It’s officially time for spring cleaning, which means you’ll
be spending more time in your attic than usual. As you tidy up, you may notice
some startling signs like discoloration along your attic ceiling or sweltering
attic temperatures. But are these causes for concern, and will attic ventilation
solve these problems?
Attic ventilation is actually more helpful during winter
than summer. To understand why, you need to know the relationship between air
temperature and moisture.
In the winter, the inside of your home is warm. Meanwhile,
the roof and the air around it are freezing cold. As the warm indoor air rises
and gets closer to the roof, it begins to cool. Because cooler air holds less
moisture than warm air, the moisture begins to condense on the underside of
your roof in the attic. This condensation can cause severe problems, including:
· Growth of
mold and mildew
– Reduces indoor air quality and triggers allergies and
asthma in some people
· Wood rot
– Weakens your home’s structure, making it more susceptible to additional
damage
· Water
dripping onto your insulation
– Damages the insulation and decreases its
R-value, making your home more susceptible to air leaks
Poor attic ventilation can also cause ice dams if you live
in a snowy environment. Without ventilation, warm air has no way to escape the
attic, so it gradually heats the roof just enough for the snow and ice on top
of it to melt. The melted snow then trickles down the roof toward the gutters.
As the water rolls down the slope of your roof, it moves farther and farther
away from the heat source, allowing it to refreeze around the edges of your
roof. This ice dam effectively blocks the path for water runoff to escape the
roof, and since the water has nowhere else to go, it seeps back inside your
roof causing leaks, water damage, rot and mold growth.
This isn’t to say attic ventilation doesn’t help during the
summer; it does allow moisture to escape and air to circulate, thus cooling
your attic. But much of the damage attributable to poor attic ventilation will
happen during the cooler months and in cold climates like we have here in the
Spokane area.
While attic vents may slightly increase the energy efficiency
of your home during summer, that really isn’t the reason you should be
installing them. They are much better at letting moisture escape and bringing
fresh air into your attic than they are at cooling your home.
If you are worried about the opposite problem – that attic
vents will let all your heated air escape during winter – fear not! Good
insulation and air sealing prevent this from happening. In fact, improving
sealing and insulation is much more likely to increase the energy efficiency of
your home than adding a couple of attic vents. You may also wish to switch out
your roofing material, whether with better shingles, tiles or metal, to reflect
more sun and keep your home cool.
Attic ventilation relies upon a balance of intake and
exhaust vents for air to properly circulate. The intake vents are typically
soffit vents located along the eaves. The exhaust vents are usually ridge vents
located along the peak of your roof, or sometimes gable vents.
When deciding which vents to install, keep in mind that you
generally want a 50/50 split between intake and exhaust vents. If there are too
few intake vents, the desired air flow may reverse, causing the exhaust vents
to function as intake vents. This will make circulation inefficient and make it
more difficult for heat and moisture to escape.
If you want less moisture and cooler air in your attic, it
may seem like you should simply add more ventilation. However, most attics only
require about one square foot of ventilation for 300 square feet of attic
space. Exceeding this ratio won’t necessarily prevent or solve attic
ventilation related issues.1 If anything, unnecessary openings make
your roof more susceptible to wind, water and fire damage.
Another solution popular with many homeowners is installing
a power vent. This vent uses electricity or sometimes solar power to pump air
out of the attic instead of waiting for the effects of passive ventilation.
While this may be a good solution for a hip roof, an improperly installed power
vent can also suck your conditioned air up into the attic, resulting in wasted
energy. It’s best to consult a professional before installing any attic vents
in your home.
