Moisture intrusion can be the cause of building defects, as well as health ailments for the building's occupants. Inspectors should have at least a basic understanding of how moisture may enter a building, and where problem areas commonly occur.
Some common moisture-related problems include:
structural wood decay;
high indoor humidity and resulting condensation;
expansive soil, which may crack the foundation through changes in volume, or softened soil, which may lose its ability to support an overlying structure;
ice dams; and
mold growth. Mold can only grow in the presence of high levels of moisture. People who suffer from the following conditions can be seriously (even fatally) harmed if exposed to elevated levels of airborne mold spores:
lung disease; and/or
compromised immune systems.
Note: People who do not suffer from these ailments may still be harmed by elevated levels of airborne mold spores.
How does moisture get into the house?
Moisture or water vapor moves into a house in the following ways:
air infiltration. Air movement accounts for more than 98% of all water vapor movement in building cavities. Air naturally moves from high-pressure areas to lower ones by the easiest path possible, such as a hole or crack in the building envelope. Moisture transfer by air currents is very fast (in the range of several hundred cubic feet of air per minute). Replacement air will infiltrate through the building envelope unless unintended air paths are carefully and permanently sealed;
by diffusion through building material. Most building materials slow moisture diffusion, to a large degree, although they never stop it completely;
leaks from roof;
flooding, which can be caused by seepage from runoff or rising groundwater; it may be seasonal or catastrophic; and
human activities, including bathing, cooking, dishwashing and washing clothes. Indoor plants, too, may be a significant source of high levels of humidity.
In the northern U.S., moisture vapor problems are driven primarily by high indoor relative humidity levels, combined with low outdoor temperatures during the winter. In the southern U.S. (especially the southeast), the problem is largely driven by high outdoor humidity and low indoor temperatures during summer months. Mixed climates are exposed to both conditions and can experience both types of problems. Humid climates, in general, will be more of a problem than dry climates. Wind-driven rain is the main cause of leaks through the building envelope.
Inspectors can check for moisture intrusion in the following areas:
A roof leak may lead to the growth of visible mold colonies in the attic that can grow unnoticed. Roof penetrations increase the likelihood of water leaks due to failed gaskets, sealants and flashing. The number of roof penetrations may be reduced by a variety of technologies and strategies, including:
consolidation of vent stacks below the roof;
exhaust fan caps routed through walls instead of the roof;
high-efficiency combustion appliances, which can be sidewall-vented;
electrically powered HVAC equipment and hot water heaters that do not require flue; and
Distribution pipes and plumbing fixtures can be the source of large amounts of moisture intrusion. If the wall is moist and/or discolored, then moisture damage is already in progress. Most plumbing is hidden in the walls, so serious problems can begin unnoticed.
One of the most important means of moisture management in the bathroom is the exhaust fan. A non-functioning exhaust fan overloads the bathroom with damp air. If the exhaust fan doesn’t turn on automatically when the bathroom is in use, consider recommending switching the wiring or switch. The lack of an exhaust fan should be called out in the inspection report. The fan should vent into the exterior, not into the attic.
The bathroom sink, in particular, is a common source of moisture intrusion and damage. Although overflow drains can prevent the spillage of water onto the floor, they can become corroded and allow water to enter the cabinet.
Use a moisture meter to check for elevated moisture levels in the sub-floor around the toilet and tub.
Bathroom windows need to perform properly in a wide range of humidity and temperature conditions. Check to see if there are any obvious breaks in the weatherstripping and seals. Are there are stains or flaking on the painted surfaces?
Check showers and bathtubs.Is the caulking is cracked, stiff or loose in spots? Are there cracked tiles or missing grout that may channel water to vulnerable areas? If some water remains in the bathtub after draining, it may be a warning sign of possible structural weakening and settlement in the floor beneath the tub.
The water heater tank should be clean and rust-free.
The area around the water softener tank should be clean and dry.
Check that all through-the-wall penetrations for fuel lines, ducts, and electrical systems of heating system are well-sealed. All ducts should be clean and dust-free. Inspect the air supply registers in the house for dust accumulation.
Filters, supply lines, exterior wall penetrations, vents, ductwork and drainage of the cooling system must all be in good working order to avoid moisture problems.
Look for stains or discolorations at all roof penetrations. Chimneys, plumbing vents and skylight wells are common places where moisture may pass through the roof. Any such locations must be inspected for wetness, a musty smell and/or visible signs of mold.
Are there areas of the insulation that appear unusually thin?
Rust or corrosion around recessed lights are signs of a potential electrical hazard.
Model building codes typically require damp-proofing of foundation walls. The damp-proofing shall be applied from the top of the footing to the finished grade. Parging of foundation walls should be damp-proofed in one of the following ways:
3 pounds per square yard of acrylic modified cement;
1/8-inch coat of surface-bonding cement; or
any material permitted for water-proofing.
In summary, moisture can enter a building in a number of different ways. High levels of moisture can cause building defects and health ailments.
Water may be essential to life, but, as a destructive force, water can diminish the value of your home or building. Homes as well as commercial buildings can suffer water damage that results in increased maintenance costs, a decrease in the value of the property, lowered productivity, and potential liability associated with a decline in indoor air quality. The best way to protect against this potential loss is to ensure that the building components which enclose the structure, known as the building envelope, are water-resistant. Also, you will want to ensure that manufacturing processes, if present, do not allow excess water to accumulate. Finally, make sure that the plumbing and ventilation systems, which can be quite complicated in buildings, operate efficiently and are well-maintained. This article provides some basic steps for identifying and eliminating potentially damaging excess moisture.
Identify and Repair All Leaks and Cracks
The following are common building-related sources of water intrusion:
windows and doors: Check for leaks around your windows, storefront systems and doors.
roof: Improper drainage systems and roof sloping reduce roof life and become a primary source of moisture intrusion. Leaks are also common around vents for exhaust or plumbing, rooftop air-conditioning units, or other specialized equipment.
foundation and exterior walls: Seal any cracks and holes in exterior walls, joints and foundations. These often develop as a naturally occurring byproduct of differential soil settlement.
plumbing: Check for leaking plumbing fixtures, dripping pipes (including fire sprinkler systems), clogged drains (both interior and exterior), defective water drainage systems and damaged manufacturing equipment.
ventilation, heating and air conditioning (HVAC) systems: Numerous types, some very sophisticated, are a crucial component to maintaining a healthy, comfortable work environment. They are comprised of a number of components (including chilled water piping and condensation drains) that can directly contribute to excessive moisture in the work environment. In addition, in humid climates, one of the functions of the system is to reduce the ambient air moisture level (relative humidity) throughout the building. An improperly operating HVAC system will not perform this function.
Prevent Water Intrusion Through Good Inspection and Maintenance Programs
Hire a qualified InterNACHI inspector to perform an inspection of the following elements of your building to ensure that they remain in good condition:
flashings and sealants: Flashing, which is typically a thin metal strip found around doors, windows and roofs, are designed to prevent water intrusion in spaces where two building materials come together. Sealants and caulking are specifically applied to prevent moisture intrusion at building joints. Both must be maintained and in good condition.
vents: All vents should have appropriate hoods, exhaust to the exterior, and be in good working order.
Review the use of manufacturing equipment that may include water for processing or cooling. Ensure wastewater drains adequately away, with no spillage. Check for condensation around hot or cold materials or heat-transfer equipment.
HVAC systems are much more complicated in commercial buildings. Check for leakage in supply and return water lines, pumps, air handlers and other components. Drain lines should be clean and clear of obstructions. Ductwork should be insulated to prevent condensation on exterior surfaces.
humidity: Except in specialized facilities, the relative humidity in your building should be between 30% and 50%. Condensation on windows, wet stains on walls and ceilings, and musty smells are signs that relative humidity may be high. If you are concerned about the humidity level in your building, consult with a mechanical engineer, contractor or air-conditioning repair company to determine if your HVAC system is properly sized and in good working order. A mechanical engineer should be consulted when renovations to interior spaces take place.
moist areas: Regularly clean off, then dry all surfaces where moisture frequently collects.
expansion joints: Expansion joints are materials between bricks, pipes and other building materials that absorb movement. If expansion joints are not in good condition, water intrusion can occur.
Protection From Water Damage
interior finish materials: Replace drywall, plaster, carpet and stained or water-damaged ceiling tiles. These are not only good evidence of a moisture intrusion problem, but can lead to deterioration of the work environment, if they remain over time.
exterior walls: Exterior walls are generally comprised of a number of materials combined into a wall assembly. When properly designed and constructed, the assembly is the first line of defense between water and the interior of your building. It is essential that they be maintained properly (including regular refinishing and/or resealing with the correct materials).
storage areas: Storage areas should be kept clean. Allow air to circulate to prevent potential moisture accumulation.
Act Quickly if Water Intrusion Occurs
Label shut-off valves so that the water supply can be easily closed in the event of a plumbing leak. If water intrusion does occur, you can minimize the damage by addressing the problem quickly and thoroughly. Immediately remove standing water and all moist materials, and consult with a building professional. Should your building become damaged by a catastrophic event, such as fire, flood or storm, take appropriate action to prevent further water damage, once it is safe to do so. This may include boarding up damaged windows, covering a damaged roof with plastic sheeting, and/or removing wet materials and supplies. Fast action on your part will help minimize the time and expense for repairs, resulting in a faster recovery.
Wood decay, also known as wood rot, is the decomposition of wood as the result of actions by certain species of fungi.
Facts about wood decay and decay fungi:
According to Ohio State University, replacement materials needed to repair damage caused by decay account for nearly 10% of U.S. annual wood production.
Carpenter ants, termites and other wood-destroying insects do not cause wood decay. These insects are, however, attracted to wood that has been softened by decay.
Decay fungi are active in temperatures between 77° to 90° Fahrenheit, and need water, oxygen and a food source to survive.
Fungi that cause wood decay are called saprophytic, a term also applied to other organisms that consume decayed material. Many species of fungi, along with saprophytic beetles, worms, protists and bacteria are essential components of the decomposition and nutrient cycles.
How does wood decay happen?
Fungi reproduce by manufacturing single-celled spores, similar to microscopic seeds. Spores are tough; they're able to resist extreme conditions of temperature and humidity and, under adverse conditions, they may go dormant for long periods. Spread primarily by air currents, they collect on horizontal surfaces. Decay fungi feed on the cellulose and lignin of which wood cell walls are composed. Their hyphae, which are threadlike tubes that penetrate the wood, secrete enzymes which dissolve at least part of the wood cell being fed upon, changing it into a form which can then be absorbed as food. Spores require a moisture content higher than the Fiber Saturation Point (FSP) of the wood species upon which they rest, typically between 27% and 30%. Once sufficient water and favorable temperatures are available, spores germinate and develop by extending a hyphal tube. As more spores germinate, fungi multiply to form a colony. Under the right conditions, colonies can expand quickly.
Common types of wood decay:
brown rot: This type of decay causes the wood to break down into brown cubes that split against the grain. Advanced stages of brown decay result in dry, powdery wood that is unable to support much weight, and crumbles easily.
white rot: This type of decay appears whitish, stringy and mushy, and tends to be more common in hardwoods.
dry rot: A misnomer, this term has been used to describe decayed wood that has since dried and ceased decaying. Some people may erroneously assume that the wood is still in the process of decay. Moisture is required for wood decay to occur, so no literal “dry rot” exists.
InterNACHI'S Guide to Identification of wood decay:
Inspectors should check any areas suspected of containing decay by probing. A screwdriver works well for this. Wood with advanced decay will be soft and the probe will penetrate easily. Areas with incipient decay may be a little trickier to identify.
The pick test can also be used to identify decayed wood. To perform this test, a pointed tool, such as an ice pick, is inserted beneath the wood grain to pry loose a thin section of wood till it breaks free. Sound wood will snap crisply and typically breaks off to one side of the pick. Decayed wood will break with a dull sound and usually breaks above the pick's point of insertion.
Although wood-destroying insects, such as termites, are attracted to decayed wood, they also inhabit sound wood. Always probe or use the pick test to confirm that what you’ve found is sound wood.
If the decay hazard is high, select the heartwood of decay-resistant species, or use wood properly treated with a good preservative. (A list of decay-resistant species can be found later in this article.)
Proper grading can prevent water from seeping under the house.
Effective roof overhangs, gutters and downspouts should be installed.
No untreated wood should be placed within 18 inches of the ground.
Adequate cross-ventilation in crawlspaces will help eliminate dead air pockets, which contribute to wood decay.
A vapor barrier can be installed on the soil surface to help limit evaporation and return moisture to the soil, rather than allowing it to condense on the floor and above joists. Plastic sheets can cover the soil to act as satisfactory barriers.
Dehumidifiers and bathroom and kitchen fans will reduce indoor water vapor, and potentially dry wood enough to prevent decay.
Likely decay locations:
stairs and attachment points to the house in decks;
improperly installed door thresholds, especially beneath sliding glass doors;
decks at or near grade;
roof penetrations with improper or corroded flashing;
support post bases of decks;
near corrosion of fittings on plumbing;
in basements where housebibs may have burst;
in sub-floors at the base of toilets and tub corners;
the uphill side of chimneys;
sidewall and headwall locations; and
untreated wood in direct contact with concrete, masonry or soil.
Moisture can come from:
general moisture intrusion of building envelope;
improperly installed, damaged or corroded flashing;
finish grades that slope toward the foundation; and
Types of naturally resistant and non-resistant wood:
Resistant woods: teak, rosewood, oak, redwood, cedar, black locust, red mulberry and yews.