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How to stop hurricane or wind-blown rain leaks at roof ridge vents:
This article describes the cause of leaks into buildings at the ridge vent on both steep and lower-slope roofs during heavy winds, wind-blown rainy conditions, or hurricanes. We describe methods to cure a roof that leaks at the ridge vent and we list products specifically designed to resist stormwater entry at ridge vents.
This article series describes the best practices for roofing, attic, & cathedral ceiling ventilation to prevent attic or roof-space condensation mold contamination and to reduce building energy costs.
Prevent or Cure Wind-blown Rain Leaks at Ridge Vents on Roofs
Question: how to vent a roof in high wind areas while stopping windblown rain-leaks
2017/06/06 Yolanda Ferrandi said:
We have a low sloped roof over our carolina room which has a raised vent at the top of the roof and ther roof slopes down from the vent at both sides of the vent.
Rain does not come in when we have heavy rain, however, with strong winds with last october's hurricane, the tape at the seam of our sheetrock ceiling in the carolina room opened, but still no water came into the room.
We've had heavy rain several times over the past month, but no water enters from the ceiling.
I believe the raised vent at the top middle of roof over carolina room has a problem only when we have a hurricane or very heavy winds, m before we have the ceiling tape re-sealed and the ceiling repainted, I need to have the raised vent
Reply: causes of & cures for wind-blown leaks at ridge vents
Indeed heavy wind and rain can cause water entry at a roof vent if the vent flashing designed to prevent that is missing, bent-down, or otherwise damaged or inadequate in height for your climate. You don't give your location, but if you are in a coastal area you may indeed need a different ridge vent.
If your home has an older-style conventional metal ridge vent, wind-blown rain leaks in high-wind areas are a well-known topic; leaks typically occur at the exposed roofing nails used to nail down the ridge vent and worse leaks when wind blowing rain up-roof overpowers the rather low (about 1" high) flange flashing along the lower edges of the ridge vent. These problems are likely to be more severe on lower-sloped roofs.
Your options to stop leaks at your roof's ridge vent during high wind and rain include:
Add ridge vent closure foam that will reduce wind-blown rain entry through the vent openings
Add a taller ridge vent flange along the entire ridge run so that wind blowing rain "up" the roof won't send water over the existing vent flange and into the ridge vent. I've done this with complete success on several homes.
Replace the ridge vent with a model designed to resist wind-blown rain water entry such as the CobraVent, CoraVent, or CertatinTeed's 12" Filtered Ridge Vent that includes both a "weather filter" and external water-blocking baffles.
Follow hurricane Ike, FEMA issued an advisory giving tips for avoiding wind-driven rain leaks into buildings through the roof venting system. For ridge vents - which is what I think you're discussing - FEMA offers more advice that we have adapted from their document and cited below:
Key Issues with Ridge Vent Leaks During Storms:
Ridge vents are frequently fastened down
using ordinary roofing nails since these are
normally handy. It is pretty common to find
ridge vents dislodged or blown off during a
hurricane (Figure 8). Even a partially dislodged
ridge vent can begin to act like a scoop that
collects wind-driven rain and directs it into the
Most roofing manufacturers now make ridge
vents that have passed wind-driven water
tests. They are identified as having passed
Florida Building Code’s Product Approvals or
Testing Application Standard (TAS) 100(A).
Typically, they include a baffle in front of the
vent tubes that provide the passageway for hot
attic gasses to escape. This baffle is intended
to trip any flow of wind and water blowing up
the surface of the roof and deflect it over the
top of the roof ridge.
Check Ridge Vents and Their Installation
When they are used, ridge vents are the last part of the roof to be installed. Consequently, the connection is
readily accessible and frequently visible without having to pry up the edge of the vent cover top. Check the
type and condition of the fasteners. If the fasteners are nails, replacement of the fasteners is in order.
the vent has clear holes or slots without any baffle or trip next to the edge of the vent channels, the vent is
probably not one that is resistant to water intrusion and you should consider replacing the ridge vent with one
that has passed the wind-driven water intrusion tests.
Remedial Measures to Stop Wind-Driven Rain Entry
Replace nails with gasketed stainless steel wood
screws that are slightly larger than the existing nails
and, if possible, try to add fasteners at locations where
they will be embedded in the roof structure below
and not just into the roof sheathing.
Close spacing of
fasteners is recommended (e.g., in the range of 3 to 6On center, commensurate with the design wind loads).
If the ridge vents are damaged or are one of the older
types that are not resistant to water intrusion, they
should be replaced with vents that have passed the
wind-driven water intrusion tests - FEMA (2009)
CertainTeed Corporation, "CertainTeed® Ridge Vent 12" Filtered Shingle-Over Ridge Vent" [PDF], CertainTeed Corporation, PO Box 860, Valley Forge PA 19482, Tel: 800-782-8777 or professionals: 800-233-8990, retrieved 2017/06/06 original source: https://www.certainteed.com/resources/CTRidgeVent12F-SellSheet.pdf
Cobra® Exhaust Vent for Roof Ridge, GAF Roofing Products. This is a plastic-foam like product that is shingled-over at the ridge. In our OPINION it may provide less air movement than other vent products. Cobra Vent is approved under Miami-Dade Approval 14-1224.18, and is evaluated under ICC ESR-1265, Texas Department of Insurance Evaluation Report RV-19
Other shingle-over rolled ridge vent products are available such as RigidRoll® R90 from Quarrix Building Products; the venting output rate varies among these systems.
Francisco, Paul, and Robert Nemeth. Aleutian Islands Housing Authority Trip Report: St. Paul Island, False Pass and King Cove Assessment of Mold and Moisture Conditions. Building Research Council. School of Architecture. College of Fine and Applied Arts. University of Illinois at Urbana-Champaign, 2004. - "The area's strong winds drive rain nearly horizontal, ..."
Grant, E. and Jones, J., 2011. Counteracting High Winds With Low Pressure: Development And Testing Of A New Roof Vent System. College Publishing, 6(4), pp.65-76. Abstract: Roof system failures are common during high wind events. In locations subject to high wind conditions, membrane roofing systems must typically be either physically attached or fully adhered to the substrate or ballast may be added to weigh down the membrane. An alternative to these installation approaches could be to use aerodynamics principles such as the Bernoulli and Venturi effects to create a low-pressure region beneath the membrane roof that is lower than the ambient pressure and thus counteracts the uplifting force.
A new omnidirectional vent has been designed and tested that takes advantage of these aerodynamics principles to induce low pressure under the membrane layer. This new vent operates with no moving parts and was tested in the high-speed stability wind tunnel at Virginia Tech to wind speeds up to 233 km/h. The results demonstrate that this new vent generates pressures lower than the ambient when subjected to high wind conditions. This paper presents the design principles and performance test results for this new roof vent system and other applications for roof vent technologies.
ShingleVent II, AirVent Corporation, includes an externa wind baffle and other features claimed to avoid wind-blown rain from entering the attic. Quoting: The external wind baffle also deflects rain and snow over the vent, protecting the roof and attic from weather infiltration.
Snow Country Ridge Vent products available from Cobra, GAF, and othe rmanufacturers
John, C. Headrick II, and J. Charles Headrick. "Manually separable ridge vent." U.S. Patent 7,165,363, issued January 23, 2007. Headrick, J. Charles. "Ridge ventilation system." U.S. Patent 6,227,963, issued May 8, 2001 and Headrick, J. Charles. "Ridge ventilation system." U.S. Patent 6,371,847, issued April 16, 2002. Abstract:
A ridge ventilation system includes a plurality of ridge vent sections joined together in end-to-end relationship covering the open ridge of a roof. Each ridge vent section has a laterally flexible central panel flanked by ventilation grids and wind baffles. Attachment means are formed on the ends of each ridge vent section for attaching the sections together and a drain trough on one end of each ridge vent section is configured to underlie the junction between two attached ridge vent sections to drain water that may seep into the junction away from the open ridge of the roof. Buttresses that support the wind baffles are configured to hold nails for use in attaching each section to a roof.
Quarles, Stephen L., Tanya M. Brown, Anne D. Cope, Carlos Lopez, and Forrest J. Masters. "Water Entry through Roof Sheathing Joints and Attic Vents: A Preliminary Study." In Advances in Hurricane Engineering: Learning from Our Past, pp. 283-294. 2013. Abstract: A study at the Insurance Institute for Business & Home Safety (IBHS) Research Center was conducted to evaluate the potential for water entry into the attic through typical vents and through a sealed and unsealed roof deck under wind-driven rain exposures. A duplex building was constructed where sheathing joints on one-half of the roof deck were sealed and the other half was not sealed prior to installing an asphalt shingle roof covering. Water entry through gable end and soffited eave vents were also evaluated. Drainage panels were installed between the lower chords of the roof trusses.
This drainage system allowed for the collected water to be segregated by zones. A target rain deposition rate of 8 inches per hour was used for all tests. Water entry through gable end vents and soffited eaves was evaluated using up to three wind exposure regimes. Water entry tests for the sealed and unsealed roof decks were conducted after the shingles were removed. Water entry through the un-taped roof deck joints exceeded that through the taped deck and the vents. This study demonstrated the value of sealing the roof deck and provided information on the relative importance of water entry through vents compared to the roof.
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