How Humidity Affects Your Home

Window Condensation

Condensation will often occur during colder weather when the moist air inside the home comes into contact with cooler surfaces. The moisture in the air can condense to form water droplets or even frost. The risk of condensation increases as the weather gets colder and/or the inside humidity rises.

For windows, doors and skylights, condensation can form:

• on the glass
• on the frames and sashes
• near the weather seals
• on the walls around a skylight
• between the glass panes if the seal is broken

Reducing window condensation: buy high-performance units

Buy high performance certified windows, doors and skylights. They are more energy efficient and have less condensation compared to ordinary models. Features that contribute to better energy efficiency include triple glazing, low-emissivity (low-e) coatings on the glass, inert gas between the glass panes, thermally improved spacer bars, insulated frames, sashes and doors, and greater air tightness.

Note: low-e coatings on high performance windows make the glass more energy efficient by reducing heat loss. However, if the night has been cool and calm and the air is humid, condensation may form on the outside surface of the glass around sunrise. There is also a higher risk of condensation if the low-e coating has been applied to the room-side surface of the glass.

Reducing window condensation: air circulation

Proper air circulation near windows is also necessary to minimize condensation. Air flow across the glass surface helps to keep it warmer, and that is one reason heat sources such as central heating vents and electric baseboards are located beneath windows in many homes. Deep window sills, closed drapes and blinds, and even nearby furniture can block air movement and allow cool air to pool near a window, which can lead to condensation on the glass.

Humidity levels — cooling and ventilating equipment

Homes today are more airtight than houses of the past. As a result, moisture can build up inside, especially during winter when windows are kept closed. Dampness, mould growth on walls and heavy condensation on windows are signs of too much moisture. Over time, this excess wetness can cause poor air quality and damage the structure of a home.

Follow these suggestions to reduce moisture

• Check your humidifier. If your furnace has a humidifier, set it lower to reduce humidity levels.
• Ventilate. Ensure that your clothes dryer vents outside. Install exhaust fans in bathrooms and kitchens, and make sure the fans vent directly to the outside. Consider installing a heat recovery ventilator to increase ventilation and reduce humidity.
• Create less moisture. Use lids on pots when cooking. Keep your showers short. Store wood outdoors.
• Keep moisture out. Cover exposed earth floors in basements and crawl spaces with moisture barriers. Install a sump pump to remove excess moisture under the foundation. Fix water leaks in the basement. Make sure the grading slopes away from your house so water does not flow towards the foundation. Ensure eavestroughs adequately divert water away from your home.

Hardwood and Humidity

Anyone who is looking at putting hardwood flooring into their home should have a basic understanding of how humidity affects wood flooring. Many times the problems that can arise when wood floors come in contact with water or water vapor can be prevented if the flooring contractor properly educates the homeowner. Unfortunately this information isn't always communicated to the homeowner, leaving them feeling frustrated or even feeling like they've been given inferior products or poor craftsmanship. A simple explanation of how wood is affected by water and how to prevent this being a problem for your floor will greatly reduce the incidence of poor experiences.

First and foremost, wood is hygroscopic. Webster defines hygroscopic as “absorbing or attracting moisture from the air.” So wood can easily absorb moisture from the air or its environment. That doesn't sound so bad until you realize that when wood absorbs moisture it will also change in size — and it changes size when it dries out as well.

To understand this from the manufacturing side: when the sawmill cuts lumber it is “green” lumber, meaning it still retains a lot of the moisture that was traveling up the trunk of the tree. Green lumber may have a moisture content of 30%. If you made 5-inch-wide flooring out of that green lumber, the flooring would shrink as it dried below 30%. That is why flooring manufacturers dry lumber down to 6–9% before making it into flooring. Going from 30% down to 9%, lumber will lose about 7% of its size.

Your floor will come in at around 6–9% moisture content. It will need to acclimate to the interior conditions of your home to achieve equilibrium so that it does not shrink or swell as it adjusts to its new environment. This is why experienced flooring contractors will measure the moisture content prior to installing it and will also make sure your home has stable conditions — constant humidity and temperature — before installing the floor. If the floor is 9% moisture content and is installed into an environment that is 20% relative humidity, the floor will begin to shrink and you'll see gaps between the rows. If the floor is 6% and is installed into 50% relative humidity, it will begin to grow, which can make the floor “cup” or take on a washboard appearance. This can be caused by contractors not testing moisture in the wood and the home prior to installation — but also by homeowners not maintaining stable interior moisture conditions.

Rules of thumb when buying wood flooring

Engineered products made from multiple plies of hardwood with a hardwood veneer will be more stable than solid wood flooring in most conditions. Narrower widths are less affected than wider widths, and some species are naturally more stable than others. For example, a 6” wide solid Hickory floor will be more likely to move in a higher moisture environment than a 3 1/4” wide engineered red oak floor.

When getting bids for your floor work, ask the contractor if he will measure and document the moisture content of the flooring and sub-flooring and the interior relative humidity prior to installation. If he says it's not important, beware that he might not be taking all proper precautions to ensure your wood flooring installation will perform up to expectations.

Take care to make sure the interior conditions of your home stay between 30% and 50% relative humidity — this requires a hygrometer, which measures relative humidity. If your home dries out in the wintertime, expect to see cracks in the floor unless the relative humidity stays stable. If the relative humidity rises, expect the floor to swell and possibly cup unless you can control or lower the humidity during the more humid season. Two bonus factors: keeping your home in these humidity levels will lower your winter heating costs, and physicians will tell you it is much healthier to breathe air at these humidity levels than extremely dry or extremely wet conditions.

Moisture Problems — Two Types

There are two types of moisture problems: leaks and condensation. This guide focuses on condensation problems. When warm, moist air comes into contact with a surface that is too cold, the moisture in the air condenses — forms water — on the cold surface. The water and frost that can be seen collecting on windows are visible examples of condensation. Condensation can also collect in the attic and inside the exterior walls where it can, over time, cause mould, wood rot and structural decay. If the air inside is too humid for too long, the result may be damage to the house structure, finishes, furnishings and personal possessions — and possibly even the health of those living in the home.

Controlling moisture in the home is the best way to prevent mould problems. Leaks from roofs, through walls and from plumbing also cause moisture problems in homes, but are more readily detected and solved than indoor condensation-related problems.

Moisture-related indoor air quality problems

A home should have an exchange of air between the indoors and outdoors. Without this air exchange, a home can accumulate moisture, mould can become a problem, and you can experience poor air quality. Mould growing in the home can release mould spores, toxins and odours, and this can represent a health concern for members of the household. The exchange of stale air in the home with fresh outdoor air reduces potential air quality problems and helps to prevent moisture buildup in the home. Indoor-outdoor air exchange also helps deal with harmful chemicals that can be released from synthetic fabrics, furnishings, household products, cigarette smoke and burning candles.