Evaluate
your needs.
There are
a number of variables to consider when selecting the most
effective ventilation system for your home. Before you
make any decisions, 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 check is evidence
of moisture, such as mold, mildew, rusted nail heads,
damp or compressed insulation or wood rot.
Once you've
completed a general inspection of your attic, look for
ventilation systems already in place, such as gable vents
or roof louvers. Note the size and locations of each.
Do the same with intake vents, including soffit and eave
vents.
Finally,
make an estimate of the square footage of your attic.
Most are slightly larger than the size of one floor in
your home. You'll need this figure to make sure you install
adequate ventilation.
If your
roof pitch is 7/12 to 10/12, plan to add 20% to your calculation
for vent requirements; 30% for roof pitches of 11/12 and
steeper.
Vent Requirements
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 there is a vapor retarder or the
space is balanced between the ridge and intake vents.
A balanced ventilation system means about 50 percent of
the required ventilating area should be provided by exhaust
vents in the upper portion of your attic with the remaining
50 percent provided by intake vents.
Please
remember, building codes specify the minimum amount of
ventilation. You may want to increase the requirement
to ensure proper ventilation.
Common
Mistakes
Too many
times, homeowners install products that short-circuit
their ventilation system. When designing a ventilation
system, avoid these common pitfalls:
- Using
a combination of different types of exhaust vents, like
power vents with ridge vents. In this case, competing
vents pull air from each other instead of from soffit
vents.
- Underestimating
your ventilation needs. Remember that 15 roof louvers
or 5 turbine vents would be needed to provide the same
ventilation as 42 feet of ridge vent on the same house.
- Installing
exhaust vents without adequate intake. An effective
balance of intake and exhaust must be achieved to properly
ventilate your home. The flow of air in your attic is
limited to the amount of intake.
- Installing
a ridge vent that doesn't have an external baffle to
increase air flow and protect from weather infiltration.
ntake
and Exhaust
