Roofing Ventilation 101

1

Why Ventilate?

There are four main reasons to ventilate your
home’s attic space.

• Reduce Heat Gain and Reduce Energy Bills in the Summer
Radiant heat from the sun warms the roof and radiates into
the attic. If not properly vented out, it could radiate into the
living space affecting the comfort level inside the house
and contributing to higher utility bills (because appliances
such as fans/refrigerators/air conditioners may have to work
harder to keep your home cooler).
• Reduce Moisture and Condensation in the Winter
In northern climates, heated air from the home escapes into
the attic through openings in the walls or ceilings (such as
recessed lights, electrical chases, the attic access door, etc.).
Some of this moisture vapor rises to the colder/dryer attic
where it can potentially condense if not properly vented. If it
condenses, it could dampen the attic insulation (which could
weaken the R-value of the insulation), contributing to wood
rot, mold, mildew and poor indoor air quality.
• Fight Ice Dams
Ice Dams are formed when in winter conditions, heated air
from the home migrates into the unheated attic through
the ceiling, under insulated areas and through bypasses,
such as light fixtures or exhaust systems found in kitchens
and bathrooms. This creates warm areas on the roof
and unevenly melts the underside of the snow that has
accumulated on the roof. The melted snow flows down the
roof until it reaches a colder spot, such as the eaves, where it
refreezes, forming a back up of ice commonly called an ice
dam. The ice dam is a result of energy loss from inside the
house, which could cost a homeowner hundreds of dollars
or more. It could also lead to rotted roofs and rafters, ruined
insulation, moisture inside the walls, mold and peeling
paint. Proper attic ventilation can help prevent the conditions
that contribute to ice dams.
• Prolongs the Service Life of the Building Materials
Finally, the shingles and decking of your roofing system may
deteriorate prematurely due to heat and excessive moisture
buildup. By reducing the surface temperature of the shingles
and the existence of moisture on the underside of the
decking by properly ventilating the attic space, a homeowner
may be able to extend the life of both of these materials.

2

How to Ventilate

Effective Ventilation is achieved by providing
intake ventilation at the lower edge of your roof
and exhaust ventilation at the upper portion of
your roof. The flow of air from the lower portion
of the roof to the upper portion the upper portion

through these vents is often called the “stack effect,”

which is similar to how a chimney works.

3

How to
Ventilate
Common
Mistakes
to avoid

Contractors and homeowners are urged to check
the following:
• Make sure two different types of exhaust vents are not on
the same roof of a common attic, so as to avoid possible
short-circuiting of the system (see Section 2 above).
• Make sure the intake vents are not covered with insulation.
To avoid this possibility be sure to insert attic insulation
baffles keeping the insulation away from the intake vents.
• Check that the intake vents have not been painted shut.
If they’ve been painted over that could restrict or reduce intake airflow.

4

Sealed
Versus
Ventilated

If you’re considering sealing your attic instead
of ventilating your attic be sure to ask your
contractor these important questions:
• Where will all the internal moisture go?
• How can I visually inspect for a roof leak if the underside
of the deck is sealed with insulation?
• Will I have more of a threat with mold and mildew?
• How does this impact my shingle warranty?
• Will this cause more ice damming?

5

Attic
Ventilation
IS Green
Effective ventilation is achieved by providing
intake ventilation at the lower edge of your roof
and exhaust ventilation at the upper portion of
your roof. The flow of air from the lower portion
of the roof to the upper portion through these
vents is often called the “stack effect,” which is
similar to how a chimney operates.
Contractors and homeowners are urged to check
the following:
• Make sure two different types of exhaust vents are not on
the same roof of a common attic, so as to avoid possible
short-circuiting of the system (see Section 2 above).
• Make sure the intake vents are not covered with insulation.
To avoid this possibility be sure to insert attic insulation
baffles keeping the insulation away from the intake vents.
• Check that the intake vents have not been painted shut.
If they’ve been painted over that could restrict or reduce
intake airflow.
• If using vented soffit panels for intake ventilation (typically
made by siding manufacturers) check the net-free area
rating of the panels to ensure they allow proper intake
airflow.
• Make sure bathroom, kitchen and dryer exhaust fans are
properly vented to the exterior of the house and not into
the attic cavity as this practice will add excess moisture
inside the attic.
If you’re considering sealing your attic instead
of ventilating your attic be sure to ask your
contractor these important questions:
• Where will all the internal moisture go?
• How can I visually inspect for a roof leak if the underside
of the deck is sealed with insulation?
• Will I have more of a threat with mold and mildew?
• How does this impact my shingle warranty?
• Will this cause more ice damming?
…and it’s contractor tested and trusted. A balanced
ventilation system allows fresh, dry air to flow into
your attic structure through your intake vents. As
this occurs, warm moist air is drawn through your
exhaust vents to the outside. This is what is known
as a passive ventilation system and is one of the
most energy-efficient systems in the industry, as it
requires no energy to run and can help reduce your
cooling bills in the summer time.