During winter conditions attic frost is a problem associated with attic bypasses. When warm air from inside the house escapes traveling up through the bypasses, the moisture condenses on the roof boards and rafters, where the frost can form.
When the outside temperature rises again, the frost thaws, water collects and can leak into your house. If the water stays in the attic, mold can be a potential problem.
Adding more attic ventilation is not the right solution. Additional roof vents allow more air to escape from the attic and that pulls more warm moist air from the house into the attic.
The real solution is to have Houle Insulation seal off your attic bypasses and install adequate levels of insulation. This should eliminate frost from accumulating in your attic.
Solving moisture problems can be complicated. The problems are usually created by an assortment of causes and often require a combination of efforts to eliminate. It's a matter of achieving a balance between adequate ventilation and adequate moisture input, to create a healthy living environment.
Symptoms of excess moisture
Many signs of excess moisture are readily apparent; others are difficult to detect. One moisture symptom can have several sources, and one moisture source can create a number of seemingly unrelated moisture symptoms.
There are a number of symptoms:
Odors. Odors increase in intensity with high relative humidity. Musty smells likely signal mold, mildew, or, in the worst cases, rot. Odors from everyday household activities that seem to linger too long may be a signal of too much moisture.
Frost and ice on cold surfaces; fogging windows
Frost or ice on any surface is an indication of trouble. Condensation on windows and other smooth surfaces can be a sign of excess moisture and the need to stop air leaks, add insulation, or otherwise warm the surface.
Another possible cause of condensation is a faulty heating plant or other flame-fired appliance, which is causing excess moisture and combustion gases to enter the living space. Physical symptoms include frequent headaches, drowsiness, or other unexplainable illnesses. This possibility should be checked immediately. Keep in mind the need for annual maintenance of all combustion appliances such as water heaters, furnaces and boilers. Equip your home with a carbon monoxide detector or alarm.
Damp feeling. The sensation of dampness is common in areas with high humidity.
Discoloration, staining, texture changes. These usually indicate some moisture damage, no matter what the material. These changes may appear as black or dark streaks or lines which border a discoloration. The area may or may not be wet.
Mold and mildew, often seen as a discoloration may be white, orange, green brown or black. They are surface conditions that may indicate decay and are often noticed as a musty odor.
Water-carrying fungi look like a dirty white or slightly yellow fan with vine-like strands. The fungus can spread over moist or dry wood, and can be found under carpets, behind cupboards, on framing between subfloors or on damp concrete foundations. Wood swells when it becomes wet and warps, cups or cracks when allowed to dry.
Rot and decay. Wood rot and decay indicate advanced moisture damage. Wood-decay fungi penetrate the wood and make it soft and weak. Look for any type of rot or mushroom-like growths.
Sweating pipes, water leaks and dripping. Water vapor may be condensing on cold pipes, or the pipes may be leaking.
Peeling, blistering, cracking paint. Moisture may be working from outside or inside the home to damage paint. Exposed surfaces between cracks or under blisters are a major signal of moisture-caused paint damage.
Crusty, powdery, chipping concrete and masonry. Concrete or masonry may show signs of deterioration after moisture has moved through it. Freeze-thaw cycles speed the process of deterioration, causing chipping and crumbling. A buildup of salt or other powdery substance indicates that water was evaporated.
Poor drainage is a major exterior moisture problem. Proper drainage for foundations is critical. Construction details, such as flat ledges, inadequate drip edges or bad flashing, can also cause problems. Lack of maintenance can and does lead to water intrusion through siding, windows, doors, exterior light fixtures and other penetrations.
Precipitation, humidity, soil moisture content surface water, ground water table and outdoor water use can all change seasonally, creating problems that show only at certain times in the year.
Water in the ground moves through basement floors and walls. This water then evaporates into the air inside the house. If ground water is a suspect use the capillary test to determine if large amounts of moisture is wicking up through the ground or coming from the interior space.
High outdoor humidity. Consistently high outdoor humidity can cause a variety of problems, particularly constant mold, mildew and decay. Ventilating basements, crawl spaces and interior living spaces with high-humidity outside air in the summer can aggravate existing moisture problems or cause new ones. Typical foundation construction materials are very permeable to water vapor migration. This permeability allows high humidity to migrate inwards from outdoor air on hot summer days.
Blocked exterior air circulation. Closely planted foliage or items stored next to the house, such as firewood, can block air circulation and cause localized areas of high humidity.
New construction. Construction materials contain a large volume of water that is gradually released into the house as the materials dry. All new homes need a mechanical ventilation system that can provide a minimum of 0.35 air changes per hour to all rooms. The mechanical ventilation system should be set to operate whenever the house is closed, especially during the summer and winter months. Proper maintenance of the system is essential for optimum performance.
Basements and foundations are often the major source of excess moisture, particularly for homes in areas with high ground water and poor drainage.
Inadequate interior ventilation. Poor ventilation of high moisture areas such as kitchens and baths commonly leads to damage. If the house has inadequate ventilation overall, moisture problems may be the first clue.
Attic moisture problems. Attic bypasses are areas where warm air escapes into your attic: around light fixtures, up walls, etc. Bypasses can allow enormous amounts of warm, moist air to leak into the attic. Sealing them can save on winter heating expenses while preventing some moisture damage.
High building occupancy. People generate moisture. If there is less than 250 square feet of living space per person, there could be a problem.
Wood. Storing wood in the house can lead to big problems. Though seemingly dry, wood can contain a great deal of water that will evaporate into the house as the wood dries.
Domestic activities. Cooking, appliances, baths, showers, houseplants, and hanging wet clothing inside to dry can produce excessive moisture. Most low-volume showerheads save energy, but generate greater amounts of water vapor. In addition, large numbers of houseplants can produce a considerable amount of moisture.
Clothes dryer vented into the living space. Do not vent gas or electric clothes dryers into your house. The exhaust emits large amounts of water vapor in a short period of time. In addition to the excessive moisture, significant air pollution may result from combustion by-products, lint, and residual detergent fabric softener and bleach products.
Temperature differences, lack of insulation. When warm, moist air hits a cold surface, condensation can occur causing water or frost damage, which leads to the growth of mold or mildew. Rooms shut off from heating sources or used only intermittently, such as bedrooms or closets, can be problem areas, as can areas made cold by drafts or spaces behind furniture on outside walls. Uninsulated walls and windows, and wall, ceiling or floor areas where insulation is missing or has shifted, such as the junction where wall meets ceiling, are other key locations.
Faulty heating systems. Faulty appliances used for heating, water heating or cooking can be sources of moisture problems. Without adequate combustion air or in a "negative pressure" environment these appliances can spill water vapor and deadly carbon monoxide gas into the living area. Carbon monoxide can cause drowsiness, recurring headaches or even death.
Humidifiers. When operated in a new or newly retrofitted house, improper use of humidifiers only adds to moisture problems. Improper use of a humidifier can cause trouble in any house. Humidifier use should be limited to avoid condensation on windows. As a general rule humidifiers are needed when homes have over-ventilated living space.
Plumbing leaks. The best way to check the plumbing is to run each part of the system for 10 to 15 minutes while watching and listening for leaks. Check all accessible connections. Leaking pipes may be buried in a concrete slab floor or, hidden in the walls.
Summertime moisture problems
Some common moisture problems occur only during the humid summer months and need special mention.
Air conditioners. Most air conditioners turn on and off by sensing temperature, not humidity. if not properly sized, they may lower the temperature more than dehumidify the air. Over time, humidity can be raised, and if the indoor temperature has dropped enough, moisture can condense on interior surfaces such as ducts moving chilled air. Air conditioners that are too large for the space they are cooling can make the problem worse. Properly designed, sized, and maintained, air conditioning systems should cause no problems.
Condensation on cold water supply pipes. Best step to take here is to wrap with closed cell foam pipe insulation and bind the insulation to permanently fasten it in place.
Ventilation is a major moisture control strategy. Passive ventilation is important for attics. Mechanical ventilation is needed in kitchens, baths and sometimes other areas of the home. In newer and renovated homes, mechanical whole-house ventilation is a necessity. As we weatherize, update and remodel older existing homes the ventilation becomes a necessity also.
Indoor ventilation. The first preventative and corrective action with kitchens and bathrooms is to install a fan to pull moisture out quickly. Ductless kitchen and bath recirculating units simply filter air, not remove it and do not remove moisture. Because the addition of a fan could cause a combustion appliance to malfunction, a carbon monoxide detector or alarm should be installed BEFORE you install any ventilation improvement. If it is impossible to install the vent fans in the kitchen and bath, another option is to put an exhaust fan in a central location as close as possible to the humidity source and duct it to the outdoors.
For automatic control of unwanted moisture, any of these vent fans can be successfully connected to a dehumidistat that operates the fan automatically.
There are several methods of exhausting air from bathrooms and kitchens. Each has its strengths and weaknesses. ALWAYS vent exhaust fans directly to the outside-do not dump the air into the attic or the soffit areas. Extensive damage can result when the moisture condenses on cold surfaces.
Installing a fan in the ceiling and running exhaust tubing to a vent on the roof is common. Always seal all cracks and joints in the tubing and insulate it well. Also seal all cracks around the fan itself to reduce the amount of warm air that escapes through the bypass into the attic. Ducting that runs through cold spaces must be insulated to avoid condensation from forming and leaking back into the home.
In cold weather, roof exhausts will act like chimneys and send a constant stream of warm air out of the house. If the exhaust pipe is not well insulated, water vapor can condense on the walls of the pipe and leak back down into the living space.
Running the exhaust pipe down an inside wall and venting the air out through the rim joist works well. The fan can be placed at the bottom of the duct and can be quieter than a ceiling unit. Running the exhaust duct down and out also eliminates the penetration of ceiling and roof surface, further protecting the home from water intrusion.
In kitchen fan systems, use a replaceable or washable filter element that will keep grease from accumulating in the ductwork. Clean the filter often.
Attics. Eliminating attic bypasses is the main strategy to avoid moisture problems in attics.
Seal around all penetrations into the attic, such as plumbing pipes, chimney chaseway and electrical wiring.
Attics should be ventilated with passive vents that are located to promote good air circulation. Half of the vents should be placed high on the roof, at least three feet higher than the lower vents, which should be as close to the eave as possible. Using a fan for attic ventilation is costly and can draw moisture and heated air into the attic. Power attic ventilators should generally be avoided.
The size of the passive vents depends on four factors: total area to be vented, type of vent opening (screens or louvers), vent location and whether an air-vapor barrier is present.
The general rule is to provide, a vent-to-space ratio of 1:300; that is, one square-foot of attic ventilation area is needed for every 300 square feet of space to be vented if a vapor barrier is in place and half of the vent area is located at least three feet above the eave vents. If roof vents are less than three feet above eave vents and there is no vapor barrier the ratio is 1:150-one square foot of vent area for each 150 square feet of attic area. Several coats of oil-based paint will serve the function of a vapor barrier.
Basements and Crawlspaces. During warm, humid weather, ventilation with outdoor air causes, condensation in basements, and crawlspaces making indoor moisture problems worse. If the floor or walls are sweating, close basement windows and doors to keep out the humid air. To dry the space, use a large fan to circulate the air in the basement or crawlspace. It may be necessary to use a dehumidifier to keep the basement dry during the humid months.
Insulating the walls of older homes usually means blowing loose insulation into the stud wall cavities. It is still desirable to have an air-vapor barrier in those situations. The first coats of oil-based paint in older homes will serve this purpose. Condensation problems are rare. The control of air leakage, such as around leaky electrical outlets and plumbing penetrations, is important.
Built-in cabinets, windows, doors and baseboards are other potential areas of air leakage need to be addressed. The control of air leakage is a critical first step in preventing moisture problems within walls and attic spaces. Densely packed insulation materials can control air leakage.
If the interior wall surfaces are to be removed as part of a remodeling or renovation effort a 6-mil or thicker air-vapor barrier can be easily installed at that time. Mechanical ventilation and scaling of all penetrations are always recommended.
Water vapor moves into wall cavities both by air movement and diffusion, but air movement is by far the more powerful force. Seal penetrations around windows, doors, where the wall meets the ceiling and floor, and any cracks or holes in wall surfaces.
Home moisture problems are complex to solve, especially with our unique climate of cold winters and hot humid summers. In general, problems will occur whenever there is an imbalance between the moisture input to your home and the ventilation rate of your home. The thermal characteristics of building materials also enter into the mix. The solution often lies with some combination of reducing the moisture input, increasing the ventilation, and improving the thermal performance of the building materials.
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