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.

ARMA’s New Video Illustrates Why Homeowners Need Proper Attic Ventilation

Is your roof properly ventilated? The Asphalt Roofing Manufacturers Association’s (ARMA) latest whiteboard video outlines the components to a properly functioning attic ventilation system and the many ways it benefits a roof, such as protection against shingle deterioration and roof system damage.

How Does Proper Attic Ventilation Protect my Roof?” highlights how a balanced system of intake and exhaust results in a continuous flow of air in an unconditioned attic, helping to reduce heat and moisture buildup year-round and prolong the life of the roofing system.

Proper attic ventilation can assist in reducing energy consumption, and preventing mold, mildew and wood rot. Additionally, it can help prevent ice dams, which can cause leaking and costly damage to shingles, gutters, insulation and the whole roof system.

“Homeowners may not be aware of just how important attic ventilation is to the longevity and performance of their asphalt shingle roofing system,” said Tim McQuillen, ARMA’s director of technical services and a 25-year industry veteran. “ARMA wants to educate homeowners on proper attic ventilation and why it’s important, as well as how to recognize the signs indicating it’s time to call a roofing contractor if there are issues.”

ARMA encourages homeowners planning to install a new asphalt shingle roof to consult with their roofing contractor or the manufacturer of their roofing system to ensure their attic is properly ventilated. To view ARMA’s latest attic ventilation video, or its library of other educational videos on asphalt roofing systems, visit ARMA’s website or YouTube Channel.

Calculate Attic Ventilation with Free App

Roofing professionals can now take Air Vent’s attic ventilation tools on the go via a free app.

Roofing professionals can now take Air Vent’s attic ventilation tools on the go via a free app.

Roofing professionals can now take Air Vent’s attic ventilation tools on the go via a free app. The interactive Attic Ventilation Calculator figures the exact quantity of intake and exhaust vents needed for any attic size. Users then can email results to a client. The Roof Pitch Tool confirms if the vent being considered for the project is compatible, as well as if the amount of ventilation needs to increase. The “location address” and “camera” features customize photos for a proposal. Direct links to product specs, videos and industry articles support any ventilation project. The app is available for Android and iOS systems.

Attic Ventilation in Accessory Structures

Construction Code Requirements for Proper Attic Ventilation Should Not Be Overlooked in Buildings That Don’t Contain Conditioned Space

The 2015 International Residential Code and International Building Code, published by the International Code Council, include requirements for attic ventilation to help manage temperature and moisture that could accumulate in attic spaces. Although the code requirements are understood to apply to habitable buildings, not everyone understands how the code addresses accessory structures, like workshops, storage buildings, detached garages and other buildings. What’s the answer? The code treats all attic spaces the same, whether the space below the attic is conditioned or not. (A conditioned space is a space that is heated and/or cooled.)

The 2015 International Residential Code and International Building Code include requirements for attic ventilation to help manage temperature and moisture that could accumulate in attic spaces. Although the code requirements are understood to apply to habitable buildings, not everyone understands the code also addresses accessory structures, like workshops, storage buildings, detached garages and other buildings.

The 2015 International Residential Code and International Building Code include requirements for attic ventilation to help manage temperature and moisture that could accumulate in attic spaces. Although the code requirements are understood to apply to habitable buildings, not everyone understands the code also addresses accessory structures, like workshops, storage buildings, detached garages and other buildings.


The administrative provisions of the IRC that set the scope for the code are found in Chapter 1. Section R101.2 and read:

    The provisions of the International Residential Code for One- and Two-family Dwellings shall apply to the construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, removal and demolition of detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress and their accessory structures not more than three stories above grade plane in height.

Let’s clear up any confusion about the code. The ventilated attic requirements in the 2015 IRC include the following language in Section R806.1:

    Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow.

An accessory structure is actually defined in the IRC:

    ACCESSORY STRUCTURE. A structure that is accessory to and incidental to that of the dwelling(s) and that is located on the same lot.

The IBC also includes attic ventilation requirements that are essentially the same as the IRC. Section 101.2 of the 2015 IBC contains this text:

    The provisions of this code shall apply to the construction, alteration, relocation, enlargement, replacement, repair, equipment, use and occupancy, location, maintenance, removal and demolition of every building or structure or any appurtenances connected or attached to such buildings or structures.

This requirement for ventilated at-tics in accessory structures in the IBC and IRC is mandatory unless the attic is part of the conditioned space and is sealed within the building envelope. Unvented, or sealed, attics allow any ducts located in the attic to be inside the conditioned space, which can have beneficial effects on energy efficiency. For accessory structures, which are typically unheated, that provision does not apply.

It’s important to note the codes do contain detailed requirements for the design and construction of sealed at-tics to reduce the chance of moisture accumulation in the attic. These requirements have been in the codes for a relatively short time and remain the subject of continued debate at ICC as advocates of sealed attics work to improve the code language in response to concerns about performance issues from the field.

Traditional construction methods for wood-framed buildings include ventilated attics (with insulation at the ceiling level) as a means of isolating the roof assembly from the heated and cooled space inside the building. Attic ventilation makes sense for a variety of reasons. Allowing outside air into the attic helps equalize the temperature of the attic with outdoor space. This equalization has several benefits, including lower roof deck and roof covering temperatures, which can extend the life of the deck and roof covering. However, it is not just temperature that can be equalized by a properly ventilated attic. Relative humidity differences can also be addressed by vented attics. Moisture from activity in dwelling units including single-family residences and other commercial occupancies can lead to humidity entering the attic space by diffusion or airflow. It is important to ensure moisture is removed or it can remain in the attic and lead to premature deterioration and decay of the structure and corrosion of metal components, including fasteners and connectors.

In northern climate zones, a ventilated attic can isolate heat flow escaping from the conditioned space and reduce the chance of uneven snow melt, ice dams, and icicle formation on the roof and eaves. Ice damming can lead to all kinds of moisture problems for roof assemblies; it is bad enough that roof assemblies have to deal with moisture coming from inside the attic, but ice damming can allow water to find its way into roof covering assemblies by interrupting the normal water-shedding process. For buildings with conditioned space, the attic can isolate the roof assembly from the heat source but only if there is sufficient ceiling insulation, properly installed over the top of the wall assemblies to form a continuous envelope. Failure to ensure continuity in the thermal envelope is a recipe for disaster in parts of the country where snow can accumulate on the roof.

Accessory buildings, like workshops, that occasionally may be heated with space heaters or other sources are less likely to have insulation to block heat flow to the roof, which can result in ice damming. Ventilating the attic can prevent this phenomenon.

Accessory buildings, like workshops, that occasionally may be heated with space heaters or other sources are less likely to have insulation to block heat flow to the roof, which can result in ice damming. Ventilating the attic can prevent this phenomenon.


For unheated buildings in the north, ice damming is less likely to occur, unless the structure is occasionally heated. Accessory buildings, like workshops, that might be heated from time to time with space heaters or other sources are less likely to have insulation to block heat flow to the roof. In these situations, a little heat can go a long way toward melting snow on the roof.

While the ice damming and related performance problems are a real concern even for accessory structures, it is the removal of humidity via convective airflow in the attic space that is the benefit of ventilated attics in accessory structures. We know that moisture will find its way into buildings. Providing a way for it to escape is a necessity, especially for enclosed areas like attics.

There are many types of accessory structures, and some will include conditioned space. Depending on the use of the structure, moisture accumulation within the building will vary. For residential dwelling units, building scientists understand the normal moisture drive arising from occupancy. Cooking, laundering and showering all contribute moisture to the interior environment.

The IRC and IBC include requirements for the net-free vent area of intake (lower) and exhaust (upper) vents and also require the vents be installed in accordance with the vent manufacturer’s installation instructions. The amount of required vent area is reduced when a balanced system is installed; most ventilation product manufacturers recommend a balance between intake and exhaust. The IRC recommends that balanced systems include intake vents with between 50 to 60 percent of the total vent area to reduce the chance of negative pressure in the attic system, which can draw conditioned air and moisture from conditioned space within the building. This is less of an issue for non-habitable spaces from an energy-efficiency perspective, but moisture accumulation is a concern in all structures.

PHOTOS: Lomanco Vents

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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.

NRCA’s Online Column Outlines Benefits of a Properly Designed Attic Ventilation System

NRCA’s “From the Experts” column outlines the benefits of a properly designed attic ventilation system.

When properly designed, attic ventilation systems can make a home more comfortable and prevent numerous roof-related problems, according to Nick Sabino, president of Cincinnati-based Deer Park Roofing.

Sabino outlines the importance of attic ventilation in his column “The importance of attic ventilation,” the official consumer website of the National Roofing Contractors Association (NRCA). The column is posted on the sites “From the Experts” page.

The column states that because attic heat radiates into living spaces, a cooler attic will lead to a more comfortable home and reduced cooling costs.

In addition, roof system components benefit from increased longevity when an attic is well-ventilated. Because all building materials expand and contract as temperatures change, higher attic temperatures lead to increased expansion of the roof, sheathing and structural components, which are negatively affected by an increase in thermal movement.

To read Sabino’s column in its entirety visit the “From the Experts” column on the Everybody Needs a Roof website.

New CertainTeed Webisode Highlights Attic Ventilation

CertainTeed’s fourth webisode in the 2013 Living Spaces Facebook Home Makeover Video Contest, featuring the Bielfelt family of Mentor, Ohio, dives deep into the importance of superior weather-resistance and proper ventilation as part of a healthy whole-home system.

CertainTeed 5-Star Green and Master Shingle Applicator contractor, RJK Construction Co., of Willoughby, Ohio, installs Winterguard and DiamondDeck roofing underlayment as well as CertaWrap, CertaTape andCertaFlash housewrap products in the webisode to create a water- and wind-tight barrier to protect the century-old home’s original structure.

Grand prize winner of the $75,000 exterior makeover contest, the Bielfelts are the subject of a series of CertainTeed Living Spaces webisodes documenting the renovation of their 100-year-old home. The series follows the family, along with local contractors, from the planning stages of the renovation through its completion.

In the first few webisodes, the homeowner selected multiple products, including Cedar Impressions and Monogram siding, Restoration Millwork trim, EverNew decking and railing, Bufftech fence and Landmark Pro roofing. The homeowner also utilized the CurbAppeal iPad app, ColorCoach virtual swatch book and ColorView design tool, which allows homeowners to visualize how products will look on their home.

To view all of the webisodes, music videos and video entries from the 2013 $75,000 Exterior Living Spaces Home Makeover, visit the CertainTeed Living Spaces Facebook page or YouTube channel.