Proper roof ventilation is normally an oversite for most homeowners when discussing roofing, but there are many reasons why it should be.

A good rule of thumb is for 1 sq. ft. of vented area for every 300 square feet of attic space, this has been adopted into most building codes.

DID YOU KNOW? Not having proper ventilation may void your shingle warranty?

DID YOU KNOW? Not having adequate ventilation can also put stress on your air-conditioning unit(s) and make it work harder to cool your house, especially with our summer heat.

DID YOU KNOW? That over time trapped heat can literally “bake” your roof.

DID YOU KNOW? Studies show attics can reach temperatures in excess of 160 degrees on a typical summer day, with outside air temperatures of 95 to 97 degrees. Just think how hot it gets on those 100 degree days.

Proper roof ventilation is very cheap insurance for your roof. Inadequate ventilation becomes apparent when problems occur in form of ineffective insulation, leaking roofs, rotting sheathing, peeling paint, high utility cost, etc.

Three Must Do Steps For Attic Ventilation

1.     Install all Exhaust Ventilation at the SAME HEIGHT within a common attic area. Installation of exhaust vents at more than one level of a roof allows the upper ehaust vent to pull air in from lower exhaust vents rather than from the soffit Intake Vents. Intake air must come from the soffit vent area to properly ventilate the total attic area and eliminate weather infiltration. 

2.     Install ONLY ONE TYPE of Exhaust Ventilation within a common attic area. Exhaust Vents pull air from the easiest intake source. The use of two or more types of exhaust vents such as Power Vents with Roof Vents or Gavle Bents with Ridge Vents or Roof Vents could make one of these vents act as intake for the other. Intake ari must come from the soffit vent area to properly ventilate the total attic area and eliminate weather infiltration.

3.   Install a BALANCED SYSTEM of Intake and Exhaust Ventilation.

50% Intake Vents – Soffit Panel Systems are a common source of intake ventilation in todays homes. Keep in mind that it takes ten or more vented soffit panels to equal the ventilation capacity of one 13 x 8 soffit vent. We highly recommend that you install all vented soffit panels and use air chutes or baffles in every rafter/truss soffit opening.

50% Exhaust Vents – Use the 1/300 rule. For every 300 square feet of attic floor space, 1 square foot of net free area of ventilation must be provided.

Which is better  Too much intake or too much exhaust?

If an exhaust vent is looking for intake and a balanced intake is not provided, the exhaut vent will use another exhaust vent for intake.

Can you over ventilate?

As long as the system is balanced, you cannot over ventilate. If soffit ventilation is over 50% the system will still vent properly. You should never have more roof ventilation than soffit ventilation.

Factors Affecting Attic Ventilation

• Lack of under eave soffit ventilation. This is the #1 reason for weather infiltration. There should be an equal or slightly greater amount of free area in the soffit regardless of the type of exhaust system used. Make sure that the soffit vents are not covered by insulation, light should be visible in the soffit area.
• If lanced or perforated soffit panels are used, the ones that provide maximum ventilation should be used. Vented panels should be used continuously around the soffit area. Panels with holes typically have more free area than panels that are lanced. Also, some lanced panels are often not lanced cleanly and can cause more resistance to air flow.
• Do not mix different exhaust products on a single attic, i.e., do not use roof vents with ridge vents, ridge vents with power vents, turbines with roof vents, etc… Avoid using ridge vents or roof vents near gable vents. Depending on wind direction, the gable vents can act as exhaust vents and cause the ridge or roof vents to act as intake vents. If problems occur, make the gable vents non-functional.
• Keep roof vents on the same side of the ridge. Do not place them across the ridge from one another. Depending on the wind conditions, one roof vent may try to feed from the other roof vent.
• Do not use roof louvers on the lower part of the roof for intake. Roof louvers are designed to be exhaust vents and may not offer the desired weather protection when being used as intake.
• Do not use ridge vents on rakes or hips of hip roof designs. Ridge vents are designed to be exhaust vents. When installed on the rakes, the exhaust / intake systems are indefinable.
• Avoid placing ridge vents or roof vents on dormers when dormers are lower than the main ridge and connected to the main attic. If vents are put on lower dormers which are connected to the main attic, separate the dormer from the main attic and let the dormer be a “mini attic”.
• If ridge vents are used on homes with multiple ridge line heights, it may be desirable to separate the attic areas where the ridge lines change. This may be done with plastic sheeting or roofing felt.

Source - Lomanco, Inc

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