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Attic / Roof
Ventilation, Where Are You?
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Attic / roof ventilation is probably the least
understood requirement, necessary for achieving a healthy home, world-wide!
Proper ventilation is absolutely necessary and vital, not only to the
health and well being of every home, but, it is also necessary and vital
to the health and well being of every home's "occupant"! This
article will show you how to install ridge vents, using some unique
roofing and hand tools.
Nine times out of ten, when inspecting a home, I recommend installing
proper attic ventilation, most frequently including the installation
of continuous soffit vents and continuous ridge vents. My clients look
at me like I am speaking a foreign language, looking confused and bewildered
by my comments.
Although I no longer do professional contracting, I am in the process
of renovating my own, newly purchased, 100-year-old building, for use
as both my residence and my office. As part of that renovation, I too
must install proper attic ventilation. So, I thought this might be a
perfect opportunity to share my ventilation knowledge and experience
with you.
There are two kinds of vents, inlet air vents and outlet air vents.
Having only one or the other type of vent is the equivalent of having
neither vent. Therefore, for proper attic / roof ventilation, both types
of vents "must" be present, and in equal amounts of net free
air flow.
What is net free air flow? Simple. The amount of air that can pass through
the "gross" opening you create, minus the area of the screens,
mesh, louvers or other blockages, that reduce that air flow, is the
"net" free air flow. Each manufacturer rates their various
vents by the net free air flow capacity. A basic rule-of-thumb is 1/300.
For every 300 square feet of attic floor space being ventilated, one
square foot (144 square inches) of net free air flow must be present
in both inlet and outlet vent capacities. For areas insulated without
a vapour barrier, that ratio doubles to 1/150.
For this article, I have compiled a pictorial tutorial on how to install
ridge vents. And, since they say a picture is worth a thousand words,
this little article will be equivalent to at least 15,000 words, but
can be pictorially scanned in a few seconds. (A soffit vent article
will follow shortly, since I need them, too!)
One often hears the expression, "To talk the talk, you have to
walk the walk!" So, as I do my ridge vents, I will walk you through
the process of installing your ridge vents.
Before we begin, here is a helpful hint: If your roof is really hot,
spray it down with water periodically. The evaporation of only one gallon
of water dissipates 8,265 BTUs of energy. (http://www.ecoology.com)
The sheen in various photographs is from wetting down the roof, on the
90 degree day, that I was installing these vents, and is the reason
the roof appears to be changing colours, and sometimes appearing to
be blotchy. Note: Use a THOR® Shingle Clip to secure your hose to the
roof, when not in use.
Note: The photographs are a mixture of three different sections of roof,
including a 24' section over the intersecting gable roof, a 12' section
over the hip roof of the garage, and a 44' section over the main gable
roof. I chose the photograph most appropriate to depict each step in
the ridge vent installation process, just in case you become confused
about the varying backgrounds. The last three photographs are of those
three, completed roof lines, respectively.
After the existing roofing caps have been removed, snap two chalk lines,
marking the area on the overlapping shingles to be cut away and removed
for the vent opening. This process will also mark the locations where
you should then cut away the roof sheathing, allowing air flow out of
the attic space.
Always try to cut the sheathing with a plumb cut, meaning that the blade
should be as vertical as possible. Most manufacturer's instructions
will provide the necessary dimensions of the cut size, and will tell
you to use a circle saw. But, I prefer using a reciprocal saw with a
bi-metal blade, which will cut through any nails I failed to remove
in the cutting path.
Now you have your "gross" opening cut through your roof sheathing.
If you have soffit vents on your home, hot air will immediately begin
to flow out of this opening, just like heat flows out of a chimney!
If you do not have soffit vents, like me, only a minimal air flow will
be felt. Remember, you need both types of vents to achieve the needed
air flow. For something to go out, something else must come in.
After cleaning up the roof from the sawing process, strike two more
lines, marking both outside edges of the ridge vent to be installed.
I am installing "Shingle Vent II" by Air VentTM. After talking
with my friend Roger B. Lyle, President of R.B.L. Builders, Inc. from
Mahtomedi, MN, USA, he said roofers in the heavy snow belt areas have
had the fewest problems with these vents, heavy snow loads, and ice
dam infiltrations.
"Shingle Vent II" comes in 4' sections, 10 sections per box.
Pre-drilled holes are present to accommodate the initial aligning and
nailing to the roof.
Since the caps being used are a standard 5" reveal (12" high)
shingle, a standard, 5" reveal, THOR® Roofing Layout Tape was used.
I simply stapled the tape to the top of the vent at one end, and then
unrolled it to the other end, instantly and accurately marking the location
of the caps, without any manual measurement, as quickly as I was able
to unroll the Tape and staple it to the centre line of the vent, about
15 seconds!
Note: The water droplets in the spool photograph are remnants of wetting
down the roof with a hose, to help keep it cool enough to work on safely,
and somewhat comfortably.
With the cap tops instantly marked by the roofing layout tape, I was
ready to complete this project. I simply placed the tops of the caps
on the centre markings of the roofing layout tape, identifying the 5"
increments, and nailed the caps in place!
Note: Always start the roofing layout tape at the end of the vent that
requires you to unroll the tape "into" the direction of the
prevailing wind. That trick will ensure that the caps will always be
installed with the best wind resistance orientation, and least susceptible
to weather infiltration.
Below, left, is the 24' section of intersecting roof ridge vent; and,
below, right, is the 12' garage section of ridge vent.
And finally, the 44 linear feet of newly installed ridge vent on the
main roof of this 100 year old building, constructed with individual
board roof sheathing, was perfect!
Clarification: Ridge vent manufacturers recommend removing gable vents
and other outlet roof vents, such as the nine-inch vents visible in
several of my photographs. Their presence interferes with, and reduces
the chimney effect air flow, necessary for removing heat and humidity
from the attic / roof space. I will be removing my old, nine-inch vents.
by Ron Hungarter |
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