Is Your Attic Properly Ventilated? Why is this important?
The dog days of summer are right around the corner which means it is a good time to think about attic ventilation. Adequate ventilation pays dividends in many ways.
Having proper ventilation will keep your attic cooler this summer.
Longer shingle life
Lower cooling costs
More consistent temperatures throughout your home.
Proper venting will also help to reduce and even prevent ice dams this winter. Many of the “leaks” we see in the winter and spring are caused by condensation as a result of poor ventilation.
By considering ventilation now you can reduce time and hassle later all while saving money and reducing energy consumption.
A professionally designed ventilation system needs to do 3 things:
Provide enough air
Provide balanced pressure
Control heat and moisture
Quite simply your roof vents must allow enough air to move through to evacuate heat and moisture so not to allow condensation, heat, or mold to accumulate.
Our attic is just like a bathtub, if the drain flow is slower than the faucet, water will slowly fill the tub. Similarly, our attic must balance pressure as it can only let out as much air as it can take in. When the volume of air coming in and the rate at which it moves through the attic are correct, heat and moisture will be controlled.
How do we make sure we have enough ventilation in our roofs? The current energy code in Minnesota calls for 1 sq. ft of ventilation for every 150 sq. ft of attic space, or 1/150 ft sq. This amount of space is reduced to 1/300 ft sq. if 40%, but no more than 50%, of the ventilation is located near the top of the roof.
When we break down what that means, we find that:
1 turtle/static vent, or 2 ft. of ridge vent, is needed per 75 sq. ft of attic space if there are no soffit intake vents.
If soffit intake vents are adequate and roughly equal to venting on the roof, that number doubles to 150 sq. ft of attic space.
On a building that has 2400 sq. ft of attic space, assuming the 50% rule, we require 1/300 sq. ft of venting, or 8 sq. ft of ventilation at or near the peak. A turtle/static vent provides ½ sq. ft of venting so we would need 16 turtle vents. Ridge vent cut in properly at 3 ½ inches wide would need to be 27 ½ ft. long.
Please keep in mind these are the MINIMUM requirements required by code and are assuming proper intake venting at the soffits. It is always recommended to error on the side of caution and install vents at a higher standard than code.
These calculations are for simple roof systems and are not considering the many design features in newer homes. For example, many townhome attics are not connected to reduce the rate at which a fire will spread. While this is an essential safety feature it also means each unit must be evaluated individually for its venting needs.
Of course, here in Minnesota, our attics are all insulated. Attic insulation many times can cover and interfere with intake venting creating a bottle neck in the system. Also, simple remodeling projects such as recessed lighting can have an impact on heat buildup in an attic.
The bottom line is even if current code is met you may still have a problem with the design of your roof ventilation system. If you are getting unexplained “leaks” when it is not raining, or your AC just cannot keep up, it is probably time to consider the possibility of inadequate ventilation.
Parkway is committed to helping Property Managers and Homeowners Associations maintain beautiful, healthy communities, through consultation, maintenance, repair, and replacement. If you have questions, please do not hesitate to ask us, we are here to help.
Parkway Building Services & Parkway Custom Construction