How To Calculate For Proper Attic & Roof Ventilation.

Attic Ventilation

Most people underestimate just how important proper attic ventilation is to the survival of their home. Proper roof venting prevents costly problems like: attic mold, rotting of roof sheathing and framing, shortened roof life, cracked paint and siding failure, or an overheated home.

Daily activities in your home such as showering, dishwater, laundry or having the furnace on generate heat and moisture. This moisture is pulled into the attic by powered exhaust fans. If the attic does not have a proper roof venting system the moisture will remain in the attic and begin to wreak unseen havoc.

In times past roof and attic ventilation were not as critical because moisture would escape out old windows, doors and even right through the walls. With modern building codes and construction materials such as vapor barriers, vinyl siding and high tech windows very little moisture gets in or out of the house.

The facts:

Attics can heat up to 165 degrees F or more (73.9 C). This in turn overheats the home if not vented properly costing homeowners thousands of dollars in air conditioning.

Roof decks can reach over 170 degrees F (76.7 C). Improperly vented roofs can cook roofing materials.

How to calculate your roof venting requirements:

In order to have a balanced ventilation system you need to have the right roof vent calculation. The Federal Housing Authority (FHA) and the Urban Development (HUD) have established minimum requirements for attic ventilation. According to their requirements you should have 1 sq foot of attic ventilation per 300 sq ft of attic floor space. There should also be a 50/50 balance soffit venting and roof venting. If your roof is 1200 sq ft of attic floor space you will need 4 sq feet of roof ventilation. In order to find the right calculation divide the attic floor space by 300 sq feet. 1200 sq feet/300=4. Next multiply the 4 sq feet into cubic inches. 1 cubic foot is 12” x 12”+144 cubic inches. In our case the required 4 vents for the 1200 sq ft house multiply the 144 cubic inches by 4=576 cubic inches. That gives you the required attic ventilation requirement. Next divide that number by 2: 576/2=288”. Now you know how many cubic inches of attic/roof venting you need for the roof and soffit.

Roof Venting Chart

One of the easiest and most effective ways to vent a roof is to use a ridge vent. A ridge vent is installed at the peak of the roof where the heat rises to. In order to install a ridge vent a certified roofing contractor will cut back the roof sheathing in order to create an opening for the attic to vent through. The ridge vent is installed on the peak with nails and shingled over for aesthetic purposes. Ridge vents are one of the easiest ways to meet roof venting requirements.  Other options to meet your attic ventilation needs are: standard attic vents like AF-50’s, ventilation fans, or solar powered attic fans.

Continuous Ridge Vent

If you are in the Puget Sound area of Washington State and would like to have a free attic ventilation evaluation or roof estimate please contact us at 253-445-8950 or fill out our quick estimate form.

Roof Venting Calculator App

Apple has a great roof venting calculation app that makes finding your required venting ratio very easy. Check out this link to roof venting made easy: http://www.roofingcalculator.org/roofing-calculator-for-iphone-and-android.php

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3 Responses to How To Calculate For Proper Attic & Roof Ventilation.

  1. Good post on ventilation. It’s annoying driving by homes and visually seeing improperly ventilated homes.

  2. Ted Johnson says:

    Do you have any suggestions for a roofing person in Lewis County? Also, I’d like to get rid of the roof vents that are leaking water. I don’t have soffetts. Would a ridge vent with gable vents be enough to properly vent a roof? Thanks for your help.

 

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