forgotten until it stops heating or starts leaking. But the leakage can cause a lot of damage and mold before it shows itself through the adjoining walls. We recommend checking your water heater every six months or so, even if there is no musty smell in your home.

5) Water-using appliances, like the dishwasher and washing machine - Look for leakage under the door and at hose fittings of dishwasher, and at the wall below the faucet box behind a washing machine. Also, peek under the home, looking for any bulges in the plastic belly wrap material that would indicate water pooling on it from a leak above.

6) Air conditioning duct leaks or registers that are closed off - When you close off the air conditioning supply vent (register) into a room, it creates back-pressure than can cause air leakage at the duct connection and condensate can form behind the vent which causes mold around it. Also, conditioned air leakage can occur from a loose connection of duct to register as shown below. Look carefully, because sometimes it is only dirt/dust accumulation from the leakage—or a combination of both.

7) Air conditioning temperature split too high - If the air conditioning system is cooling the air more than about 24º F below the temperature of the air in your home, condensate can form around the duct and just inside it, also leading to mold.

8) Indoor unit of an air conditioner - Most HVAC systems for mobile homes are self-contained “package units.” Everything is in one big box outside. But if you have what is called a “split system,” with an indoor air handler in a closet or compartment in your home, then leakage of the condensate water that is created by the system’s dehumidification of your home may be the problem. Check under the plenum under the indoor unit (example at right) and, if possible, examine the evaporator coils (below) for a wet gunk buildup on the surface of the fins that would breed mold and spread the smell around the house.

9) Roof leak - A roof leak over your living area causes a stain in the ceiling after just a few days. But if the leak is near the edge of the roof, it may run down the wall cavity. Examine your roof on a ladder from the edge, looking for any signs of missing or damaged shingles, corrosion spots on metal roofs, and damage at the weatherproofing “boots” that seal around the plumbing vent pipes that stick up through the roof.

 10) Trim at windows and doors - Unfortunately, some mobile home manufacturers do a sloppy job of installing the flashing and trim around windows and doors, which can be an extra-big problem when you have vinyl siding. When installed correctly, the channels drain rain water away from the wall. But incorrectly installed or damaged trim funnels water behind the siding. Look for staining or wetness around the bottom corners of windows and doors.

    If your search turns up visible areas of mold, congratulations! You have identified the location of the problem. But sometimes the mold is concealed inside a wall or under flooring, and you have to find a moist area, then investigate further. This may possibly involve removing an area of wallboard or flooring.

    Home inspectors use high-tech tools, like an infrared camera and electronic moisture meter, to evaluate suspected wet areas. But fingers are also exquisitely sensitive to wetness. “Your fingertips are a great moisture-sensing tool. And the best part is that you recalibrate them every time you wash your hands,” according to Joe Lstiburek, a nationally known professional engineer that does extensive research in construction methods and materials for Building Science Corporation. So, if the area looks suspicious, touch it to feel for wetness. Because any moisture in a material evaporates continuously until it is dry, and the evaporation cools the area where it is located, a moist spot will also be slightly cooler than its surroundings.

    Also, see our blog posts What can I do to prevent dampness and mold in my mobile home? and How can I prevent mold in my Florida winter home when I'm gone for the summer?

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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?

• What is a D-sticker mobile home? 

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

• What walls can I remove in a 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 MOLD, LEAD AND OTHER CONTAMINANTS and MANUFACTURED/MOBILE HOMES pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.