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Moisture Problems Found in Crawl Spaces

By : John Martino | In : mold

I come across many homes built on crawl spaces while performing home inspections in New Jersey. Unfortunately many crawlspaces have moisture problems. There are several main causes of crawlspace water and moisture issues.

Before we discuss moisture we must talk briefly about the different venting methodologies involved in crawl spaces. Most crawlspaces have vents that provide cross ventilation. The sub-floor is insulated as well as the piping inside the space in order to help keep things from freezing. There is usually a vapor barrier on the crawlspace floor. This is the type of crawlspace that are most found while performing NJ Home inspections.

The second type of crawlspace is a non-vented type. The crawlspace walls are insulated however the sub-floor is not. The vents are permanently sealed up so that exterior air is not introduced into the crawlspace. There is usually a vapor barrier installed on the crawlspace floor as well as the use of a dehumidifier in order to help keep moisture levels in the crawlspace under control. Pipe insulation is also recommended.

Several of the causes of crawlspace moisture and water problems are:

Lack of gutters installed or gutters improperly installed:

The average roof will shed over 1000 gallons of water for every one inch of rainfall. If there are no gutters installed on the home this water collects quickly against the exterior foundation walls. Because foundation walls are porous water will make its way into the interior of the crawlspace and can cause moisture and mold problems. The installation of gutters on a home is very much recommended.

Poor downspout termination:

Another culprit contributing to crawlspace water and moisture are downspouts that discharge too close to the exterior of the home. Downspouts should extend at least 5 feet away from all exterior walls. This will help pipe water away and prevent water from collecting and ultimately making its way into the crawlspace of the house.

Poor grading:

Many times the grade or earth around a home or building is improperly sloped toward the structure. This improper sloping will direct rainwater toward the structure where it will collect and eventually end up in the crawlspace of the home or building do to over saturation of the surrounding soils. All soil around the home or building should slope away roughly ¼ inch per foot around the entire perimeter of the home or building.

Poor crawlspace ventilation:

A crawlspace requires a minimum of one square foot of ventilation for every 150 ft.² of floor area. The crawlspace vents should be installed within 3 feet of the corners allowing for cross ventilation to take place. Oftentimes crawlspace vents are obstructed with decking, materials, or vegetation. Make sure that all crawlspace vents are unobstructed and make sure that adequate crawlspace ventilation exists.

Improperly installed insulation:

Often times insulation on the interior of the crawlspace under the sub-floor is installed backwards. In other words the crawlspace vapor barrier is installed toward the cold side of the space. The paper side of the insulation should always be installed against the hot side of the space. This will allow for proper control of moisture conditions and also help avoid mold growth in the crawlspace if the crawlspace is a non-vented type that is properly constructed there is no need for this type of installation.

Missing vapor barrier:

Often times a vapor barrier is missing altogether or is damaged. There should be a minimum of a six mill thick vapor barrier installed on the ground and up the crawlspace interior walls. The proper use and installation of a vapor barrier will help maintain proper moisture control inside the crawlspace. Gravel can also be installed on the vapor barrier in order to properly keep it in place.

Lack of or nonoperational sump pump:

A sump pump should be installed at the lowest point in the crawlspace. Sump pumps are often neglected and must be maintained and inspected in order to function properly. An operational sump pump will be somewhat effective in controlling basement water and moisture problems. Each sump pump should have a battery backup or other backup system so that the pump can function in the event of a power outage.

Lack of dehumidifier:

In a non-vented crawlspace, a dehumidifier should be installed in order to help keep moisture levels under 40% inside the space. The dehumidifier should be hard piped to the exterior of the home with the use of a condensation pump in order to prevent you the homeowner from having to empty the humidifier on a regular basis. Most humidifiers today have an adjustable setting system so they do not have to operate all the time.

The crawlspace of your home should be inspected regularly in order to determine if any problems exist in the space. Many times crawl spaces are neglected and forgotten about. If you use the above as a guide and regularly inspect the crawlspace you will be on the right path to limiting crawlspace moisture and preventing the mold growth that goes along with it. A New Jersey home inspector should attempt to enter any crawlspaces if he or she finds it safe to do so.

John Martino (64 Posts)

LookSmart Home Inspections, LLC is owned and operated by John Martino. He has successfully performed over 3000 inspections for clients throughout northern and central NJ and has an exemplary track record of customer satisfaction. Mr. Martino completed a 300-hour approved NJ Home Inspector training program and was mentored by one of the most respected names in NJ home inspections. He continues to attend over 30 hours of continuing education classes each year.


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Buying a house is one of life’s biggest decisions. Before you close, you’ll want a professional inspection of the house to ascertain its true condition. John Martino is a formally trained New Jersey home inspector and member of the American Society of Home Inspectors...ReadMore