Moisture in Your Home

Excess moisture is a common problem that can lead to an uncomfortable living environment for you and your family. If you are unsure if you have excess moisture inside your home, look out for common symptoms, such as condensation between window panes or sweating pipes. You may also notice a musty smell or damp feeling. Over time, moisture issues can become more serious and turn into warped floor boards, peeling paint, wood rot, or mold growth. Moisture inside the home can come from both indoor sources, like appliances and outdoor sources, like foundation cracks.

Indoor Sources of Moisture

Most types of indoor moisture are unavoidable, however, it is useful to be aware of them and how they affect your home. For instance, one of the biggest contributors to indoor moisture is respiration of the people and pets living in the home. This is especially true in small areas, when each person has less than 250 square feet of living space.

Common household tasks can also produce moisture, such as cooking that produces steam or hanging clothes to dry indoors. Additionally, using the clothes dryer can produce a large amount of moisture inside your home. Because of this, it’s a good idea to ensure that your dryer vent is directed outside and does not exhaust into the living space.

The kitchen and bathrooms are typically the rooms with the highest moisture and thus, are often the source of issues. For example, ventilation plays a critical role in moisture control so kitchens and bathrooms are usually vented with exhaust fans. However, if the fans aren’t working properly or are not used, moisture problems can occur. Additionally, these areas are often sources of plumbing leaks.

Systems meant to provide comfort in the home can actually lead to moisture problems as well, if they are misused. For instance, using a humidifier when it’s not necessary can lead to too much moisture in the air. Another example would be using an air conditioner that is too large for the space it’s conditioning. An air conditioner’s main purpose is to cool the air, however, a side benefit of running the air conditioner is that it dehumidifies the air. If an air conditioner is oversized, it will never run long enough to actually dehumidify, which can lead to moisture problems.

In addition, portions of the home that aren’t checked regularly or used for living space can be common areas for moisture. This includes crawl spaces, basements, and attics and other areas that are often not properly insulated or sealed. Furthermore, they may be sources of pests, moisture, or mold. All of these factors contribute to them often being sources of moisture.

Back to Top

Outdoor Sources of Moisture

The exterior of your home and the area around it also contribute to indoor moisture levels. A crucial area to pay attention to is the foundation. Moisture can move through the cement block walls of a foundation creating issues throughout the home, not just in the crawl space or basement. Additionally, if foundation walls are cracked, or lack proper waterproofing, it can lead to extensive moisture.

Drainage is another important factor in moisture control. If ground water or rain water is draining into your foundation, it is going to cause issues. For example, make sure gutters and downspouts aren’t clogged or broken so the water can drain properly. In addition, verify that the siding on the exterior of your home does not come within 12 inches of the ground. Having siding too close to the ground, makes it more vulnerable to water damage.

Believe it or not, landscaping can affect the moisture content of your home, as well. If there are plants or bushes close to the foundation, they can become sources of moisture and humidity. Plus, they can attract pests and bugs to the foundation. Also, it is important to make sure the grade of the yard is sloped away from your house, not towards it. In addition to the foundation, other parts of the home exterior can affect indoor moisture levels. For instance, if there are missing roof shingles, water could leak into the home. Other potential sources are leaking chimney flashing, caulking, or drip edges.

Back to Top

How Outdoor Moisture Enters Your Home

You may not think that outdoor moisture has much affect on what happens on the interior of your home. If you don’t have any leaks or cracks, can it really get inside your home? In fact, there are four ways that moisture can travel into your home- bulk moisture, capillary action, air movement, and water vapor.

1. Bulk Moisture Transport
Bulk moisture transport is when large amounts of water enter the home through holes, gaps or cracks. For bulk moisture transport to occurs there needs to be water source, a force, such a gravity to move the water, and a gap in the home structure, for the water to enter. An example of bulk moisture transport would be snow leaking into a crawl space.

2. Capillary Action
Capillary action occurs when water moves through permeable materials against the flow of gravity. Capillary action typically occurs with rain and groundwater, and is often in locations that are not immediately noticeable. Capillary action works best in materials with small pores such as brick or concrete. Because of this, capillary action is very common in basement and crawl spaces with concrete block foundations.

3. Air Transport
Air transport describes water vapor being carried through air leakage.This often occurs when there are unsealed portions between conditioned and unconditioned areas. The amount of condensation will vary based on factors such as indoor and outdoor temperature, relative humidity and air speed. Air transport can be made worse by factors that aid in moving the air such as the stack effect, wind, or fans. One example of air transport would be leaking duct work.

4. Vapor Diffusion
Vapor diffusion describes moisture filtering through vapor permeable materials, such as gypsum drywall or concrete. Vapor diffusion can dramatically increase the moisture levels in a home and can occur even when there are no gaps or leaks. Vapor diffusion is the reason vapor barriers are needed to help regulate ground moisture in a crawl space.

Back to Top


No matter where you live moisture can build up in your home and cause issues. Whether its from indoor or outdoor sources, too much moisture can be quite detrimental to the structure of your home, in addition to affecting the health of the people living in it. Now that you know the sources of moisture, and the ways it can enter your home, keep an eye out for potential problems and correct them before they cause excessive damage.

Back to Top

Brook, David. "Home Moisture Problems ." Home Moisture Problems. Oregon State University Extension Service, Jan. 2007. Web. 22 Dec. 2016.
"Building Science Introduction - Moisture Flow." Building Science Introduction - Moisture Flow | Building America Solution Center. US Department of Energy, 1 Aug. 2014. Web. 22 Dec. 2016.
Holladay, Martin. "All About Vapor Diffusion." Green Building Advisor, 12 June 2015. Web. 22 Dec. 2016.
USA. US Department of Energy. Building Technologies Program. Guide to Closing and Conditioning Ventilated Crawlspaces. US Department of Energy, Jan. 2013. Web. 22 Dec. 2016.