Crawlspace Moisture Management. The smart and scientific way to manage moisture in the crawlspace.

Transcription

1 Crawlspace Moisture Management The smart and scientific way to manage moisture in the crawlspace.

2 NC Building Code: Wall Vented Crawl Spaces R Foundation vent sizing. The minimum net area of ventilation openings shall be not less than 1 square foot for each 150 square feet of crawl space ground area Square Foot Home

3 Wall Vented Crawlspaces Natural ventilation works under these conditions: No outside groundwater or water intrusion. Good height of airflow. Natural cross- ventilation of air. No blockages. Crawlspace stays reasonably warm.

4 Moisture in Crawlspace Understanding dynamics of moisture in a crawlspace is not so simple.

5 What is healthy for a crawlspace? Most research out today agrees wood moisture for a substructure should be 10%-16%. 12% is generally ideal for wood.

6 Outside Air Supports This Equilibrium moisture content (EMC) of wood exposed to outdoor atmosphere: State - City Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec NC- Charlotte SC- Charleston VA- Richmond TN- Knoxville MA- Boston OK Oklahoma City CA- San Francisco Source: William Simpson, Research Forest Products Technologist Forest Products Laboratory, Madison, Wisconsin Wood Moisture stays fairly consistent in most geographic climates in U.S.

7 Why is wood moisture a better judge of moisture levels? Humidity sensors vary greatly in accuracy Humidity can vary greatly with just a few degrees of temperature Wood moisture directly relates to humidity levels in a measured area

8 Wood Moisture Table Dependence of equilibrium moisture content (EMC) of wood on relative humidity (RH) and temperature: Temp (F) 10% RH 20% RH 30% RH 40% RH 50% RH 60% RH 70% RH 80% RH 90% RH Source: William Simpson, Research Forest Products Technologist Forest Products Laboratory, Madison, Wisconsin

9 Understand Moisture Problem Which has more moisture? 95 Degrees 45% Relative Humidity 70 Degrees 90% Relative Humidity

10 Understand Moisture Problem Dew point is a better measurement of moisture. In this illustration, there is actually more moisture outside than in the crawlspace. 67 Degree Dew Point 70 Degree Dew Point 95 Degrees 45% Relative Humidity 70 Degrees 90% Relative Humidity

11 Why Dew Point Matters Dew point is a measurement of the moisture in the air Humidity levels can trick you. Humidity is relative to the temperature Once you get to 100% relative humidity at a given temperature the capacity of moisture in the air has been reached This is when you get condensation.

12 Why Dew Point Matters The warmer air is the more water it can hold. For example take and air mass the size of an average 2000 sq foot crawlspace that is 3 feet high. That crawlspace at 68 degrees can hold around 185 cubic inches of water in the air before it is full of water. The same amount of air at 95 degrees can hold up to around 420 cubic inches of water before it is full.

13 Why Dew Point Matters Think about it? 95 degree air can hold over twice as much water as 68 degree air.

14 Crawlspace Moisture What is causing the moisture? Water W intrusion Ground G moisture Limited height and airflow blockage Decks and porches HVAC systems Sprinkler systems

15 Crawlspace Moisture What W is causing the moisture? Water intrusion Water intrusion problems are always better solved on the outside of the home but often you have to use an interior drain system. Whenever you use an interior system you will have moisture you will have to deal with.

16 Crawlspace Moisture What is causing the moisture? Ground G moisture This occurs when the ground of the house has a high water table, the outside dirt is higher or the lot naturally allows water to push back up. It is hard to ever waterproof this problem outside of the crawlspace and often this water has to be managed rather than eliminated.

17 Crawlspace Moisture What is causing the moisture? Limited height and airflow blockage HVAC is cooling this area and its limited size and height allows it to cool and handle very little moisture.

18 Crawlspace Moisture What is causing the moisture? Decks and porches Decks and porches allow water under them. When the sun hits them the air underneath heats up and allows moisture to evaporate. When this air drifts back into a crawlspace and meets colder air, it immediately condenses allowing moisture to form. These decks also contribute to air blockage.

19 Crawlspace Moisture What is causing the moisture? HVAC systems This cools the crawlspace to a lower than normal level which as discussed earlier doesn t t allow the air to handle water in volumes necessary.

20 Crawlspace Moisture What is causing the moisture? Sprinkler systems Improperly installed sprinkler systems pour water against the foundation allowing water intrusion and makes for higher levels of moisture around vents in house.

21 Dealing with Problems What are the options? Vapor Barrier Temperature sensitive vents Fans on humidistat or timer Closed crawlspace with dehumidifier Conditioned crawlspace with HVAC Controlled ventilation system

22 Dealing with Problems Vapor Barrier Benefit Slows evaporation of moisture from ground Listed in NC Code (Section R408 Wall Vented Crawl Spaces) R Ground vapor retarder. Requires full coverage ground vapor retarders for all wall vented crawl spaces. Wall vented crawl spaces shall be protected from water entry by the evaporation of water from the ground surface....

23 Dealing with Problems What are the options? Temperature sensitive vents These vents are designed to save energy and protect pipes. They were never designed to dry a house as their primary function. They start to close up during the driest times outside and open during the highest humidity weather.

24 Dealing with Problems What are the options? Fans on humidistat This may be the worst thing you can do on an air conditioned house. You cannot put a wetter air mass into a crawlspace and improve it.

25 For example How a dehumidifier works. A dehumidifier pulls air into a refrigerated coil which causes the air to cool. This air is now colder and the moisture must condense out of the air. Then the air exits the dehumidifier after the motor heats the air back up making it a lower humidity

26 Building your own dehumidifier for the outdoors When you pull air with a higher dew point across a surface colder than the dew point the surface acts like a coil in a dehumidifier. The fan running is working to help pull that air across the surface creating a dehumidifier for the outdoors. 67 Degree Dew Point 73 Degree Dew Point 95 Degrees 50% Relative Humidity 70 Degrees 90% Relative Humidity

27 Dealing with Problems What are the options? Closed crawlspace with dehumidifier No fresh air (which can just as easily lead to air quality issues) Dehumidifiers are costly to operate. The humidistats in dehumidifiers are not consistent. Radon concerns Gas leaks (If gas system is improperly vented) Can overdry the wood in a home.

28 Dealing with Problems What are the options? Conditioned crawlspace with HVAC No fresh air Air must return to the cold air return or be pushed out of the house to dehumidify the air HVAC system must be working to dry the house Radon concerns Gas leaks/combustion problems Many cases of problems with new construction Cold air from A/C being pumped into crawlspace allows for a cooler environment meaning air can hold less moisture.

29 Dealing with Problems What are the options? Controlled Ventilation System Use the outside air only when it will improve the conditions in a crawlspace. Enhance cross ventilation through use of fans. Can integrate a dehumidifier as needed.

30 Cross Ventilation is Key Section R of NC Building Code lists minimum number of vent openings. Exception:: The total area of ventilation openings may be reduced to 1/1,500 of the crawl space ground area where the required openings are placed so as to provide cross-ventilation of the crawlspace. The installation of operable louvers shall not be prohibited. Fewer vent openings are allowed with cross ventilation. Air movement is critical to reduce moisture.

31 Crawlspace Environment Crawlspaces need to be kept in balance for a healthy home. Crawlspaces need PROPER ventilation.

32 How A Controlled Ventilation System m Works Controls use sensors to measure dew point inside and outside the crawlspace. The system knows when to ventilate to improve conditions. It is completely automatic and adjusts for temperature conditions and time of year. This conserves energy by not pumping extreme temperatures into the crawlspace.

33 Fans Fans create a cross circulation of natural air flow Fans are extremely quiet UL AC-Fan DC-Based Fan Vent opening fans are either intake or exhaust. Joist-mounted fans are mounted internally for dead corner ventilation.

34 Dehumidifier Option In very humid climates in certain homes, the crawlspace may need supplemental drying. A controlled ventilation system can incorporate the use of a dehumidifier when fans alone are not enough. Energy efficient use of a dehumidifier by only using when absolutely necessary.

35 Crawlspace Environment The principle of a controlled ventilation system is very simple. Use the outside air when it is drier and it will improve the crawlspace conditions. If a house is getting too much moisture during peak humidity times, the system can use a dehumidifier to dry the area until the system can use the outside air again.

36 Healthy House Think of a controlled ventilation system as an automatic system that knows when to open and close your windows. It will only open the windows when the air outside will improve the air quality and dry the home.

37 Modular Solution Every crawlspace is different. A controlled ventilation system is easily adapted to unusual crawlspaces. These systems can be modified to accommodate crawlspaces as needed through various systems and fans.

38 Keystone For more information: Office: