FAQS
Edge Vent FAQs
How much attic ventilation does the house need for best performance?
What does the International Residential Building Code specifically state regarding attic ventilation?
How do building codes determine “attic square footage”?
How much attic ventilation does Air Vent recommend for a typical attic? How do I calculate proper attic ventilation?
Do building codes factor in roof pitch?
Is mixing exhaust vents of any combination (ridge vents, roof louvers, wind turbines, gable louvers, and power fans) on the same roof when it’s a common attic OK to do?
Why should I install a balanced ridge vent system for my customers?
Should gable louvers be used on the same roof that already has another type of exhaust vent?
Can you have too much intake ventilation?
Are there any disadvantages of vented soffit panels (made by siding manufacturers) as intake vents?
How does the Air Vent external baffle work?
Will rain, snow and other weather elements infiltrate through my ridge vent?
Does the ridge vent’s external baffle trap debris, pine needles and other weather elements?
Does roof pitch affect the performance of the external baffle; ridge vent?
What if the ridge vent I select doesn't have an external baffle?
What is the recommended way to nail ShingleVent II; what size nail should be used to install ShingleVent II?
What does Air Vent's internal weather filter do?
Does the ridge vent’s internal weather filter clog?
Will a wider slot cut into the peak of the roof provide more Net Free Area for the ridge vent?
How can I prevent ice dams for my customers?
What is a cold roof system and how does it help prevent ice dams?
How can I explain air exchange to my customers?
What are the benefits of installing a power vent with a thermostat/humidistat?
What is the recommended thermostat setting and humidistat setting on Air Vent power vents?
Is it OK to connect multiple power vents to a single thermostat or a single thermostat/humidistat?
Do you have any guidelines for venting cathedral ceilings?
Q. How much attic ventilation does the house need for best performance?
A. - For non-powered attic vents (ridge vents, roof louvers, wind turbines, etc.)
Building codes give minimum attic ventilation requirements. Most attics require more. In fact, research suggests you need 1 square foot of ventilation space, or net free area, for every 150 square feet of attic floor space. Net free area is the total unobstructed area through which air can enter or exhaust a non-powered vent.
For new home construction with a vapor retarder, the minimum is 1 square foot of ventilation or net free area for every 300 square feet of attic floor space. For more information read the "Tips and Answers" booklet found in the Resource Center.
If your vents are split between ridge vents and intake vents, the minimum requirement is also 1 square foot of ventilation or net free area for every 300 square feet of attic floor space.
- For power attic vents
Power Attic Ventilators are rated in CFM, the cubic feet of air moved per minute. The higher the CFM, the more powerful the ventilator. According to the Home Ventilating Institute, to determine the correct CFM rating needed, multiply attic square footage by 0.7. For example: 1500 square footage (attic) x 0.7 = 1050 CFM (look for a power ventilator rated 1050 CFM or higher).
When using power vents, be sure to provide sufficient attic intake ventilation to match the exhaust capacity of the fan. To determine this, divide the CFM by 300 for the number of square feet of intake needed. Because most vents are rated in inches instead of feet, simply multiply the number of square feet by 144 to calculate the net free area of intake needed.
- For whole-house fans
Whole-House Fans are also rated in CFM. To determine the right size for your house, calculate the interior square footage of living area (do not include garage, attic or basement) and multiply the total square footage by three. This will give you the CFM number to look for when choosing your whole-house fan.
Q. What does the International Residential Building Code specifically state regarding attic ventilation?
A. This is an excerpt from the 2006 IRC Building Code regarding attic ventilation:
R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilating openings shall be provided with corrosion-resistant wire mesh, with 1/8 inch (3.2 mm) minimum to ¼ inch (6 mm) maximum openings.
R806.2 Minimum area. The total net free ventilating area shall not be less than 1/150 of the area of the space ventilated except that reduction of the total area to 1/300 is permitted, provided that at least 50 percent and not more than 80 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above the eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents. As an alternative, the net free cross-ventilation area may be reduced to 1/300 when a vapor barrier having a transmission rate not exceeding 1 perm is installed on the warm-in-winter side of the ceiling.
Q. How do building codes determine “attic square footage”?
A. Code defines attic square footage as the length x the width of the attic floor. If measuring the length x the width of the attic floor is not possible then the plan view, footprint of the house will do.
Q. How much attic ventilation does Air Vent recommend for a typical attic? How do I calculate proper attic ventilation?
A. Research has shown that the best way to ventilate an attic is with a system that provides continuous airflow along the entire underside of the roof sheathing. Achieving this desired airflow requires a balanced system of intake ventilation low at the roof’s edge or in the soffit/eaves and exhaust ventilation at the ridge. For optimum attic ventilation for today’s tighter built, tighter remodeled homes that have more efficient building materials, Air Vent recommends exceeding minimum building codes. Air Vent recommends 1 square foot of ventilation for every 150 square feet of attic floor space with half the ventilation represented by intake vents and half by exhaust vents such as ridge vents. For minimum building code requirements use the 1/300 ratio instead of the 1/150 ratio.
Q. Do building codes factor in roof pitch?
A. Unfortunately, building code does not factor in roof pitch or cathedral ceilings. However, due to increased volume inside the attic as the roof pitch increases, Air Vent recommends increasing the amount of attic ventilation by 20% for roof pitches greater than 6/12; and increasing by 30% for roof pitches greater than 10/12.
Q. Is mixing exhaust vents of any combination (ridge vents, roof louvers, wind turbines, gable louvers, and power fans) on the same roof when it’s a common attic OK to do?
A. Air Vent does not recommend mixing two types of exhaust vents on the same roof when it’s a common attic because it could result in short-circuiting the attic ventilation system in which one of the two exhaust vents becomes intake resulting in possible weather infiltration and less than optimal attic ventilation for the entire underside of the roof deck.
There are generally four groups of exhaust vents: ridge vents, wind turbines, roof louvers/gable louvers, and power vents. Each group uses the wind differently. If any of these different groups of exhaust vents are mixed there will potentially be a short-circuiting situation. Short-circuiting the ventilation system will result in areas of the attic being bypassed (skipped). The system will still be venting, but it will not be performing optimally. Furthermore, weather infiltration is a very real possibility.
Go to www.airvent.com on the “Resources” page to download free publications for further discussion about the potential problems associated with mixing different exhaust vents on the same roof: “What Homeowners Should Know About Attic Ventilation,” “Tips and Answers from the Experts” and “Ventilation Views: Ridge Vents.”
Q. Why should I install a balanced ridge vent system for my customers?
A. A balanced system of intake and exhaust airflow through the attic is the best way to create effective, year-round ventilation. Thus, in addition to installing ridge vents, which act as exhaust vents, be sure your attic has intake vents either low at the roof’s edge or in the soffit/eaves.
To ensure a balanced ventilation system, match the amount of net free area the ridge vent provides with as much, or more, intake area. To do so, measure the length of ridge vent you will be installing, then double that length for Air Vent’s The Edge™ Vent, ProFlow Vented Drip Edge or continuous soffit vents because the net free area (NFA) of each of those intake vents is 9" and the NFA of the ridge vent is 18". For more information read the "What Homeowners Should Know About Attic Ventilation" brochure found in the Resource Center.
Q. Should gable louvers be used on the same roof that already has another type of exhaust vent?
A. No. Please visit www.airvent.com for a free copy of “Ventilation Views: Ridge Vents” in the Resources section for discussion about mixing different types of exhaust vents on the same roof.
Gable louvers are a type of exhaust vent and should not be mixed with another type of exhaust vent on the same roof. However, many homeowners like the aesthetic touch gable louvers add to the house and would rather they remain in place even if another type of exhaust vent were installed on the roof.
A quick solution is to block off the opening to the gable louver from inside the attic with plywood, Styrofoam or plastic sheeting. Blocking off the opening successfully prevents short-circuiting problems, maintains the aesthetic appearance the homeowners prefer and avoids the hassle of re-siding the house.
Q. Can you have too much intake ventilation?
A. No, you cannot have too much intake ventilation. In cases where there is an abundance of intake vents (more intake than is required to balance the attic ventilation system) the windward intake vents will be supplying more than the exhaust vents require, but the leeward intake vents will change to exhaust vents because the inside of the attic becomes pressurized by the windward intake vents. For more information on intake ventilation visit www.airvent.com for a free copy of “Ventilation Views: Intake Vents” in the Resources section.
Q. Are there any disadvantages of vented soffit panels (made by siding manufacturers) as intake vents?
A. The primary disadvantage of the vented soffit panels is that they do not provide much net free area. The average net free area of a perforated panel is around 6 square inches per square foot. That would mean that a 1½ foot overhang with fully perforated panels the full run (not every third panel or one every 6 feet, but completely perforated) would be required to balance an ridge vent that provides 18 square inches of net free area per linear foot.
This assumes that the perforated soffit panels are installed correctly. Very often there will be a solid plywood soffit behind the panels, which effectively render them useless.
Another problem with the soffit panels is they become blocked/clogged very easily. Depending on the method of manufacturing, a perforated soffit panel may have been rolled, lanced, or punched. The punched soffit panels are best because the material is removed as opposed to displaced. Soffit panels in which the material has been displaced leave places where debris can get caught or easily trapped on the excess material and start to block the vent. Also perforated panels are easily painted shut with one or two coats of paint because of the generally small holes used in them. For more information on intake ventilation visit www.airvent.com for a free copy of “Ventilation Views: Intake Vents” in the Resources section.
Q. How does the Air Vent external baffle work?
A. Air Vent ridge vents feature an advanced designed, external baffle that is one of the keys to the ridge vent’s outstanding performance. The baffle deflects wind up and over the vent, creating an area of low pressure above the vent openings that causes lift. This is called the Bernoulli Effect. It’s the same effect that causes airplane wings to lift. This low pressure works to pull air out of the attic. The baffle also deflects wind over the vent to help prevent wind-blown rain and snow from entering the attic. For more information read the "ShingleVentII Ridge Vent" brochure found in the Resource Center.
Q. Will rain, snow and other weather elements infiltrate through my ridge vent?
A. The external baffle on the ridge vent is designed to block the severe storms from driving weather into the vent. It has been extensively tested for wind driven rains up to 110 mph. For extreme situations the weather filter was designed to be the second line of defense. Check to see that the ridge vent has been installed correctly. For architectural shingles make sure there is no gap between the shingles and the ridge vent. For more information on how to prevent a gap between the architectural shingles and the ridge vent please visit www.airvent.com for a free copy of “Ventilation Views: Ridge Vents” in the Resources section.
Next check the intake vents. Weather infiltration, be it rain or snow, is usually caused by a lack intake. Make sure there are enough intake vents. Make sure the intake vents are not blocked by insulation or clogged with paint or debris. Finally, make sure the intake vents have been installed correctly including the hole has been cut for the vent.
Q. Does the ridge vent’s external baffle trap debris, pine needles and other weather elements?
A. Generally, leaves and debris that can fall in behind the external baffle are not a concern because of the low pressure created by the external baffle when wind hits it -- essentially self-cleaning the ridge vent. In Air Vent’s video you can see in the wind driven rain tests that there is a significant amount of low pressure created which can draw water up and out of the ridge vent. Thus, leaves and debris are not an issue.
Another benefit to ShingleVent II’s design is that it does not have any external ribs perpendicular to the external baffle. This allows leaves or debris to blow down the ridge vent parallel to the ridge and eventually be blown out the end of the ridge vent run.
In cases where there is little or no wind (middle of a dense forest, for example) pine needles and debris that fall and stick behind the external baffle will not be pulled out. In these cases shingle manufacturers require that the roof be cleaned off because the pine needles and debris left on the roof can degrade the shingles prematurely. If the roof is being maintained for the shingles the ridge vent should be cleared at the same time. Keep in mind, where there is little to no wind, the best option is a power attic ventilator because all non-powered vents require the wind to work well.
Q. Does roof pitch affect the performance of the external baffle; ridge vent?
A. The external baffle on the ridge vent performs the same (airflow enhancement and weather protection) regardless of the roof pitch because the external baffle is always perpendicular to the roof regardless of the roof pitch. The wind generally will hit a house and run up the roof parallel with the slope (roof pitch), hit the external baffle -- which is perpendicular -- and be deflected up and over the external baffle, then over the ridge.
Q. What if the ridge vent I select doesn’t have an external baffle?
A. With an unbaffled ridge vent, wind and other elements can blow directly in through the ridge vent. Air entering the vent can create pressure in the attic, which prevents air and moisture from being pulled out. Also, stronger winds can actually pass through one side of the vent and out the other, which also prevents air and moisture from escaping the attic. Tests show that externally baffled vents outperform unbaffled ridge vents. For more information read the "Tips and Answers" booklet found in the Resource Center.
Q. What is the recommended way to nail ShingleVent II; what size nail should be used to install ShingleVent II?
A. The best way to nail ShingleVent II is to fasten through the nail bosses first to position the ridge vent for line and spacing. Next, fasten the ridge cap shingles along the full length. The nails used to fasten the ridge cap shingles are the primary fasteners protecting the ridge vent against wind blow off; therefore it is important to use nails that will penetrate the underside of the roof deck.
Air Vent does not specify size of nail because the thickness of materials the nail will penetrate varies job-to-job (15-lb felt or 30-lb felt; ½” OSB or tongue-and-groove deck; 3-tab shingle or dimensional shingle?). Air Vent’s only guidance specific to nail size is that the nail must penetrate the underside of the roof deck.
For the same reasons listed above, Air Vent does not specify what pressure setting should be used for nail guns. Air Vent’s only guidance specific to nail gun pressure is that it should be set at a pressure that will allow the nail to penetrate the underside of the roof deck without dimpling the shingles. For more information on nailing requirements please visit www.airvent.com for a free copy of “Ventilation Views: Ridge Vents” in the Resources section.
Q. What does Air Vent's internal weather filter do?
A. Air Vent's internal weather filter provides a more complete barrier from the elements. Wind-driven rain, snow, dust and insects are trapped by the filter. And because Air Vent ridge vents provide continuous airflow along the entire roof, the internal weather filter is cleaned by the flow of air coming out of the attic. For more information read the "Tips and Answers" booklet found in the Resource Center.
Q. Does the ridge vent’s internal weather filter clog?
A. The internal weather filter will not clog significantly over time. A 10-year accelerated dust exposure test conducted in accordance with an accepted industry standard test criteria showed that the filter is restricted by only 5%. This small collection of dust may result in discoloration of the filter over time.
The filter is untreated, non-woven fiberglass material that is not designed to provide same filtration performance as a central heat and air conditioning filtration system. It is not the intent to trap (collect) dust particles from the air that travels through the ridge vent. However, over time, passing moisture and dust may collect in small amounts. This collection will be enough to cause a darkening of the filter, which may appear dusty, but is not affecting performance substantially.
Care should be taken to avoid contaminating the filter with building materials such as saw dust, blown-in insulation, etc.
Q. Will a wider slot cut into the peak of the roof provide more Net Free Area for the ridge vent?
A.
Cutting a wider slot will not increase the Net Free Area of the ridge vent because the Net Free Area of ShingleVent II is a maximum of 18 square inches per linear foot. Even if the slot were wider than recommended the airflow through the wider slot must still go through the actual ridge vent. The ridge vent will not allow more than 18 square inches of Net Free Area per linear foot.
If the slot for a ridge vent is cut too wide there is potential for weather infiltration because the slot may be too close to the louver openings on the ridge vent. For more information on slot width and slot length visit www.airvent.com for a free copy of “Ventilation Views: Ridge Vents” in the Resources section.
Q. How can I prevent ice dams for my customers?
A. Ice dams are barriers to water runoff on the roof. They usually form at the roof edge, just above the gutter, in cold, snowy climates. They form when snow melting on warmer areas of the roof, usually near the ridge, runs down and refreezes at colder roof overhangs. Warm spots on the roof are caused by the heat that escapes from the living space into the attic. Once this cycle of melting and refreezing begins, a barrier is formed, trapping the snowmelt and allowing it to flow up and under shingles. As water begins to penetrate sheathing, insulation, wall cavities, and sheetrock or plaster:
- paint can begin peeling on both inside and outside walls
- roof coverings, fascia and gutters can be damaged
- structural damage can result from the weight of the ice dam
Homeowners usually blame their gutters, since that's where the problem appears to be. But newer, wider, deeper gutters won't solve the problem. Nor will additional layers of insulation alone. What will solve it is adequate ventilation combined with proper levels of insulation. For more information read "Ventilation Views: Ice Dams" found in the Resource Center.
Back to the topQ. What is a cold roof system and how does it help prevent ice dams?
A. The key to solving ice dams is to create a cold roof, with the temperature of the inside roof sheathing near that of the outside air temperature. To create such a condition, large volumes of outside air must enter low on the roof through the intake vents, sweep along ridge rafters, then exit at vents near the ridge. To prevent trapping warm air in the attic, an equal balance must be established between intake and exhaust air volumes.
Since such a ventilation system is bringing cold air into an attic, the insulation must minimize heat loss at the attic floor. As an added precaution, use waterproofing shingle underlayment. It provides a waterproof-barrier beneath roof shingles that pooled water from melting ice dams and driven rain cannot penetrate.
Back to the topQ. How can I explain air exchange to my customers?
A. Air exchange is a system of air intake and exhaust that occurs with effective air circulation. When stale, overheated air in your home or attic is vented out and fresh air is pulled in to replace it, that's air exchange. In an attic, for example, cool air enters intake vents, which are located at the roof’s edge or along the underside of the eaves. It's warmed, then rises out of the roof or gable attic vents to expel heat.
Q. What are the benefits of installing a power vent with a thermostat/humidistat?
A. With combination thermostat/humidistat controls, power attic ventilators monitor heat and humidity levels in summer through winter for year-round attic protection from the damaging effects of moisture and heat buildup.
Moisture naturally generates in homes from washers, dryers, dishwashers and showers. The water vapor travels upward, passing through ceilings and insulation until it reaches cooler, dryer conditions in the attic. When the vapor hits cooler rafters, trusses and roof sheathing, it rapidly condenses into water droplets or frost. The trouble starts as water begins to drip into the attic or wick into the sheathing.
- Water stains may form on ceilings just under the attic and the paint may peel
- Up in the attic, the insulation may become damp and compressed
- Mold and mildew can develop in the attic
- Wood can rot
- Deterioration of roof shingles accelerates
The advantage of the combination thermostat/humidistat is it provides double protection throughout the year. For more information read "Ventilation Views: Ridge Vents and Power Vent Installation Tips" found in the Resource Center.
Q. What is the recommended thermostat setting and humidistat setting on Air Vent power vents?
A. Generally, 100 to 110F will be sufficient for the thermostat control; and 80% relative humidity will be sufficient for the humidistat control. However, both the thermostat and the humidistat controls are adjustable by the installer or the homeowner should it be necessary to make adjustments dictated by climate.
There are regions where those settings will cause the fan to run all the time, the south or the coast, respectively. In these extreme climates it is recommended to set the thermostat/humidistat higher to prevent the power vent from running non-stop, which they are not designed to do.
Placement of the thermostat/humidistat should be as far from the power vent hole (opening cut into the roof) as possible to help prevent the outside conditions from triggering the power vent thermostat/humidistat. This is true for both the roof-mount and the gable-mount power vents.
Q. Is it OK to connect multiple power vents to a single thermostat or a single thermostat/humidistat?
A. Multiple power vents should not be connected to the same controller (thermostat or thermostat/humidistat) because the controller has not been certified through UL to handle more than one power vent. The power vents are only tested and certified under the one-for-one configuration. Any alterations to the power vent will result in the loss of the UL certification for that particular product(s).
Q. Do you have any guidelines for venting cathedral ceilings?
A. Air Vent recommends a 1” to 1 ½” air space in all cathedral/vaulted or otherwise compact roof systems. The maximum length of rafter that one should use the 1 ½” air space is 30-35 feet. For longer rafter runs a 2” or even 3” air space is recommended. Air Vent recommends insulation baffles be used for the entire length even with fiberglass batt insulation. For more information on cathedral ceilings visit www.airvent.com for a free copy of “Ventilation Views: Hip Roofs and Specialty Applications” in the Resources section.
Frequently Asked Questions about The Edge™ Vent, Air Vent’s NEW Shingle-Over, Roof-top Installed Intake Vent
Q: Is there a potential for pooling water behind The Edge Vent on 3/12 & 4/12 pitch roofs?
A: No, The Edge Vent was designed to shed water at these roof pitches. Any water will be traveling from the peak of the roof all the way down to the edge of the roof with increased speed and volume. Thus, the water should safely clear The Edge Vent and the roof. The Edge Vent was designed so that when installed on a minimum pitch 3/12 roof the roof would still maintain an angle of decent towards the bottom edge of the roof. When installed on a 3/12 pitch, it can be deceiving because the angle is not very steep; only 2-3 degrees and may look like a pool area. It rapidly transitions back to 14 degrees.
Q: How will The Edge Vent perform in snow, ice regions of the country?
A: In terms of structural integrity, The Edge Vent will perform similarly to Air Vent’s ShingleVent® II ridge vent, which is the same exact copolymer resin material as The Edge Vent. ShingleVent II has been on the market 20+ years on hundreds of thousands of roofs in northern climates.
As for its durability in northern climates, The Edge Vent should last the life of the roof provided that it is not subjected to conditions beyond what starter course and first course shingles typically experience.
Finally, regarding weather protection, interior features have been incorporated into the design of The Edge Vent to help prevent problems associated with northern climates (ice damming, snow accumulation, snow & moisture infiltration, etc.). Those interior features are: an internal weather filter (the same filter, by the way, used in ShingleVent II); patented internal baffles; and a patented drainage system.
Q: Will every brand of shingle correctly align on The Edge Vent in terms of nailing requirements?
A: No, every brand of shingle will not correctly align on The Edge Vent in terms of nailing requirements. Even if they did, Air Vent would not make that claim because we do not control shingle manufacturer’s nailing requirements for current shingles or for roofing materials that will be introduced to the market in the future. It is very possible that the installer of The Edge Vent will have to deviate from the shingle manufacturer’s recommended nailing location to ensure that both The Edge Vent and the shingles are adequately secured to the roof deck. Note: Nailing over the slot opening should be avoided to prevent damage and possible shingle and product wind uplift. Avoid nailing between 5-3/4” and 7-1/4” from the drip edge of The Edge Vent.
For example, for shingles that have a 5 5/8” course exposure, it should be acceptable to nail the first course right above the course exposure given that there will be at least a ½” overhang. A ¾” overhang will provide even more distance from the slot. NOTE: The slot is cut 5” from the edge flashing beneath the vent. The actual drip edge of the vent extends another inch beyond the edge flashing located beneath the vent for a total distance of approximately 6” from the slot. With a ½” shingle overhang, the lower edge of the shingle should be 6 ½” from the slot. This leaves approximately 1” between the shingle overlap line with a 5 5/8” course exposure and the lower edge of the slot.
Q: What does Air Vent recommend regarding the usage and placement of underlayment with The Edge?
A: With regard to the placement of underlayment, Air Vent recommends it be placed both under The Edge Vent (i.e. directly on the deck) and over The Edge Vent. NOTE: The slot should also be cut into the underlayment that is applied directly over the roof deck slot before securing The Edge Vent to the roof.
Use the type of underlayment commonly used for the specific climate and ensure that local building code requirements are met. For example, in snow regions, the underlayment typically used at the edge of the roof (e.g. ice and water shield) should be installed over the top of The Edge Vent to ensure proper protection from any water that could potentially backup under the shingles on the roof top. Additionally, Air Vent recommends that the same underlayment also be used to protect the roof deck directly beneath the vent in northern climates. In warmer regions of the country, with little or no snow, the use of standard shingle underlayment beneath and over The Edge Vent should be sufficient.
Q: In northern climates where snow is common, can I use window flashing tape or caulk under The Edge Vent instead of applying ice and water shield under The Edge Vent the first 5 inches on the deck?
A: Air Vent will not specify what materials are to be used beneath The Edge Vent in any climate. However, it is recommended that waterproofing underlayment or a similar performing product be used beneath The Edge Vent to protect the roof deck from possible moisture damage in northern climates. NOTE: Local building code should be referenced before an alternate material is selected.
Q: Is the integrated, built-in end plug truly sealed from the weather?
A: The integrated end plugs of The Edge Vent terminate each end of the vent to help prevent weather infiltration. The end plug feature is essentially a vertical rib with a top edge that matches the contour of the vent’s curved, tapered profile. The top half of The Edge Vent rests on this rib in the assembly and provides a tight joint once the installation is complete. Additional weather protection for this joint is provided by the shingles which typically extend ½” to ¾” beyond the end plug of The Edge Vent at the gable end of a roof. It should be noted that the slot is to be terminated at least 6” inside of the gable end wall and The Edge Vent should be installed flush with the edge of the roof. For maximum roof deck protection, at the edge of the gable end, it is recommended that the roof deck be covered with underlayment beneath the vent.
Q: Will Air Vent specify a type of fastener?
A: Air Vent will not specify a particular fastener to be used for the installation of The Edge Vent or for shingles installed over the product because of possible variations in the construction details. Air Vent does specify that the roofing nail used to secure The Edge Vent to the roof deck AND to install the shingles over the vent be of sufficient length to fully penetrate the underside of the roof deck. However, Air Vent recommends that the fastener must be at least 1-3/4” long.
Q: If the ridge vent (exhaust vent) is snow covered and The Edge Vent (intake vent) is snow covered what happens to the attic ventilation?
A: If they are both covered, then there will be no attic ventilation. Eventually, the snow will clear from both the peak and the eave and the attic ventilation system will be functioning once again. Keep in mind, the only reason The Edge Vent would be temporarily blocked is because of snow accumulation in the gutter installed below the product.
In the event that The Edge Vent is covered with snow when the ridge vent is clear, the ridge vent will evacuate heat and moisture via thermal buoyancy. Once The Edge Vent is no longer blocked, the balanced attic ventilation system will be working as normal.
Q: Will building inspectors red flag a slot opening in the roof area where nonstop waterproofing underlayment should be placed?
A: It may be possible that a roofing inspector would red flag a slot opening in the roof deck in an area required to have a waterproofing underlayment from the edge of the roof up to at least 24” inside the exterior wall line (Ref. Section 905.2.7.1 of 2006 IRC). Currently, however, there is no code which addresses a continuous roof penetration in this area of the roof. Air Vent will be working with code and regulatory agencies to address the questions as they arise.
Q: Will Air Vent specify gutter size?
A: Air Vent has never specified the gutter size for use with its product and will not do so with The Edge Vent because of the infinite variables that are structure specific. Obviously, the drip edge of the shingles can be as much as 1-1/4” further from the fascia board compared to shingle installations without The Edge Vent. Therefore, narrow profiled gutters that have long runs and significant elevation drops could present some issues. Compatibility of The Edge Vent with existing or new gutter systems will need to be investigated for each specific structure by the installer.
Q: Is there room for installer error in cutting the slot 5 inches from the roof edge?
A: Yes, as with most building construction practices, there is some latitude with the precise slot dimensions to be cut. It is recommended that the lower cut for the slot be maintained as close as possible to 5” from the drip edge flashing and that the slot width be maintained between ¾” to 1” wide (Note: An edge flashing must be used when installing The Edge Vent). A nice, straight lower cut will assist in properly locating The Edge Vent on the roof with the locating tabs on the underside the product.
Q: How do you handle Edge Vent installation with open valleys?
A: There are three possible options in dealing with open valley installations of The Edge Vent.
Option 1: Position The Edge Vent so that it terminates 2 feet from the open valley with the built-in end plug on the vent facing the open valley. Remember, the slot cut in the deck for The Edge Vent terminates 6 inches from the very end of the vent, or 2-½ feet from the centerline of the valley. Install shingle underlayment over The Edge Vent, followed by flashing material wrapped over the end of the vent onto the deck at the location facing the open valley, and then install the shingles. (NOTE: Install the valley underlayment and valley flashing as normal.) As the shingles are installed toward the valley, they will need to be cut at the end of the vent run so that the flashing covering the end plug is exposed and the shingles are completely supported by both the vent and the roof deck beside the vent. This will result in a slight step of the shingles at the end of the vent run.
Option 2: Similar to Option 1 except that the flashing is not required. After the slot is cut 2-½ feet from the centerline of the valley and The Edge Vent is installed, install a shim (field constructed) to taper the end profile of the vent to the roof deck (towards the valley and uphill from the drip edge of the roof). Install the underlayment over the vent and the shim. (NOTE: Install the valley underlayment and valley flashing as normal.) Finally, install the shingles towards the cut valley as normal. This second option could provide better aesthetics than the first option by eliminating the slight step in the shingles at the end of the vent run.
Option 3: Terminate the roof deck slot for The Edge Vent 12” from the centerline of the valley. Miter cut two sticks of The Edge Vent and install into the centerline from both sides of the valley. Depending on the gauge and features of the valley flashing metal, it may be necessary to install a shim in the valley uphill from The Edge Vent to fully support the valley flashing. Install the valley underlayment, valley flashing, and shingles as normal for an open valley roofing application. This option could be the most aesthetically pleasing of the three options.
Q: What are the roof pitch requirements for installing The Edge Vent?
A: The Edge Vent can be installed on roofs with a minimum 3/12 roof pitch. There is no maximum roof pitch.
Q: Can The Edge Vent be installed on roofs with vented nail base?
A: When using The Edge Vent with vented nail base products, there are a few things to consider:
Is there an attic space below the vented nail base which is desired to be vented? If so, is there independent intake ventilation for the attic or would The Edge be relied on to supply ventilation to both the attic and the vented nail base? If The Edge Vent is to supply intake to both, then the slot would have to be cut through the vented nail base and any other layers that may exist below in order to accomplish intake ventilation for the attic. If there is a compact (cathedral ceiling) roof application, see number 2 below.
If it is cathedral ceiling construction with vented nail base over a compact roof system, then it may be possible to cut the slot into the top surface of the vented nail base. WARNING: The manufacturer of the specific vented nail base needs to be consulted regarding the structural integrity of a continuous slot being cut in the top surface of their product. They may require that the slot not be continuous, but interrupted, to maintain the structure integrity.
Use a vented nail base that has a minimum of 1 ½” air space to allow the incoming intake air from The Edge Vent to safely travel to the exhaust vent. There are brands of vented nail base with less than 1 ½” air space but Air Vent recommends a minimum of 1 ½”.
Q: Can The Edge Vent be used with other types of intake vents on the same roof?
A: Yes, it is OK to use The Edge Vent in conjunction with all existing intake vents on the same side of the house (whatever type of intake vents they happen to be) because they will all be in the same pressure zone. Additionally, if it happens to be that there is excess intake ventilation than the exhaust system needs the intake vents become exhaust vents on the leeward side of the house.
Q: Can The Edge Vent be used on one side of the house (the side that does not have an overhang, for example) and another type of intake vent on the opposite side of the house (the side that does have an overhang)?
A: Yes, it’s OK to use The Edge Vent on one side of the house and use a different type of intake vent on the other side of the house. This will not cause any problems for the overall attic ventilation system.
Q: Could The Edge Vent be used under concrete tile? The load is 10 pounds per square foot.
A: Air Vent has not looked at this application in detail, but it could possibly work. Underlayment will have to cover the product regardless of the roof covering material. It should be able to handle the static load of 10#/sq. ft. with no problem. The concerns include attachment of the product to the roof deck and elevating the first course of tile to match the rest of the roof. We rely not only on the 10 pre-fastening locations of The Edge Vent to secure the product to the roof deck, but also the nails for the starter course and first course shingles. With a tile installation, these additional fasteners are not installed to help secure the product to the roof.
The bottom line: It could work, but Air Vent can’t say that it will at this time until more of an investigation is conducted.
Q: Are there any special considerations when trying to install The Edge Vent on a slate roof?
A: Air Vent has not performed an installation with slate roofing. It is possible that it could work, but Air Vent has not investigated all of the possible installation details that would need to be addressed. It will be critical that the underlayment is installed adequately over the vent and that the vent is secured to the roof deck at more locations than the 10 reinforced nail bosses.
Q: Could The Edge Vent be safely used for intake at the transition where a pitched roof meets a flat roof?
A: Air Vent does not recommend the use of The Edge Vent for this application where a sloped roof meets a flat roof. Not only is there an increased possibility for infiltration, the vent would be covered most of the winter with snow.
Q: Are there any concerns using Pro Flow™ Vented Drip Edge and The Edge Vent on same roof?
A: There are a couple concerns:
The top flange of the Pro Flow Vented Drip Edge is approximately 6.5”. The slot for The Edge Vent is supposed to be cut between 5” and 5-3/4” from the edge of the flashing. This means that the upper flange of the vented drip edge would have to be cut.
The space beneath the roof deck would need to be sufficient for the 18 square inches per linear foot of the combined intake Net Free Area.
Other than these two items, both intake vents should be under similar pressure conditions allowing them to perform as designed.
Q: Has Air Vent done any research on how The Edge Vent works with gutter protection products (Leaf Proof, for example)?
A: Air Vent has not tested the compatibility of gutter protection products in general with The Edge Vent.
In a quick review of the Leaf Proof gutter protection product, Air Vent does not believe that The Edge Vent will work without significant customization of the installation. This gutter protection product has features that slow the water speed down so that it will be diverted in the gutter. This requires that the first course shingles overlap the top flange of the Leaf Proof product. It may be possible to block out a sub fascia to support the gutter and create a ventilation space to allow air to get to The Edge Vent from directly below the slots. Then the gutter protection product could be flashed under the first course of shingles that are installed over The Edge Vent. Fastening of this upper flange could be challenging.
Q: How do I install The Edge Vent on a house with a 6” overhang that is insulated to the roof sheeting from inside the attic in an older home?
A: Install insulation baffles in every rafter bay to create an air space between the insulation and the underside of the roof deck. For situations where there may be limited or no access to the attic areas from the living space, it is possible to cut an access panel into the roof sheathing during the re-roof job so that the insulation baffles can be installed. The created air space will allow air to exhaust from The Edge Vent, through the roof deck slot, and into the attic area.
Q: Is it OK to install The Edge Vent 2-3 feet down from the ridge as an exhaust vent?
A: No, it’s not recommended that The Edge Vent be used up the roof as an attic ventilation exhaust vent. The product was specifically designed for intake venting applications.
Q: Can The Edge Vent be used on a gambrel roof?
A: The use of The Edge Vent at the roof transition for a gambrel roof should be acceptable. NOTE: The deck below The Edge Vent at the roof transition line will have to be protected. The contractor may want to install water proof shingle underlayment and flashing beneath The Edge Vent to finish the roof transition.
Q: Has The Edge Vent been tested in an asphalt shingle installation for fire resistance Class A applications?
A: The Edge Vent is not Class A. Perhaps one day Air Vent will have it tested/rated as such.
This document was last modified on January 18, 2010.
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