Roof ventilation is the same as attic ventilation. Proper attic space ventilation and insulation are essential to your roof’s durability, longevity, and overall health of the upper building envelope. Proper venting will help ensure a healthy home and one that is as energy efficient as possible. In other words, roof ventilation is a big deal.
Let’s talk about what roof ventilation is, why it is important, passive, and active roof vents and what roof ventilation costs. Ventilation is important to consider during roof replacement. This guide includes the how-to’s for venting your roof and FAQs that answer related questions.
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The Purpose of Roof Ventilation
The space beneath your roof, which is often an attic, shouldn’t be dead space unless the attic is encapsulated, meaning it isn’t vented at all. But most homes don’t have encapsulated attics. An effectively vented roof structure allows air to freely flow into and out of the space.
The climate inside your roof structure or attic should be the same as it is outside, the same temperature and same humidity, or close to it, with both rising and falling with conditions outside. That’s the sign of proper air flow into and out of the space – or correct ventilation.
In summer / warm weather, if the space is nearly the same temperature and humidity as the outside air – and not a whole lot hotter or wetter – you’re in good shape.
In winter / cool weather, the space beneath your roof can be as bitter cold as the outside air – it won’t get colder – and this shows you have correct roof ventilation. Of course, the attic floor should be well insulated too, and that’s a part of roof venting discussed below.
When your roof venting system accomplishes this climatic balance, you will have a healthy attic and roof.
The Need for Roof Ventilation in Summer
In summer, the surface of your roof absorbs heat, especially if the roofing material covering your home’s roof is asphalt. You can reduce this heating process by choosing one of the few solar reflective asphalt shingles available that meet Cool Roof Rating Council (CRRC) guidelines for high solar reflectance.
Inside the attic, hot air rises, a process known as convection, and the hot air should leave the attic through ridge vents and/or passive or active vents installed in the roof deck toward the peak of the roof.
As the heat makes its exit, cooler outside air is pulled into the roof/attic to replace it. Most of the air comes in through soffit vents, which are sometimes called eave vents.
Gable vents also facilitate the flow of air into and out of the roof structure, but they should not be used in place of ridge vents or in combination with ridge vents. If there are soffit vents (air intake vents) already in place, then install ridge vents (exhaust vents) to facilitate proper airflow through the attic space.
Heat absorption in a poorly vented roof causes the temperature inside the attic to rise dramatically. The potential damage of excess heat includes cupped or cracked shingles, warped roof deck boards and dry rot of the roof framing.
When moist air enters the hot space from outside or rises into the attic from normal household activities like cooking, taking a shower and even breathing, mold, rot and warping of the roofing become issues too. You might also get an infestation of carpenter ants or termites that feed on wet wood.
Plus, that heat pushes down into your living space, making the house warm and the air conditioning to work extra-hard to keep it cool. This causes a noticeable rise in your utility costs.
The graph below shows how vents affect the temperature inside an attic – and the heat that can build up without proper venting. Note that the temperature within the structure varies less when it has both soffit ventilation for the intake of cooler air and ridge ventilation for exhausting hot air.
The Need for Roof Ventilation in Winter
In winter, even well-insulated homes leak some heat into the attic. A fresh flow of air through proper ventilation will reduce it, helping to prevent the heat from melting snow on the roof. If snow does melt, the water can run down the roof to the eaves, which are not heated.
In freezing weather, the moisture and melted snow/water runoff will freeze and cause ice dams along the eaves. Those ice dams prevent water run-off, and the moisture and melted water backs up underneath the shingles, soaking the roof deck and potentially causing rot.
Secondly, when moisture isn’t vented from a cold attic, it condenses on the roof structure. The same issues can develop – rot, mold, and warping.
Signs your Roof Isn’t Properly Vented / Ventilated
Many have been mentioned such as clear signs of roofing damage – cupped or cracked shingles, a warped roof deck or insect infestation.
You might also notice higher energy costs in summer, and any time of the year, mold in the roof structure can cause musty smells. You might even notice feeling sick breathing mold-infected air.
Roof Vent Types
Most residential roofs can be effectively vented by taking advantage of natural occurrences – wind, rising heat, settling cold air and the fact that air pressure stays stable. If some air leaves, a roughly equal amount of air is drawn into the attic beneath the roof through soffit vents in a balanced system (assuming soffit vents are not blocked).
However, there are times when mechanical or powered ventilation is recommended to adequately vent the roof.
Passive Roof Ventilation
Every good roof design has passive roof vents for inflow and outflow of air.
By “passive,” the term simply means the vents aren’t powered. The only moving parts they may have are louvers that open as air is pushed out them. Wind, warm air rising through convection and cooler air sinking are the natural elements that move air through and out of passive ventilation.
Here are the most common passive roof vents:
Ridge vents are commonly designed with baffles to keep out debris and insects or open, but you’ll find them without baffles too. They are rigid with openings to allow for air flow.
Most roofers prefer to install ridge vents the entire length of the peak, but you’ll often see it stop 4-6 feet short of the end of the roof. Ridge vents are installed at roof peaks and are covered with ridge shingles as shown here.
Soffit vents are installed on the underside of roof eaves – the portion of the roof that creates an overhang. They are of two types:
First, vents might be installed into solid soffit material, or vented soffit can be installed along part or the entire eave. There are many styles including perforated vinyl and aluminum as shown here.
Every roof with soffit vents should have ridge vents.
Box vents are a type of static vent installed on the slope of the roof, usually toward the peak to allow warm air to rise and exit through them. They have a closed top and “high” side to prevent rain from entering. Air exits a box vent through the venting on the sides and the “low” side, or side facing the eave. Box vents or similar are a “must” on large expanses of roof.
For example, if the distance from the eave to the peak is more than 24 feet, box vents should be spaced along the roof just below the ridge. As you can see, these vents include flashing to prevent rain from penetrating around them to the roof deck.
Pro Tip: Use a box vent with a steel (preferred) or fiberglass screen lining the interior perimeter, which will keep out debris, insects, and rodents.
Turtle vents are round or look like a square cap with rounded corners. They sit quite low to the roof deck. While useful in dry conditions, some roofers avoid them where heavy snow is possible. This is because the natural airflow tends to suck snow into the attic space. Still, in most climates these static vents are an acceptable option.
Gable vents are installed near the peak of gables – but are only necessary when the ridge vents do not run all the way to the edge of the roof. The reason for this is found in the FAQs below.
Styles include round, half-round, house-shaped and those with 5, 6 or 8 sides. Most are vinyl and feature downward-slanted louvers to keep out rain. They are screened on the inside to prevent insects getting into the attic.
Active Roof Ventilation
Large roofs and those where high summer heat is common often benefit from active roof vents. They have moving parts, like a rotating turbine, or are operated by a motor.
Turbine-style vents, often called whirlybird vents because of their design. They are solid on top, and the blades are placed so that rain and insects can’t get into the vents.
As heat rises out of the attic, it passes through the turbine. This movement causes the blades to turn naturally through heat convection, which facilitates exhausting more hot air from the attic.
As noted earlier, pushing hot air out through any vent causes cooler fresh air to be pulled into the attic space through soffit vents. Experienced roofer Bill Ragan says, “Properly sized, [turbine vents] exchange the air in your attic 10-12 times per hour. Shortly after the sun goes down, the air inside the attic is the same temperature as the air outside.”
Motorized deck vents come in wired and solar-powered options. When in operation, some have a lid that opens. Others are dome shaped. All types use a fan to pull hot air out of the attic space, venting it above the roof deck.
Attic vent fans are also called gable fans. They are an effective option for exchanging the air in your attic – quickly exhausting hot, moist air and replacing it with cooler air. Usually placed in a gable end of a house, they aren’t technically a “roof vent.”
However, they can be a useful part of complete roof ventilation. Many include a thermostat, and when the attic temperature exceeds the thermostat setting, the fan turns on. A few can be operated using a smartphone app.
Attic Insulation and Roof Ventilation
A critical mistake often made when insulating an attic is covering the soffit vents with insulation. This prevents airflow and leads to all the types of trouble mentioned above.
To maintain attic ventilation when insulating the attic, use insulation baffles. Installed between the rafters before insulation is added, they prevent loose-fill and blown-in insulation from covering the soffit vents. Insulation baffles are also called rafter vents because they are placed between the rafters or trusses to protect the vented area from being covered.
Pro Tip: We highly recommend using plastic or metal baffles. Most are cardboard. However, in a few months, cardboard insulation baffles often warp and bend with humidity changes. The result can be that they collapse onto the soffit, partially or completely covering the vent and defeating their purpose.
The Cost of Roof Ventilation
|Material||Retail Cost||Installed Cost|
|Ridge Vent||$2.50-$4.50/linear foot||$3.85-$6.00/linear foot|
|Vented Soffit||$1.50-$3.00/linear foot||$2.50-$5.50/linear foot|
|Box Vents||$30-$45 each||$100-$150 each|
|Turtle Vents||$25-$40 each||$80-$150 each|
|Turbine Vents||$1215-$200 each||$200-$400 each|
|Wired Attic Vents||$125-$250 each||$300-$500 each|
|Solar-powered Vents||$300-$575 each||$500-$900 each|
|Attic/Gable Fans||$130-$250 each||$300-$500 each|
|Rigid Insulation Baffles (1)||$2.25-$4.00 each||N/A|
|(1) Baffles are sold in packs from 10 to 50+. When an insulation contractor|
|is hired, baffles are usually not itemized in the labor quote.|
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Note: Installation costs are always toward the higher end for vent replacement rather than installing a vent where none existed.
Roof Ventilation and Roof Replacement
If you’re having your roof replaced, this is the right time to make sure your roof is thoroughly vented.
Any good roofing contractor will inspect the current roof ventilation and make recommendations for improving it, if necessary, to create a healthier roof. Both the amount of ventilation and the location of the vents, plus vent types, will be considered.
Roof vent replacement during a re-roofing process is also the most affordable time to do the work – the roofers are onsite and can integrate all types of roof ventilation into the project rather than making it a stand-alone project.
Roof Ventilation FAQs
Here are a collection of common roofing ventilation questions and their answers.
- What are the signs of poor roof ventilation?
Inspect the roofing material from outside, but also check inside the attic – view the roof deck and trusses from below. And consider the comfort of your home and your utility bills. Specifically:
Summer clues that your attic needs ventilation include cupped or split asphalt shingles, warped or wavy roofing which are visible from outside. Inside the attic, you might notice the growth of mold on the underside of the roof or on the trusses. Musty and moldy smells are a give-away too that warm, moist air isn’t being vented.
Is the ceiling of your home below the attic very warm on hot summer days? Do you notice your AC running “overtime?” Do your electric bills spike during hot months? These are all signs your attic needs ventilation to let out the heat and bring in cooler air.
Winter signs include frost on the roof framing in freezing weather, visible from the attic. This means that moisture isn’t being exhausted, and it is condensing and freezing.
Ice dams along the eaves are also a sign that heat escaping from your living space isn’t being vented quickly but is melting snow on the roof that flows down and freezes at the eaves.
Ice dams also likely mean you don’t have enough insulation in the attic. R40 to R60 insulation value is recommended.
- How much ventilation do you need?
FHA recommends 1 square foot of ventilation for every 150 to 300 square feet of roof covered.
Given these figures, a roof covering 1,500 square feet of a home would need 100 square feet of ventilation on the high side and 50 square feet using the lower FHAcrecommendation.
Balance the ventilation too between upper and lower parts of the roof. In other words, if you install roughly 50 square feet of soffit vent, you should install about the same amount of ridge, gable, and roof deck ventilation. This balances the amount of air being exhausted through the ridge/deck/gable vents with fresh air being drawn in through soffit ventilation.
- How much does it cost to ventilate an attic?
Adding ventilation to a new construction project costs about $450-$900, but it is essential to roof health – and it must be done to meet building code.
Almost all new roofs include ridge vent and soffit vents. Depending on the climate, roof size and design, gable vents, box vents, turbine vents and other options might be included.
Replacing existing vents during a roof tear-off can cost an additional $550 – $1,000 because of the added labor and disposal fees.
Sometimes roof vents replacement costs are rolled into the overall roof replacement quote and don’t show as separate charges aside from the job description (i.e., replace the old vents as part of the replacement job, etc.)
- Is it possible to have too much ventilation?
No, as long as you’re balancing exhaust air with intake air, or ridge vent with soffit vents, for example. Without the balance, excess venting van be a waste and can even hinder and disrupt the proper airflow from intake vents to exhaust vents, as part of the attic space venting process.
- My attic seems well vented, but it is still warmer than outside air.
This is common. Even a properly vented attic space will be 15-30 degrees warmer during the heat of the day. One of the signs the roof is correctly vented is if the space cools down within an hour or so of the sun going down.
- How big a gap should I cut at the peak for the ridge vent?
Roofs built with trusses should include total gap space of 1.5 to 2 inches, or up to 1” on each side of the peak. If your roof has a ridgepole, then similar dimensions apply – cut .75 (3/4”) to 1” on either side of the pole.
- Will a powered vent improve my attic ventilation?
Not on most roofs with adequate ventilation. Here’s the longer answer.
No: If you have adequate ridge ventilation, then a fan vent might hinder ventilation. How? The fan will suck air toward it, diverting airflow from other areas. The area around the fan will be well ventilated. But air in further reaches of the roof might not get proper airflow – and heat and humidity could damage the roof structure.
Possibly: If you have a very large roof with wide truss spans, then a series of motorized vents across the length of the roof might be necessary.
Tip: Consult a roofing contractor that understands healthy ventilation.
8 Should I install ridge vents on hips?
No. Since the hips run downhill, placing vents on them could lead to water infiltration – leaks you definitely do not want.
- When are gable vents used? When should I not use gable vents?
Vents should be placed at the highest point of the structure, which is the ridge since hot air rises. You don’t want it accumulating there and damaging the roof. When the ridge vent runs the entire length of the peak, gable vents aren’t necessary.
Some roofers install them anyway – others suggest that you should not use them because they could disrupt the flow of air exiting the roof peak. If the ridge vent stops several feet short of the roof edge, then a gable vent is useful for exhausting heat in that location.
- Can Lack of Proper Vents or Venting Void the Roofing Manufacturer’s warranty?
Yes, most asphalt roofing shingle manufacturers require your attic space to be properly ventilated to avoid damage to the roofing shingles.
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