About Paul Scelsi

Paul Scelsi is marketing communications manager at Air Vent Inc. and the leader of its Attic Ventilation: Ask the Expert seminars for residential roofing professionals. He also is chairman of the Asphalt Roofing Manufacturers Association Ventilation Task Force.

Clearing the Hurdles to an Attic Ventilation Upgrade

New ventilation products on this home were installed as part of a roof replacement completed by Ameritech Services, LLC, Deptford, New Jersey. Photo: Larry Deyo, Ameritech Services

The best time to evaluate and improve the residential attic ventilation system is during the installation of a new roof. Access and installation are generally easiest at that time, so a re-roofing application is an ideal time to fix existing problems and/or increase the airflow in an under-ventilated attic . But just because the roofing contractor determines the attic ventilation system needs a fix does not mean it happens.

We asked roofing contractors who have attended our best practices in residential attic ventilation seminars this question: What keeps you from upgrading the attic ventilation system during the installation of a new roof?Other than roof or house construction obstacles such as certain types of framing, incorrectly added house additions, or vaulted ceilings that are incorrectly insulated, here are the common hurdles — and suggestions to overcome them — from roofing professionals across North America.

HURDLE: “We’ve Never Had Ventilation, So Why Now?”

Many homeowners will challenge the roofing contractor who points out that the attic does not have enough ventilation — or any ventilation at all — if it’s been that way for a long time and there aren’t any noticeable problems. They reason that there’s nothing to fix.

“They typically say, ‘Well, it has been like this forever, why does it need to be changed now?’” says Clayton Putman, commercial project manager, Elite Roofing, Denver, Colorado.

Such comments are rooted in a reluctance to make an unnecessary purchase. “Customers do not want to pay for something they didn’t think they needed before and do not think they need now,” says Dale Johnson, project manager, HomeZone Improvements, Grand Blanc, Michigan.

Tips for Clearing this Hurdle: “I have trained our team to discuss the benefits of updating the attic ventilation system and count on them to present the information to the customer well,” says Putman. Here are some talking points to help overcome the hurdle of homeowners not wanting attic ventilation they previously never had or needed.

· Just because there are no obvious signs of trouble does not mean all is fine. Has anyone checked inside the attic to see the condition of the underside of the deck and the attic insulation? Any signs of mold or condensation buildup? Are there any signs of premature shingle failure?

· The house may be more airtight than in past years and will benefit from improved attic ventilation.Since buying this house have there been energy-efficiency upgrades such as new windows, doors, or insulation? If so, the house does not “breathe” as easily as it did previously. Tighter houses benefit from attic airflow to remove heat buildup in the warmer months, moisture buildup in the colder months and fight ice dams in snow climates.

· Your new roof will meet current standards. The full terms of the warranty that comes with your brand-new shingles is tied to proper attic ventilation. Current International Residential Building Code specifies the amount of attic ventilation needed and your attic does not meet those numbers. Even if the local municipality does not enforce building code, you’re knowingly paying for an inferior roof.

HURDLE: “You’re too Expensive.”

Good luck to the roofing contractor who is thorough, diligent yet considered too expensive compared to the other contractors who have submitted estimates to the homeowner. While price certainly should be evaluated, there is more to a roof estimate than just dollars.

“Very few contractors look at attic ventilation as an important factor in a new roof, so they do not include it in their estimate; and most of the contractors think there is a one-size-fits-all solution. As a result, their estimates are less expensive than mine,” says Matt Cooper, general manager, Redemption Roofing, Conroe, Texas.

Is less expensive better?

“Homeowners question my reasoning for additional attic ventilation since most other contractors do not mention the need. The homeowners almost feel as if I am trying to take advantage of them rather than make their roof ‘system’ a best practices/optimal operating one,” says Sabrina Johnson, president, KDCO Home Improvement Inc., Akron, Ohio.

Not understanding the overall project contributes to the price objections from homeowners. “Improperly educated customers make it challenging to upgrade the attic ventilation system,” says Greg Pike, project consultant, Campo Roofing, Twinsburg, Ohio.

If homeowners understood that all the exhaust vents in the world on their roof are useless without proper intake vents, perhaps price concerns would be reduced. “The main cause that prevents me from upgrading is the homeowner not wanting to pay for improved intake ventilation,” says Richard Turner, owner, R.J. Turner Remodeling, LLC., Winston Salem, North Carolina.

Tips for Clearing this Hurdle: “I will explain the importance of proper attic ventilation and provide documentation (brochures, website links, etc.) detailing why adding intake ventilation is critical,” says Turner. Here are some talking points to help overcome the hurdle of homeowners who believe the roof estimate is over-priced because the contractor included proper attic ventilation.

· Make sure we’re comparing apples to apples. A roofing estimate without intake and exhaust vents is not the same as a roofing estimate with a balanced system of attic ventilation. Those are two very different roofs that will deliver very different performances. I’m recommending a complete roofing system for longevity.

· Your new roof needs attic ventilation to perform properly. Anyone can install a roof covering. I’m installing a roof system that includes balanced attic ventilation to fight heat buildup in the summer, which will lighten the burden on your air conditioning system and improve the comfort in the living space. It will help fight the moisture buildup inside the attic from the 2 to 4 gallons of water vapor the average family of four generates indoors daily by occupying the house (cooking, cleaning, laundry, perspiration, breathing, etc.). And in snowy climates, attic ventilation helps keep the roof temperature fairly even so that ice dams are reduced.

· Our company has a great reputation. I’m not sure why the other contractors did not mention attic ventilation, but they should have. Our company always does because it’s needed for a properly installed roof. We’ve been in business here locally a long time and enjoy a solid reputation. We stand behind our projects which includes a comprehensive estimate for an entire roofing system.

HURDLE: “I’m Selling the House Soon.”

For the homeowner who is selling the house soon, spending money on the property for anything viewed as non-essential is a red flag. “People selling their home will not do anything they view as ‘extra’ like attic ventilation,” says Sue May, owner, A Better Way Construction and Roofing, LLC., Lincoln, Nebraska.

Tips for Clearing this Hurdle: Broaden the conversation to include the perspective of the potential buyer of the house. Here are some talking points to help overcome the hurdle of homeowners not interested in attic ventilation upgrades because they are selling the house.

· Your potential buyer will be looking very closely. I understand you’re selling the house and want to avoid any unnecessary spending. Someone will be buying your house and wants the best value for the money. If the potential buyer does not catch the lack of proper attic ventilation, the home inspector hired by the buyer likely will. You can avoid that possibility by addressing the attic ventilation deficiencies now. Otherwise, be prepared to negotiate with the potential buyers why your attic is incorrectly ventilated and how that will impact the selling price.

HURDLE: “Insurance Will Not Pay for It.”

A storm-damaged roof is being replaced and covered in price by the homeowner’s insurance policy but the cost to upgrade or improve the attic ventilation system is not. “If insurance will not pay for the upgrade, the homeowner will not either,” says Bryan Epley, former senior director of business development and sales, Gen 3 Roofing, Centennial, Colorado.

Tips for Clearing this Hurdle: Many roofing contractors will either arm homeowners with the needed information to get the insurance company to pay or will write a letter to the insurance company on the homeowners’ behalf. Here are some talking points to help overcome the insurance policy hurdle.

· Let’s change the insurance company’s mind. Let me get this right: Your insurance company is willing to pay the cost for a new roof — which is a significant purchase totaling thousands of dollars — but will not cover the cost of a needed attic ventilation upgrade, which is a small fraction of the cost of the total roof. We’re going to help the insurance company to reconsider. First, check your insurance policy for any “code upgrade” language. You’re about to get a new roof. If it’s not installed according to today’s building code standards, tell the insurance company. Second, the full terms of the warranty for your new roof are tied directly to proper, balanced attic ventilation. You don’t have proper attic ventilation. If we don’t upgrade your attic ventilation system, your insurance company will be paying for a new roof that has a reduced warranty. Third, the official representing organization of asphalt shingle manufacturers, ARMA, says point blank in its technical bulletin for residential roofing: the roof needs balanced attic ventilation. Let’s pass that along to the insurance company.

Willing to Walk Away

For many contractors, there is no insurmountable hurdle to upgrading the attic ventilation during a roofing project because they refuse to take the roofing project otherwise. For them, there’s no other option. It’s mandatory if the homeowner hires them. They are unwilling to put their company name on a roofing project knowingly done incorrectly. And if this requirement by contractors to upgrade the attic ventilation causes them to lose the project to other contractors, they’re fine with that.

“Our company will not do a roof without making sure it’s vented correctly,” says Jeffrey Heitzenrater, president operations, Triple Peaks Roofing and Construction, Inc., Olmsted Falls, Ohio.

“Nothing prevents me from upgrading,” says Sean Jegen, owner, Gorilla Exteriors Contracting LLC, Shawnee, Kansas. “I tell the homeowner these are mandatory improvements and if we don’t do them the shingle warranty is affected.”

“We always do it right or we don’t do it,” says Chris Arrington, vice president, Arrington Roofing, Dallas, Texas.

To the quality-conscious contractors in business for the long haul, doing it incorrectly just to make some profit is not worth the risks that could be lurking around the corner: callbacks and a damaged reputation.

“Contractors need to be smart and know when to walk away from a job to avoid getting wrapped up in a possible mold remediation or shingle failure claim,” says Jeff Barnett, Barnett Roofing and Siding, Inc., Canton, Michigan.

“We always upgrade,” says Sandra Daffer, owner, Hawaiian Built Roofing, Boise, Idaho. “It’s automatically in our bid if it’s needed. If the roof is a good one for ridge vent, then we go that route. Otherwise, we’ll pursue other venting options.”

“We will not upgrade to a ridge vent if the homeowner won’t upgrade an insufficient intake airflow system for balance,” says Corey Ballweg, owner, Mid Towne Construction, Inc., Cross Plains, Wisconsin.

“We check for proper attic ventilation on every roof replacement we do. We upgrade if needed, or we refuse to do the job,” says Trevor Atwell, owner, Atwell Exterior Services LLC, Greenville, North Carolina.

“We always upgrade the attic ventilation system,” says Patrick Readyhough, president, Pond Roofing Company, Inc., Fairfax, Virginia. “We include it as part of our whole roof system,”

Turn the Tables in Your Favor

Some contractors who take the hard stance of refusing to do the roof without upgrading the attic ventilation separate themselves from their competition in a positive way that actually leads to more business.

“Many times, we are hired because we make it a point to show the homeowner attic ventilation is needed,” says Heitzenrater. “All shingle manufacturers’ warranties that we deal with point out there is no warranty after a specified time unless there is proper attic ventilation.”

“After I teach the homeowner the importance of attic ventilation, nothing prevents me from upgrading the ventilation system,” says Ron Bastian, owner, Bastian Roofing, Richfield, Wisconsin. “Both in the summer and winter the homeowner clearly understands the benefits they will acquire by me doing their roofing project.”

About the author: Paul Scelsi is marketing communications manager at Air Vent Inc. and leader of its Attic Ventilation: Ask the Expert™ in-person seminars (www.airvent.com). He hosts the podcast “Airing it out with Air Vent” and is the chairman the Asphalt Roofing Manufacturers Association Ventilation Task Force. He is the author of the book, Grab and Hold Their Attention: Creating and Delivering Presentations that Move Your Audience to Action.

Focused on Proper Residential Attic Ventilation, Roofing Contractors Documented These Mistakes

Since 1998 our best practices in residential attic ventilation seminars have featured the real-world situations roofing contractors are seeing. Here we cover a handful of attic ventilation mistakes contractors found in the field. (Note: Some photos show multiple mistakes but were chosen to highlight one.)

Problem: Bagged Wind Turbines Suffocate the Attic Airflow

Solution: Unbag the wind turbines.

Photo: Jake Jacobson, SF5 Construction, LLC, Little Elm, Texas

It’s impossible for a covered attic exhaust vent to work if it’s smothered under a bag. Attic ventilation is supposed to provide year-round benefits, fighting heat buildup in the warmer weather and moisture buildup in the colder weather. It’s sometimes forgotten (and maybe never known) that occupants of a house generate water vapor daily through activities such as cooking, cleaning, bathing, breathing, etc. It amounts to 2-4 gallons per day for the average family of four. That warm, moist air can make its way into the colder attic in the winter months, where it can condense and cause trouble as water droplets and frost.

Problem: Bath Fan Ductwork Terminating in the Attic Damages Roof

Solution: Run the bath fan ductwork either vertically through the roof or out the side gable wall.

Photo: Trevor Atwell, Atwell Exterior Services, LLC, Greenville, North Carolina

Even a perfectly balanced attic ventilation system cannot handle the quantity of moisture dumped into the attic by the bath fan. It overwhelms the system. That moisture should be vented directly to the outdoors without any pitstops into the attic. In the home pictured here, Trevor Atwell found three bathroom fans venting directly into the attic. He also found a lot of rotted sheathing.

Problem: Painted Soffit Vents Result in Reduced Intake Airflow

Solution: Buy pre-painted soffits, or paint them more carefully, or replace them with new vents.

Photo: Daniel White, Roof Life of Oregon, Tigard, Oregon

Soffit vents have a specified amount of Net Free Area (airflow capability) when they are manufactured. For example, 9 square inches of NFA per linear foot. That amount, by the way, would balance nicely with a ridge vent (exhaust vent) that is capable of 18 square inches of Net Free Area per linear foot (9 NFA at the soffit on the left of the ridge vent + 9 NFA at the soffit on the ridge of the ridge vent = 18 NFA at the peak of the roof). But the airflow capability of the soffit is reduced if the vent openings become clogged or blocked because of a careless paint job. While house exterior colors are important, don’t sacrifice attic ventilation performance. It’s possible to have both a nicely painted soffit and it’s full, intended net free area (airflow capability).

Problem: Two Rows of Box Vents = One Path of Inefficient Airflow

Solution: Always keep attic exhaust vents in one row.

Photo: Daniel White, Roof Life of Oregon, Tigard, Oregon

Let’s cut to the chase. If it takes two rows of attic exhaust vents to meet the attic’s exhaust ventilation needs, it’s time to find another category of exhaust (maybe horizontal ridge vent; or diagonal hip ridge vent; or a combination of horizontal and diagonal ridge vent; or a power fan). But when attic exhaust vents are aligned in two rows, the primary path of the airflow will be from one row to the next because air will allows follow the path of least resistance seeking the closest exit point from its entry point. The intake vents in the soffit or low on the roof’s edge are supposed to be the intake vents. The pictured scenario here is producing inefficient attic airflow and could cause one row of box vents to ingest weather.

Problem: Mixed Types of Attic Exhaust Vents = Problematic Airflow

Solution: Only use one type of attic exhaust vent on the same roof above a common attic.

Daniel White, Roof Life of Oregon, Tigard, Oregon

Regardless what combination of two or more different types of attic exhaust vents either the homeowner demands (we’ve heard the stories) or a well-intended but misguided roofing contractor recommends (it’s happening), do not mix two different types of attic exhaust vents on the same roof above a common attic. Pictured here are wind turbines with ridge vents; box vents with ridge vents; solar powered fans with box vents; and traditional electric power fans with ridge vents. Now shown is the all-time classic: Gable-end louvers with any other type of attic exhaust.

When attic exhaust types are mixed, it short-circuits the airflow system because air always follows the path of least resistance. The air is looking for the easiest, least difficult exit path. That path is inevitably the distance between the two types of attic exhaust vents because they are closest to each other. That means the airflow will be concentrated in that area of the attic; which leaves significant areas of the attic incorrectly vented. The intake vents low on the roof’s edge or in the soffit/overhang have been pretty much bypassed. Furthermore, if one of the exhaust vents is suddenly an intake vent, does than mean it’s ingesting weather along with the air? You do not want to find out.

Trevor Atwell, Atwell Exteriors, LLC, Greenville, North Carolina.

About the author: Paul Scelsi is marketing communications manager at Air Vent Inc., the leader of its Attic Ventilation: Ask the Expert in-person seminars, and the host of the podcast “Airing it out with Air Vent.” He’s also chairman the Asphalt Roofing Manufacturers Association Ventilation Task Force and the author of the book Grab and Hold Their Attention: Creating and Delivering Presentations that Move Your Audience to Action. For more information about the company, visit www.airvent.com.

Fact or Fiction? Mixing Exhaust Vent Types Is Problematic

Too often, attic exhaust vent types are mixed, which can short-circuit the airflow pattern in the attic space. Photo: Jerry Becker

Airflow dynamics dictates avoiding it. The manufacturers’ Installation Instructions caution against it. Building Code cites it as a violation. And yet it remains one of the most questioned, challenged and, unfortunately, ignored tips offered during our best practices in residential attic ventilation seminars.

Is it really a problem to mix or combine different types of attic exhaust ventilation (ridge vents, wind turbines, gable louvers, box vents and power fans) on the same roof above a common attic? And if it is, why will you see it so often driving through any city in North America?

Lack of information, misunderstanding the science, and resistance to breaking old habits all contribute to the persistence of mixed exhaust vents on today’s roofs. We asked roofing contractors to share their experiences to help explain what could go wrong.

Problem No. 1: Inefficient Airflow

The main reason combining different types of exhaust vents is problematic is that it disturbs the proper flow of the attic air. To best help fight heat buildup, moisture buildup and ice dams, attic ventilation must be a balanced system of intake vents (placed low on the roof in the soffit or at the roof’s edge) and exhaust vents (placed at or near the roof’s peak). This allows the incoming cooler, drier air to enter the attic at the lowest possible location, flush out any built-up heat and moisture from inside the attic all along the entire underside of the roof deck, and push it out through the exhaust vents high on the roof.

Power fans are a good exhaust vent option. So are ridge vents. But not when they are mixed together on the same roof above a common attic. Doing so could lead to inefficient airflow and weather infiltration. Photo: Sean Toms

But, if two or more different types of exhaust vents are in place, it short-circuits the system. Instead of the primary path of air being into the intake vents and out of the exhaust vents, the path is mostly between the two styles of exhaust vents. One of the types of exhaust vents becomes an intake vent because air will always follow the path of least resistance. Air will always look for the easiest, closest path to take. That path happens to be between the two types of exhaust vents. And that limits the distribution of the air to the upper region of the roof; or worse, it keeps the air circulating between the distances of the two vents closest to the peak. That is not the best way to remove heat and moisture buildup inside an attic.

“About five years ago, I had a seasoned roofer with me that just started working for our company,” recalls roofing consultant Jerry Becker, Roof Life of Oregon, Tigard, Oregon. “We walked up to this apartment complex and I noticed that there was a power fan alongside can vents (box vents) and very little intake ventilation. I placed a friendly bet with him stating that I know what the plywood already looks like underneath without looking at it. He argued with me and said, ‘This roof has plenty of ventilation; look at all the vents up top and it even has a fan!’ So, I told him that the plywood next to the fan and the closest can vents and up to the ridge is going to be perfect, but as soon as you drop down about a foot from the power fan the plywood will be as black as night.

“We go inside the attic and what do you think we found? Black microbial growth on the lower section of the roof. It was so black that it was wet. It is important not to mix exhaust vent types. It’s bad enough when you do it on a single dwelling home, but that same mistake in a multi-family home is deadly. Think of all the moisture that is created by all the families — the washer/dryer, dishwasher, sinks, showers and ourselves.”

Inefficient airflow not only can damage the roof deck but it can also prematurely age the asphalt shingles. “I see examples of this all the time,” says Trevor Atwell, owner, Atwell Exterior Services LLC, Greenville, North Carolina. “Premature aging of roofing materials, buckled sheathing and signs of rotten wood all due to the moisture and heat being trapped.”

Ironically, sometimes the desire to mix types of attic exhaust vents seems reasonable on the surface. The homeowner or the roofing contractor wants to improve the flow of air. Thus, adding more vents — even if they are different types — seems logical. But more is only better in this case if it’s more of the same type. If improved airflow is the goal, double-check if the correct type of exhaust vent is being used to match the size and design of the roof/attic and if it’s being supplied with a balanced amount of intake ventilation. Mixing exhaust is not the solution.

Box vents or power vents installed near a ridge vent can lead to inefficient airflow, which can damage the roof deck and prematurely age asphalt shingles. Photo: Trevor Atwell

“I have seen this in action and until it was explained to me why I should avoid it, the concept of mixed exhaust was a mystery I had to punt to a colleague or competitor” says Tim Chapin, owner, Your Safe and Healthy Home, Akron, Ohio. “I had a condo project with a very complex roof made even worse by the presence of ridge vents, gable vents, soffit vents, and box vents. I was amazed there was a problem because it seemed to be ventilated to the max. But now I know it was short-circuited.”

“We see it often with ridge vents and a power fan just below the ridge vent, or with box vents combined with ridge vents; sometimes all three. We call it the Ventilation Trifecta,” says Tom Picha, steep slope consultant, Affordable Roofing Inc., Aurora, Illinois. “More is good in some cases. Not all.”

“I had a house I was asked to inspect. The house had a ridge vent, box vents and vented drip edge on it,” says Jeffrey Heitzenrater, owner, Triple Peaks Roofing & Construction Inc., Westlake, Ohio. “The first thing wrong was two different types of exhaust vents. Upon a complete attic inspection, we found mold and mildew. The insulation was also packed tight at the bottom, blocking off the intake system the previous company installed. This particular roof was only eight years old and all the plywood is now bad. This was caused from the trifecta — no intake, box vents turning into intake and venting out of the ridge vent.”

Problem No. 2: Weather Infiltration

When you ask a vent to perform a task it has not been designed to tackle, you’re rolling the dice against Mother Nature. An exhaust vent mixed with another type of exhaust vent that suddenly is pulled into intake airflow duties as a result of short-circuiting is not only pulling in air, but whatever the air is carrying that very moment: rain, snow, debris. Exhaust vents are not designed to ingest anything.

One of the consequences of mixing attic exhaust vent types can be weather infiltration, such as the snow in this photo. Photo: Ron Bastian

“In the winter when freezing rain turns into fine ice particles, I observed several times the lower exhaust vents on the roof becoming intake vents instead of exhaust as designed and drawing in ice particles and snow,” says Steve DuCharme, owner, Innovative Builders Roofing & Construction, Edmond, Oklahoma.

“I have witnessed snow ingestion into the attic due to mixed exhaust vents,” says Corey Ballweg, owner and president, Mid Towne Construction Inc., Cross Plains, Wisconsin.

“I recall an attic several years ago that had ridge vent and two power fans. They installed two because they were told one wouldn’t pull enough heat out,” says Paul Vosen, president, Degenhardt Home Improvement, Madison, Wisconsin. “The house had no overhangs and the attic floor was insulated with a good vapor barrier. I was there in the rain and both power fans were running. The attic was so tight that the power fans were actually pulling rain in through the ridge vent. Never have I seen that before — nor have I seen it since, but I never forgot it.”

The weather infiltration problems that can result from mixing exhaust vent types may not catch a homeowner’s attention right away. Not many homeowners regularly check their attic.

“I worked on a roof that did not have any intake vents at the soffit but did have two gable vents in addition, a power fan, and four box vents,” says Scott Dennison, president, Dennison Exterior Solutions & Gutter Topper, Saint Joseph, Michigan. “Over the brief 15-year life of the roof, when the power vent would turn on it turned the four box vents into intake vents which sucked water into the attic and destroyed the roof deck adjacent and below the vent.”

The most common exhaust mixture our seminar attendees tell us they see: gable end louvers combined with something else. Often the homeowner demands that the roofing contractor leave the gable end vent in place despite the fact a ridge vent is being installed as an exhaust vent improvement. The homeowner’s reasoning: The gable louver adds a decorative touch to the home’s exterior. Solution: Do what Ron Bastian does.

“I’ve noticed snow and wind-driven rain coming in a gable end vent which was combined with a ridge vent,” says Bastian, owner and president, Bastian Roofing Inc., Richfield, Wisconsin. “We closed up the gable end vent from inside the attic and this cured the problem I was called out for.” By closing up the gable vent from inside, the attic short-circuiting is eliminated and the homeowner can still enjoy the cosmetics from the exterior.

“We have witnessed numerous issues related to short-circuiting,” says Shawn Bellis, owner, EPIC Exteriors, Overland Park, Kansas. “We’ve seen fine wind-driven Midwest snow sucked into the exhaust vents — gable vents mixed with ridge vents, for example.”

There’s a Much Better Way

Inefficient airflow, mold, rotted decking, prematurely aging shingles, and weather infiltration into the attic does not have to be the final outcome. There’s a better way, but it may take a commitment to educating the homeowner and fellow roofing contractors. I believe that’s one of the reasons our best practices seminars are so well received.

“I had mixed attic ventilation on my own home,” says Sean Toms, quality control inspector, S & K Roofing, Eldersburg, Maryland. “After attending the seminar a few years ago, I looked in my attic. I had condensation on the roof nails. I had a ridge vent, fully vented soffit and gable vents. I closed the gable vents and added insulation to my attic floor. Problem solved.”

“I seem to run into mixed exhaust vents every week. Homeowners think that the more types of ventilation on the roof the better they are,” says Richard Turner, owner, RJ Turner Remodeling, LLC, High Point, North Carolina. “After explaining the things I have learned in the Air Vent Inc. seminars, they quickly understand the correct way things should be done.”

About the Author: Paul Scelsi is marketing communications manager at Air Vent Inc., and leader of its Attic Ventilation: Ask the Expert™ seminars. He’s also chairman of the Asphalt Roofing Manufacturers Association Ventilation Task Force. For more information, visit www.airvent.com.

The Attic Needs Ventilation but How Much Exactly?

Good news, roofing contractors: You do not have to be good with numbers nor do you have to enjoy math to be able to quickly—and accurately—calculate the amount of attic ventilation needed for residential attics. Here it is, a handy shortcut for quick calculations:

Intake exhaust airflow in a house

Intake exhaust airflow in a house

Attic square footage ÷ 2 = square inches of EXHAUST and square inches of INTAKE Net Free Area (NFA) needed. (NFA is the unobstructed area through which air can pass through a vent, usually measured in square inches. Ventilation manufacturers assign an NFA value to the non-motorized vents they make.)

This shortcut conveniently calculates the 2015 International Residential Building Code MINIMUM (IRC Section R806 – Roof Ventilation 1, which states, in part, 1 square foot of Net Free Area for every 150 square feet of attic floor space with the attic defined as length x width floor of the attic). The shortcut actually overestimates a bit but that’s OK. It puts the roofing contractor in the ballpark which is useful when estimating.

To calculate the allowable IRC EXCEPTION to the MINIUMUM (that is, 1/300 ratio) here’s the shortcut:

Attic square footage ÷ 4 = square inches of EXHAUST and square inches of INTAKE Net Free Area needed.

Here’s an example using the shortcut for the 1/150 Code Minimum.
Say the contractor is standing in front of a house that has an attic with 2,200 square feet.

    2,200 ÷ 2 =

  • 1,100 square inches of EXHAUST net free area needed
  • 1,100 square inches of INTAKE net free area needed
  • The next step is to select a suitable exhaust vent and intake vent that fits the roof design for best performance and best aesthetics. After that, find out the vent’s NFA as rated by the manufacturer. Divide the vent’s NFA into 1,100 to yield the number of vents needed (either in linear feet or units/pieces). That’s it. It’s time to install.

There is a longer “official” formula based on building code you can reference or point your clients to for reassurance that you know what you’re talking about. Most attic ventilation manufacturers list the longer formula on their websites and inside key product brochures. But the shortcut is just as good and faster!

Calculation Q & A

Here are the answers to the five most frequent questions pertaining to calculating attic ventilation.

1. “Why is it important that the amount of intake ventilation matches the amount of exhaust?”
The goal of an effective attic ventilation system is to help fight heat buildup inside the attic during the warmer months and moisture buildup in the colder months. Additionally, in climates where snow and ice are common, attic ventilation can help fight the formation of ice dams. To achieve these goals the attic needs cooler, dryer air entering low (near the eave or the roof’s lowest edge) so it can flush out any warm, moist air that may have built up inside, pushing it out through the roof’s exhaust vents positioned as close to the peak as possible. This balanced-airflow approach allows the air to “wash” the entire underside of the roof deck from low to high.

2. “What if it’s not possible to balance the attic ventilation system 50 percent intake/50 percent exhaust?”
If it cannot be balanced it’s better to have more intake than exhaust because it has been our experience most attics lack proper intake ventilation, which is the leading cause of venting callbacks. Additionally, any excess intake will become exhaust on the leeward side of the house because the intake vents on the windward side of the house will have “pressurized” the attic. As a result, the intake vents on the leeward side of the house will work “with” the exhaust vents to release air.

However, if the attic has more exhaust than intake it potentially can cause the extra exhaust to pull its missing intake from itself (if it’s a ridge vent) or from another nearby exhaust vent (from one wind turbine to another or one roof louver to another), which means possible weather ingestion.

3. “What if the roof has 40 feet of available ridge length but the math calls for only 30 feet of ridge vent needed?”
It is OK to install all 40 feet of ridge vent as long as it can be balanced with intake ventilation. If the amount of intake ventilation cannot match the entire 40 feet of ridge vent, consider reducing the width of the ridge vent slot (thereby reducing the vent’s NFA per linear foot) to accommodate the amount of intake NFA available. Doing this keeps the airflow continuous along the entire horizontal ridge and balanced high and low. As always, be sure the overall amount of ventilation meets code requirements.

4. “If attic access is not practical is there another way to measure the attic square footage?”
Ideally, the attic square footage would be measured at the attic floor length x width (regardless of roof pitch, by the way). If this is not possible, and the homeowner does not have any documentation on file listing attic square footage, you could use the footprint of the house (aerial view of the house) or the number of shingle squares (one shingle square equals 100 square feet) to estimate the attic square footage. Neither of the alternate measuring tactics, however, is as accurate as an attic floor measurement.

5. “How does roof pitch come into play when calculating attic ventilation?”
Current IRC requirements do not factor the role a roof’s pitch plays in the amount of attic ventilation needed, but ventilation manufacturers do. Generally, as the roof pitch increases the volume inside the attic also increases along with the amount of needed attic ventilation. Here’s a rule of thumb to follow:

  • Up to 6:12 roof pitch use the standard formula as explained in this article.
  • 7:12 to 10:12 roof pitches increase the amount of ventilation by 20 percent.
  • 11:12 roof pitch and higher increase the amount of ventilation by 30 percent.

For projects involving vents with motors, the calculation formula is different.