Back to School Time for Roofers

Now that the kids are back in school and you are urging them to do their best, let’s see how you perform on our favorite topic: attic ventilation.  Quiz to follow!!!

By Andy Swan, Roof Saver.

By now you know that attic ventilation is a means to allow hot, moist air to escape from the attic.  The excess heat needs to escape for the comfort of the occupants, to reduce air conditioning demand and to get as much life from the roofing covering materials as possible.  You want the moist air to exhaust from the attic primarily to deter the growth of mold and mildew but also because too much moisture in the attic reduces the effectiveness of attic insulation.

An effective attic ventilation system requires a balance of intake and exhaust vents.  The use of vented soffit as an intake and continuous ridge vent as exhaust is a popular way to achieve the requirements of the building code.  The building code offers two ratios depending on construction materials.  If the warm in winter side of the attic has a vapor retarder such as Kraft faced insulation you can install one square foot of net free area per 300 square feet of attic area.  If the attic lacks a vapor retarder you need twice the total net free area of attic ventilation and use the 1:150 ratio.

Quiz time:

1. How does water vapor enter the attic?
   1. Roof leaks
   2. Bathroom or kitchen vents terminating inside the attic
   3. Indoor cooking, bathing and laundry
   4. All of the above
2. The International Building Code requires
   1. Intake net free area equal to or greater than exhaust net free area
   2. Intake net free area up to 60% of total net free area
   3. Any combination of intake and exhaust vents
3. All vents are tested and certified to meet local building codes
   1. True
   2. False

Answers:

1. d is correct – All of the above. Kitchen and bathroom vents are not allowed to vent directly into the attic.  This is a common error but you only know if you look.  Indoor cooking, bathing and laundry put 2 to 4 GALLONS of water vapor into the air inside the typical home each day.
2. a and b are correct. The attic ventilation system needs more intake than exhaust to operate properly.  The International Building Code requires intake equal to or greater than exhaust NFA.  Common practice is to have up to 60% of the total net free area as intake.
3. b – False is the correct answer. Only those products tested by an independent third party and proven to meet or exceed the International Building Code have an ICC Evaluation Service report number on the product or packaging. The Miami-Dade County NOA appears only on products tested to meet the High Velocity Hurricane Zone requirements.

If you remember your school days, checking your work was a best practice.  The same is true for the roofing materials you use – who’s checking their work? We do have a complete study guide to help you become a ventilation expert - click here.

Andy Swan is president of Blocksom and Co., manufacturer of Roof Saver Ridge Vent. For more information on Roof Saver visit www.roofsaver.com.