|Central California's Roofing Experts
Could my roof be causing higher energy bills?
Is ventilation really important?
What is the best type of ventilation?
How can I tell if I need more ventilation?
Attic ventilation might seem like a minor consideration, but when done properly, it can extend the
life of your attic and roof structure; and save you hundreds of dollars in repair and energy costs.
In the summer, hot, moist air in the attic can warp roof sheathing and cause shingles to
deteriorate prematurely. A hot attic also makes a home more difficult to cool and can result in
added energy costs. In the winter, an overheated attic melts snow and can form ice dams at the
roof edge. Water can back up under your shingles, wetting and damaging insulation and,
eventually, the structure of the roof itself. Ice dams can even cause leaks inside your home,
resulting in drywall damage.
The only way to combat these problems is with good attic ventilation. The wind blowing over the
exhaust vent, near the top of your roof, creates a negative pressure that draws the warmer air
out of the attic. Replacement air enters through the under eave or soffit vents, bathes the
underside of the roof while absorbing heat and moisture, and again exits through the exhaust.
Even with no wind, the natural convection action of rising warm air maintains a continuous airflow
along the underside of the roof. It’s a system that works year round with no moving parts or
To decide if your home is adequately ventilated, go up into your attic and take a look around.
A sure sign of poor ventilation is an unbearably hot attic in the summer. Another thing to look
for is evidence of moisture, such as mold, mildew, rusted nail heads, damp or compressed
insulation or wood rot.
According to most building codes, you need one square foot of vent area for each 150 square
feet of attic floor space. The minimum is one square foot for every 300 square feet of attic
floor space, if the space is balanced between the ridge and intake vents. A balanced
ventilation system means that about 50 percent of the required ventilating area should be
provided by vents located in the upper portion of your attic to serve as exhaust vents, with the
remaining 50 percent provided by eave vents for intake.
There are a number of variables to consider when selecting the ventilation system that's going
to be most effective for your home. Review the types below to decide what is best for you:
A ridge vent is positioned along the entire
length of the roof peak. In addition to being
excellent exhaust vents, ridge vents blend in
with the roof line, making a more attractive
home. Years of research has proven that
ridge vents with external baffles, combined
with under eave venting, is the most efficient
and effective system you can install.
Gable louvers are installed in the gable
end of the attic. The higher these vents
are placed, the more effective they become
as exhaust vents. Gable louvers are not
a preferred method of ventilating an attic
because they provide only limited air flow
across the underside of the roof deck,
resulting in "hot spots." They are also dependent
on wind direction.
Wind Turbines or Whirlybirds
Turbine vents protrude from the roof and
use a series of specially shaped vanes to
catch the wind and allow the turbine to spin,
pulling air out of the attic. Although not as
effective as ridge vents, turbine vents
provide a low-cost alternative in areas
where consistent wind speeds of at least
5 mph are typical. Without that minimal
wind speed, turbine vents act essentially as roof louvers.
Roof louvers are covered openings that
allow air to escape the attic. Most attics
require several of these vents to be installed
to properly ventilate the attic. They should
be placed evenly, in line, across one side
of the roof. Roof louvers only provide a
small, confined area of movement, which
means air does not move along the entire
under side of the roof deck. And because
multiple holes must be put in the roof, most
people try to avoid roof louvers.
A power ventilator is a motor-driven fan
that is controlled by a thermostat. It works
quickly to pull air out of the attic. A
humidistat is also required if you want
to control winter humidity problems.
Intake vents are installed in the soffit or
under eave (overhang) section of the
house. They are critical to the overall
performance of the attic ventilation
system. Intake vents feed the exhaust
vent with cool, dry air at the lowest
point in the attic so that the warm,
moist air can be pushed out at the
top of the roof. An effective attic
ventilation system should include
a balance of intake and exhaust vents.
Remember to avoid using a combination of different types of exhaust vents, such as power
vents with ridge vents. In this case, competing vents pull air from each other, instead of from
the soffit vents. This will short-circuit your ventilation system and render it ineffective.
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