ATTIC VENTILATION HAS NEVER BEEN MORE IMPORTANT.
Construction practices and products have changed dramatically over the past 20 years.  Windows and doors are more airtight, insulation levels have increased, and the use of house wraps and vapor retarders is commonplace.  Yes, houses are more airtight and that helps save energy.  But these changes have created new issues with indoor air quality and attic ventilation.

WORKING TO CODE MAY NOT BE ENOUGH.
As construction has changed, code requirements have not always kept up.  Heat or moisture problems can develop in an attic, even when the contractor has installed an attic ventilation system up to code.  At the same time, shingle manufacturers are requiring "proper attic ventilation" to validate shingle warranties.  That's why it's never been more important for contractors to know all the "ins and outs" of attic ventilation.

LOOK TO US FOR ANSWERS.
Air Vent is the attic ventilation expert.  Our intensive research and testing have lead to the development of superior ventilation products.  The performance of these products has been proven again and again through testing and tens of thousands of successful real-world installations.

As the acknowledged industry experts, we at Air Vent are committed to informing and educating contractors, builders, architects, code officials and other industry professionals.

This booklet is a compilation of tips and answers to some of the questions most commonly asked at Air Vent's Attic Ventilation:  Ask the Expert seminars.  We home you find it useful.  Please be aware that this booklet is not intended to serve as an installation manual or to replace any instructional literature which may accompany Air Vent products.  Please consult installation instructions which accompany Air Vent products for all pertinent information.

TIP 1
DON'T SHORT-CIRCUIT YOUR VENTILATION SYSTEM.

There are two important principles to remember when installing attic ventilation: Ventilation is a system of intake and exhaust Air follows the path of least resistance Air should never enter the attic at the lowest point, move up through the attic and exit at the ridge. Never install more than one type of exhaust system.  If you do, the stronger exhaust vent will pull from the other one.  When that happens, one of the vents is functioning as an intake vent and one works as an exhaust vent, short-circuiting the ventilation system. Short circuiting the exhaust has its consequences:

If more than one type of exhaust vent system is installed (for example, ridge vents and roof louvers as in this illustration), one acts as intake and the other as exhaust, leaving large areas of the attic unventilated and possible weather infiltration problems

1. Large areas of the attic  are left unventilated because air circulates only at the top of the attic.
2. If the secondary exhaust vent becomes an intake vent it is prone to weather infiltration because exhaust vents are not designed to pull air into the attic. 

TIP 2
BALANCE INTAKE AND EXHAUST.

Ventilation is a system of intake and exhaust.  That means that the flow of air will always be restricted to the lesser area.

To get the most exhaust out of the attic, the intake area should be equal to or exceed the exhaust area.

According to building codes a balanced ventilation system means at least 50% of the required vent area must be intake and 50% exhaust.  However, many ventilation engineers recommend installing additional intake to maximize airflow.

TIP 3
INSPECT THE ATTIC.

Always inspect the attic when estimating a roofing job.  Check for damage and to assess the current ventilation system.  Here's why:

1. It allows you to find any damage due to a lack of ventilation and what may need to be done to repair the damage.
2. It helps you determine how you can improve the attic ventilation system.
3. It adds to your professionalism.

HERE ARE SOME THINGS TO LOOK FOR WHEN INSPECTING THE ATTIC:

• Note the size and location of existing intake and exhaust vents.
• Check for signs of moisture damage such as mold stains on wood, compacted insulation from moisture droplets and rust on nails.
• Make sure intake vents are clear of debris.  If there are rectangular under eave vents make sure that there's at least one installed between every rafter space or every 2 or 4 ft. apart as required to balance the system.
• Is the insulation blocking the soffit area?  If so, pull it back and insert an insulation baffle.
• If an insulation baffle is already in place, make sure dirt, debris or insulation isn't clogging it.
• Can you see light at the soffit?  If so, this ensures that there is in fact a hole cut for the intake vent.
• Inform the homeowner of what you found and the benefits of improving the attic ventilation system.

TIP 4
THINGS TO LOOK FOR OUTSIDE AN ATTIC:

Don't laugh, but make sure there is a hole cut for the intake vent.  We've seen applications where the intake vent was in place without holes.

Is there dirt or debris clogging the intake vent?

Have the intake vents been painted and plugged with paint?  If so, replace them.

TIP 5
MAKE SURE VENTS PROTECT THE ATTIC FROM THE WEATHER.

Some ridge vents without external baffles have been known to leak.  Here's how it happens:

Wind blows up the roof and hits the ridge.  If there's nothing to deflect or stop it, air enters through the vent.

Snow and rain can be carried with it.  Some ridge vents are designed to trap the weather when it hits the vent to protect from weather infiltration.  This method doesn't always work.

Testing in accordance with Dade County Protocol was conducted on different ridge vents on a 4/12 roof.  After being subjected to 8" per hour rain with winds that varies from 35-110 mph, some ridge vents leaked over 400 ounces of water.  ShingleVent II passed the test without even a drop of water in the bucket. 

TIP 6
INSTALL RIDGE VENTS FROM END TO END.

Ridge vents are generally regarded as the preferred method of attic ventilation for two reasons: They're installed along the entire ridge to provide a continuous flow of air along the underside of the roof deck (when balanced with proper intake). They blend in with the ridge of the roof, making them nearly invisible from the ground. One giveaway that a ridge vent is installed on the roof is the staggered appearance when it's not installed from end to end. Even though you cut the slot length 6" from the interior end wall when installing Air Vent ridge vents, run the vent along the entire ridge for a clean, even roofline.

For best appearance, install ridge vents along the entire ridge.  Stopping short of the end creates a staggered roofline.