Thursday, November 5th, 2015
Proper ventilation of your attic has many benefits for the health of your home and your family. Studies done in recent years has prompted the building codes to require ventilation in every region of the United States, and all asphalt shingle manufacturers will not issue warranties without it. Proper ventilation will:
We need to breathe to get fresh air in and out of our bodies. For similar reasons, your attic needs to breathe also. While we have an active process, most homes have a passive venting system which requires a balance between the intakes and outlets. Intakes and outlets are placed strategically to allow for the greatest amount of air circulation. As hot air rises, intake vents are placed at lower points of the attic with outlets higher up. As the hotter air escapes through the outlet vents, it creates a minor vacuum that draws in fresh air through the lower intake vents.
Powered vents can also be used. These vents use electric-powered fans to force air through the vents at a much higher rate than passive vents.
The size and placement of vents depends on the roof configuration and the size of the attic. The commonly accepted calculation for sizing vents is 1 square foot of vent opening to 175 square foot of attic area. In most cases, the more vents the better. This is true for most climate regions, except for extreme cold areas where concerns for allowing too much cold air into attic can present problems. These areas should calculate vent sizing at 1 square foot of vent opening to 200 square feet of attic area.
Placement of attic vents should be determined by the size and shape of attic area. Care should be taken to verify that the vent locations will vent all attic areas. If sheathing or fire stopping blocks off an area of the attic, additional vents are recommended.
Every home is different when comes to determining what type and how many vents you need for optimal ventilation of your attic.
Most modern homes have soffits for intake vents because they offer the best circulation per square footage of venting needed. Although, gable vents can be used for intake depending on your home’s design. A combination of roof vents, ridge vents and gable vents can be used to create the best overall outlet circulation.
Power vents use a fan to force air through the vent. There are powered roof and gable vents available. Some use electricity and others are solar-powered. Most are thermostatically controlled, set to run when the attic temperature reaches a defined temperature and stop when the air cools by a predetermined amount (usually 15 degrees).
Power vents have both benefits and drawbacks. If you are having difficulty cooling your attic with passive vents due to architectural design, lack of venting options, and/or too many problems are causing heat to enter the attic, powered vents are a good option and possibly your last resort without making drastic changes to your home’s design.
Drawbacks; you’ll need a licensed electrician if you plan on installing an electricity-powered vent, and your electric bill will increase. If you use the powered vent in the winter you may increase the chances of forming an ice dam. If you don’t have an air tight attic, the vent may pull warm air up from below, increasing the heat in your attic which can cause snow to melt faster near the top of your roof. The snow melt can then refreeze near the end of the roof (the eaves) forming an ice dam.
A thorough inspection of your attic space should be done to determine if you are having any problems that can be attributed to poor venting.
Check for frost on the underside of the roof or on the rafters. This is caused by warm, moist air that has been trapped, has condensed and subsequently frozen on the wood.
Properly venting above a cathedral ceiling is more difficult than a typical attic. The framing of a cathedral ceiling creates individual plenums between each rafter, every one of which should be vented. To properly vent there must be a minimum of 1½” between the underside of the sheathing and the top of the insulation to allow for air flow. Each individual plenum must connect to an intake vent and an attic vent. For a cathedral ceiling, the vent types most easily connected to each plenum are a soffit vent (intake) and a ridge vent (outlet).
Some ridge vent manufactures claim that adding a ridge vent can reduce air conditioning costs with the additional ventilation. While a properly vented attic does lower the attic temperature, the only way to dramatically lower the attic temperature is with a power vent. However, when the cost of running the power vent’s fan is calculated against the savings in air conditioner power consumption, the net savings in energy can often be short of what is claimed.
Make sure that your shingle manufacturer’s guidelines and building codes are followed for proper attic vent design and layout. This will reduce the amount of condensation and excess heat that can build up leading to a longer life for your roof shingles and sheathing. Also, the proper ventilation will help remove the excess heat in the winter, and reduce the chances of forming an ice dam which can backup into your attic causing water damage, mold and rot.
Roof Services has been installing and repairing roofs for over 45 years in the Chicagoland area. Ventilation systems are a regular part of the roof installation process.
If you suspect that you are having a ventilation problem, give us a call. We’ll inspect your attic, roof and ventilation system and determine what needs to be done to make your home safer and healthier.
We’re committed to providing you with the highest quality installation, service and support so you can experience the greatest life expectancy from your roof. We’re fully insured and bonded to protect your home or business.
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