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Greg Liebig, CIAQT
Certified Home Inspector
B.S. Mechanical Engineering
WI License #1955-106
Certified Home Inspector
B.S. Mechanical Engineering
WI License #1955-106
| Updated: 6/12/08 |
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Many years ago it was thought that attic ventilation wasted energy. Many people make an
effort to block the ventilation or opted to not install ventilation when their roofs were
replaced. Since the 1980's, it was found that this practice can actually increase energy
costs! Also, improper ventilation can
Click on any picture to enlarge
effort to block the ventilation or opted to not install ventilation when their roofs were
replaced. Since the 1980's, it was found that this practice can actually increase energy
costs! Also, improper ventilation can
- Decrease the life of your shingles
- Ruin your attic insulation
- Damage the roof's framing components
- Contribute to mold growth
Click on any picture to enlarge
Winter Time Problems
Most people don't ever venture into their attics, Especially in winter. We inspect hundreds
of homes each year and here are some of the things that can happen during the winter
months when you have poor ventilation. Make sure to check out our Ice Dam Article!
The heat and moisture from your home naturally migrates to your attic. If this isn't properly
vented, the moisture will condense (and even freeze) on cold surfaces in your attic.
Eventually, this moisture will melt, soaking your attic insulation and reducing its
effectiveness. It can also contribute to mold growth that can affect your family's health.
Most people don't ever venture into their attics, Especially in winter. We inspect hundreds
of homes each year and here are some of the things that can happen during the winter
months when you have poor ventilation. Make sure to check out our Ice Dam Article!
The heat and moisture from your home naturally migrates to your attic. If this isn't properly
vented, the moisture will condense (and even freeze) on cold surfaces in your attic.
Eventually, this moisture will melt, soaking your attic insulation and reducing its
effectiveness. It can also contribute to mold growth that can affect your family's health.
Summer Time Problems
Temperatures in your attic during the summer can easily exceed
160 degrees F. This heat can penetrate your ceilings contributing
to higher cooling costs. It also accelerates the aging process of
your wood rafters and trussed weakening them to the point where
they can begin to fail. A typical condition is called Honeying. You
can see this condition on the rafters and is caused by the high
temperatures that literally bake the sap out of the wood.
Temperatures in your attic during the summer can easily exceed
160 degrees F. This heat can penetrate your ceilings contributing
to higher cooling costs. It also accelerates the aging process of
your wood rafters and trussed weakening them to the point where
they can begin to fail. A typical condition is called Honeying. You
can see this condition on the rafters and is caused by the high
temperatures that literally bake the sap out of the wood.
One of the most frequent questions we get on older homes is,
"The roof never had vents, why do we need it now?" Most old
homes originally had cedar shakes or cedar shingles. These
homes had a roof deck constructed using lap boards or ship
boards that had about an inch gap between them. This was
done because the cedar roof needed a way to dry out.
"The roof never had vents, why do we need it now?" Most old
homes originally had cedar shakes or cedar shingles. These
homes had a roof deck constructed using lap boards or ship
boards that had about an inch gap between them. This was
done because the cedar roof needed a way to dry out.
Those gaps allowed air to flow between them through the shingles. It worked great! But
eventually, those roofs had asphalt paper laid over the top followed by a layer (or two) of
asphalt shingles. This sealed up the natural ventilation leaving no way for the air to flow out
of the attic space.
eventually, those roofs had asphalt paper laid over the top followed by a layer (or two) of
asphalt shingles. This sealed up the natural ventilation leaving no way for the air to flow out
of the attic space.
Mold Growth
Mold typically won't grow when the temperatures are below 32 degrees F or
when the humidity levels are below 65%. But there is chance your attic can
be an ideal spot for mold to really thrive. Your roof and some insulation
provides a great food source!
Mold typically won't grow when the temperatures are below 32 degrees F or
when the humidity levels are below 65%. But there is chance your attic can
be an ideal spot for mold to really thrive. Your roof and some insulation
provides a great food source!
Vent Your Attic and Protect Your Home
by: Greg Liebig
by: Greg Liebig
Any defects that are naturally part of the lumber like knots, etc
usually can handle the stresses of the home. But over years of
exposure to these high temperatures can eventually weaken
these supporting members to the point where they can fail.
That's why controlling the temperature is so important.
Properly ventilating you attic will most certainly help.
usually can handle the stresses of the home. But over years of
exposure to these high temperatures can eventually weaken
these supporting members to the point where they can fail.
That's why controlling the temperature is so important.
Properly ventilating you attic will most certainly help.
How Ventilation Works - Convection
Proper ventilation provides a continuous flow of air from the
outside through your attic space. This protects your insulation
and reduces the load on your heating and cooling systems. Air
enters you home either from the soffits (your overhang) and
then exits out of either a roof louver or a ridge vent.
Proper ventilation provides a continuous flow of air from the
outside through your attic space. This protects your insulation
and reduces the load on your heating and cooling systems. Air
enters you home either from the soffits (your overhang) and
then exits out of either a roof louver or a ridge vent.
The process happens from natural convection. During the day the sun heats your roof and
the air in your attic. As the warm air rises, it draws in cooler air from the vents in your eves.
Half of the vented area should be on the high side and the other half on the low side.
the air in your attic. As the warm air rises, it draws in cooler air from the vents in your eves.
Half of the vented area should be on the high side and the other half on the low side.
Cross Ventilation
Some home may only have a gable vent or two. We've
inspected some homes where these vents have been totally
blocked from the inside and unless someone takes a trip into
the attic you may never know it. If you live in a home with
louvers near the peak of the roof, you should check them out
or give us a call and we will do it for you.
Some home may only have a gable vent or two. We've
inspected some homes where these vents have been totally
blocked from the inside and unless someone takes a trip into
the attic you may never know it. If you live in a home with
louvers near the peak of the roof, you should check them out
or give us a call and we will do it for you.
This type of ventilation isn't as effective as convection mentioned above. It mostly relies
on the prevailing winds to ventilate the attic space. Remember the cedar roofs? Well,
this was the opening that was built into the home to provide air to dry out those cedar
shingles.
on the prevailing winds to ventilate the attic space. Remember the cedar roofs? Well,
this was the opening that was built into the home to provide air to dry out those cedar
shingles.
How Much Ventilation do you Need?
The FHA, VA, and HUD requires 1 square foot for every 300 square feet of attic space.
Figuring your ventilation requirements requires a little bit of simple math. Just follow this
example and you can most certainly do it yourself!
1. Calculate the square footage of your attic space
The FHA, VA, and HUD requires 1 square foot for every 300 square feet of attic space.
Figuring your ventilation requirements requires a little bit of simple math. Just follow this
example and you can most certainly do it yourself!
- Assume you've selected a 9" roof louver (50 sq inches each) and 8 in x 6 in under
eves soffit vent (56 sq inches each)
1. Calculate the square footage of your attic space
- Length (in feet) x Width (in feet)
A 32ft x 42 ft house with a 10 ft x 20 ft addition
32 ft x 42 ft = 1,344 sq ft
10 ft x 20 ft = 200 sq ft
1,344 + 160 = 1,544 sq ft
- Use the 1/300 rule
1,544 sq ft ÷ 300 = 5.147 sq ft
Convert square feet to square inches
5.147 x 144 = 741.1 square inches
741.1 ÷ 2 = 370 square inches on the high side
741.1 ÷ 2 = 370 square inches on the low side
- You will need to substitute the square inches of vent area for the product you
select in the formulas below.
High Vents
370 ÷ 50 = 7 high vents
Low Vents
370 ÷ 56 = 7 low vents
Types of Ventilation Products
There are many ventilation products available. The most common
are roof louvers. They are those little square boxes you can see on
the roofs of many homes. Most of these types are 9 in x 9 inches
and provide about 50 square inches of free ventilation area.
There are many ventilation products available. The most common
are roof louvers. They are those little square boxes you can see on
the roofs of many homes. Most of these types are 9 in x 9 inches
and provide about 50 square inches of free ventilation area.
There are many new products coming
into the market that not only improves
your attic ventilation but also is "Green".
Check out this solar powered ventilator!
into the market that not only improves
your attic ventilation but also is "Green".
Check out this solar powered ventilator!
Ridge vents are probably the most popular type of a high venting
product that is in use today. It's very effective but in our climate you
need to make sure it's designed to be "snow proof".
product that is in use today. It's very effective but in our climate you
need to make sure it's designed to be "snow proof".
Another source of moisture than can contribute to mold growth
comes from kitchen and bathroom fans that vent into the attic
space and not to the exterior of your home. In the picture to
the right, the duct attached to the bathroom vent that was
directed to the soffit but not attached to any exterior vent. The
heat and humidity rose from the end of the duct and rotted out
the roof. This is why positive ventilation is important!
comes from kitchen and bathroom fans that vent into the attic
space and not to the exterior of your home. In the picture to
the right, the duct attached to the bathroom vent that was
directed to the soffit but not attached to any exterior vent. The
heat and humidity rose from the end of the duct and rotted out
the roof. This is why positive ventilation is important!
We hope you've found this article helpful! If you have any questions or comments,
please fill out our Contact Us Form or give us a call at (920) 451-4646. We would be
happy to serve you!
please fill out our Contact Us Form or give us a call at (920) 451-4646. We would be
happy to serve you!
Spring Time Problems - Check for Birds!
Many times, our feathered friends love the shelter and warmth that
Roof Louvers provide for their new family. Unfortunately, the nests
can cause problems. Not only do the nests block the vents, but birds
can also transmit many diseases that are not healthy for your family!
Peek your head into the attic and take a look at the vents. If you see
something similar to the picture to the right, you will need to replace
your screens. Make sure to use metal screening (Hardware Cloth)
with at 1/4" spacing. Staple this to the underside of the roof.
Many times, our feathered friends love the shelter and warmth that
Roof Louvers provide for their new family. Unfortunately, the nests
can cause problems. Not only do the nests block the vents, but birds
can also transmit many diseases that are not healthy for your family!
Peek your head into the attic and take a look at the vents. If you see
something similar to the picture to the right, you will need to replace
your screens. Make sure to use metal screening (Hardware Cloth)
with at 1/4" spacing. Staple this to the underside of the roof.
Fiberglass screening can be easily torn (see left). Make sure
you wear a respirator, eye protection, and gloves when you do
the clean-up! You will be stirring up dust and feces. Take a
garbage bag with you to clean up any debris. Just don't overfill
it because it still needs to fit through the scuttle hole!
you wear a respirator, eye protection, and gloves when you do
the clean-up! You will be stirring up dust and feces. Take a
garbage bag with you to clean up any debris. Just don't overfill
it because it still needs to fit through the scuttle hole!
Birds usually return to their same
nesting area each year. One method
to help discourage this revisiting is to
hang a small nylon stocking filled with
moth balls under each attic louver.
nesting area each year. One method
to help discourage this revisiting is to
hang a small nylon stocking filled with
moth balls under each attic louver.
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before they come back. Otherwise, you should wait until the offspring are able to fly away.
The pictures above were taken during an actual home inspection. The offspring were
heard chirping noisily when the food arrived!
The pictures above were taken during an actual home inspection. The offspring were
heard chirping noisily when the food arrived!