Roof Ventilation – Is Improper Ventilation Destroying Your Roof

Get the most value out of your roof by learning everything you need to know about roof ventilation.

Roof Ventilation – Is Improper Ventilation Destroying Your Roof?

When it comes to home repairs, a roof replacement is oftentimes one of the most expensive repair bills you’ll encounter throughout the lifecycle of your home. But are you and your roofing contractor doing everything you can to protect your investment? Even if the remainder of the roofing system is installed correctly, failure to account for proper roof ventilation can dramatically shorten the lifespan of your roof, and lead to a whole host of issues in regards to your roof’s structural components and attic space. Today, we’ll teach you how to get the most value out of your roof by explaining everything you need to know about roof ventilation.

roof with no apparent intake or exhaust ventilation

What is Roof Ventilation?

Roof ventilation refers to the process of allowing fresh air to circulate through the attic or roof space of a building, similar to opening a window to let fresh air in and stale air out. The goal of roof ventilation is to remove excess heat and moisture from the attic, which can help to prevent damage to the roof and the building’s structure, improve indoor air quality, and help prevent condensation and mold growth.

Roof Ventilation and The International Roofing Code (IRC)

Roof ventilation isn’t just a recommendation, it is also code required. The specific code can be found in section 806 Roof Ventilation, of the International Roofing Code, but can vary depending on local municipality codes.  

R806.2 Minimum vent area. The minimum net free ventilating area shall be 1/150 of the area of the vented space.

Exception: The minimum net free ventilation area shall be 1/300 of the vented space provided both of the following conditions are met:

  1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
  2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

While ventilation code requirements are sometimes overlooked on home or roof inspections, it’s important to realize that any code violations are subject to penalty. Penalties, typically in the form of monetary fines, will continue to accrue until the violation is rectified. If the fines aren’t paid, this can result in a lien being placed against the property, which can prevent you from selling your home, or in extreme cases, foreclosure. This is also something to be aware of when buying a home as well, as code violation penalties will often be transferred to the buyer if not dealt with prior to the sale.

The Different Types of Roof Ventilation

While there are many types of ventilation that are ventilated through the roof, the focus of this article is related to intake and exhaust ventilation.

What Are Intake Vents?

Intake vents are the primary source of bringing fresh air into the attic, and should always be located on the lowest part of the roof. Some common examples of intake vents include:

  • Soffit Vents: Soffit vents come in a variety of shapes and forms depending on the construction of your soffits, but will always be located on the underside of the soffits, which are the overhangs located at the eaves and rakes of your home. 
  • Edge Vents: If your home doesn’t have an overhang, soffit vents are not an option. In this case, edge vents which typically come in set lengths or rolls, can be installed at the base of the eaves, and provide air flow to the lowest part of the roof that is able to be vented.
  • Gable Vents: Only available on gable roofs, gable vents are a type of ventilation that actually serves as both intake and exhaust, due to their reliance on cross ventilation. As such, gable vents should be located on each side of the attic, allowing air flow to have an unobstructed line in and out. Gable vents are most effective when located parallel to the prevailing winds.

What Are Exhaust Vents?

Exhaust vents are the primary source of allowing hot and humid air to escape the attic, and should always be located near the ridge of the roof. Some common examples of exhaust vents include:

  • Ridge Vent: Similar to edge vents, ridge vents typically come in set lengths or rolls, but are installed at the ridge of the roof. This maximizes air flow by allowing air to escape out of the very highest point of the roof. 
  • Hip Vents: Hip vents function the same as ridge vents, but are used on hip roofs that have a limited ridgeline.
  • Turtle Vents: Also commonly referred to as box vents or slant backs, turtle vents are static exhaust vents installed on the slope of the roof, a few feet under the ridge. Turtle vents are often numerous, and installed parallel to the ridge. 
  • Power Vents: Power vents, which can be both solar powered and electrical, utilize a fan powered by a motor, which is connected to a thermostat or a humidistat that controls the operation of the fan. When functioning properly, the fan will only operate when the temperature or humidity level in the attic reaches a certain level.
  • Turbine Vents: Turbine vents consist of a turbine or a spinning fan that sits on top of a vent pipe that runs from the attic to the roof. Turbine vents function similarly to power vents, however in the case of turbine vents, the turbine is wind powered. As such, the exhaust capacity of the fan is completely reliant on the strength and frequency of the wind.
Roof with proper exhaust and intake ventilation
Credit: Brahma Roofing & Construction

What is the Best Kind of Roof Ventilation?

As a general rule, the best ventilation system is going to be one that utilizes intake vents on the lowest possible point of the attic, and exhaust vents on the highest possible point of the roof. Ideally, this would be in the form of soffit vents and ridge vent. However, due to the many configurations of homes and roofs, this is not always possible.

Finding the most optimal ventilation system is a unique process for each home. In summary, this includes finding the total NFA (net free area) of IRC required ventilation, determining which intake and exhaust vents are best suited for your roof configuration, and examining the NFA provided by each vent to determine the total number of vents needed.

Ventilation Imbalances & Problems with Mixing and Matching Vents

Another important aspect of ventilation that is often overlooked, even by trained professionals, is the issue of mixing and matching different kinds of intake or exhaust vents. For example, while mixing and matching turtle vents and ridge vents can ensure you aren’t violating code, it can limit the efficiency of your ventilation system, and in some cases, even cause exhaust vents to function as intake vents, drawing rain or snow into your attic! This is due to the mechanics of air flow.

*** Warning! Technical information incoming!!!!! ***

The Mechanics of Air Flow Explained

The mechanics of air flow in roof ventilation is based on the principles of convection and the stack effect.

Convection is the natural movement of air caused by differences in temperature. Hot air rises, while cool air sinks. This is the basic principle behind how the air flows through the attic in a properly ventilated roof.

The stack effect is the natural tendency of warm air to rise and create an area of low pressure at the highest point of the attic, while the intake vents located at the lower points of the roof create an area of high pressure. This difference in pressure creates a natural flow of air from the intake vents to the exhaust vents.

The Importance of Ventilation Balance & Consistency in Ventilation Types

If there are not enough intake vents to replace the hot air that is escaping through the exhaust vents, the attic may become pressurized, which means that the pressure inside the attic is lower than the pressure outside the attic. This pressure difference causes the outside air (including any elements in the air such as rain or snow) to be pulled into the attic through any opening, including the turtle vents that are located lower on the roof.

Even if your intake and exhaust system is perfectly balanced to begin with, failure to maintain your ventilation system can lead to imbalances from clogging or other issues. By installing a ventilation system that is consistent in its intake and exhaust vents, you limit the chances of issues arising due to imbalances.

Roof with limited ventilation

What Are the Signs of Damage Caused by Poor Roof Ventilation?

So now that we’re familiar with what an attic/roof ventilation system is, how can we tell if it’s functioning properly? Unfortunately, the best way to tell if your ventilation system is malfunctioning, is often by identifying signs of damage caused by poor ventilation. However, the earlier we catch signs of damage, the better we can mitigate the amount of damage caused. 

The signs of poor roof ventilation come in a variety of different forms and are not always easy to spot. While there are signs of damage caused by poor roof ventilation that can be viewed from inside the home or outside the home from ground level, a rooftop inspection and an inspection of the attic itself are sometimes required. Unfortunately, many attics are not easily accessible, and rooftop inspections by anyone other than a trained professional are hazardous for both the person performing the inspection, as well as your roof, which can be damaged by foot traffic. That being said, here are a few signs of damage caused by poor ventilation that you can look for as a homeowner:

Signs of Damage Visible from Outside the home 

  • No vents: Do you notice any vents on your roof, soffits, or gable ends? While some ventilation blends into the roof such as ridge, hip, and eave vents, if no intake or exhaust ventilation is present, that is an obvious red flag for potential damage. 
  • Sagging or curling shingles: If the attic is not properly ventilated, it can cause the shingles to become overheated and buckle or warp, which can be visible from the ground.
  • Ice dams: Poor roof ventilation can cause ice dams to form on the roof, which can be visible from ground level as icicles or ridges of ice along the eaves of the roof. To learn more about ice dams click here!
  • Dark stains: A lack of ventilation can cause moisture to build up in the attic, which can lead to mold and mildew growth. This can be visible as dark stains on the roof or walls of the building.

Signs of Damage Visible from Inside the Home 

  • Peeling or blistering paint: If the attic is not properly ventilated, it can cause the paint on the walls and ceilings to peel or blister due to the excess moisture in the air. This is most likely to occur on the ceiling and upper walls of rooms located directly below the attic.
  • Water stains: Poor ventilation can cause water stains on the ceilings, walls, and even floors from moisture buildup seeping through the attic.    
  • Musty odors: A musty or damp smell in the house can be a sign that there is mold growing in the attic due to poor ventilation.
  • Condensation on windows: When the attic is not properly ventilated, it can cause condensation to form on windows, especially in the winter months.
  • Allergies and respiratory issues: Poor ventilation can cause an increase in mold and mildew growth, which can lead to allergies and respiratory issues for the occupants of the home.
  • High energy bills: Poor ventilation can cause the house to be less energy efficient, resulting in higher energy bills.

Signs of Damage Visible from The Rooftop 

  • Rotting wood: If the attic is not properly ventilated, it can cause the wood to rot, which can be visible as discoloration or soft spots on the roof.
  • Clogged vents: Exhaust vents include screens which are used to prevent the entry of animals, insects, and debris into the attic. However, these screens can become clogged over time which reduces the efficiency of the vents.
  • Shingle condition: While it can be possible to view curled shingles or dark stains from outside the home, the architecture of the roof as well as various roof penetrations can make it difficult to view the entirety of the roof. Additionally, signs of damage are not always obvious to the untrained eye, or significant enough to be obvious from a distance.

Signs of Damage Visible from The Attic

  • Condensation: Poor ventilation can cause condensation to form on the roof deck, rafters, and other surfaces in the attic, which can be visible as water droplets or stains on the surfaces.
  • Mold and mildew: The presence of moisture can lead to mold and mildew growth in the attic, which can be visible as discoloration on surfaces.
  • Rotting wood: Attics have an abundance of exposed wood such as the roof decking, rafters, trusses, and joists which are all susceptible to rot. Wood rot is often visible as soft or discolored spots on the surfaces.
  • Insulation issues: Poor ventilation can cause the insulation in the attic to become damp and lose its effectiveness, which can be visible as clumps or discoloration on the insulation.
  • High temperature: Heat build caused by poor ventilation can cause the temperature in the attic to be higher than it should be, which can be noticeable when entering the attic.
  • Animal droppings: If you find droppings or nests in the attic, it could be a sign of poor ventilation and that animals have found a way to enter into the attic.

*It’s important to note that the signs of damage listed above can be caused by other issues, and it’s always best to have a professional inspect the attic if you suspect there may be a problem, to confirm the cause and recommend the best course of action.


A well-balanced ventilation system is one of the most important yet underrated aspects of a roofing system. Armed with the knowledge of what a roof ventilation system is, the components of the ventilation system, how it functions, and the signs of faulty ventilation system, you’ll be better able to identify any issues before they lead to excess damage.   

In regards to designing and installing a ventilation system for your roof, consulting with a trained roofing professional is your best bet, as not only can mistakes create a code violation, they can also limit the efficiency of your ventilation system which can result in damage to your home. If you have any questions about your home’s ventilation system, contact Brahma Roofing & Construction for an inspection!

Leave a Reply