Attic Ventilation Is Vital, But Roofers Don’t Care

March 28, 2022

Why Attic Ventilation Is Important…
& Why Seattle Roofers Get It So, So Wrong

Greater Seattle Is Especially Wet & Humid,
So Proper Attic Ventilation Is Crucial.

Unfortunately, Most Roofers Either
Mess It Up… Or Don’t Do It At All.


According to a Yahoo Finance article I recently read, Seattle is the fifth-most humid city in the country. FIFTH.

To put that in perspective, there are 19,495 cities, towns, and villages in the United States. That means, humidity-wise, Seattle beats all but four of them—including Miami, Tampa, and San Antonio.

Why am I telling you this? Because it’s verifiable proof that PROPER attic ventilation is especially important for homes in the Greater Seattle area.

Attic ventilation affects everything from your roof’s shingles to your energy bills to your health. If your attic has trapped moisture, it’s going to cause you serious problems.

Here’s the bad news: attic ventilation is what roofers mess up MOST… if they bother to do it at all.

In this article, I tell you A) why attic ventilation is important, B) what proper attic ventilation consists of, and C) how the majority of companies get it so wrong.

Why Attic Ventilation Is Important, Especially In Greater Seattle

Proper attic ventilation is important year-round. This goes doubly in highly humid parts of the country like ours.

During the warm months, proper attic ventilation helps combat heat buildup. A hot, humid attic can cause all kinds of problems. It will make your home warmer, causing your air conditioning to work harder and increasing your energy costs. It can lead to rot and mold. It can even “cook” your roofing shingles and cause them to deteriorate.

During the cool months, proper attic ventilation helps prevent moisture buildup. The typical household generates two to four gallons of water vapor per day from activities like showering, doing laundry, cooking—and even breathing. The moisture these activities produce is attracted to your cool attic. Once it’s in your attic, that moisture will condense and ultimately lead to rot, mold, damp attic insulation, and substandard indoor air quality.

Unfortunately, the overwhelming majority of Greater Seattle homes have poor attic ventilation. In fact, just about ALL attic ventilation installed prior to 2018 is no longer up to code.

Here’s why…

What, Exactly, Is Proper Attic Ventilation?

A long time ago, people thought the earth was flat. But as scientific research progressed over the years, people discovered that the earth is actually a sphere.

The same kind of thing happened—still happens—with attic ventilation.

Decades ago, experts determined a 1/600 ratio for attic ventilation was adequate. In layman’s terms, that means one square foot of attic ventilation per 600 square feet of attic floor space.

Later on, the experts determined the 1/600 ratio was inadequate. So they changed it to 1/300. That meant one square foot of ventilation per 300 square foot for attic floor space. Eighty percent of ventilation could be exhaust, and 20% would be intake.

The experts THEN determined 1/300 ratio. Not only was this not enough ventilation, but there were also no requirements for exhaust-intake ventilation balance. When you have too much exhaust ventilation, it can create a backfeeding pressure effect in your attic. This can cause the exhaust ventilation to pull conditioned air in your home through light fixtures, cracks, and other gaps… OR it can cause the outside air to come back in through the exhaust.

What’s that mean for you? The moisture never leaves. It sits. It marinates in your structure and framing. It causes mold and rot. It is, in short, a “very bad thing.”

So in 2018, attic ventilation guidelines were updated to what they are today: a 1/150 ratio, with intake and exhaust ventilation equally balanced under most circumstances. That means one square foot of attic ventilation per 150 square feet of attic floor space… with a 50% intake, 50% exhaust balance.

After installing attic ventilation in countless homes, I can confidently say this is the “Goldilocks” ratio. It’s not too little or too much. It’s just right for keeping your attic properly vented.

Other Articles You’ll Find Interesting:

Why So Many Roofers Get Attic Ventilation Wrong

Roofers get attic ventilation wrong—A LOT. And that’s typically because they either A) don’t care or B) lack knowledge and experience.

I’m not kidding when I say that 9 of every 10 roofs we inspect have inadequate attic ventilation. Some of that is because building codes have been updated since the last time the homeowner had roofing work done. But a lot of it is roofing companies just plain messing up… or neglecting attic ventilation all together.

Here are a few recent examples of poorly vented attics we’ve inspected…

Moldy Attic In Renton, WA

Mold In Attic Of Renton Home

Moldy Attic In Issaquah, WA

Moldy Attic In Issaquah

Bellevue, WA Home With Rotted Wood Due To Poor Attic Ventilation

Bellevue Home With Rotted Wood Due To Poor Ventilation

As you can see, the results of inadequate ventilation aren’t pretty… or healthy.

How To Ensure Your Roofer Gets Attic Ventilation RIGHT

Luckily, vetting a roofer’s attic ventilation process is simple. Just ask them the following questions…

  1. Do you adhere to the U.S. Federal Housing Administration’s guidelines of one square foot of attic ventilation for every 150 square feet of attic?
  2. What is your plan for balancing intake and exhaust ventilation in my attic?
  3. Are you going to use more than one type of exhaust ventilation? (If they say “yes,” show them the door. When more than one exhaust type is in the same attic, the bigger one will pull air from the smaller one, creating negative air pressure.)

If you’re looking for a Greater Seattle roofer that takes attic ventilation seriously, get in touch. We’ll perform a meticulous inspection of your roof and attic, determine the right solution for your needs, and provide you with a fair price. Then we’ll execute your roof replacement with our famous “Egghead’ Installation.

We would be honored to hear from you.

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