How Your Roof and Home Are Affected By Your Attic Ventilation

In Windsor, Ontario and Essex County, your attic needs to be ventilated to most effectively work
with our particular climate. From our extremely cold winters, to our excessively hot and humid
summers, your attic ventilation is one of the most important aspects of your home in keeping it
protected and comfortable year round. The efficiency of your ventilation system greatly effects the
performance of your heating and air conditioning systems. Ventilation in attics is required by the
Ontario Building Code and shingle manufacture’s to meet their warranties.

Life Expectancy Of Shingles

When it comes to the shingles on your roof, so many homeowners are under the assumption that
shingles only last half as long as the manufacture’s say they will last. Jason Mills, President of Mills
Roofing and Renovations Inc. has seen first hand, 30 year shingles that have lasted 30 years, and 25
year shingles that have cracks developing as early as 8 and 9 years old. There are many variables that
determine how long a shingle will last. You could have a premium shingle on a poorly ventilated roof,
that may only last 1/3rd the amount of time it should. On the other hand, you could have a poor, low end
quality shingle on an extremely well ventilated roof that may actually last almost as long as the
manufacturer says it will last.

The Ventilation System

The ideal, most efficient ventilation system has a point of entry and a point of exit for air flow.
Fresh outdoor air should come into your attic through intake vents, as low as possible on your roof, and
exit out through your roof exhaust vents, installed as high as possible on your roof. Ventilation in
almost all cases is about circulating air to keep it fresh and reduce moisture levels. Along with this
system, your living spaces should be sealed with a Vapour Barrier and have sufficient insulation.
Ventilation Products
There are a variety of different ventilation products from intake vents to exhaust vents and
everything in between. There is no one particular solution that is best for all homes and situations. All
homes are different and may require different intake or exhaust vents.

Intake Vents

A very common problem in attics is when insulation blocks the air intake vents located at the
bottoms of the roof (Eaves trough level). Within the attic space, Insulation Baffles (also called Rafter
vents, or More vents) need to be installed between the Rafters or Trusses of the roof at the bottom of
the roof. These keep insulation from blocking the airflow from the soffit vents. The soffit vents
(perforated or ventilated), and insulation baffles together, should be located every 36” or 3 ft along the
soffit. It is just as important to verify that perforated soffits are not blocked by wood, which is another
common problem with older homes. Insulation Baffles should also be installed in between the upper
floor ceiling insulation and the underside of the roof deck, where knee walls are present and this upper
ceiling follows along the roof line. This provides a non interupted passage for the air to continue to
properly flow through the attic spaces, and not get trapped in this lower attic space.
In the case of some older homes, there may not be any overhang where soffits would be present. In
this situation, there is a product called Edge Venting that can be installed to provide you with a very
effective intake vent. It requires a slot to be cut into the roof deck as low as possible. If the slot is cut
slightly above the attic insulation level, Insulation Baffles are not required. Your roof shingles get
installed over top of this product. From the ground, the bottom (open end) of the Edge vent sticks up
about 1”. The design of this product prevents ice, snow, and bee /wasp sized insects from entering the

Exhaust Vents

The most important thing that homeowners need to know is that different types of exhaust vents
cannot be mixed within the same elevated roof peak. All too often different types of exhaust vents can
be seen on top of a large number of roofs. The reason for this is that different exhaust vents installed on
a home, take away from the performance of intake vents. The stronger of two different types of vents
will make the weaker type of vent act like an intake vent. This will disrupt the air flow in the attic and
lead to problems. A very common problem with this situation is when snow blows into the attic
through an exhaust vent.

There are a number of different exhaust vents available to be installed on your home. The most
effective exhaust vent for your home is Ridge Vent with external baffles. This low profile strip vent
spans the length of ridge peak on a home. A 1” strip of roof deck is cut and removed from each side of
the peak. The opening is one continuous cut from one end to the other, usually staying approximately
8” from the outside edges of the roof or any disruptions in the peak (chimney, valley or hip). Hot air is
being exhausted out from in between all of the roof trusses that join the peak. This vent cannot be used
on all homes. For it to be as effective as possible, you need to have a certain amount of linear ridge
peak length, depending on the amount of square feet of your home. This product installed on your
home makes for a very clean looking roof, as it only sticks up about an inch. All other vents must be
removed from that same peak of your roof.

Power Exhaust Vents are the strongest exhaust vent. They are critiqued for the cost of energy that is
consumed for these vents to operate. Also, if intake vents are not present or are blocked, the strength of
these exhaust vents can draw conditioned air out of improperly sealed and insulated living spaces
causing your air conditioner to work more, increasing your utility bill in the summer. Most power
exhaust vents operate with a thermostat. They turn on and off depending on the temperature in your
attic. In our climate, the motors sometimes wear out due to being overworked.
Turbine exhaust vents that spin around draw adequate air out of an attic space. Some of these over
time squeak or cease to spin if the bearings or other movable parts dry out. The squeaking can be
annoying to some homeowners. If this type of vent stops spinning, it is now prone to allowing rain
water and blowing snow to enter the attic, as its water deflectors are no longer working.
Standard Roof vents (mushroom vents), work sufficiently if there are enough of them installed and
there is sufficient air flow within the attic. If attic air flow is sub par, these vents sometimes allow snow
to enter the attic.

Solar Powered vents initially purchased are pricey. They work very well. They do not have any
operating costs like a Power Exhaust vent. They do however have similar motors that over time, can
wear out and stop working.

Our Climate And Your Ventilation system

The majority of attic ventilation issues come to the homeowners attention in the Winter months.
Whether it is ice dam problems due to insufficient insulation, what may appear to be a leak due to
condensation in the attic, or perhaps a bathroom or kitchen exhaust fan not having an insulated exhaust
hose leaking into living space. Insufficient insulation allows warm moist air to escape from your living
space and enter your attic cavity. When it is extremely cold out, the temperature in your attic should
also be very cold. If you do not have good air flow in the attic, when you have heat loss, this air
collects on the underside of your roof turning into frost. This can easily be seen within the attic cavity.
When the sun warms up your roof through the shingles, it causes the frost to melt which then drips
down onto your insulation, sometimes leaking through to your ceilings or walls. This can lead to roof
deck rot, mold, damage to insulation and even damage to drywall or plaster ceilings and walls.
Sufficient air flow helps prevent this from happening. Ice dams generate from snow melting on the
roof, the water running down and then re freezing. This process happens over and over again.
Eventually this water will back up on the roof, possibly get under the shingles and leak through into the

In the Summer months, it is just as important to have adequate insulation. It will resist attic heat
from transferring into your living spaces, keeping your air conditioning from working too hard. Thus
keeping your upper floor rooms more comfortable and cooler. The extremely hot air in your attic (up to
150 degrees) does not build up in the attic when you have an ideal attic ventilation system. This is a
large factor in how long the shingles on your roof will last.

You may be surprised to find out that your shingle manufacture’s warranty is void due to insufficient
intake and exhaust vents. Typically, alterations or repairs to your ventilation system do not cost a huge
sum of money. For what you would invest to update your ventilation system, you would save that over
the years in energy savings. With optimum air flow, you will achieve the most out of the lifespan of
your shingles, as long as you have a good quality of shingle installed.

Mills Roofing and Renovations Inc., Roofing Contractors, Windsor, ON