All About Attic Ventilation!
Recently, we wrote about ice dams on roof overhangs, how they are created and how to prevent them. Our discussion on prevention – or at least reduction — included improving attic ventilation and adding ceiling insulation to keep the house warmer and the attic cooler. Often, there isn’t enough room in our column to completely elaborate on ALL of the methods available to solve a particular problem. So, this week we would like to tell you about the various methods that can be used to ventilate an attic. Keep in mind that our suggestions also affect summer comfort too.
The first thing that we want to do is dispel an old wives tale which suggests that you cover your roof vents up in the winter to keep the cold out of the attic and the warm air in. An attic must be well ventilated year round. Never cover a roof or eave vent. No matter how cold it gets. The trick to keeping your house warm is with a thick layer of ceiling insulation. Covering the vents when it gets cold will cause reduced air flow in the attic that in turn will promote excessive condensation. This can result in mildew growth and other types of moisture damage. The condensation can get so bad that it will trickle down the rafters into the house and make you think you have a roof leak. Constant air flow in the attic will reduce condensation – year round.
Keep in mind that insulation has its limits. Regardless of the R-value, the greater the difference between inside and outside temperatures the greater the heat loss (or gain) will be. Hot air always travels toward cold air. So, in the winter warm air escapes to the outside. And in the summer warm air travels to the inside. Having said that, just make sure that you are well insulated and the air cannot pass through holes between the ceiling and the attic. O.K., or visa versa.
Attic venting is always included as a standard part of construction when a new home is built. Codes require a specific amount of ventilation. But then the building department doesn’t necessarily specify what is best – only what minimums must be met. In the case of attic ventilation – the more the merrier.
Vents are positioned to allow air into the attic at its lowest point — the underside of the roof overhang (the eave or soffit). And since warm air rises, exhaust vents are mounted high on the roof, at its ridge, above the ridge or near the peak of a gable wall. These are known respectively as a roof vent, a ridge vent, a cupola vent or a gable vent. The gable vent is the only type that is not actually mounted somewhere on the roof itself. So why are gable vents used you ask? Well, with a gable vent there is less risk of leak. This is because it is separate from the water-shed configuration of the roof covering. And, installation is cheaper because it doesn’t have to be woven into the shingles. But even with gable vents we like the idea of seeing them mounted on the roof as well. Also, the ridge vent system is very effective, reasonably easy to retrofit and less expensive than other alternatives. We have to say that adding a ridge vent to an existing home is more “user friendly” than other alternatives. By the way, the cupola is not an addition that will necessarily work well with every home’s architecture. Study such an addition thoroughly. Even though the cupola is the highest point on the roof, costs could easily cause this good looking alternative to be scrapped for a more practical retrofit.
The higher the exhaust venting is located on the roof the more effective it can be. Air currents are created between the upper and lower vents. As the hot air rises and leaves the attic cooler air is drawn in from the vents below. The siphoning action that results can cause air to move in an unusually rapid cycle. This is called passive ventilation. After you provide the inlets and outlets mother nature does all the work. Sometimes though, nature needs a kick in the pants. This is when active methods are used such as turbine vents and electric attic fans. Since these babies are sometimes difficult to use in snow country it is a good idea to consider their use during non-snow months only. Stay warm – and dry. And, good luck!
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