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Old 05-10-2019, 04:58 PM   #1 (permalink)
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Attic/roof Ventilation

I'm looking to purchase a home and have some concern about inadequate ventilation for the attic.

There are 2 sheets of plywood that show some mold on this 2004 home.

The tiny air inlets in the soffits seem inadequate to me. Any expert roofers out there that can comment?

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Old 05-10-2019, 09:57 PM   #2 (permalink)
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Looks like nowhere near enough. I replaced the soffits on my house. The new roof I had when I got the house had a nice ridge vent, but no other vents! I seem to recall that there was a recommended 10% of the square footage of your attic. A quick google search confirms this:

https://www.todayshomeowner.com/adding-soffit-vents/

Quote:
Calculate the total vent area needed: Multiply the length of the attic times the width in feet to find the attic area, then divide by 150 to find the total square feet of vent space needed. [(length x width of attic in feet) ÷ 150 = total sq. ft. vent area]
Example: a 50′ x 30′ attic would have a total area of 1,500 sq. ft., divided by 150 equals 10 sq. ft. of total vent space needed.
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Old 05-14-2019, 12:32 PM   #3 (permalink)
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I just bought new soffit vents for mine. Haven't put them in yet, but they also looked woefully inadequate.
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Old 05-14-2019, 01:38 PM   #4 (permalink)
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I'm not buying a new house soon, nor looking to redo my roof, but I'm just curious. If you insulate and finish an attic does it need to be vented still? How does this work if that space is supposed to be heated and/or cooled? It just seems like intentionally letting outside air leak into a controlled environment in substantial quantities would be wasteful?
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Old 05-14-2019, 02:04 PM   #5 (permalink)
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Quote:
Originally Posted by Shaneajanderson View Post
I'm not buying a new house soon, nor looking to redo my roof, but I'm just curious. If you insulate and finish an attic does it need to be vented still? How does this work if that space is supposed to be heated and/or cooled? It just seems like intentionally letting outside air leak into a controlled environment in substantial quantities would be wasteful?
You don’t want to ventilate your heated or cooled air to the outside.

I can’t speak for elsewhere but in Vermont there are some disadvantages to finishing an attic. It’s what you’d called a “hot roof”, because no matter how well you insulate it, if there’s no vented space between insulation and roof, the roof will be warmer than the air around it and in winter you’ll get ice dams, increased risk of water damage and generally just far lower roof lifespan.

I’m being facetious when I say this, but if you want to finish an attic and turn it into living space, ideally you’d rip the roof off and build a new vented attic on top of your attic so your roof can be cold.

In summer, having a vented space between shingles/sheathing and insulation greatly improves thermal performance of the structure.

Think of your roof as just being a tarp or shield to keep rain and snow off.

Last edited by Ecky; 05-14-2019 at 02:15 PM..
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Old 05-14-2019, 02:21 PM   #6 (permalink)
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Quote:
Originally Posted by Shaneajanderson View Post
I'm not buying a new house soon, nor looking to redo my roof, but I'm just curious. If you insulate and finish an attic does it need to be vented still? How does this work if that space is supposed to be heated and/or cooled? It just seems like intentionally letting outside air leak into a controlled environment in substantial quantities would be wasteful?
Finished rooms in the attic are a whole other topic. Most homes don't have finished attics.

If a home is constructed properly, the floor of the attic (ceiling of the room below) is insulated sufficiently, and the space in the attic should have adequate ventilation so that it isn't much different than ambient outdoor temperature. When the space heats up in winter, it indicates that there isn't adequate insulation on the floor, and that there isn't adequate ventilation. You don't want snow melting off the roof (an indication of the 2 problems mentioned). You also don't want it hot as hades in the summer because that reduces the longevity of an asphalt shingle roof.

At any rate, I requested the intake/ventilation be inspected and fixed by a licensed contractor, and the sellers accepted. One less project for me to tackle when I move in.
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Old 05-14-2019, 02:40 PM   #7 (permalink)
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Quote:
Originally Posted by Ecky View Post
You don’t want to ventilate your heated or cooled air to the outside.

I can’t speak for elsewhere but in Vermont there are some disadvantages to finishing an attic. It’s what you’d called a “hot roof”, because no matter how well you insulate it, if there’s no vented space between insulation and roof, the roof will be warmer than the air around it and in winter you’ll get ice dams, increased risk of water damage and generally just far lower roof lifespan.

I’m being facetious when I say this, but if you want to finish an attic and turn it into living space, ideally you’d rip the roof off and build a new vented attic on top of your attic so your roof can be cold.

In summer, having a vented space between shingles/sheathing and insulation greatly improves thermal performance of the structure.

Think of your roof as just being a tarp or shield to keep rain and snow off.
Thanks for the input, I'm not a builder, though I'm learning.

Would it make sense then to have the regular vents, sheet the inside of the rafters (to make a vented "dead space" so to speak), and then add furring strips inside of the sheeting, insulate, then finish? obviously this is a lot of extra expense/space lost, but is it worthwhile at all? I know that box stores sell room-in-attic rafters, so is the intent to be strictly unfinished rooms, or do they take something like the approach I suggested?
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Old 05-17-2019, 12:02 AM   #8 (permalink)
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It definitely needs more attic venting if you are going to go that route. I knew a few contractors in North Carolina and Georgia. Sealing the attic with spray foam is becoming popular there. High density foam insulates and acts as a vapor and moisture barrier.

Here in PDX I've had a couple companies recommend the same thing for my crawlspace.

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