There are not many things that are as misunderstood like attic ventilation is. Basically, all ventilation is about is air that circulates to reduce moisture levels and keep things fresh. In the US, about 90% of homes have levels of moisture that are unreasonably high. Understanding whether or not your home would benefit from some kind of attic ventilation may just be, if not a life-saver, at least a roof saver. Below are a few of the myths as well as the facts you should know about attic ventilation.
1. Increased Attic Ventilation is Good
Just like properly sizing your air conditioning unit and furnace, you want the exact amount of attic ventilation your home needs. Not enough ventilation can cause moisture issues during the winter, and during the summer it can cause decreased energy efficiency, however too much ventilation may be just as bad, if not even worse. An additional roof penetration is created by roof vents, basically another vulnerable area where leaks may occur. There are vents that are necessary, however the last thing you want is to unnecessarily increase the amount of penetrations in teh roof. More than leaks, what these seams can also cause are blowouts during a hurricane or allow the entry of sparks from a wildfire into your home setting it ablaze.
So how much ventilation should there be? Without exception, what you must do to determine what your home requires is talk to a professional. Generally speaking, a ratio of 1:300 what is needed, meaning that for every 300 sq. ft. of ceiling space, 1 sq. ft. of attic ventilation is needed. That being said, air interference and resistance, for example vent grates, will reduce the area of true ventilation. In other words, any vent opening areas do not count as vented space.
2. Roof Vents are for Climates that are Warmer
The majority of people believe that roof ventilation is important so that energy efficiency is increased during the summer. Although good roof ventilation can do this, what is exponentially more important when it comes to overall energy efficiency is sun exposure, shingle color, and insulation and not so much ventilation. Sure, having roof vents installed on older home can reduce levels of hot air during the summer, however there are probably more cost-effective, low-risk ways to increase the energy efficiency of your home.
Meanwhile, it is far more beneficial to prevent moisture damage and it applies to colder climates more than it does to warmer ones. As a matter of fact, the colder the climate is, your home will more likely benefit from attic ventilation. In order you have unvented roofing systems installed in climates that are colder, you need, rigid, highly rated insulation to prevent condensation from forming on your roof sheathing. In climates that are warmer, condensation is not something that you have to worry about. In these climates, the way hot attics are eliminated is with the installation of a thermal barrier along the roofline, as opposed to the attic floor.
3. During the Winter, Roof Vents Remove Warm Air
There are too many people are under the impression that due to heat rising, what ventilating an attic space during the winter means is the release of warm air and creating a drag on your heating efficiency. If this is what you believe, then you have problems that are a lot bigger than worrying about letting warm air escape from your home. Usually poor insulation is the culprit, however if you go into the attic on a day that is sunny and warm during winter, the sun can warm your attic space more than your furnace can.
Unless you have a roofing system that is designed without ventilation and has insulation on the roofing deck, your attic should not be being heated by your furnace. Even worse, inadequate insulation is almost definitely allowing air that is packed with moisture into your attic. When this air that is warm and moist hits your roof, what will likely happen is that condensation will form and lead to even more deterioration of your insulation and possibly even wood rot. If you believe this to be a concern, wait until the sun has gone down and measure your attic’s temperature. It should almost match the temperature outdoors.
4. Research Studies
There have been numerous studies conducted in regards to the effectiveness as well as optimization of general roof ventilation and certain types of roof vents. The benefits of roof ventilation cannot be disputed. Laboratory settings however are not a great indicator of real world or weather behaviors. On top of that, certain roof ventilation traits are made bigger over time due to regional differencesf. What works best in San Antonio, Texas, is probably not going to be the same as what works best in Cleveland, Ohio.
Roof ventilation, in some ways is very much like an art in its science, and using online information to install your own roof ventilation is much like using WebMD to diagnose a skin rash. Finding an experienced and trusted roofer who for his or her entire career, has worked in your region is far better for your roof than any online or research study “expert.”
5. If I Have Roof Vents, This Means I Have Roof Ventilation
Although hardly anyone will agree on the very best roof ventilation system, what everybody does agree on is that there are roof vents that don’t do much good at all. For example, ridge vents. Most roofing experts will agree that the most cost-effective and effective roof vents on the market are ridge vents. Without the blinders which are called baffles which prevent the air from outside from crossing over the vent, a ridge vent can create basically no ventilation. Air will circulate through only a small percentage of an attic with gable vents. Although effective for ventilation, static, roofline vents are not recommended due to issues with leaking. Air may be left trapped at the top of an attic with soffit vents. The ventilation which is most effective uses a ridge-and-soffit continuous system, however even designs like that can vary from one roof to the next.
If you are unsure of how your roof vents work, or if you are uncertain about the ventilation in your attic in general, you should speak with a roof inspector about the system you currently have and any inherent weakness that it may have. The risk/reward for having poor ventilation or no ventilation, combined with the negligible costs of having a good-working ventilation system installed makes them one of the home maintenance negligence sins that is unforgivable.