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How Many Roof Vents Do I Need

Calculating The Cost Of Installing Roof Vents

How much soffit vent do I need to make my ridge vents work?

Before you start calculating how much the vents in question will cost, you have to know how many vents you need in the first place, and to do that, you need to know the surface area of your roof. Generally speaking, you should have 1 square foot of vents for every 150 square area of roofing and attic space. You should further divide this between the two kinds of vents mentioned above, passive and active ventilation systems. The ratio of one to the other is up to you, and will depend in part on how much you are able to rely on the wind and weather to power a passive wind-driven rotary vent as opposed to a motor-driven one.

This is also true whether you are looking to install a whirlybird, soffit, or other type of vent.

Letâs take a more concrete example.

Say you are calculating for a 30â x 50âroof. In this case, the total surface area is 1,500 square feet. Youâll then want to divide that by 150 square feet, which gives us 10 total square feet of vent space required.

However, this is just the beginning. You now need to calculate the total area of each vent. This should be supplied by the manufacturer of the vent you are using, and may be referred to as the ânet free area.â

Once you have done that, youâll know the total square footage you need to cover with vents for the type of ventilation system youâll be using.

How To Calculate The Amount Of Ventilation You Need

Please note: the following provides advice for homes with ventilated attics. There are some styles of vaulted ceiling homes or flat roof homes that have ventilation spaces within the roof itself, and no attic. These ventilation needs are calculated differently.

The key to proper ventilation of your roof and attic is balance: the amount of space you devote to intake must be equal to the amount you allow for exhaust, and these must be calculated according to the size of your attic and slope of your roof.

You can calculate attic ventilation requirements by determining the square footage of your attic floor , and compare that to the total required net free area . Vents are rated by their net free area, or the amount of space for air to flow in or out. This helps make it easy to calculate how many vents you need for your attic, once youve determined your requirements.

If your attic floor has a vapor barrier, you will need one square foot of NFA per every 300 square feet of attic floor area . If there is no vapor barrier, double it to one square foot of NFA for every 150 square feet of attic floor space . These are broad guidelines, so be sure to check with your local building code.

Can You Have Too Many Soffit Vents

This is one of those questions that many HVAC experts tend to disagree on. The reason is that venting requirements can change on a case-by-case basis, depending on several factors including, climate conditions , roof designs, and attic structure. However, many agree that while having too many of these vents is rarely an issue, it is worth noting the minimum requirements for your home to stay in adherence to any building codes from your local government.

Also, it is generally more acceptable to have more soffits than you need for your home than to lack the necessary venting requirements. Technically, your venting systems most important goal is to have a balance with your exhaust and intake vents. If you dont, it could cause inefficiency with your venting system.

However, soffit vents tend to be quite passive in their ability to move fresh air into an attic, so a worse setup would be having too few of them or having them combined with gable vents . Generally, if you can still access your attic and no visible signs of rotting or molding on your insulation or floorboards, and you dont notice any strange spikes in your energy bills, the vent setup should be okay.

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MANUFACTURERS RECOMMENDATIONSThe patented OHagin Balanced Ventilation System utilizes OHagin vents placed strategically within the field of roofing material both high and low . This strategic high and low placement of OHagin vents allows the balanced system to fully optimize both wind and thermal effects to provide superior passive ventilation throughout the attic. Additionally, placement of OHagin vents both high and low should provide an equal, balanced rate of ventilation performance in each area. The calculations above do not include any potential Net Free Ventilation Area values provided by alternative ventilation methods that may be present in any specific structural design.

How Many Roof Vents Do You Need

How Many Roof Vents Do I Need?

Safe and practical design models recommend that there be a roofing vent for every 150 square feet of attic space. If you dont have an attic, then from whatever space that is located under the roof itself. If you have a vapour barrier installed, then the recommendation is to have a roof vent for every 300 square feet.

To calculate according to their vent rating, check their net free area . This is how much space the vent has to allow the air to get out or enter. The total NFA of your vent should be balanced by 50% to intake and 50% to exhaust. If your roof has a slope of over 6:12 , this rule might change.

To know the accurate and safe computation for your home or commercial property, its best to seek the advice of a roofing professional to get the project done right the first time. The roofing specialists at Above It All Roofing have the equipment, skills, and experience that can make your roof vent installation project as seamless as ever. We have helped many homes and business owners in Toronto to find the best and safest solutions for their roofing concerns.

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How To Calculate How Many Roof Vents You Need

Balance is the key to having an efficient attic ventilation system. Calculating the correct number of exhaust and intake vents is simple and will ensure you have an effective, balanced system.

We must first calculate the net free area required. One square foot of ventilation is required for every 300 square feet of enclosed attic space, with half being exhaust and half being intake.

1. For a home with 3000 square feet of attic floor space you will need 10 square ft of attic ventilation.

2. Since you must have a balanced system, you divide by 2 so that half of the ventilation is intake and half is the exhaust.

3. Because vents are rated in square inches, you need to convert the square feet required to square inches .

4. In our example we need 5 sqft, thus 5×144=720 square inches of intake and exhaust. If we are using regular roof vents and 10 vented vinyl soffit we would require 15 vents and at least 160 sqft vented vinyl soffit to properly ventilate a 3000 sqft attic space.

If you have any questions about roof vent Installation you can call and talk to one of our experts at or come in and visit us in our showroom. We can help you with all your building and installation needs and answer your questions.

Roof Ventilation At Work

Roof ventilation systems are unique to every home. Factors such as code requirements, regional climate and roof and ceiling designs all need to be considered when venting your roof.

There are two main types of roof ventilation:

  • Exhaust vents
  • Intake vents
  • Exhaust vents: These vents allow exhaust to escape.

    The most common type of exhaust vents are ridge vents. They are installed at the intersection of two roof planes . They are typically made of molded, high-impact copolymer and are installed underneath a final layer of shingles to give a seamless look to the roof. To the untrained eye, ridge vents can be almost invisible.

    Roof louvers, gable louvers, wind turbines and power attic ventilators are all visible exhaust vents that are mounted on the outside of your roof. Like ridge vents, roof louvers and gable louvers work without the use of electricity.

    Wind turbines also work without a power source, but they work best with a constant source of wind and are not as effective as ridge vents.

    Power attic ventilators, which run on a power source, are an exhaust vent option for certain roof designs or areas without much wind.

    Intake vents: These vents can be even harder to spot.

    Now that weve reviewed how ventilation works and how a roof can be properly vented, lets expand on the benefits of roof ventilation.

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    Different Types Of Roofing Vents Available In The Market

    Vents are meant for exhausting and intake of air in the attic and the house. Based on these two functions, we have different types of roofing vents in the market. Vents located at the extreme peak of the roof are exhaust vents while those found at the lower edge are called intake vents. Here are some types of roofing vents that you can go for:

    • Ridge vents: Ridge vents are simply exhaust-vents. They are located at the peak of the roof to help in regulating the temperatures in the attic.
    • Soffit vents: These are located on the underside of the overhanging roof to assist in the intake of fresh air in the attic.
    • Turbine vents: These are wind-powered vents that are usually placed on top of the roof to help in regulating temperatures in the attic.
    • Gable vents: These are vents located along the gables of the house.

    Benefits Of Roof Ventilation

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    Roof ventilation is essential for every homeowner as it offers a range of benefits. Roof vents work throughout the year and in all climates to give your home the best protection.

    Proper attic ventilation will extend the life of your roof by keeping the shingles cooler. In the warmer months, roof vents will allow air circulation so that hot air can escape. The attic and roof will both be kept much cooler, as a result. When the roof becomes warmer due to poor ventilation, this heats the roof shingles. When this occurs, the shingles become damaged.

    Ventilation will also help homeowners to reduce their energy costs. When we enter the warmer months and summer begins, we want to keep cool inside our homes. A well-vented roof will allow the hot air to escape efficiently. As the hot air escapes, the attic is kept cooler and therefore reducing the strain on air conditioning systems.

    Roof vents also help to reduce the extreme indoor temperatures. We have all walked upstairs to find it much warmer than downstairs. However, if this persists, it may be the result of a poorly vented roof. If hot air is unable to escape, it will stay in the upper levels of your home.

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    How Proper Ventilation Can Help Cool The Upstairs Of My Home

    This past week I was asked to check out a home because they couldnt cool their upstairs. When I got there, I didnt need to get on the roof or even go inside their home to see that they didnt have any attic ventilation at all.

    Having no ventilation caused the heat that was trapped in their attic to burn up the roof system. And now, because its burnt up, the whole roof has to be replaced.

    The sad part of this story is that the owners had the roof replaced only two years ago. The roofing company they used decided to cut a corner by not adding any ventilation at all. Because the owners didnt know anything about ventilation, they were unaware of how important it was to their whole house.

    Don’t let that happen to you. By the end of this article, you’ll learn everything you need to know about attic ventilation and how it affects your roof.

    And at the very end, don’t forget to grab your checklist of questions to ask a roofing contractor to help you find a great roofer to help with your attic’s ventilation system.

    Whirlybird Installation At Vertec Roofing

    If youre still asking the question, How many roof vents should I have?, get in contact with one of our experts today. At Vertec Roofing, we pride ourselves on our commitment to quality advice. While we offer our services at reasonable rates, we only provide accurate quotes and use the best quality roof whirlybirds. We complete whirlybird installation in Sydney on both metal and tiled roofs to ensure that your property is properly ventilated, energy-efficient and safe from mould and damp.

    If youd like to learn more about what whirlybird installation can do for you, get in touch with one of our experts today. Our roofing contractors are experienced, knowledgeable, and offer professional advice on your roofing project with a no-obligation quote.

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    Different Types Of Vents

    Roof vents have two basic functions. On the one hand, they intake air, while on the other they exhaust air. The main purpose, of course, is to keep the air constantly circulating. To that end, there are also several types of roof vents. These are:

    • Ridge Vents These run along the edge of the roof. They are long and narrow and are great exhaust vents.
    • Gable Vents As their name would suggest, gable vents attach to the gables rather than the roof. They go through the siding and come in several shapes such as triangles, squares, or rectangles.
    • Soffit Vents Also known as under-eave vents, soffit vents hang over the siding . They are installed on the underside of the roof.
    • Turbine Vents Located higher on the roofs surface, turbine vents make use of a wind-powered turbine to suck all the moisture and hot air out of the attic.
    • Other Types There are also several other types of roof vents including dome- or box-shaped vents that run through the roof, itself.

    Do I Need Soffit Vents If I Have Gable Vents

    How Many Roof Vents Do I Need : How Many Roof Vents Do I ...

    Adding soffit to a roof with gable vents is generally not recommended. The reason is that adding soffit vents will alter the airflow, especially on mildly windy days when the wind blows at right angles against the gable but parallel to the ridge. This could result in a reversal of airflow within your gable vents and can cause snow and rain to be pulled in to the attic.

    Combining rows of continuous soffit vents will make the gables ineffective, as it will cause a large portion of the attic volume to go unvented. The result would be several pockets of dead air radiating in the living spaces below the attic. This would be especially disastrous in the warmer months.

    A better option would be to add soffit vents with ridge vents. In this scenario, the gable vents would either need to be removed completely or sealed up from the inside of the attic. Most homeowners who choose this option opt to leave the gables outside to avoid having an odd space there.

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    S To Calculate The Appropriate Amount Of Ventilation Needed In Your Home

  • Calculate the square footage of your attic space. To do this, measure the length and width of your home.
  • For example:Width: 40 ft, Length: 30 ft

  • Find the amount of ventilation needed for intake and exhaust. According to the National Building Code, you need 1 sq. ft. of ventilation for every 300 sq. ft. of attic space. Divide your square footage by 300 sq. ft., then round up to make sure youre getting enough ventilation.
  • 1200 sq. ft./300 sq. ft.= 4 sq. ft. of required ventilation

  • Convert square feet of Net Free Area to square inches. Multiply square feet of NFA by 144.
  • 4.00 sq. ft. x 144 = 576 square inches of NFA needed

  • Calculate the optimal amount of ventilation required. To ensure your roof vents are drawing from your soffits and not your other roof vents, we recommend that 50% of your ventilation should be provided by your soffits, and 50% should be provided by your roof vents . This means you should divide this number by two.
  • 576 sq. in. /2= 288 sq. in. of ventilation is required on the roof

  • Determine the number of vents required. The number of vents required for your home depends on the vent selected.
  • For example, if you are choosing a 50 square inch roof vent, 6 vents are required for a 1200 sq. ft. application:288 square inches divided by 50= 5.76 vents ~6 vents

    It is important to note that if your roof pitch is less than 4/12 or you have a vaulted or cathedral ceiling you will have to double the amount of ventilation needed.

    Roof Vents For Every Climate

    Every home requires attic ventilation as it has a purpose throughout hot, cold, and mixed climates. And therefore, throughout every season. Vents work by clearing hot and wet air from the attic. As a result, homeowners can regulate the temperature of their home year-round. A well-ventilated roof will keep the temperature of the home comfortable and at the temperature you would expect for the time of year.

    In cold climates, roof vents ensure that the attic is the right temperature. When it is icy, roof vents will prevent ice dams from forming. Ice dams develop over a short period when the heat of the sun and the warmth of the roof melt the snow and ice. This water then collects, refreezes, and creates puddles along the roof. Also, ventilation will allow any moisture in the air to clear from the living space below, escaping through the attic.

    Ventilation is just as important in hot climates. When the weather is warmer, vents will work by clearing the hot air from the attic. As a result, this will cool the house and reduce the cost of running air conditioning systems.

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