Edge Vents & Off-Edge Vents: How to Inspect & Evaluate Service Life

What Are Edge and Off-Edge Vents and What Do They Do?

Edge vents and off-edge vents are intake vents that allow air to enter the attic space through a slot cut either at the eaves (edge vent) or upslope from the eaves on the roof (off-edge vent). It’s installed under shingles, blending with the roofline while performing the same function as soffit vents: supplying air to the attic space for balanced attic ventilation. It’s primarily used on homes with little or no overhang at the eaves, where traditional soffit vents are not possible.

To install Lomanco Deck-Air, our preferred edge and off-edge vent, a one-inch slot is cut into the roof deck and covered with a vent. An additional starter course, ice and water shield, underlayment, and shingles are then installed over the vent to protect it from water infiltration. The length of Deck-Air’s run is determined by how much intake is required for balanced attic ventilation. See our article covering balanced attic ventilation for more information.

We installed Lomanco Deck-Air as an edge vent on this property because its minimal overhang (under 4″) precluded the use of soffit vents, which typically require an overhang of at least one foot. 

Expected Service Life of Edge Vents & Off-Edge Vents

Lomanco’s Deck-Air is made with UV-resistant polypropylene material. Combined with the waterproofing measures listed above, Deck-Air typically holds up for the life of the roof, unless it’s installed improperly or defective. It’s like storing a gun safe inside of a gun safe. There are a few reasons why Deck-Air might prematurely fail, and each is a result of improper installation.

Evaluating Edge & Off-Edge Vents at Each Lifecycle Stage

0-5 Years: New Installation — Evaluating for Correct Installation

A soffit vent does not receive direct exposure to UV radiation or water because it is underneath an overhang. Although Deck-Air is not under an overhang, the roofing material installed over the vent prevents it from enduring direct exposure to UV radiation or water. This is one of the reasons it’s referred to “shingle-over” vent – to contrast it to “undereave vents,” like soffit vents.

• • Cut too short for adequate NFA (Intake): Attic ventilation is important for the longevity of any pitched roof system. If the slot cut into the deck is too short, Deck-Air will not provide the net free area (NFA) required for proper ventilation. This will prevent moisture and excess heat from exhausting from your attic, even if the vent is installed properly. See our article exploring why proper attic ventilation is so important for more information. To determine how much NFA your attic requires, see Lomanco’s Air Vent Calculator.
  • Top vent openings covered by underlayment (shingle stop): Shingle-over vents are thoroughly protected from UV radiation and water, but if underlayment or ice and water shield is not trimmed back, it can obstruct airflow as well. Obstructed edge vents can be identified by looking through the baffles from a ladder, but off-edge vents will either require attic or roof access to identify.
  • Insulation blockage in the attic: Edge vents can be obstructed by blown-in or batt insulation that presses against the intake slot, similar to soffit vents. Off-edge vents circumvent this problem due to their placement 18-24 inches up slope from the eave.
  • No Ice and Water Shield: Ice and water shield is a waterproof membrane that self-seals to the roof deck. We recommend installing ice and water shield at all eaves and penetrations, which are common sources of leaks. Because the vent is placed over a cut into the roof deck either at or near the eave, and it’s a penetration, Lomanco recommends installing ice and water shield, no different than standard best practice.
  • No Taper: Deck-Air sections are designed to be trimmed into a taper where the vent line terminates. Straight termination without taper is only used where Deck-Air abuts an end wall. Omitting this taper cut on the roof’s field doesn’t affect airflow, but it can create a visible bump or abrupt edge in the roofline that indicates improper finishing. The abrupt, 90-degree angle from the edge of the vent down to the roof deck makes proper shingle adherence impossible, creating a gap for water infiltration.

10-40 Years: Normal Weathering – What to Monitor

Once properly installed, Deck-Air generally ages without much visible change. It’s shingled over and shielded from sunlight and water, so it doesn’t usually crack or degrade like exposed metals or sealant can. Monitoring edge and off-edge vents at this stage is less about cosmetic changes and more about keeping the vent pathway clear.

• • Debris Buildup in Baffles: Leaves, dust, or nesting material can accumulate over time, obstructing airflow and interrupting the balanced ventilation system. This is often noticed from the attic, where light is obscured by any debris caught in the baffles. The baffles can be cleared from the attic or the roofline.
  • Fastener Loosening: After decades of thermal expansion and contraction, Lomanco’s supplied fasteners may begin to back out. This usually appears as a subtle rise in the shingles running along the vent line.

Maintenance: Clean or re-fasten backed out ring shanks. The vent and its baffles should be cleaned periodically. The vent itself will not be damaged by obstructions, but its job is to allow for adequate air intake, and blockages prevent this. If fasteners begin to lift, they need to be re-driven. Bent fasteners that damage a 4′ vent section will require more extensive repairs.

20-40+ Years: Failure & Replacement – Knowing When It’s Time

The functional life cycle of a roof component is determined by its ability to keep water out. The transition from normal aging to concerning wear isn’t always clear. Deck-Air and edge/off-edge vents don’t typically deteriorate like exposed metals or rubber, but they can still fail if physical damage or installation errors compromise the vent pathway. On almost any roof, ventilation components represent a potential failure point because a blocked or damaged vent can trap heat and moisture in the attic, leading to wider roof system issues. We created an inspection checklist to standardize our recommendations, ensuring that replacement is only suggested when it’s necessary. Similar to how an insurance adjuster defines “totaled” on a car, we only recommend component replacement when the cost to replace a component or roof is less than the potential cost of damages over the next 12 months.

Based on our experience identifying and fixing ventilation-related leaks and failures on over 13,000 homes and buildings, here are our criteria for when we recommend replacement of Deck-Air or edge/off-edge vents:

• • Localized or Widespread Physical Damage to Vent Sections: Acute impacts from foot traffic, large hailstones, or tree branches can crack the vent and cause baffle sections to break. Once the vent is fractured, its ability to effectively intake air is compromised, and an avenue for water infiltration is created. Deck-Air vents are 4’ long, so damaged sections can be replaced individually. However, replacing a single 4’ section still requires the removal and replacement of the roof system above it.
  • Water Intrusion – If any amount of moisture has seeped through the slot or surrounding decking, the intake vent will need replaced. Signs of water inside will be visible as discoloration to surrounding wood or insulation, grime lines, mold, or spots on drywall below.
  • Compromised seal with the roof deck – Thermal cycling may cause the once-flush vent to pull away from the roof deck. Similar to buckled roof decking, this presents as a visible gap at the vent’s edges or unnaturally raised shingles over the vent. These gaps can create a direct pathway for water infiltration. Proximity to a deck panel seam: if the slot is too close to a seam, it can weaken the integrity of the decking below it – applies stress.