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How do I know if my room has enough ventilation?


fredhamel
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Hi guys,

I'm trying to get some information on the net but I'm still a bit confused.

I live in Canada. My house was built in 1963. In those days the soffit were made of plywood without any sort of venting. Later aluminum soffit were added over the plywood. And then soffit vents were added by piercing a whole trough the aluminum and the plywood.

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I wonder if my roof gets enough ventilation. I just recorded the following temperature today:

Outdoor: 21 celsius or 68F

Indoor: 25 celsius or 77F

Inside my roof: 36.7 celsius or 98F

Does this temperature difference indicate a poor ventilation?

Should I have the soffit entirely replaced by the modern style with small wholes everywhere?

Thanks for you kind cooperation.

Fred

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It has enough ventilation if the relative humidity is low enough to prevent issues. I wouldn't pay much attention to the temperature of the attic air. Attic ventilation, if appropriate for your building design and climate, serves mostly to keep the attic humidity low.

Marc

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I agree that temp. has nothing to do with figuring out whether or not ventilation is adequate.

Ideally, you want appx. 1 net sq. ft. of ventilation per 150 sq. ft. of attic floor space, and it's not that hard to calculate that out.

If you have enough ventilation and notice moisture/ humidity issues in the attic, then you probably need to air seal the attic.

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You also need to be sure that there is an "air path" from the eave (above the soffit vents) across the roof/wall framing and into the attic space and out the roof vents.

Often insulation gets jammed into that space and blocks the air flow from the soffit vents into the attic space.

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The ratios used for roof ventilation are based largely on voodoo. I would say that you have enough ventilation if you have no moisture problems in your attic. Although you need to remember that things change over time, so what's fine now might not be fine next year.

If you're concerned, you should work inside the house to prevent moisture from getting into the attic in the first place (source control), rather than worrying about removing it with ventilation.

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It has enough ventilation if the relative humidity is low enough to prevent issues. I wouldn't pay much attention to the temperature of the attic air. Attic ventilation, if appropriate for your building design and climate, serves mostly to keep the attic humidity low.

Marc

Ice damming is a problem for us up North Marc in which case temperature trumps humidity (next to zero humidity in the winter anyway).

Any ice damming problems Fred?

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I'm aware of the conventional wisdom when it comes to roof venting, but I've seen lots of roofs that were inadequately vented, and the shingles were prematurely deteriorated and looked much, much older than they truly were.

I don't have anything quantitative to reinforce what I'm saying but, in my experience, here in the quasi-South, maintaining reasonable attic temperatures is as important as managing humidity when it comes to venting.

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