Are Ridge Vents Required By Code?


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Proper ventilation is a practical necessity in every home, and a specific level or quality of ventilation is also a building code requirement. There are various types of vents to use, but one of the most commonly seen is the ridge vent. While it is helpful to know that ridge vents are a good and often-used option, they are not always the easiest option, so it is also important to know what the codes say about ridge vents specifically.

Ridge vents are not required by code. The International Residential Code does require homes to have ventilation, but there are many ventilation systems that meet these standards. Ridge vents are a very effective and economical option that also meets the IRC requirements.

All homes require ventilation, and ridge vents are an excellent option to use. Let’s more thoroughly examine the role of ridge vents in home ventilation systems, the effectiveness of ridge vents according to international building codes, and how these vents work to properly ventilate an attic or rafter space. We also look at alternatives if you are unable to install ridge vents.

The IRC Does Not Require Ridge Vents

Ridge vents are commonly seen on many homes, but they are not required by the International Residential Code (IRC). The IRC does state that ventilation is required, but not specifically ridge vents.

All states follow IRC regulations, but some states make their own adaptations based on factors like climate that can influence how ventilation needs to be achieved or maintained. Thus, your state’s local residential code may stipulate the use of ridge vents, specifically, so you should always check these regulations before finalizing your ventilation plans.

Do Roofs Need Ventilation?

All roofs are required to have some form of ventilation. All of the ventilation requirements for roofs are outlined in section R806 of the Internation Residential Code.

Ventilation is mainly needed to control air temperature within the home, particularly within the attic or roof of the building.

If a roof has no ventilation or it has inadequate ventilation, the air temperature in the attic may reach as high as 150 °F (65.5 °C) in the summer months. As you can imagine, this increases the home’s overall temperature, and it may cause severe damage to the roof itself.

You can keep track of the attic temperature by placing a wireless thermometer in the attic. You would be surprised how hot it gets there during hot summer days. I recommend Oregon Scientific sensors(Amazon). I have used them for years without problems. Battery life is excellent range is about 100 ft. which is more than enough for reading the attic temperature.

Oregon Scientific BAR206AX Wireless Temperature & Humidity Weather Station: LCD Screen, Indoor/Outdoor Sensor, Weather Forecast Icon, Ice Alert, Atomic Clock/Calendar Features (White)

These high temperatures can structurally and functionally compromise the roofing shingles and materials, or lead to a build-up of condensation that can encourage the growth and propagation of molds and mildews within the roof.

Along with high temperatures in the summer, lack of roof ventilation leads to unstable air temperature in the attic during the winter. This may cause ice damming and other problems that can further damage the roof.

The most effective way to prevent these common, yet serious, problems is to ensure that the roof is adequately ventilated. However, there are some exceptions to the rule requiring a roof to be ventilated.

Exception

According to IRC section R806.5, there are numerous conditions that make a roof exempt from required ventilation. However, all of the criteria must be met in section R806.5 for the roof to legally exist without ventilation according to the IRC code.

Some of these criteria include:

  • The unvented attic must be within the thermal envelope of the building.
  • Interior Class I vapor retarders are not installed in the attic, on the attic floor, or on the ceiling assembly.
  • The shingles of the roof are ¼ inches (6.4 mm) or more apart from one another and the roofing underlayment.

You can follow the link provided above for the full list of conditions that must be met for a roof to be exempt from the ventilation requirement. I have listed some of the most important criteria, but remember that every criterion in this IRC section must be met.

What Roof Ventilation Is Required by Code?

Now that we know ridge vents are not required by the IRC, and we know that some roofs are even exempt from the ventilation requirement entirely, let’s look at what the IRC does stipulate regarding ventilation because this will apply to the majority of homes.

Section R806.1 of the International Residential code states that enclosed attics and rafter spaces that have a ceiling attached directly to the underside of the rafters must have cross ventilation for each space, this means there should be openings on either side.

Furthermore, the vents must be protected so as to not allow rain or snow to enter through them. After all, ventilation shouldn’t compromise weatherproofing because this would lead to a whole new set of issues!

The ventilation openings must meet the following criteria:

  • They must have a minimum opening of 1/16” (16 mm).
  • They must not exceed 1/4″ (6.4 mm).
  • Any ventilation opening that has a diameter larger than 1/4“ (6.4 mm) must be covered with a corrosion-resistant screen with an opening diameter between 1/16″ (16 mm) and 1/4″ (6.4 mm).
  • All vents must open directly outside.
  • All vents must be protected from birds, rodents, snakes, and other small animals.  

Related Article: How to Stop Wasps Coming Through Vents

Code-Mandated Minimum Ventilation Areas

All ventilated roofs must adhere to the IRC regulations that state the minimum ventilation areas of a roof.

The IRC refers to the net free ventilation area, which describes the amount of space available in the vents that can be used to freely pass air—i.e., it refers to the gaps in the vents.

The IRC regulations state that the net free ventilating area of the attic or rafter is required to be at least 1/150 of the area of the vented space.

This means that the size of the vents in the roof must have a minimum combined open area of 1/150th of the total area of the attic or rafter space. For example, for 150 square ft of rafter space or attic space, there must be at least 1 square foot of ventilation.

Exception

There are two criteria that exempt ventilation systems from the 1/150th net free ventilation area rule.

Both criteria must be met for the house to qualify as exempt, but if it does, then it is only required to have a net free ventilating area of at least 1/300th of the vented space. This means that for every 300 square ft of space, 1 square foot of ventilation is required. Thus, houses that meet the exception categories require smaller ventilation areas than houses that do not.

The first exemption criteria is if Class I or Class II vapor retarders are installed on the warm-in-winter side of the ceiling in houses in climate zones 6, 7, and 8, which are the coldest regions in a country. 

The second is if 40-50% of the net free ventilating area is provided by ventilators located in the upper portion of the space. However, this criterion only applies if the upper ventilators are located less than 3 ft (914 mm) below the highest point of the space. The remaining required ventilation must then be located in the bottom third of the attic space.

Ridge vents are an excellent way to achieve a 40-50% net free ventilating area located less than 3 below the highest point in the roof.

How Do Ridge Vents Help Provide Sufficient Ventilation?

Ridge vents are surprisingly effective ventilation systems. These vents encourage the natural flow of air from the attic or rafter space and promote air circulation within the home by merit of their location.

These vents work by allowing hot air to rise (as it naturally does) and exit through the vent, pulling cool air along with it. This generates an airflow that continuously removes hot air from the attic. The effect acts similarly to a vacuum and actively pulls air through the vent, but without the need for a motor of some kind. 

On windy days, the wind from outside the house will pull air from the vent even more rapidly, increasing the effectiveness of the ridge vent.

Ridge vents help provide sufficient ventilation to the roof by promoting a continuous airflow out of the attic or rafter space of the house and constantly pulling fresh air in from below. This makes ridge vents very effective yet straightforward ventilation systems.

Additionally, as they pull air through the whole house (when given a clear passage to do so), they can be used as a method for ventilating rooms without a window.

Related article: Ridge Vent Pros and Cons

Ridge Vent Alternatives

Ridge vents are only one type of upper exhaust ventilation that is available for use in homes. Ridge vents are very effective, but they are best used in homes with shingled roofs and homes with attics or rafter spaces.

This means that ridge vents are not always the best option, but there are some alternative vents that can be used.

Some ridge vent alternatives include:

  • Box Vent​​s – these vents are installed in the roofs of homes that have an attic or a rafter space. They remove hot air and moisture from the house by convection and natural air currents.
  • Soffit Vents – these vents allow air to flow into the house as they are installed under the overhang portion of the roof. There are various types of soffit vents that can be installed based on the type of roof and ventilation needs of a particular home.
  • Turbine Vents – these are the rotating vents that are very commonly seen on many types of homes. Lights winds rotate the turbine, which then pulls air out of the home through the roof.
  • Eyebrow Vents / Turtle Vents – these vents are usually installed in pairs to maximize airflow. They are usually curved open vents on sloping sections of roofs and are very effective.

Sources

https://codes.iccsafe.org/content/IRC2018/chapter-8-roof-ceiling-construction#IRC2018_Pt03_Ch08_SecR806

http://www.atticbreeze.net/ventilation.html#:~:text=When%20discussing%20ventilation%2C%20the%20term,louvers%20on%20most%20passive%20vents

https://www.greenbuildingadvisor.com/article/all-about-climate-zones

https://www.energy.gov/eere/buildings/climate-zones

https://benjaminobdyke.com/insights/how-does-ridge-vent-work/

https://www.improvenet.com/a/roof-box-vents-vs-continuous-ridge-vents 

https://greengarageblog.org/12-roof-ridge-vent-pros-and-cons

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Joonas

I like it when I'm able to fix everything that needs fixing around the house. In order to do that, I have to do a lot of research. This site will cover everything I learn and maybe help others do the same.

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