04/05/2017 by Brian Gay
Your Attic: It’s a Breeze
Today, most Canadian attics are well insulated, but many are poorly ventilated – a condition that can add to energy bills and create costly damage to the roof.
Creating air flow through the attic is important in summer to get rid of hot air and in winter to get rid of moist air, both of which can damage materials and the structure of your attic and roof.
The intense summer sun beating on an unventilated roof can heat your attic to almost double the outside temperature. Parts of the roof and the shingles can be distorted and deteriorated by such heat. Worse, the attic will stay hot all night, and the rooms immediately below will actually be gaining heat as you try to sleep.
In winter, moist air from inside the house – from cooking, bathing, laundering or humidifying – will seep into the attic. As soon as it hits the cold rafters, nails or anything metal, it will condense into water or frost. Severe condensation can drip into the insulation, lessening its effectiveness and perhaps staining the ceiling below.
A related winter problem is ice dams caused by the top of the roof being warm enough to melt snow and the lower area being cold enough to refreeze it. The resulting ice buildup is not only a threat to your eavestroughs, but can cause moisture to get under the shingles or behind the fascia boards, ruining the roof and leading to rot, insect infestation and mould.
The goal of good attic ventilation is to create air flow that will keep the underside of the roof the same temperatures as the top. Sufficient vents to let air in and let air out are required – generally, one square foot of vent for every 300 square feet of attic space.
While you can install motorized vents that are turned on and off by thermostats and humidistats, a power vent is costly and a challenge to maintain. It can also create other problems, such as siphoning cooled air from the house in summer and heated air from the house in winter, adding to your energy bills.
The best solution is just the right balance of vents, properly located, to let Mother Nature do most of the work. The wind passing over the house naturally creates areas of high pressure that will force air into the attic and areas of low pressure that will suck air out of the attic.
Normally, intake vents are located in the soffits, the area below the eaves, where wind can do its job and rain and snow are least likely to be blown in. Exhaust vents are normally located near the top of the roof.
Apart from having upstairs bedrooms that just won’t cool down on summer evenings, it’s difficult to assess the adequacy of ventilation in the summer. In the winter or early spring it’s easier to feel the insulation for dampness or search for discoloured rafters, a sure sign of mildew.
And while you’re looking around, make sure that any exhaust fans from bathrooms or kitchens are vented right through the attic to the outside. If they’re discharging into the attic, you’re simply taking moist air from a place where’s it’s merely inconvenient to a place where it’s certain to cause serious problems.
There are many kinds of vents, from single grills to long strips to those with turbine blades that spin in the wind. More important is having enough of them to change the attic air about 10 times per hour.
It’s a complex calculation to determine the exact amount of venting needed for an individual attic and local conditions can dictate what sort of venting is best. But a properly ventilated attic can add to the comfort of your home in all seasons.
And the money you save on heating and cooling costs may be enough to pay for a trip to someplace exotic!