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Ventilation key to proper insulation

Ventilation key to proper insulation

A CLOSER LOOK: Without appropriate air flow, moisture buildup in an insulated attic may lead to mould and premature failure of roof decking and framing.

Rob Parker, Special to QMI Agency
Wednesday, September 19, 2012

Posted with the permission of the author. Originally published in The London Free Press, Saturday, September 22, 2012.

One of the most effective ways to save on heating and cooling costs is to ensure your attic is properly insulated and vented. A well-insulated and vented attic will not only save you money, but will also prolong the life of your roof. With winter just around the corner, now is the time to check the state of insulation in your attic.

Just adding insulation to the attic is not enough. You must have the proper air flow to control moisture and heat buildup with proper ventilation. Moisture buildup in the attic will cause mould to grow on the wood surfaces, and lead to premature failure of the roof decking and framing. Heat buildup will lead to premature failure of the roof shingles.

According to the Canada Mortgage and Housing Corp., the attic should be vented at a ratio of at least one to three, which means for every 300 square feet of attic space there should be one square foot of roof and soffit venting installed.

More is always better, and you need both roof and soffit vents for proper ventilation. These vents can, in most cases, be easily added. Bathroom and kitchen fans should never be vented into the attic as they will force warm moist air into the attic that can lead to mould growth or even wood rot. These vents need to exhaust to the exterior of the building either through a roof-mounted vent hood or a wall vent similar to a dryer vent.

Before adding insulation, make sure you check for and repair any roof leaks, as water will ruin the new insulation. When adding insulation to your attic, makes sure you don’t block the soffit vents. Soffit vents are those vents on the underside of the roof overhang.

Soffit vent strips should be installed before insulation is added to prevent the vents from becoming blocked. If your home has little or no roof overhang, consider installing gable-end vents to improve ventilation. A power roof-mounted attic fan is another option.

What type of insulation should you use? Blown or loose fill, either cellulose or fibreglass, are the most common materials used to insulate residential attics and are the ones most commonly installed in new homes; however, bat insulation is what most home owners will use when doing it themselves.

How much insulation does your house need? Today’s standard is R50, or about 37.5 cm (15 inches). The insulation should be continuous and at a consistent level. You must be sure you have completed all the work/repairs you needed to do before adding the insulation. Once the insulation has been added, any walking or crawling on the insulation will compact it and lower its R value. Do not store personal property in the attic as this will also compact the insulation and could possibly block air flow.

R values and their metric equivalent, RSI values, are a way of labelling the effectiveness of insulating materials. Insulation products sold in Canada are labeled with R and RSI values. The higher the R or RSI value, the more the material is resistant to heat movement. Provincial building codes specify minimum values for new construction.

Rob Parker is a registered home inspector with the Ontario Association of Home Inspectors and certified master inspector with the National Association of Certified Home Inspectors who does home inspections in the London area.

Call him at ThamesSpec Home Inspection Service at 519-857-7101, e-mail thamespec@rogers.com or visit www.thamespec-inspections.com.