How to Reduce Condensation in Your Home

Factors that Cause Condensation and Tips to Keeping it in Check

• By: Michael McCabe

Condensation, as described by Wikipedia, is "the change of the physical state of aggregation of matter from gaseous phase into liquid phase and the reverse of evaporation". When the surface temperature of the window is below the dew point temperature of the air in your home, condensation, frost or ice appears. The dew point is the point where the air is no longer able to hold any more moisture. If the air has reached vapour saturation (100% relative humidity), then the air will release moisture. As temperatures drop, so does the dew point.

A good example of condensation is to take a bottle of water from the fridge and let it sit on your kitchen counter. The bottle will begin to fog over and become wet on the outside. The bottle does not have a leak but rather has become the point of interaction between the warm moist air from inside your home and the cold water inside the bottle. The resulting physical change of state is moisture collecting on the bottle. This is condensation.

Two Areas Where Condensation Occurs

(1) Windows

It’s not uncommon for windows to fog up or condensate on the inside, especially on colder days. The glass from a window has a low thermal value compared to the rest of your building's envelope, and as a result are prone to condensation. The walls of your home are made up of several building materials, including your cladding (brick or siding), wall sheathing, structural members (studs) insulation, vapour barrier, drywall and paint. All of these materials are designed to reduce the transfer of the outside cold and moisture into your home, thus reducing the amount of condensation. Exterior walls built in Ontario today generally have a thermal resistance (or R value) of about R20. Windows have an R value of about R4. And although the window manufacturers of today are coming out with great new concepts and designs to increase R values in their windows, the reality is that windows remain a weak point in the building envelope and are prone to condensation as a result.

Note: A window that fogs up in between two panes of glass is a sign that the window seal has been compromised and needs to be repaired. This is condensation as well but can be repaired by redoing the seal between the thermal panes.

(2) Attic Spaces

1. Poor Insulation
2. Lack of or poor ventilation
3. A combination of 1 & 2
4. Poor or no elimination of exhaust from bathrooms
5. Bathroom fans exhausting into the attic space

The attic is another area where the heat from your home meets the cold from the outside. If the attic has proper ventilation and insulation, you generally will not see any build up of condensation. If you see condensation in the roof space, it may take on another physical state during the winter and that is frost, as the temperature within the attic space will dip below the freezing point.

The insulation in your attic should be uniform, generally about 10” deep and not compressed. Insulation works best when it is fluffy, and has small airspaces within it, as it is the air that provides the thermal protection. Insulation that has been compressed because its been walked on, or has had boxes put on top of it, will not perform properly.

Ventilation in the attic comes in two parts: Roof vents and Soffit vents. The Building Code of Ontario says that there has to be an unobstructed area of 1 sq. ft. of roof ventilation for every 300 sq. ft of insulated ceiling area. This is a combination of the total soffit ventilation and the roof vents. A prudent decision is to put in more than this, as these are minimum standards.

If you have a problem within your attic, it should be dealt with as quickly as possible, as the condensation will eventually lead to mold. Home inspectors today are looking very closely for mold in attics, as this is a health hazard. Aside from your own health being affected, you will have issues trying to sell a home with a moldy attic.

Human Factors that Contribute to Condensation

1. The number of people/pets/plants within the home
2. Amount of cooking
3. Amount of showers taken on a daily basis
4. Aquariums within the home
5. Improper (over) use of a humidifier
6. Improper Ventilation
7. Window coverings left closed

Tips to Reducing Condensation in Your Home

The amount of condensation will vary from house to house as a result of the factors listed above. However, with the proper steps, you can reduce the amount of humidity within a home and subsequently reduce the amount of condensation.

Reducing the amount of people or pets in your home is not generally an option. However, if you have a larger family, do a lot of cooking or have a lot of showers, the key is proper ventilation. This means having a Heat Recovery Ventilator (HRV) installed, or if you already have one, using it. It means running your kitchen and bathroom fans frequently to exhaust the stale moist air to the outside. Having your humidifier set to the appropriate setting ( +/- 40%) and using it only in the winter time. If your humidity is too high, purchase a dehumidifier and run it frequently.

Lots of showers, cooking, aquariums without proper lids to contain the moisture and the simple process of people breathing all add humidity to the home. Leaving window coverings closed all the time promotes condensation and mold on the window. This is simply a factor of poor air movement between the window and the window covering. Air movement and ventilation are the keys to reducing Condensation.

The key to reducing condensation in your home is having proper ventilation.

Maintain Proper Humidity to Avoid Condensation

Maintaining proper humidity will keep condensation at a minimum. While manufacturers of wood flooring and furniture makers recommend a humidity of close to 40%, working around those guidelines also makes for a comfortable environment for the home's inhabitants. Humidity less than this will cause dry and cracked skin, cause gaps due to shrinkage in your wood floors and furniture and promotes health problems.

Humidity greater than 40% can also cause health problems, and will increase the condensation within the home - the biggest dangers of which is the onset of mold (read our article on mold). It will also cause swelling of wood flooring and furniture, ultimately causing permanent damage to the wood.

New Home Syndrome

If you have just moved into a new home, you may find the humidity is higher than at your previous residence, even though your lifestyle remains the same. This is a result of the new building materials within your home giving off moisture as they dry out or cure. There is a moisture content in virtually every new building material, and it will take a year or two for them to properly dry out and acclimatize to their new setting. The resulting factor is a higher than normal moisture content during that time.

Get a Hygrometer to Monitor the Humidity in Your Home

You can monitor the humidity within your home by purchasing a simple monitoring device called a hygrometer. These generally cost less than $20.00 and are readily available at hardware stores.

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