CONDENSATION AND YOUR NEW HOME
WHY YOUR NEW HOME IS DIFFERENT
Your new home probably looks very different from your former residence! What are much less obvious are the many changes in design, materials and construction techniques built into your new home to greatly increase your family’s comfort and energy savings. Optimum framing has eliminated most cold spots in walls, and combined with exterior foam sheathing, tape and building wrap, the building envelope has become almost infiltration-proof. Space age weather stripping and glass coatings have made windows and doors very low energy loss openings. Tighter, thicker, more dense insulation materials combined with continuous moisture retarders have reduced utility costs to new lows. The highly efficient heating systems in use require little new air and have reduced energy robbing flues to small openings. Even fireplaces and appliances have joined the trend. Where houses less than ten years old may have three air changes per hour [ACH] (the total amount of air that must be conditioned in a given time) many builders are working toward new homes with .20 ACH.
TIGHTER HOMES REQUIRE CONSCIOUS LIVING PATTERNS
As construction has become more and more energy efficient, it has gotten tighter and tighter. Formerly, escaping heat energy carried accumulated moisture with it. However, with little heat loss there is little moisture loss. Typical moisture creating personal habits in a former less tightly constructed residence may now require a new consciousness. A family of four converts 3 gallons of water into water vapor every day. Mopping the floor in a 150-square-foot kitchen can release 4 ½ pints of water; a shower bath, about ½ pint; typical cooking activities, over 5 pints per day; average clothes washing and drying, 29 pints per week, and each house plant produces over one pint of water every 24 hours. Unvented gas and kerosene heaters are not acceptable and new highly efficient power humidifiers can create hot house conditions in one day. IT TAKES ONLY 4 TO 6 PINTS OF WATER TO RAISE THE RELATIVE HUMIDITY IN A TIGHT NEW HOUSE FROM 15% TO 60%. OBVIOUSLY, A NEW CONSCIOUSNESS IS NECESSARY FOR EACH FAMILY MEMBER.
MOISTURE LEVELS IN A NEW BUILDING MATERIALS
A typical new home has almost 200,000 lbs. of building materials. Many of these materials contain a very high level of moisture or are installed with large amounts of water. Lumber must contain less than 15% moisture to qualify as kiln dry. However, 1000 lbs. of this “dry” wood contains 130 lbs. of water (almost 16 gals.). Multiply these numbers by the tens of thousands of pounds of lumber in your new home. The concrete floor in the basement contained almost 600 gallons of water when it was poured and typical concrete basement walls contain well over 800 gallons of water. If the house has plastered walls, almost 300 gallons of water were used.
Most of the moisture in new building materials eventually evaporates in time with proper ventilation, but LARGE CONCENTRATIONS OF WATER IN MATERIALS DURING THE FIRST YEAR OF A NEW HOME CAN CAUSE MAJOR HUMIDITY PROBLEMS.
UNDERSTANDING GENERAL MOISTURE ACTIVITY
The air we breathe is really a mixture of two invisible gases – dry air and water vapor. Each of these elements may act independently, but they also act together. The moisture content of air is generally given in terms of relative humidity. As example, 50% relative humidity means that the air is holding half the amount of water vapor that it could hold.
Air at 30 degrees Fahrenheit with relative humidity of 80% contains about as half as much moisture as air at 70 degrees and 35% relative humidity. This is because warm air can hold many times more moisture than cold air.
At 100% relative humidity, the air contains all the moisture that it can hold, and is said to be saturated. The dew point temperature of a moist air mixture is the temperature at which saturation is reached and condensation first begins to appear.
Condensation occurs when moist air touches a surface that is colder than the dew point of the air. Warm air is always lighter, moving to colder surfaces carrying moisture with it. As warm moist air approaches a cooler surface, it cools and drops its moisture on the surface, creating condensation, or frost if the surface is below 32 degrees Fahrenheit.
As outside temperature drops and we are less and less able to hold moisture, inside vapor pressures rises rapidly driving moisture into tiny cracks around moldings, electrical outlets and other wall openings. Once moisture is inside a cold wall, frost develops. The pressure is reduced somewhat when excessive moisture is forced through ceiling insulation materials without vapor retarders, BUT MOST ATTIC VENTILATION SYSTEMS CANNOT FLUSH OUT LARGE AMOUNTS OF MOISTURE, especially when partly covered with snow.
The winter weather in Central Illinois falls within the 6000 degree zone with average January temperatures below 35 degrees Fahrenheit. Add a great amount of local moisture and overcast conditions to the many outside temperature fluxations require THE NEW HOME OWNER TO MONITOR INSIDE HUMIDITY LEVELS DAILY.
CONCLUSION
VERY FEW NEW HOMES IN CENTRAL ILLINOIS CAN MAINTAIN A 30% (OR HIGHER) RELATIVE HUMIDITY WITH OUTSIDE TEMPERATURES IN THE LOW TEENS WITHOUT DEVELOPING UNDESIRABLE MOISTURE CONDITIONS.
SIGNS OF EXCESSIVE MOISTURE IN YOUR HOME
WINDOW/DOOR CONDENSATION
DAMP SPOTS ON WALLS/CEILINGS
MILDEW IN CLOSETS/BEHIND FURNITURE
FROSTY OT WET SHINGLE NAILS AND ROOF SHEATHING IN ATTICS
DAMP BASEMENTS AND CRAWL SPACES
TRUST UPLIFT CRACKS
EXTERIOR PAINT BLISTERING
DANGERS OF PROLONGED HIGH MOISTURE LEVELS
PERMANENT MOLD/FUNGUS
STRUCTURE DRYROT
ROOF SHEATHING DELAMINATION
EXTERIOR/INTERIOR PAINT FAILURE
IDENTIFYING YOUR PROBLEMS
1) HYDROMETER READINGS: The first step is to monitor the relative humidity of the inside air on every level of your home including the basement with an inexpensive hydrometer (available at local hardware stores).
2) SITE CONDITIONS: Carefully inspect the outside grades next to every one of your exterior walls. All ground lines must substantially slope away including the grass areas, concrete or exposed soils over plastic sheeting. A swale should be used to control water from adjacent higher property. All drain spouts must flow away from the house perimeter. Outside water should not be allowed to enter the house.
3) CRAWL SPACES: The floor of all crawl spaces should be dry and have a 4-6 mil polyethylene film covering with seams overlapped at least 12” and edges tight against all walls. Usually, these spaces cause less problems when heated with insulated walls and no vents. An uncovered 1000 SF crawl space can produce over 19 gals of water every 24 hours.
4) BASEMENTS CONSIDERATIONS: Because of furnace air movements, basement humidity levels quickly become the level in every room on every floor. Clothes dryers and basement showers must be vented to the outside. Present or former standing water on basement floors will be absorbed into masonry walls and structure lumber to be slowly released. A properly constructed basement can create almost 50 gallons of water during a winter season. Average amount of basement moisture can be controlled with a high capacity dehumidifier emptying into a floor drain.
5) KITCHENS, LAUNDRIES AND BATHS: Each of these areas create major amounts of moisture and require an exhaust fan best wired to the light switch and vented to the outside or a well vented attic space.
6) HUMIDIFIERS: The instructions for power portable or furnace humidifiers should be followed and reviewed often. All humidifiers must be turned off at the first sign of a moisture problem.
7) ATTIC VENTILATION: Attic ventilation should follow the FHA guideline ratio of 1/300 (i.e. 1350 sq ft. attic space divided by 300 = 4.5 sq. ft. of vent space). This vent space should be equally divided between the roof ridge area and the soffits for maximum efficiency.
8) OTHER CONSIDERATIONS: Carefully walk through your home looking for unusual moisture producing activities. Fish tanks, hanging laundry in the basement, or storing wood inside can cause condensation problems. Remember excessive moisture usually happens during or after cold weather. If the problem persists there may be an exterior leak caused by rain or snow.
SIMPLE SOLUTIONS: It is relativity easy to develop a new moisture consciousness; stop humidification, add ventilation, crawl space ground covers and a dehumidifier in the basement.
EFFECTIVE, QUICK HUMIDITY REDUCTION CAN BE ACHIEVED BY OPENING SELECT WINDOWS AND DOORS FOR 15 MINUTES EACH DAY. THIS DILUTES HIGH MOISTURE INDOOR AIR WITH DRY OUTSIDE AIR.
FINALLY, BE PATIENT. It sometimes takes months for high humidity levels in a new home to become apparent, and months will be required to reduce moisture levels, especially during cold weather in tight houses. Remember, every item in the house, furniture, walls, floors, carpeting, clothing, draperies, structure wood and plaster have absorbed the same moisture level and must be reduced. BE PATIENT!
This article was prepared from material in the University of Illinois Small Home Council, ‘Moisture Condensation’ vol 1 no. 1: USDA Forest Service, Bulletin #373, Condensation Problems, Prevention and Solutions; ASHRAE Handbook; USDA The Wood Handbook; and almost 45 years of insulation experience.
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