Roofing shingles remain top choice for home-building projects

Type of roofing material affects ventilation needs

October 07, 2013


Ventilation plays the role in controlling attic moisture in the winter and hot air in the summer. Care should be taken to seal around all the openings in the attic floor, such as ceiling light fixtures, plumbing stacks, exhaust fans and chimney chases. Otherwise, warm moist air can escape into the attic, where it can condense and cause damage.

Roof ventilation is important because there are so many changes that have taken place in the roofing industry. A lot of homeowners are changing from cedar roofing to duriod roofing (such as fibreglass laminated roofing shingles), aluminum or steel roofing. As soon as you remove a roof and put on a new roof, you must address ventilation. Keep in mind air will leak from the living area up into the attic area through light fixtures, electrical wiring, plumbing pipes, attic access hatches and so on.

The moist warm air that moves from the living space to the attic can cause issues in the attic such as ice damming and staining on the underside of roof sheathing. A cedar roof vents over the entire surface of the roof because the individual shingles are nailed to strapping on the roof. If you have any synthetic roofing material installed on your roof, the roofer will use tar paper or roof seal materials underneath the roofing material, so you have to increase the amount of ventilation to compensate because your roof no longer vents over the entire surface. For every 300 square feet of roofing surface, you must have at least one square foot, or 144 inches, of venting. Every vent you buy today has an indicator stamped on it so you know how many square inches of ventilation that vent provides. I recommend venting one square foot of venting for every 200 square feet; that way you are getting more than adequate venting. The venting should be a mix 50 per cent on the roof and 50 per cent under the eaves (or soffits). This distribution of venting will encourage the proper air flow in the attic space to minimize any possible concerns associated with attics that are improperly vented.

Attic insulation: Fibreglass and cellulose are the most commonly used for insulation in today's homes. Fibreglass insulation is spun from molten sand and recycled glass into fibre. Cellulose insulation is made from recycled newspapers, which is treated with a chemical-flame retardant. Both fibreglass and cellulose insulation can be made into 'loose-fill' insulation, which can be blown into attics using a blowing machine. Fibreglass insulation also comes in "batts" - precut pieces of insulation that vary in width and length. Average homes should have between R-28 (eight inches) to R-50 (15 inches) in insulation in the attic. Insulation is measured in "R-value," which is the capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating quality of the insulation.


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