Vents are rated by their net free area, or the amount of space for air to flow in or out. If your attic floor has a vapor barrier, you will need one square foot of NFA per every square feet of attic floor area half of that will be intake, half for exhaust. If there is no vapor barrier, double it to one square foot of NFA for every square feet of attic floor space half for intake, half for exhaust. These are broad guidelines, so be sure to check with your local building code.
Also, the NFA will be calculated differently if your roof slope is greater than average. If the slope of your roof is greater than you will need more ventilation to reflect the extra volume of attic space: Calculate 20 per cent more for to pitches, and 30 per cent more for a pitch that is or greater.
Homes are naturally filled with warm moist air on a daily basis thanks to human physiology and activities such as cooking and showering.
To take full advantage of this effect, a roofer will generally install intake roof vents for houses lower on the roof closer to the eaves while placing exhaust vents higher near the peak , to let the cold air push the hot air out more easily. Before a roofer gets to work installing your roof vents, they will need to determine what type of vents your home needs or which you prefer and how many you require according to the calculations above. Below we describe the different types of roof vents, which will vary according to the needs and architecture of your home, the geography and weather patterns of your region, and your roof structure.
These are general guidelines, as most manufacturers will offer instructions on how to best install roof vents and what measures are required to meet the limited warranty specifications. Soffit vents are commonly made of aluminum or vinyl and are installed into your soffit, the surface under the eave of the roof.
Soffit vents are recognizable for the narrow slits that provide open space into which air can flow. There are a number of different types and styles of soffit vents. Always be sure to check with your manufacturer that the vent you choose has sufficient NFA for your project.
Check that the insulation is pulled back, away from the vents, or ask your roofer to install attic ventilation baffles to prevent the insulation from creeping over the edge of the soffit. Source: Professional Roofing. Working from under the soffit, your roofing professional will mark the size of the vent and then cut a hole slightly smaller than the unit about two inches shorter and narrower , between the rafters. They will then install using screws, according to manufacturer specifications.
Source: NRHA. Drip edge vents are a two-in-one installation that promote water shedding at the eaves and rakes of a roof, while also allowing for ventilation into the attic. A drip edge vent is made of a corrosive-resistant material that sticks out about three inches back from the roof edge and then bends downward over them. Slits in the product allow for air to flow into the attic. Organizations such as the NRCA recommend against this roof vent style in cold climates because it can promote ice dams.
This style should also not be used with gutters. Just like a drip edge , the drip edge vent is applied along the eaves, the underlayment or waterproofing membrane is installed on top, and then the gable end drip edge can be applied on top.
This sequence will help promote waterproofing. These vents are laid along the ridge of the roof and can come as a series of separate pieces or one long piece. These exhaust vents provide a reliable open area for warm air to escape the attic, providing essential outward ventilation across the entire length of the attic versus a few isolated areas from other smaller vents. However, some pros recommend against this style because along with increased openings for air also comes the possibility for blowing snow or rain to enter.
Newer styles of ridge vents have curved channels to reduce this risk or are comprised of a mesh like material. First, the roofer should remove any cap shingles along the ridge. Next, they will outline the area using chalk and use a circular saw to cut away sheathing about one or 1. The roofer will be careful not to cut into the trusses or ridge board.
They will then remove sheathing and install the ridge vent by securing one piece of vent at a time and attaching the next piece into it, nailing each piece as he goes. The ends should be capped or sealed. Finally, the roofer will secure and weatherproof according to manufacturer instructions which will generally recommend different materials for different styles.
To do this, measure the length and width of your home. According to the National Building Code, you need 1 sq. Divide your square footage by sq. For example: sq. This means you should divide the number of vents by two. We need 10 vents for our sq. By allowing for the circulation of air in your attic, proper ventilation offers a number of advantages.
As we said, there are intake vents and exhaust vents. Toronto roofing companies determine which are intake and exhaust vents by their placement on the roof. As hot air naturally rises, vents at the lower edge of the roof are the intake vents, and those higher up on the roof at the peak are exhaust vents.
Some examples of vents are:. The rule of thumb used to determine the number of roof vents to install is one for every square feet of attic area if your attic has a vapour barrier, and one for every square feet of attic area if the attic does not have a vapour barrier. Vents are rated by their net free area NFA , which is the amount of space the vent has for air to flow in or out.
That rule can change if the slope of your roof is more than the average slope a rise of six feet for a run of 12 feet because there will be more space, heat and moisture to ventilate in the attic.
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