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R o o f V e n t i l a t i o n
Page 4 of 5
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| There are several common
misconceptions about attic ventilation. One is that many people think that if they have only
power vents or turbine vents working near the ridgeline, then their attic is properly
ventilated. Remember that in order for an exhaust vent to properly function, it has to
have intake vents working with it. If there are no intake vents, then air has to enter
somewhere so it will enter through some exhaust vents and exit through others. The result
is circulation of only the air immediately surrounding the vents or in between the vents. |
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This picture shows what happens
if you have no intake vents along the eaves. Air will circulate only between the exhaust
vents leaving the remainder of the attic space unventilated. |
| Another common
misconception is "more is better". Many people think that they can improve
ventilation of their attic by installing vents all throughout the roof surface. What they
don’t know is this causes a Ventilation Short Circuit. For instance, let’s say
that Fred has a full soffit and ridge vent system installed. But thinking that more is
better, Fred decides to install a couple of vents about halfway up the slope. Instead of
improving his ventilation, he has now hampered it because air is now exiting out the vents
in the middle of the roof, before it reaches the ridge leaving the attic partially
unvented. Depending on wind pressure, air will also be taken in at the intermediate
vents reducing the intake at the eaves where it should be. There is also the problem of weather infiltration. Wind blowing across a roof
surface creates a negative air pressure. Nature will automatically try to compensate for
it by moving air from a location of higher pressure, such as inside the attic. When the
air is then removed from the attic in this manner, it has to be replaced. If the proper
intake ventilation isn’t used, then air will be brought into the attic through the
exhaust vents and will at times bring moisture with it.
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