Fixed Intake Vents | |
Fixed ventilation components are exactly that: units that don't require moving parts or power assistance for proper functioning. But don't let that description lead you to believe fixed ventilation is a low-tech alternative to high-efficiency systems. Just the opposite is true. Fixed ventilation components form the core of all attic ventilation systems, from the simplest to the most sophisticated. In fact, in most cases, your initial goal should be to try to design a ventilation system that uses only fixed vents (or ridge vents -a special, high-efficiency type of fixed ventilation). Obviously, since fixed ventilation can be used to create an entire system, units are available for both intake and exhaust functions. Intake Vent The best place to install intake vents is in or near the roof eave. That location provides two key advantages: 1. The vents are better protected from rain and snow infiltration. Vents mounted in the eave provide almost total protection. (We qualify that statement only to acknowledge the possibility that winds at or near hurricane force could drive moisture into an undereave vent. In normal conditions, however, undereave vents don't allow moisture infiltration.) 2. Usually, when undereave vents are placed on both sides of a roof (as they should be), there's always an equal distribution of positive and negative pressure areas. NOTE: That statement doesn't mean there's an adequate distribution of positive and negative pressure areas. A ventilation system that uses only undereave vents violates the principle of high/low balance. What that means, in practical terms, is that the system will provide a continuous flow ofair along the attic floor, but not along the underside of the roof sheathing, where it does the most good. Intake vents are available in many designs. In choosing the right unit for a particular job, you have to consider the structure of the home, the area where the units will be located and the net-free area provided by each unit. The most common types of intake venting are: --Undereave vents which are mounted in soffit. Units vary in size from 16" x 8" to 16" x 4". Naturally, net-free area varies according to unit size. (See figure 12.) --Continuous-soffit vents which are also mounted in soffit. These units vary in length, with the typical length being 96". --Drip edge vents which are used on homes without an eave area. --Fascia vents which are options available to provide intake on homes without an eave area. --Mini-louvers which are typically used with other types of intake venting; theyre too small by themselves to provide sufficient net-free area of intake. In most applications, they're installed in an exterior wall to help eliminate moisture that collects in the wall cavity. To be effective, minilouvers must be installed below the source of humidity (such as a bathroom or laundry area). That placement allows a flow of air to collect the humidity and carry it into the attic. Source: Air Vent Inc. A Certainteed Company Reprinted with permission, HouseNet, Inc. |