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August 10, 2006
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Special Advisory: How to Avoid Mold and Moisture Problems

Water, in several of its many forms, flows into, under and onto most of our houses on a constant basis. Plumbing pipes wind through the house, hidden behind walls.

Excess bathroom humidity gets vented in one direction. Tubs, sinks and toilets drain in another.

The home's heating, cooling and ventilating system quietly controls indoor humidity for optimal comfort, year in and year out.

The house sheds rainwater and snow off the roof, through downspouts and gutters.

Groundwater moves under or around the foundation walls.

The structure itself absorbs and releases moisture vapor and condensation across the seasons.

In a well-built and maintained house, water is a comfort and a health-sustaining element that presents no problem. But, if water, in any of its forms, isn't properly managed, or if your home's water management systems aren't properly maintained, not only will your home lose value - it can lead to serious expense, health problems, structural damage, and the loss of valuable personal property.

Watchfulness and regular maintenance are a homeowner's keys to preventing moisture and mold problems from developing in the home. Use these handy checklists to go room-by-room and check for the tell-tale signs of undesirable moisture intrusion.

If you see any of the warning signs, take steps to have the source of the problem eliminated immediately. Some jobs are easy and you can do them yourself. Others may require additional help by a professional to assess or repair.

Either way - don't procrastinate! Have moisture problems repaired immediately. The longer you wait the more expensive and possibly even damaging the results will be.

Moisture Damage Warning Signs In the Kitchen

Moisture damage can begin in lots of areas of this high-use room!

Around and Under the Kitchen Sink Look For:

  • A steady drip at the faucet or in the trap beneath the sink
  • Broken or missing tiles around the sink
  • An unsealed edge at the bottom of the back splash behind the sink
  • Any dampness or stains on walls or cabinetry where plumbing pipes pass through

Maintenance Tip

  • Use a drain opener in the sink periodically even if it isn't backed up.

Around the Dishwasher Watch For:

  • Water left in the dishwasher after its cycle, which suggests a possible clogged drain or main filter
  • Signs that the dishwasher drain sometimes overflows into the sink, which indicates a possible clogged drain line
  • A trickle of water beneath the dishwasher sometimes, that could mean there's a leaking water hose

Maintenance Tips

  • Check the vents and drains from the dishwasher.
  • Replace hoses with braided hoses and new hose washers.

Under and Behind the Refrigerator Look For:

  • Even a small leak from the icemaker supply line

Maintenance Tips

  • Vacuum the refrigerator coils periodically.

Moisture Damage Warning Signs In the Bathroom

Around the Toilet Look For:

  • Leaks around the water line
  • Signs of staining or mushiness in the flooring around the rim seal, which indicates a leak

Around All Plumbing Lines Watch For:

  • Sounds of dripping in the wall
  • Dampness on the walls in the bathroom or the adjoining room
  • Leaks or dampness under the sink

Maintenance Tip:

  • Go to the basement and inspect the ceiling directly under the bathtub for signs of slow leaks.

Around the Exhaust Fan Look For:

  • Any signs that the fan has stopped working or has been disconnected
  • Any signs of dampness on the walls around the fan

Maintenance Tip:

  • If the fan doesn't currently come on automatically when entering the bathroom, consider having the wiring changed so that it will.

Around and In Showers and Bathtubs Look For

  • Any signs of missing, warped or broken caulking around the bathtub
  • Any cracked tiles or missing grout
  • Any sign that water stands in tub after emptying

Maintenance Tip:

  • Treat all bathroom drains regularly to prevent hair buildup and clogs.

Moisture Damage Warning Signs In the HVAC System

It's easier - and less expensive - to prevent moisture damage in or resulting from your heating, ventilating and air conditioning system that to repair it. Here's what to keep an eye on.

What to Look for in the Heating System

  • Filters are virtual incubators for possible mold growth and should be changed every month.
  • If you have a gas heating system it probably generates water as a side effect of combustion. Be sure any moisture has a proper place to drain.
  • If you have a boiler system, first be sure there is free air flow to the exterior. Look for any signs of rust. Also, be certain there are no loose fittings.
  • If your furnace has wall penetration for fuel or electrical, check the wall seals for any signs of moisture.
  • Ductwork is another breeding ground for mold. Be sure to have your ductwork professionally cleaned every five years. If you have pets or smokers in the family, do it every three years. Vacuum the air supply registers regularly.

What to Look for in the Cooling System

  • Since heating and cooling systems frequently use the same ducts, everything you should do to prevent moisture damage in a heating system duct applies to the cooling system.
  • Look behind the filter when you replace it to see if the heat exchanger coils need cleaning. If so, use the soft brush of the vacuum.
  • Clean the drain pans regularly and, when the seasons change, pour a few tablespoons of bleach mixed in hot water down the drain to clan and disinfect it.
  • If your air conditioner coils "ice up" it's not a good sign. Call a professional.

Moisture Damage Warning Signs In the Utility Closet

A room that contains a water device, such as a water heater, deserves looking into regularly.

  • Look for any signs of rust.
  • Watch for tiny leaks, which are the early warning of an impending catastrophic tank failure.
  • Be sure the floor around the tank is unstained and dry.
  • Look at the valve, drain pan and pipe for signs of rust or staining.
  • If your water heater is gas-fired, look for any signs that the exhaust vent and shield might be mal-functioning or out of position.

Moisture Damage Warning Signs In the Attic

You may not go into the attic very often, but it's worth the trip because so many expensive water damage problems start at the roof!

Around the Attic Vents Look For:

  • Any indications that the wood or insulation near the vents has been wet
  • Any looseness in the vent hardware or attachment to the wall or roof

Around Recessed Lights Look For:

  • Any sign of rust or corrosion around the canisters
  • Any color differences or stains in the wood and insulation around the canisters
  • Any signs of moisture or mold stains

At All Roof Penetrations Look For:

  • Any signs of wetness or stains around the chimneys, plumbing vent pipes, skylights, radon vents
  • A damp or musty odor
  • Any indications of mold or rot

In the Insulation Batting Look For:

  • Any areas that don't look fluffy and thick any longer
  • Any signs that the insulation close to the eaves is less thick or puffy than it is near the middle?

In Attic HVAC Systems Look For:

  • Any signs that the drain pan is clogged
  • Any indications that ductwork insulation has come loose or has lost its tape

Moisture Damage Warning Signs In the Laundry Room

By definition, laundry rooms are warm and moist. Small wonder it's a prime location for moisture and mold problems. If you spot any of these warning signs, take steps to correct them.

What to Look for at Hose Connections

  • Look for leaks - even tiny ones - at both ends of all water connections.

What to Look for at the Dryer

  • Check to see if the dryer hose connection is loose - especially where it vents to the outside.
  • Watch for too many turns or twists or in the dryer vent, which can prevent it from venting properly.
  • Check to see if lint is collecting beneath or behind the dryer.

Maintenance Tips

  • Wire-wrapped hoses prevent hose failures much better than plain rubber ones and last a very long time. Don't forget to replace the hose washers, too!
  • Use drain treatments in the utility sinks BEFORE a clog happens, as part of your periodic maintenance routine.
  • When you vacuum the rest of the house, be sure to include the laundry room.

Moisture Damage Warning Signs In the Basement

It pays to keep a sharp eye out for uncontrolled moisture or water stains in the basement. It can help you detect developing water problems in other parts of the house, including gutters and bathrooms. In addition to being a breeding ground for mold, damp basements also attract unpleasant things such as bugs, rodents and snakes!

  • Watch for "sweating" pipes with beads of moisture. Dripping water can lead to mold. It's best to insulate the pipes.
  • Be sure all ductwork is well taped and sealed. Exposed joints can lead to serious moisture problems.
  • If the HVAC system is in the basement, be sure the drain pan is clean and that it drains well.
  • Check the seals on all dryer vents, electrical, phone and cable and plumbing penetrations through the basement walls.
  • Look up at the floor above the basement for any signs of moisture or stains.
  • Be alert to how frequently your sump pump cycles on and off. Frequent running is a major warning sign of a developing water problem elsewhere, in a gutter, landscape drainage or other water management dysfunction.
  • If you have a crawlspace, keep an eye out for any signs of dampness or stains on the walls.

Moisture Damage Warning Signs On the Exterior of Your House

Watch Out for Poor Drainage

  • Ground that slopes toward the foundation is a red flag for water problems.
  • Gutter drains that don't open at least five feet away from the house are an invitation to water problems.
  • An unsealed, or cracked driveway can allow rainwater to move toward the foundation, which is why regular driveway maintenance is so important.

Watch Out for Trees

  • Limbs and leaves that touch the house can hold moisture against the roof or siding and lead to serious water damage.
  • Tree roots can clog septic fields and drain lines.

What to Look for in the Windows and Doors

  • Loose flashing
  • Cracked or old, stiff sealants
  • Indications of moisture beneath the windows
  • Doors no longer fit tightly against weather stripping
  • Locks no longer hold the doors firmly against their seals

What to Look for in Siding and the Walls

  • Unpainted, exposed, damp wood
  • New or previous termite infestation, which attracts moisture
  • Cracked caulking
  • Leaks at hose bibs
  • Any missing seals at wall penetrations

Mold and Mildew

General Subject Information: Mold and mildew (fungi) and the spores by which they reproduce are present everywhere in the environment, including indoor air and surfaces of buildings. Usually the small numbers of these tiny organisms do not cause any problems. However, high levels of moisture combined with organic materials provide conditions that can result in their rapid growth. In high concentrations, some of these fungi may consume wood and other building materials sufficiently to cause decay and rot. Others may produce stains and unattractive coatings on interior and exterior surfaces. Some people can develop allergy-like symptoms if exposed to mold. While it is quite difficult (if not impossible) to entirely eliminate these organisms in normal residential environments, control of interior humidity and preventions of leaks limits their growth and minimizes any resulting affects.

There are thousands of types of molds and mildews. A limited number of varieties are commonly associated with damage to buildings. Under conditions favorable to growth, these fungi can form dense colonies that may be visually unattractive. Of all the known varieties of mold and mildew, only a few are believed to pose health hazards. Among these few are "stachybotris chartarum" which can produce toxic mycotoxins. In the few varieties of mold and mildew that are believed to produce adverse health effects, concentrations must be relatively high to affect most healthy individuals. It is important to note that at the present time, there are no accepted federal, state, or local health-based standards for permissible exposure to mold and mildew. Nevertheless, whether it is believed that the potential for ill affects is little or large, it is universally accepted that houses should be kept as free from mold as possible.

Some common areas for mold and mildew growth in the typical residential environment are: 1) around window frames. Condensation or leaks often occur at window frames if the residence is tightly sealed and inadequately ventilated and if the temperature is colder outside than inside; 2) at and near toilets, sinks, and tubs (anywhere water splash and leaks are likely to occur); 3) in basements and other spaces which are below ground level, when drainage and/or waterproofing of walls is not adequate, or is failing due to age or lack of maintenance; 4) anywhere two or more pieces of wood are tightly fitted together, and water can get between them (typical examples are unflashed wood trim around windows and doors, wood railings and caps with open miter joints, and failure to maintain caulking in these areas); and 5) in poorly ventilated and damp enclosures.

Sometimes mold will grow in enclosed (not visible) locations, such as the cavities at exterior walls. If the building construction or lack of maintenance allows water to leak into wall cavities, mold can grow in the affected areas. Resulting damage can progress unseen for some time. Aside from gray or black stains and blotchy patches that are readily identifiable as mold, signs that should help identify some potential problems include softness in drywall, water stains at walls and ceilings, damp carpets, buckling or swelling of exterior surfaces, and a persistent musty odor. These are possible indications and do not prove that mold or mildew exist. The actual existence of mold and mildew must be established by visual observation and, in some cases, by appropriate testing and expert inspection.

Recommended Use and Maintenance:
Familiarize yourself with strategies to identify, minimize, and prevent mold growth. Watch for and eliminate condensation on walls, around windows, and other cool places. Indoor humidity should be kept low by proper use of ventilation devices. Generally, a relative humidity of 60% or less should limit condensation-caused mold. The following are thirteen essential Maintenance and Use Recommendations for mold and mildew.

  1. Vacuum and clean regularly. Use mold-killing products while cleaning bathrooms.
  2. Use air conditioners and dehumidifiers, especially in hot, humid weather. Clean dehumidifiers often. Empty them daily or have the appliance drip directly into a drain.
  3. Vent clothes dryers to the outside.
  4. Keep attics and crawl spaces ventilated and insulated.
  5. Clean refrigerator drip pans regularly according to manufacturer's instructions.
  6. Inspect and maintain air conditioning and heating systems on a periodic basis. Clear out or repair the condensate line if the air conditioner's drip pan overflows.
  7. Promptly dry any damp or wet indoor areas. This includes shower stalls and tubs.
  8. Always use vent fans in baths, kitchens, and laundries. Keep the vent fan running for 15 to 30 minutes after use of room to assure condensation is adequately removed. Open windows whenever possible.
  9. If mold or mildew begins to grow around the edges of window frames (where condensation is the cause), remove it promptly with a detergent / water mixture and a disposable rag.
  10. Establish / maintain roof drainage into gutters and downspouts. Maintain the ground slope away from the house foundation.
  11. Repair leaks as soon as they are discovered. Keep in mind that mold can grow within 24 hours after the start of a leak. Proper homeowner inspections and prompt maintenance are essential.
  12. Do not store organic materials (such as paper, wood, cardboard, books, or clothes) in damp locations.
  13. If the house experiences a flood or sewer overflow, make sure that all affected areas are cleaned up thoroughly and promptly.

You should seek help if you are concerned about possible indications of mold and mildew. Some sources for help include biology departments of major universities, city and county health departments, and the organizations to which health and hygiene specialists belong, such as the American Conference of Governmental Industrial Hygienists (ACGIH). This group can be contacted through their website:http://www.acgih.org.

For more detailed information, try these web sites:
US Environmental Protection Agency - http://www.epa.gov
Centers for Disease Control and Prevention - http://www.cdc.gov/nceh
California Department of Health Services - http://www.dhs.ca.gov
Illinois Department of Public Health - http://www.idph.state.il.us
New York State Department of Health - http://www.health,state.ny.us
Oregon Department of Human Services - http://www.ohd.hr.state.or.us
Washington State Department of Health - http://www.doh.wa.gov


Comments: Prevention and elimination of leaks is discussed in other sections of this Manual (See Chapters on Walls, Roofs, Exterior Components and Utility Systems). Nevertheless, where leaks do occur, it is possible that mold and mildew may follow. If mold and mildew are present as a result of leaks, the repair of leaks should include removal of materials that are stained, coated or otherwise adversely affected by such organisms. Because removal of moisture can arrest the growth of these organisms and because surfaces that are not significantly damaged can be cleaned or treated, it may be possible to retain some or all affected building components during the repair process. In severe cases, removal or retention of building components is a technical matter that is best handled by a specialist in mold and mildew. The specialist will determine the molds and mildews present and the best way to remove them.

Most of the molds and mildews that appear around window frames and doors, in tile grout at tubs, showers and kitchens, as well as other interior locations, are the result of inadequate maintenance or improper use. At times interior humidity may rise sufficiently so that moisture condenses on cool surfaces (such as windows, doors, and walls). These conditions provide a fertile environment for the growth of molds and mildews, which most frequently appear around window and door frames, and at joints between frames and surrounding drywall and wood trim. Because of their warm and moist conditions, shower stalls and tub surrounds are also ideal places for mold and mildew to grow. Most of these conditions are controllable through appropriate use and maintenance of the house.

The appearance of mildew or fungi on outdoor siding may result from three principal sources: 1) leaks that allow water to enter between the siding and the material behind the siding; 2) an environment that is excessively damp, shady and lacking in air circulation; and 3) condensation of moist air on interior surfaces.

Mildew or mold should not be allowed to remain in the heating and ventilating systems. The problem usually results from moisture getting into the ductwork, either from a leak or condensation. Improperly insulated ductwork can also be a cause. It may be difficult to identify the presence of mold or mildew in ductwork, although a musty odor can be an indicator.

Recommended Use and Maintenance:

  • Promptly address any instances of leakage, report to the builder any instances of leakage, so that preventive repairs can be accomplished before significant damage occurs. If leaks are corrected quickly, mold and mildew may not flourish, and repairs and clean-ups are much easier to accomplish.
  • Showers and tubs should be routinely cleaned and towel dried after each use
  • Window frames and joints should be periodically cleaned in order to prevent mold and mildew growth.
  • If mildew or mold is observed, use a mildewcide (available at cleaning supply or hardware stores) to prevent any regrowth.
  • It is helpful to air out rooms on a frequent basis.
  • Ensure that all exhaust fans and other air circulation devices are functioning properly and used routinely. Windows should be open or vent fans should be operating at all times while showering or bathing. Allow fan to run 15 to 30 minutes after showering or bathing.
  • Do not install air deflectors over heat supply grills.
  • Open draperies often during rainy periods to allow air to circulate around windows.
  • Limit the use of atomizers or humidifiers.
  • Window tracks and weep holes should be cleaned at least twice yearly to prevent mold and mildew.
  • Keep siding sealed and painted. Avoid spraying siding and stucco with landscape sprinklers.
  • If mold and mildew grows on outside walls, take prompt action. Use of mildew-killing sprays and brushing with water and soap can arrest or reverse mildew conditions.
  • Avoid planting shrubbery that will block sunlight and ventilation from siding. Do not allow ivy or other vine plants to grow on siding and keep existing shrubbery pruned back from siding.
  • Notify the builder promptly of any suspected problem of this nature.


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