Maintenance | Moisture Problems

Winter Moisture Problems: About Condensation

Cesar Collado
January 25, 2023

Reading Time: 6 minutes

All About Condensation

Throughout winter, temperatures vary and conditioned air in your home can create several different environments where condensation can become problematic. Condensation can be the source of moisture issues throughout any finished or unfinished spaces in your home. When moisture is combined with organic material (building materials, dust, upholstery), mold can reproduce rapidly. Cold weather can slow the growth; however, winter weather and HVAC activity change quickly spurring microbial growth. Interior windows have a low insulation rating and the cool glass often allows condensation from the warm inside air during the winter months. This leads to moisture issues on and below windowsills as seen above.

Our Purpose

These articles are researched and written to provide helpful information to anyone with a debilitating chronic illness. In most traditional medical practices, mold falls in a blind spot. 

  • Mold can cause severe illness or death, caused by toxins, biological and chemical pollutants. 
  • Today’s healthcare system processes are not designed or equipped to diagnose and treat environmental illness.
  • Recent awareness of environmental illness has been magnified due to the severity of Covid pandemic. 
  • There are thousands of molecules, derived from chemicals or microbes, that are poorly understood, untested, or unrecgonized.


About Condensation

Condensation is the process by which water vapor in the air is transformed into liquid water. It occurs when the air becomes saturated with moisture and the temperature of the air drops below the dew point. The dew point is the temperature at which water vapor in the air will condense into liquid form. Windows appear visibly wet and water can accumulate on windowsills. Outdoors, condensation occurs in clouds as water from the ground evaporates into clouds where condensation results in rain.

Window Condensation

Condensation is a natural occurrence in the environment, but it can be a problem in buildings when it occurs on walls, ceilings, and other surfaces. High humidity levels inside buildings are a big contributor to condensation, which can cause the growth of mold and mildew. 

There are several common places where condensation can occur in homes:

  • Windows: Condensation on windows is common.  It can be a sign of high humidity levels in the home.  Window condensation is an issue as windows typically have wood frames surrounded by drywall, both of which will grow mold.
  • Walls: Condensation on walls are a sign of a moisture problem. This problem may be a leak, inadequate insulation, or excess interior humidity.
  • Ceilings: If you notice condensation on your ceiling, it could also be a sign of a leak, inadequate insulation, or excess interior humidity. Mold is sometimes seen growing on bathroom ceilings due to inadequate ventilation and high humidity..
  • Attic: Poor ventilation in the attic can lead to condensation and moisture build-up, often on metal nails sticking through the roof, on ducting, on metal pipes, or on mending plates.
  • Basement: Condensation in the basement is often a sign of high humidity levels or a leak in the foundation.
  • Crawlspaces: Condensation is common in crawlspaces where the ventilation is inadequate and water is allowed to infiltrate from landscaping, poor drainage, flooding, or a high water table.  It is important to ensure that all ductwork and metal pipes in a crawlspace are properly insulated to prevent condensation. More will be said about crawlspaces below, as they are often problem areas.
  • To prevent condensation in buildings, it is important to maintain a humidity level inside the building that is less than 50%. This may require use of a dehumidifier, ensuring that there is proper ventilation in the building, and limiting activities that can increase humidity levels, such as drying clothes indoors or taking long, hot showers. Assure that cooking appliances are properly vented to the outside of the home.

It is also important to keep windows and doors closed during cold weather to prevent cold air from entering the home and lowering the temperature of the air inside, which can cause condensation. Wiping window condensation with a dry microfiber cloth to remove condensation is a necessary chore that is required throughout the cold months to avoid moisture problems on windowsills.

When condensation results in dark spots or potential mold, you can verify whether or not mold is growing and determine the type of mold using an ImmunoLytics Mold Test Kit.  You can order swabs that can sample mold in corners and crevices.  The tests come with easy-to-follow instructions and detailed lab results.

Immunolytics swab testing for Condensation

Moisture in Crawlspaces

Moisture in a crawlspace can be caused by a variety of factors, including poor drainage, high humidity levels, and leaks or flooding. When moisture accumulates in a crawlspace, it can lead to several systemic problems in your home, including the growth of mold, yeast, and other microorganisms.

Moisture can be detected through visual inspection and through the use of moisture meters and other moisture-detection tools. To prevent moisture in a crawlspace, it is important to address the source of the moisture and to take steps to improve ventilation and drainage in the crawlspace. This may include:

  • Installing a dehumidifier
  • Sealing any leaks or cracks
  • Ensuring that the crawlspace is properly graded
  • Making sure there is some air ventilation
  • Ensuring water drains away from the foundation. In some cases, it may involve installation of a French Drain
  • Keeping the crawlspace clean and free of debris.  Avoid using as storage.
  • In the event you are severely mold or chemical sensitive, you can ensure better quality air by having the crawlspace air conditioned and sealed with a vapor barrier.

About Vapor Barriers

One common solution to addressing an unfinished crawlspace is to install a vapor barrier. A vapor barrier is a material that is used to prevent the movement of moisture through walls, floors, and other building structures. Vapor barriers are typically made of plastic sheets or woven fabrics that are resistant to water vapor.

Stacking effect causing condensation

Jonathan Smegal, 2017. Understanding Stack Effect. Professional Remodeler. Available from

Up to 50% of the air you breathe in your home will rise from the crawlspace due to physical phenomenon called the stacking effect.  The simplest explanation is that warm air rises.

Condensation can occur when the crawlspace air becomes saturated with moisture and the temperature drops below the dew point. When this happens, the excess moisture in the air will condense into droplets on the surface of the vapor barrier or on other surfaces in the building. This process is like what happens when you see condensation on the outside of a cold glass of water on a hot day.

Crawlspace vapor barrier

Condensation in and on HVAC Systems

Moisture in a HVAC (heating, ventilation, and air conditioning) system can be caused by a variety of factors, including leaks in the ductwork, high humidity levels, and the presence of water in the air handling unit. Condensation often occurs on the cooling coils.  When moisture accumulates inside the HVAC system, it can lead to a number of problems, including the growth of mold, yeast, and bacteria throughout the system, the deterioration of the system’s components, and the development of unpleasant odors.  Read more about excessive moisture and contamination HERE.  Once an HVAC is contaminated with mold, it must be cleaned by an HVAC professional.  The EPA estimates the cost to clean an entire HVAC and Duct system is approximately $450-1,000.

Moisture in an HVAC system is typically detected through visual inspection. A well-kept HVAC system will be free of dust and insulation, with the main unit being in a clean room.  Ideally, an HVAC system would be in a finished and conditioned room; however, it is standard practice to place HVAC systems in unfinished attics, basements, and on occasion in a crawlspace.

HVAC system without condensation

A well-kept HVAC system will be free of dust and insulation, with the main unit being in a clean room.

To prevent moisture accumulation in an HVAC system, it is important to address the source of the moisture and to take steps to improve ventilation and drainage in the system. This may include sealing any leaks or cracks in the ductwork, installing a dehumidifier, cleaning the condensation pan drain, and ensuring that the system is properly maintained and serviced. If moisture is already present in the HVAC system, it is important to address the issue as soon as possible to prevent further damage and to protect the health of those living in the home.