Vented vinyl or OSB Soffits and related questions

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Old 05-26-15, 06:35 AM
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Vented vinyl or OSB Soffits and related questions

I have existing soffits that appear to be made out of Masonite or similar clap board type material, with a continuous aluminum vent strip. The soffit on a portion over my garage has pulled away, so needs to be replaced. I am considering installing vented vinyl soffits (will also have a ridge vent installed to work in conjunction with the soffit vents). I have read that OSB soffits withstand high winds much better than vinyl. I want to avoid potential soffit blow-offs and consequent wind-driven rain in the attic. My questions are: (1) if the soffit material is in good shape elsewhere, should I leave it for any protection it provides, and install the vented vinyl soffit on the bottom side of it? Or (2) should I tear it all out and just install the vinyl soffit (less than 12-inch wide) to a horizontal nailer at the wall and then to the fascia board, and (3) should the aluminum vent in the existing soffit be removed first before installing the new vinyl soffit, to improve ventilation/air flow to the attic, or would that let bugs and/or wind-driven rain in? (4) Or should I drill holes between the joists in the existing soffit to increase ventilation if/as needed. And (5) Is it advisable to put a wire mesh or screen above the vented soffit to help keep bugs out? And (6), is there any kind of a baffle or diverter that is/could be used in conjunction with the soffit vents to reduce any potential wind-driven rain from being driven or sucked into the attic (without unduly disrupting the proper air flow)? I am new to all this, and appreciate your help!
 
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Old 05-26-15, 08:24 AM
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The basic guideline is to have equal vent area high and low, that being NFA or net free area. A hole with a screen over it typically loses a third to a half of its effective area but keeping the bugs out is a must. Your total NFA is based upon the attic floor area and how well the ceiling below is air sealed and if there is a proper vapor barrier. Air sealing is far more important than a vapor barrier, especially in VA. If well air sealed and that takes a lot of work, they use 1 ft² of NFA for every 300 ft² of floor area, 1/300. If not well air sealed, double that, 1/150. Divide your results, half high and half low.

As a guesstimate, where you don't have a published NFA for your vents, use 50%.

Putting vented vinyl soffits over existing holes will leave you with slightly less than those existing holes, since the vented vinyl has a much greater surface area. Hard for me to be more accurate from where I'm sitting.

Combine your existing gable vents with your ridge vents and see how that balances with your soffit vent area.

As for wind driven rain coming in the soffits that area is considered to be the most protected. Gable vents and a ridge vent are usually a greater concern. If you have a specific orientation to your house where you get extreme winds then perhaps some concern is warranted, but that same wind would flood most ridge vents and pour in through gable vents.

They do make baffles for insulation facing the soffits, but they are not specifically marketed as rain protection, just keeping the wind off of the insulation.

Bud
 
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Old 05-26-15, 07:24 PM
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I have read that OSB soffits withstand high winds much better than vinyl.
True, vinyl is usually the worst when it comes to blowing off. The wider the soffit, the greater the potential. You might also consider fiber cement soffits, which will probably last longer than OSB and need paint less often. Aluminum soffit is also an option, it is much more rigid than vinyl and can be stapled on every 4", making it more secure.

I want to avoid potential soffit blow-offs and consequent wind-driven rain in the attic.
There is almost NO possibility of water getting in the soffit, but there is the possibility it could come in the ridge vent. The liklihood of that depends on the wind conditions, the pitch of your roof, the style of ridge venting used, and whether it is installed per mfg instructions.

(1) if the soffit material is in good shape elsewhere, should I leave it for any protection it provides, and install the vented vinyl soffit on the bottom side of it?
Yes and no. If you plan to use vinyl soffit, yes I would leave it. However you should either cut out vent holes that correspond to the soffit venting, or if it is continuously vented soffit, ensure that you currently have adequate ventilation, and remove the existing vent grilles before putting up the new soffit.

Or (2) should I tear it all out and just install the vinyl soffit (less than 12-inch wide) to a horizontal nailer at the wall and then to the fascia board
You could, but only if you install baffles as needed and block off any rafters not equipped with baffles.

(3) should the aluminum vent in the existing soffit be removed first before installing the new vinyl soffit, to improve ventilation/air flow to the attic, or would that let bugs and/or wind-driven rain in?
Yes, yes, and no. Yes it should be removed (no way to clean it later if it becomes clogged with dirt and lint), yes it may let more bugs in than if you left it in place (never seen that become a problem) and no it will not let rain in. If there is a hurricane, your roof would probably be gone if it is that windy to drive rain UP against gravity.

(4) Or should I drill holes between the joists in the existing soffit to increase ventilation if/as needed.
Small holes are generally ineffective at allowing airflow. To make a hole big enough to allow air flow, you would probably IMO want to use a 4 to 6" hole saw.

(5) Is it advisable to put a wire mesh or screen above the vented soffit to help keep bugs out?
I would not, screens eventually get clogged. Again, no way to clean them.

(6), is there any kind of a baffle or diverter that is/could be used in conjunction with the soffit vents to reduce any potential wind-driven rain from being driven or sucked into the attic (without unduly disrupting the proper air flow)?
Again, the soffit intake is not like the intake of a jet engine. LOL When the wind is still, warm air rising will create a very slow and gentle draw from the soffits. When it is windy, it is more likely for air to enter the soffit on the windward side of the house and then some will exit out the ridge on the leeward side while some will exit out the opposite soffit on the leeward side. But wind driven rain will not enter the soffits unless your house is rolling on its side.
 
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Old 05-26-15, 10:23 PM
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Thank You X Sleeper and Bud9051!

Thank you X Sleeper and Bud9051! The way you guys and others on this forum share your knowledge and experience with others is a selfless and invaluable service to a great many people. You have been a great help to me, and I sincerely appreciate it! Thank you for being a great example of how we can all share the skills we have been given with others who are in need. Job well done!
 
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