Home Brands Products Deals Promo Finder Store Features Forums Add Review What's Knoji? Sign Up Login

Identifying Sources of Moisture in the Home

Knoji reviews products and up-and-coming brands we think you'll love. In certain cases, we may receive a commission from brands mentioned in our guides. Learn more.
How to locate and reduce sources of moisture inside the home by repairing plumbing leaks, insulating attics, caulking, or adding exhaust fans.

Unwanted moisture inside the home can be very destructive. With time condensation on windows can rot wood framing or the window itself if it is constructed of wood. Condensation on piping can damage flooring, walls, and cabinetry. Improperly sized air conditioning equipment can elevate the indoor humidity levels and promote mold growth and pose serious health risks. Humidity levels should be no higher than 60% in the summer and between 20-40% in the winter.

Condensation forms when the moisture in the air comes in contacts with a surface whose temperature is below the dew point of the air.

Problem Areas

Inadequate Room Ventilation

Install externally vented fans in kitchens and baths. Provide circulation and ventilation inside the home by opening windows to promote cross-ventilation, and similar strategies. If a significant amount of ventilation is needed, a central exhaust fan or air-to-air heat exchanger could also be considered.

Inadequate Attic Ventilation

Verify that there are gable, ridge, or soffit vents installed in the attic. Check insulation to see if it is blocking ventilation routes along the eaves. Seal attic bypasses around plumbing vent pipes and electrical wiring.


In the winter be aware of the potential for ice damming which can occur when warm interior air enters the attic and melts snow of the roof. https://knoji.com/how-to-prevent-ice-damming-in-your-homes-roof/


If you have too many people living or animals are occupying a small home there will be a significant increase the amount of moisture. Dishwashing and showering are the two largest sources for moisture. Look to add additional ventilation or reduce the occupancy.

Windows and Doors

Inspect weatherstripping around doors and replace any loose or damaged weatherstripping. Check for damp areas around window sashes and condensation on glass panes. In the summer, hot humid air can be drawn into the home and aggravate moisture problems.

It is standard practice that the heat source, such as a baseboard heater or supply register be placed beneath the windows to warm them. In some instances the depth of the window sill prevents the warm air from contacting the bottom of the pane which is the coldest part of the window.

Arrange your window treatments so that they allow warm air flow between window treatments and window. Draperies keep heat away from the window but they do not keep moisture from inside the home away. A phenomenon known as “vapor drive” pushes moisture through the fabric where it comes in contact with the cold glass and condenses. Opening drapes and improving air circulation will minimize condensation.

Gaps in exterior caulking can bring cold air to the interior pane of the window.

Metal windows typically have a thermal break to stop the cold temperatures outside from being conducted through the metal frame and into the interior spaces.



Make sure that existing exhaust equipment in kitchens and bathrooms is being used when moisture is being generated. Install fans if they are not present. Become aware of moisture-generating activity and reduce moisture production. Step up overall ventilation, if necessary, by opening windows, using whole-house or local exhaust fans. Consider installing an air-to-air heat exchanger if appropriate.

Clothes Dryer Venting Inside Home

Exhausting dryer vents indoors by way of a bucket trap is never a good idea. While there is a small heat gain during the winter there is also a large amount of moisture and other airborne pollutants.


Cold Walls and Ceilings - Lack Insulation

Locate and seal any leaks first, then insulate. Make sure you use proper insulating and vapor barrier techniques for your part of the country.

Insulate windows with additional glazing or other treatments that seal around all edges. If insulation is impossible, continuous circulation of air with a fan in the problem area will help reduce condensation. For closets or other out-of-the-way places, leave doors open or install louvered doors for better air and heat circulation.

Missing or Poorly Installed Air-Vapor Barrier

Inspect materials on the cold side of the home to determine whether a sheathing or siding may be acting as an unwanted vapor barrier. Search for places where the air-vapor barrier may not have been installed, such as the rim joists. Install air-vapor barriers where needed. Exterior Insulation Finish System (EIFS) which is synthetic stucco over foam insulation can trap moisture behind the insulation and rot the framing and sheathing.

EIFS Components

Missing vapor barriers will also allow moisture to come in contact with the backside of the drywall within the wall cavity. Air conditioning will cause the wall to become cold and the moisture can condense on the backside of the drywall. If vinyl wallcoverings are installed, the moisture can become trapped inside the wall and cause mold to grow.

Exterior Walls – Moisture Intrusion

If you have a brick or stone façade, make sure that weep holes are located every 4 to 5 feet along the bottom of the wall and that they are not blocked with dirt, debris, or insects. For wood siding make sure that there are no split or warped clapboards which can allow moisture to enter. For vinyl or aluminum siding, make sure that the weep holes along the bottom edge of the panels are clear. A light cleaning with a pressure washer will clean out the weep holes and allow moisture to drain away from the sheathing underneath.

New Construction, Retrofit, Remodeling

Install mechanical ventilation to provide 0.35 air changes per hour.

Unvented Heaters and Misfiring Heaters

Check for blocked furnace vents, chimney blockage, chimneys that are too short, insufficient combustion air or whether the system is vented at all. Do not use unvented kerosene heaters or unvented gas fireplaces. Make sure your home has an adequate supply of combustion air and call your local natural gas supplier if you have any concerns.

Air Conditioners and Humidifiers

Use humidifiers only when needed and only in the winter. An unnecessary central humidification system should be disconnected. Setting the thermostat at 75ºF or above will help save money and keep surface temperatures above the point at which condensation will occur. Drain air conditioning condensation to the sewer system or the outdoors, not into crawl spaces. If condensate is dumped into sump pits, make sure that sump pumps are discharging condensate when necessary.


Running Air Conditioning

If it is necessary to run the air conditioning system continuously, turn off the air conditioner and ventilate the house when the outside humidity is low.

Plumbing Leaks

Run water at each location in the plumbing system for 10 minutes and watch and listen for leaks. Check all accessible connections. Leaking pipes may be buried in a concrete slab floor or inside walls.

You may also inspect cold water supply lines in the basement or under cabinets to see if they are sweating. If so, insulate with polyethylene or neoprene foam sleeves.


Houseplants and Attached Greenhouses

Provide adequate air circulation and ventilation in rooms where plants are located. Avoid excessive watering. Keep the greenhouse at recommended humidity levels. If the humidity is high, avoid venting into the home. Provide proper exterior drainage away from the house and the greenhouse. Use proper air-vapor barrier and insulation techniques on walls between the greenhouse and home. Make sure that the door has weatherstripping or magnetic seal.

Exterior Drainage

Slope the ground around the foundation so that water will drain away from the house. Check for blocked downspouts and gutters. Install rain gutters where necessary. Check for cracks in foundations, and install proper perimeter footing drains, if necessary.

Ground Water

Add an air-vapor barrier to crawl spaces. Fix basement drainage with drain pipe or sump pump. Seal cracks in the foundation and use foundation waterproofing.


Firewood can contain between 10% and 30% moisture, but wood absorbs moisture when the humidity level is higher and release it back into the air when the humidity level drops. Do not store more than a few days supply of wood inside the house.


Roberta Baxter
Posted on Aug 11, 2011
Abdel-moniem El-Shorbagy
Posted on Aug 10, 2011
Francina Marie Parks
Posted on Aug 10, 2011

About This Article

Daniel Snyder

Explore Top Fitness Equipment Brands

Expand more
Top-ranked fitness equipment brands