The Truth About Attic Ventilation
Attic ventilation is, excuse the pun, a hot topic. A quick search online will come up with a variety of perspectives. Some experts extol the virtues of attic ventilation, claiming it is one of the most important ways of preserving your roof, among other benefits. Others suggest that attic ventilation is overhyped and the claims made about it are just not true. So what is the truth about attic ventilation? It’s complicated. The experts at Eagle Watch Roofing have put together this guide to help you decipher the truth about attic ventilation.
If you’re confused about the benefits of attic ventilation, you are in good company. Roofing experts, energy efficiency experts, and the people who write municipal and other building codes aren’t sure either. It’s an ongoing discussion with a number of competing claims. Ultimately, more research needs to be done. But in the meantime, there are some important things you can do for your roof, your attic, and your home.
Claims for the Benefit of Attic Ventilation
Roofers and building codes have long touted the benefits of sufficient attic ventilation. Many homes are not up to code or simply don’t have enough ventilation. Increasing attic ventilation, they say, will help with a number of potential issues.
Adequate ventilation will keep your attic from overheating in the hot summer months, which can damage your roof. Keeping the temperature down will also help reduce cooling costs for your home. In the cooler winter months, attic ventilation can prevent warm air from your house from building up in the attic. The warm air carries moisture which can condense on the ceiling and walls of your attic as it hits the colder air. That moisture can cause rot, which damages your attic and your roof. In fact, if you have an asphalt shingle roof, insufficient attic ventilation may void your warranty.
The Other Side of the Argument
Some energy efficiency and building experts are beginning to question the benefits of attic ventilation. Many of the issues that experts blame on inadequate ventilation may actually be caused and solved by other methods. The most significant factor touted by the dissenting parties is insulation between your living space and the attic floor. If you’re worried about hot, moist air building up in your attic in the winter months, seal off the attic from your heated living space. If you are concerned about a hot attic raising your cooling costs in the summer, insulate the floor of your attic.
There’s no doubt that both sides of the argument carry some merit. At Eagle Watch Roofing, we would never suggest that you should ignore attic ventilation. It is vital to the health of your roof and your home. But we also agree that you need to insulate the floor of your attic and seal it off from your living spaces. These don’t have to be mutually exclusive solutions. Instead, we recommend a balanced approach that will take into account all the ways to extend the life of your roof and the health of your home.
How Much Ventilation Does an Attic Need
Let’s start with the part of the discussion that covers the benefits of attic ventilation. Without a doubt, you will see some benefits from adequate attic ventilation. But how much attic ventilation is enough attic ventilation? If you want to get the results, you will need enough ventilation to get the full effect and benefits.
The easy way to answer the question is to refer to the ICC values. The ICC, the International Code Council, puts out model building codes. The International Building Code (IBC) put out by the ICC have been adopted by all 50 states, the District of Columbia, and U.S. Territories. According to the IBC, most attics require 1:150, that is 1 square foot of ventilation per 150 square feet of attic space. The ventilation is split evenly between intake and exhaust. For an attic with a moisture barrier, you may reduce the ventilation to 1:300, or 1 square foot of ventilation for every 300 square feet of attic space. However, if you are unsure, more ventilation is better than less.
The Best Attic Ventilation
The gold standard for attic ventilation is a combination of soffit vents and ridge vents. That means that you have half of your required ventilation square footage in the soffits of your home. The soffit vents will be your intake vents. The easiest way to do this is to cut a long opening in the soffit and cover that with mesh or a plastic vent fitting. Remember that the ventilation area, referred to as the net free area (NFA) is only the open portions. Depending on how you cover the vent, you will gain less square footage of NFA than if there was no covering, so calculate accordingly.
The other half of your NFA should be in ridge vents. The ridge vents serve at the exhaust vents. A ridge vent is a vent formed when the ridge of your roof is raised slightly, creating a space between the ridge and the roof below it. This creates a vent along the length of the ridge. With ridge vents, it should be easy to get the necessary square footage.
The benefit of the soffit and ridge vent combination is that it takes advantage of the natural movement of air. This is sometimes called the chimney effect. Basically, it just means that hot air rises. As the hot air in your attic rises and exits the exhaust ridge ventilation, cooler air is drawn in through the soffit vents. This keeps heat from building up in your attic.
Other Types of Attic Ventilation
Other types of ventilation include gable vents, fan vents, and can or power vents. Gable vents are often found in older homes and look like open slats in the wall that forms the side of your attic. Gable vents rely on wind to carry air in and out of the attic and are best in climates with a steady breeze. Fan, can, and power vents all have vents in the roof, but not at the ridge, and function to mechanically draw air out of the attic.
Alternatives to Attic Ventilation
While there is no complete replacement for attic ventilation, there are those who argue for other solutions to the typical problems solved by attic ventilation. The primary solution put forth is sealing off your attic. That means tightly sealing any penetration between your living space and the attic. Typical penetrations include duct registers, recessed lighting, plumbing stack, and of course your attic hatch. In addition to sealing off the attic, make sure that there is significant insulation between the ceiling of your living space and floor of the attic. The goal is to minimize or even preclude the movement of air and heat between your living space and your attic.
By sealing off your attic, you can prevent a few of the issues typically addressed by attic ventilation. First, you can reduce energy bills. Most attics are not air-conditioned and heated. This means that they are cold in the winter and hot in the summer. Sealing off the attic keeps warm air from escaping your home in the winter and heated air from entering your air-conditioned home in the summer. Second, it can reduce moisture in the attic, especially in the winter, by preventing warm, moist air from your living space from entering the attic.
Roof Color and Attic Temperature
Another way to control some attic problems, besides ventilation, is to look at your roof itself. One function of attic ventilation is to prevent heat buildup in the summer. But have you thought about your roof and the role it plays in attic temperatures? A dark colored roof absorbs much more heat than a light colored one. It’s just like getting into a black car on a summer day compared to a white one. The difference between a dark and light roof in the summer can be significant. According to the U.S. Department of Energy, a dark roof in the summer can reach 150 degrees. A light roof can stay up to 50 degrees cooler. The heat of your roof is transferred to the attic, so a light colored roof can have a substantial effect on the temperature of your attic.
For some homeowners who live in cold climates, a dark roof may actually be a benefit. It could reduce heating costs slightly in the winter. However, in warmer climates, including the Southeast, cooler light-colored roofs are more advantageous. A cooler roof means a cooler attic. A cooler attic, in turn, means less heat damage to the underside of your roof. However, if your attic is sufficiently sealed off from your living space, the energy consumption differences should be negligible.
How Important is Attic Ventilation
After all we’ve said above, your head may be spinning a bit when it comes to the value of attic ventilation. If so, you are simply experiencing the same indecision faced by many experts. So what should you do when it comes to your own attic? Our best advice is to take note of both sides of the argument. Ventilate your attic to code, 1 square foot of ventilation for every 150 square feet of attic. But also make sure to seal off your attic. Like any non-conditioned area of your home (for example, your garage), keeping it sealed off from the temperature controlled parts of your home will help with energy costs.
If you’re still confused, just contact Eagle Watch Roofing, and we’ll be happy to come take a look. Also, if your attic has been inadequately ventilated for some time, you may have hidden damage to your roof. Eagle Watch Roofing is happy to inspect your roof, both from above and below, for any signs of damage. It is always cheaper to repair damage before it spreads than to wait for it to become a major repair or even replacement.