A well-designed home has an attic ventilation system that requires no homeowner action whatsoever. Not living in a perfect world, most of us should examine our attic ventilation needs and the deficiencies in our home's design. There are many things that can be done to improve attic ventilation... and many problems that can occur if you ignore it!
Some ventilation solutions require a "powered assist". ATTIC VENTILATION FANS are designed to remove the heated air from the attic only, lowering attic temperatures and thus reducing the temperature of the rooms below. Sometimes they work wonderfully... sometimes not.
The second type of attic fan... the WHOLE HOUSE ATTIC EXHAUST FAN... is designed to draw a large volume of hot air out of your living space, replacing it with cooler outside air.... assuming the outside air is cooler! Though these may assist your attic ventilation strategies, whole house fans are primarily designed to increase your own comfort. Ahhh... a worthwhile goal!!
These articles should help you make some decisions as to whether you need to improve your attic ventilation, how far you should go, and where you could go wrong. Enjoy!
Keep Heat Under Control With Proper Attic Ventilation
Fine, Mr. Attic. Breathe in deeply... breathe out. Now, cough...
Since the energy crisis of the '70's, the climate of our attics has taken on more importance as we have insulated, weather-stripped and sealed our homes into virtual mausoleums. The idea of actually allowing a part of our home to be cold... and to do it intentionally... can give one the chills! It seems a contradiction to all the brainwashing we have received regarding the absolute need for an energy efficient home. But your attic is unlike other areas of your home, performs different functions and, to do its job, must be allowed to... breathe!!
Your attic is your friend... understand it, respect it, appreciate it and care for it!
Think of your attic as a buffer zone. Outside in the "real world" meet Mother Nature in all her glory, with temperature swings and moody weather. Inside your home, you have relatively constant temperature and humidity hopefully matching the health needs of the folks inside. The attic allows for a transition between the wild and the wonderful through the cooperation of your roof, insulation, vapor barriers and ventilation.
The attic roof, of course, keeps rain and melting snow from ruining your Persian carpets.
Insulation in the attic slows down the movement of heat up from your living space, trying its darndest to keep the inside of your home warm or cool regardless of the attic temperature.
Vapor barriers in the attic keep moisture rising from your living space away from the insulation. They are needed because damp insulation loses much of its value. Vapor barriers can take the form of plastic sheets installed on the attic floor (under the insulation), a built-in paper or aluminum foil facing on the insulation itself (always installed towards the living space), or in the form of special vapor barrier paints (See article on insulation for more information).
Sufficient ventilation helps to keep attic temperature and moisture at their optimum levels for the season. In winter, the perfect attic temperature is the outside temperature... cold and dry. In summer, the ideal is to have lots of air movement so the attic is as cool as possible... without adding refrigeration!
Proper attic ventilation has year-round benefits...
The obvious benefit of increased ventilation in the warmer months is a lower attic temperature, which can decrease cooling costs in the home. This is true regardless of how much insulation there is in the attic. In fact, attic insulation can actually cause increases in temperature in the home as the insulation holds the heat long after the sun is gone, continuing to transfer it slowly through the ceilings into your living space. Though we think of attic insulation as a barrier to the movement of heat, the oppressive heat of an underventilated attic can make your insulation a "fair weather" friend.
In the warmer months, a not-so-obvious effect of lower attic temperatures is increased roof shingle life. Though asphalt shingles are designed to take the abuse of the sun for many years, they are subjected to greater temperatures when the roof decking is allowed to overheat... which is just what happens in an underventilated attic.
In the cooler months, moisture is the most serious concern. Even with the use of vapor barriers to keep moisture from entering the attic, there are air leaks around ceiling light fixtures, bathroom exhaust fans, access panels and fold-down attic stairways that allow unwanted moisture into the attic. Just going into the attic to bring down that old Monopoly game can increase the moisture level in the attic a hundred fold.
Moisture condensing on the framing members and the inside of the roof deck can lead to the growth of mold, mildew and rot in the roof deck and framing. And for those of you who use the attic area for storage, watch those roofing nails and any metal reinforcements! Have you ever noticed that items in the attic seem to have evidence of slight water drips, but there doesn't seem to be a roof leak? Glance at the business end of the roof nails sticking through the roof deck. Are they rusty... or is the wood around them stained? If so, you almost definitely have an attic moisture problem. Moisture from the living area is entering the attic and freezing on the nails. When the attic warms slightly, the ice melts and drips onto your stuff. Mystery solved!
As if that wasn't enough, relative warm and cold spots on the inside of the roof deck can lead to the nightmare of ice dams and their associated roof leaks when the roof is snow-covered (see article on ice dams for more information).
Understanding non-mechanical attic venting...
One common type of vent, especially in homes built prior to 1980, is the gable vent, which is a louvered and screened vent located at or near the peak in the sidewall of the attic. Gable vents come in different sizes, materials, and shapes... triangular, rectangular, wood, plastic or metal. They offer a reasonable amount of ventilation in the upper-most areas of the attic but they do not produce uniform temperatures throughout the attic, leading to the formation of "hot spots" of overheated motionless air.
By far the best non-mechanical venting system is the combination of soffit vents and ridge vents. This type of ventilation requires a specific roof design with an overhanging area at the lower edge of the roof called a soffit. Vents are installed into the underside of the soffit overhang to allow air to move into the attic. The graphic shows a continuous soffit vent which runs the entire length of the soffit.
To complement the soffit vents, another vent is installed at the peak of the roof, called a ridge vent. This is a screened replacement for the uppermost shingles bridging the peak of the roof, allowing air to flow in or out of the attic along the entire peak. The system is devilishly simple in function yet effective... warm air in the attic rises and exits through the ridge vents to be replaced by cooler air entering the soffit vents. Because the path of the cool air is along the underside of the roof deck, it provides uniform air movement and the best possible ventilating action.
Living in an imperfectly vented world...
Oh if only the world was perfect... but it's not. And if only all the builders took attic ventilation seriously years ago. Dream on! They didn't. As usual, we all have to make compromises and "make do" with what we have. Here are a few suggestions to help you with some of these imperfect situations...
If your home has gable vents but unvented soffits, the installation of soffit venting will be a great improvement over gable vents alone. Though you might be able to install continuous soffit vents, it is much easier for the homeowner to install circular aluminum vents. Just bore the right size hole and press them into place! They are available in sizes from 2" up to over 16". Just make sure there is no insulation blocking the inside opening to the soffit, or the vents will be useless. By the way, the addition of a ridge vent would make this retrofitting perfect (see below).Vent louver pictured is manufactured by Seiho International.
Installation of a vent or vents in the lower sidewall of the attic can also increase the air flow to a gable or ridge vent. Don't use a gable-type vent in this low location... it's not too aesthetically pleasing. A few circular aluminum vents painted to match the house are much less obvious.
Installation of a ridge vent in a home with gable vents will dramatically increase the ventilation of the attic, though not as much as if soffit vents were installed. However, if your moisture problem is not extreme, it may give you just enough ventilation to avoid more drastic measures, such as a powered ventilator, discussed in the next section.
Unfortunately, installation of soffits onto an existing house is not a small task. If you just simply must have them, I suggest pricing out a new house first!
Do not allow your attic insulation to come in contact with any part of the roof, or to cover your soffits.
If you use your attic for storage, be sure to leave space around your vents for air movement.
Mechanical attic venting...
If you have noticed any of the symptoms of inadequate ventilation as mentioned earlier and cannot increase ventilation through conventional means, you may be a candidate for one of the various mechanical attic ventilators. They all increase ventilation through the use of fans or turbines which forcefully remove air from the attic. As you will see, they work in concert with other vents to lower attic temperatures in the summer and also remove moisture in the winter.
Gable Mounted Ventilators...
Gable mounted ventilators are the simplest type to install, and can really increase the air flow through the attic. They are mounted inside of an existing gable vent, and in many cases require no carpentry at all to install. A typical unit can ventilate over 2000 square feet of attic space. You will need electrical skills, however, since these are powered units.
There is a second type of gable mounted ventilator that is mounted through the wall, with its own self-opening shutter system to prevent the entrance of bees, bats or other undesirables into your attic when not in use. These units require more advanced carpentry skills for installation but the reward is increased ventilation. Unlike the gable vent-mounted units, they do not have to blow through the gable vent's protective screening. As mentioned in the article on whole house exhaust fans, insect screening can decrease the total air flow through a vent by up to 25%!
Roof Mounted Ventilators...
Roof mounted ventilators come in two flavors... powered and unpowered. Unpowered ventilators, also called turbine attic ventilators, rotate with the slightest breeze and cause a powerful updraft in the attic to effectively pump out the heated air. Varying in size from 12" up to 24" in diameter, the largest of these turbines can move as much air (with a little assist from Mother Nature's breath) as the most powerful electric ventilators!
Avoid steel ventilators... as Neil Young once sang "Rust never sleeps!" Instead insist on rust-proof aluminum or plastic ventilators. The SupaVent unit shown at the right, for example, is made from ABS plastic and is virtually indestructible!
Supavent Turbine Ventilator
Graphic courtesy of
Edmonds Industries Australia
Powered roof mounted ventilators are the most effective ventilators available able to ventilate over 2500 square feet of attic floor space. They share the same two advantages of the turbine ventilators... the high mounting position allows them to most effectively suck out the heated air, and you have greater flexibility in choosing the mounting position... especially useful if your attic is "complicated" due to architectural design!
Graphic courtesy
Sun Tunnel Skylights
If your roof faces the right way... south-facing roofs are the best... you might be able to benefit from the energy saving features of a solar powered attic exhaust fan. Though not as powerful as the largest electric ventilators, solar units offer the advantages of zero energy cost during use.
They are the most effective when needed the most since their fans increase in power and speed as the intensity of the sunlight increases. And even if you are "electrically challenged", there's no problem 'cause there's no wiring!
Pictured above is the
Fan-Attic
Solar Ventilator.
For more information visit their website at http://www.fan-attic.com
Whole house exhaust fans...
If you already have a whole house exhaust fan, you already have some of the benefits of attic ventilation fans. Each time you use your exhaust fan the attic air is quickly cooled. Initially there will be "hot spots" since the exhausted air will be directed towards the existing vents, but the sheer volume of the exhausted air will soon cool the entire attic.
Of course, most of us will not use our whole house fans during the day since it would be silly to draw heated air into your home just to cool the attic! If your existing attic ventilation system is doing its job, a whole house exhaust fan will only add to the benefits of a cooler attic in the evenings.
See the article on whole house exhaust fans for more information!
Watch out for unintended consequences!
Murphy's law rears its head in the strangest places... your attic, for instance. Who would think that that beautiful powered ventilator might do absolutely nothing to cool your attic? If you have lots of ventilation already, adding a powered ventilator may be a waste of time and money.
This is especially true if you have a soffit-ridge vent system, the most efficient natural ventilation system. Face it... ventilators are stupid machines! They will draw air from wherever they can with the least effort. This means that a ventilator will draw air from ridge vents, gable vents or soffit vents. Fine. But if the fan draws much of its air from a nearby gable or ridge vent, there is no benefit to anyone except the electric company! So placement of the ventilator is essential... as well as careful consideration of whether or not it is a wise investment in the first place.
If you have installed an unpowered roof turbine vent, you have a year-round ventilation increase (unless the two feet of snow on the roof freezes it solid). Unfortunately, powered systems use heat sensors to control their operation. They only run when the attic reaches a certain temperature... typically ranging from as low as 70 degrees F to as high as 140 degrees F. This is great for the summer, but what about the winter? As you have learned, the moisture that accumulates in a poorly ventilated attic can be as destructive as the summer heat. Unfortunately, a thermostat is not a viable solution for wintertime ventilation. A suggestion... install a timer that will automatically turn on the ventilator for a certain number of hours each day to give you a true four-season ventilation boost!
Safety considerations with powered ventilators...
It is a wise idea to have a master cutoff switch for your attic ventilator in your living space. This allows you do perform maintenance safely as well as being able to stop the air flow if you need to go into the attic. No need to pull cooler house air into the attic, right?
All attic ventilators should be installed with a fusible link, a type of fuse that melts in the presence of high heat, disconnecting the power. It is mounted near the fan in the attic, automatically turning off the fan in the event of fire... a valuable safety feature!
Do-It Yourself installations...
Both powered and unpowered ventilators come with detailed installation instructions, and should be within the abilities of even the novice do-it-yourselfer. Getting electrical power safely to the ventilator (if needed) requires electrical knowledge concerning proper wiring practice and local code requirements.
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