Moisture can have a detrimental effect on your manufactured home. 

Did you know HUD has guidelines for the minimum amount of ventilation that should be part of the underpinning of your home?  This easy calculator will do the math for you!
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Federal Model Installation Standards as Adopted by Wisconsin for Manufactured Homes Produced on or After April 1, 2007.

Federal Model Installation Standards as Adopted by Wisconsin for Manufactured Homes Produced on or After April 1, 2007. §3285.505 Crawlspace Ventilation. (a) A crawlspace with skirting must be provided with ventilation openings. The minimum net area of ventilation openings must not be less than one square foot (ft.2) for every 150 square feet (ft.2) of the home's floor area. The total area of ventilation openings may be reduced to one square foot (ft.2) for every 1,500 square feet (ft.2) of the home's floor area, where a uniform 6-mil polyethylene sheet material or other acceptable vapor retarder is installed, according to §3285.204, on the ground surface beneath the entire floor area of the home. (b) Ventilation openings must be placed as high as practicable above the ground. (c) Ventilation openings must be located on at least two opposite sides to provide cross-ventilation. (d) Ventilation openings shall be covered for their full height and width with a perforated corrosion- and weather-resistant covering that is designed to prevent entry of rodents. (e) Access opening(s) not less than 18 inches in width and 24 inches in height and not less than three square feet (ft.2) in area must be provided and must be located so that any utility connections located under the home are accessible. (f) Dryer vents and combustion air inlets must pass through the skirting to the outside. Any surface water runoff from the furnace, air conditioning, or water heater drains must be directed away from under the home or collected by other methods identified in §3285.203.

[Federal] Model Installation Standards for Manufactured Homes Produced on or After April 1, 2007.

§3285.505 Crawlspace Ventilation. (a) A crawlspace with skirting must be provided with ventilation openings. The minimum net area of ventilation openings must not be less than one square foot (ft.2) for every 150 square feet (ft.2) of the home's floor area. The total area of ventilation openings may be reduced to one square foot (ft.2) for every 1,500 square feet (ft.2) of the home's floor area, where a uniform 6-mil polyethylene sheet material or other acceptable vapor retarder is installed, according to §3285.204, on the ground surface beneath the entire floor area of the home. (b) Ventilation openings must be placed as high as practicable above the ground. (c) Ventilation openings must be located on at least two opposite sides to provide cross-ventilation. (d) Ventilation openings must be covered for their full height and width with a perforated corrosion and weather-resistant covering that is designed to prevent the entry of rodents. In areas subject to freezing, the coverings for the ventilation openings must also be of the adjustable type, permitting them to be in the open or closed position, depending on the climatic conditions. (e) Access opening(s) not less than 18 inches in width and 24 inches in height and not less than three square feet (ft.2) in area must be provided and must be located so that any utility connections located under the home are accessible. (f) Dryer vents and combustion air inlets must pass through the skirting to the outside. Any surface water runoff from the furnace, air conditioning, or water heater drains must be directed away from under the home or collected by other methods identified in §3285.203.

[Federal] Model Manufactured Home Installation Standards (2003)

8.8.2 Ventilation 8.8.2.1 Ventilation shall be provided for the crawl space with skirting as follows: (1) At a minimum of 1 ft squared (0.1 m squared) of free area for every 150 ft squared (14m squared) of the home's floor area (2) Except in arid regions with dry soil conditions, the following shall be permitted:      (a) A uniform 6-mil (0.15 mm) polyethylene sheet material or other acceptable vapor barrier material shall be permitted to be installed on the ground surface beneath the home to further reduce moisture.      (b) Where an acceptable ground vapor barrier is installed and one such ventilation opening is within 3 ft (914.4 mm) of each corner of the home, the total area of ventilation openings shall be permitted to be reduced to 1 ft2 (0.1 m2) for every 1500 ft2 (140 m2) of the home's floor area. ​8.8.2.2 Ventilation openings shall be placed at or near each corner of the home and as high as practicable. ​8.8.2.3 Openings shall be located on at least two opposite sides to provide cross-ventilation.
Disclaimer: While we do our best to make calculations as accurate as possible, we cannot guarantee the accuracy of these results. Use at your own risk and always follow your own local regulations.