Because of the greater amount of desired and required insulation, vapor barriers, caulking, tighter windows and building practices used to cut down air infiltration, new homes have become more energy efficient. In some homes this can also cause problems with high humidity. The homes are so tight that normal humidity caused by cooking, breathing, showering, etc. builds up inside the home. This can cause steamed-up windows, condensation around outlets or recessed lights, and even drywall damage. When these conditions are first noticed, it is important to exhaust the humidity from the home. This can be done by running bath fans and vented cooking exhaust fans when necessary, using a dehumidifier, making sure the owner’s dryer is vented outside, installing an air to air heat exchanger, or opening the house and letting the inside air exchange with the outside air.

The installation of de-humidification and humidification equipment and air to air exchangers is usually an owner option. Proper levels of humidity must be maintained. Just as too much moisture causes problems as described above, insufficient humidity, or excessive dryness can cause other serious problems.

It should be pointed out that household size; lifestyle and outdoor temperatures will affect the humidity level in the home. A home with an enclosed pool can be the source of excessive damaging moisture and requires special care in design, use and maintenance. To a lesser degree, saunas, hot tubs, and whirlpools also require similar care. The owners are responsible for maintaining proper temperatures and humidity in the home as well as for damage caused by failure to do so.

Craig’s Comments: Tight houses will reduce infitration, and allow for better control of what ahppens in a house. In the winter, this may result in increased inside moisture levels, whereas in summer, it may result in lowered inside moisture levels. In all cases, venting high moisture sources such as gas fireplaces, clothes dryers and bathrooms is a good idea. Proper sizing of air conditioners is also critical. Auxilliary dehumidifiers are very beneficial, especially in the spring and fall. In our climate, I do not think we need humidifiers, nor do I believe the heat or energy recovery ventilators are very beneficial. Also, please do not confuse the condensation of moisture from outside air around light fixtures or outlets for a problem with indide humidity levels.

As outside temperature drop, the indoor relative humidity level of your home should be decreased. For homes equipped with at least insulating glass on their windows, the following levels can be used to keep window condensation to a minimum:

Humidity for:                                             Inside Relative:
Outside Air Temperature                   70 Degrees F Indoor Air Temp.

-20 degrees F                                            15 to 20 percent
-10 degrees F                                            20 to 25 percent
0 degrees F                                                 25 to 30 percent
+1 degrees F                                              30 to 35 percent
+20 degrees F                                           35 to 40 percent

Common Defects or Problems:

  1. Moisture condensation on windows
  2. Moisture in attic.
  3. Dampness and moisture on basement walls, floors, pipes, etc
  4. Water appears on interior crawl space surfaces
  5. Condensation on skylights
  6. Condensation on toilets.
  7. Condensation or frost on electrical outlets
  8. Mildew or fungus on painted surfaces.

1. Common Defect or Problem – Moisture condensation on windows.

Performance Standard – Moisture condensation on the window since it is the coldest object in any given room with the glass having a much higher rate of heat transmission and, hence, being the colder surface during the normal heating season. Moisture condensation on windows is an indication of either too much moisture in the room, or poor circulation of the moisture that is present. The owner can minimize this condition by merely opening the window to permit the excess moisture to escape or by installing a dehumidifying system if the condition persists. It should be noted that in homes with humidification equipment, the formation of moisture on the windows is an indication that the humidifying equipment is set too high and producing too much moisture. It is recommended that screens be removed from casement windows during the heating season.

Builder Repair Responsibility – None, except to explain to the owner more thoroughly how this condition is caused.

Craig’s Comments: Condensation on windows in the winter can also be caused by faulty windows. Properly functioning, code-required windows should not have condensation on them except possibly when it is very cold outside, or the inside air is too humid. Unvented gas fireplaces and improperly vented clothes dryers can easily cause high humidity levels. Look at my other information on window condensation.

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2. Common Defect or Problem – Moisture in attic.

Performance Standard – Builder must provide adequate ventilation to all areas of attic.

Builder Repair Responsibility – Builder to meet performance standards so that no moisture forms in the attic during normal weather conditions.

Craig’s Comments: Moisture in the attic ususally results from two sources: Either from a roof leak, or from elsewhere in the house. Adequate ventilation will NOT solve a roof leak problem. Adequate ventilation MAY make an attic problem worse. If you have an attic moisture problem, it is probably from a wet crawl space or air leakage from within the house, or something like a bathroom exhaust fan venting into the attic. Building codes state that leakage spots between inside and outside be sealed. This includes the ceiling, and recessed lights. Make sure you have a ground cover over 100% of the soil in the crawl space. Current national research shows that vented attics do not perform as well as unvented ones, and can even cause attic moisture problems. Solve the moisture problem, but not by adding ventilation (or an attic fan).

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3. Common Defect or Problem – Dampness and moisture on basement walls, floors, pipes, etc.

Performance Standard – Owner should make sure that clothes dryer has been vented to the outside and no internal heat moisture recovery device is being used. Electronic dampers, if applicable, on furnace should be checked. Walls and slabs are cold due to ground conditions; war moist air strikes the cold surfaces and condenses. Direct outside air should not be brought in as it is usually very moist during spring, summer and fall and the problem will be increased if such air is brought into the home.

Builder Repair Responsibility – None, other than explaining the causes to the owner and advising the use of a dehumidifier and increasing air circulation.

Craig’s Comments: Basements are usually the coldest area in a house, so humidity levels will naturally be higher there. Carpeting helps keep the basement floor cold and is therefore prone to condensation. Therefore, carpeting is not recommended for basement floors. Proper sizing of the air conditioner is crucial to helping control indoor humidity levels and condensation throughout the house. A standalone dehumidifier may also be necessary in the basement.

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4. Common Defect or Problem – Water appears on interior crawl space surfaces.

Performance Standard – Crawl spaces should be graded and drained properly to prevent water from accumulating deeper than ¾ inch and larger than 36 inches in diameter in crawl spaces area. Standing or ponding water shall not remain for extended periods after a rain (generally, no more than 48 hours) except in surfaces that drain other areas or in areas where sump pumps discharge. In these areas a longer period can be anticipated. The possibility of standing water after an unusually heavy rainfall should be anticipated by the owner.

Builder Repair Responsibility – The Builder will take the necessary corrective measures to create positive flow within the crawl space to discharge to the exterior of the structure.

Craig’s Comments: These standards do not really fit the problem. Water on ducts, rim joists, pipes and other surfaces in the crawl space may or may not be related to puddles on the ground. Crawl spaces, like basements, are usually the coldest place in the house during the humid summer. Therefore, condensation can easily occur if the humidity is high enough. Moisture from the soil, clothes dryers, air conditioner condensate and even outside air can cause water to appear on crawl space surfaces. Cover the soil completely with a ground cover. Vent dryers and AC condensate lines outside. Research shows that we can make unvented crawl spaces work better all year long than we can if the crawl space is vented. But this also requires other detail, that are worth doing to maintain a good foundation under your house. See my other crawl space information on venting fallacies and sealed crawl space specifications.

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5. Common Defect or Problem – Condensation on skylights.

Performance Standard – All skylights can develop condensation due to high humidity levels. If skylight is in bathroom, ventilating fans should always be used or the window opened.

Builder Repair Responsibility – Builder not responsible for humidity levels in home.

Craig’s Comments: If the condensation is between the panes of glass or plastic, the window is defective. I would say that under many situations, the builder IS responsible for indoor humidity levels. Clothes dryers and bathroom exhaust fans that are not installed correctly can increase humidity levels. Improperly sized or installed air conditioners can also increase indoor humidity levels, as can a defective one. Excessive infiltration can lead to high humidity levels. One of the biggest sources of winter humidity is unvented gas fireplaces or other combustion devices (like space heaters.) Backdrafting gas furnaces or water heaters can also lead to high humidity levels.

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6. Common Defect or Problem – Condensation on toilets.

Performance Standard – Condensation may occur during high humidity times of the year.

Builder Repair Responsibility – Builder not responsible for humidity levels in the home.

Craig’s Comments: See my comments for #5 above. A toilet tank blanket helps reduce the amount of condensation that forms. Bathroom exhaust fan should be used, and run during and for a minimum of 30 minutes after each shower or bath.

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7. Common Defect or Problem – Condensation or frost on electrical outlets.

Performance Standard – Electrical junction boxes on exterior walls may produce airflow whereby the cold air can be drawn through the outlet into a room, sometimes creating condensation or frost.

Builder Repair Responsibility – None.

Craig’s Comments: Sorry, but condensation or frost on an electrical outlet is the builder’s responsibility. The code says leakage points should be sealed to reduce infiltration. Condensation or frost indicates that it wasn’t sealed properly. This is a good indicator that there may also be mold inside the walls. Large range hoods and even attic exhaust fans can worsen the situation.

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8. Common Defect or Problem – Mildew or fungus on painted surfaces.

Performance Standard – Mildew or fungus will form on a painted surface if the structure is subject to abnormal exposures or excessive moisture.

Builder Repair Responsibility – Mildew or fungus formation is a condition the builder cannot control and is a homeowner maintenance item.

Craig’s Comments: Mildew or fungus growth indicated very moist conditions. This is usually associated with a cold surface and humid air. Mold on an outside wall or ceiling near an outside wall may mean missing insulation. Mold or fungus behind wall paper may mean excessive air leakage in the wall. Other items in this section cover other issues with high indoor humidity levels. On the ouside of a house, mold is a maintenance issue.

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