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Old 07-28-2017, 03:27 PM   #1
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Attic ventilation


I have an attic space that's about 1000 sq ft. The ridge line above the entire space has a ridge vent, and there's a gable end vent that's about 20"x20" on one end. The other end is the wall that separates a large vaulted ceiling from the attic (is that called a knee wall?). We do not have soffit vents.

I'd like to add a powered roof vent like this:
https://mobileimages.lowes.com/produ...6388121241.jpg

The model I'm looking at vents 1000 CFM and says it's good for attics up to 1600 sq ft.

If I add that type of powered vent to my roof, are the existing vent openings going to be enough?
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Old 07-28-2017, 03:35 PM   #2
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Re: Attic ventilation


That wall is called a wall. Knee wall is a short wall a few feet away from the outside wall where the rafters meet the ceiling.

How hard would it be to put in soffit vents.?
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Old 07-28-2017, 03:48 PM   #3
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Re: Attic ventilation


Power venting is a go-to quick fix but it can be expensive as it will pull a lot of conditioned air from inside the house. You should do an aggressive air sealing job as well. There are guides available.

Summer heat is only part of the attic ventilation reasoning and KC still gets some winter. During cold weather you will want to remove any moisture that migrates up there.

Best to improve the passive ventilation with some form of low venting, several options, and then air seal and add more insulation. After that, if powered ventilation is still needed (probably wouldn't be) then you consider the options.

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Old 07-28-2017, 03:48 PM   #4
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Re: Attic ventilation


With no soffit vents all a power vent is going to do is suck in hot outside air in from the gable vents and flow out the ridge vent, and create a negative pressure inside the attic sucking conditioned air from inside the home into the attic.
Post a picture of the home showing the Fachia and soffit area so we can see why there's no vents.
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Old 07-28-2017, 03:51 PM   #5
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Re: Attic ventilation


Quote:
Originally Posted by Nealtw View Post
That wall is called a wall.


As for adding soffit vents. I wish I could say how hard it is, but I'm not really sure. We have vinyl siding and the soffits also have the vinyl over them. I haven't peeked in there but I do not believe the plywood soffit boards underneath have vents cut in them but I know the vinyl is not the perforated vent kind. I'm also not certain whether the insulation in the attic goes all the way to the roof sheathing on the end of the rafter bays or leaves an air gap - if it does go to the end, I'm not sure I can get to it to pull it away due to the slope of the roof.

Does adding soffit vents with vinyl entail pulling the vinyl, cutting the standard vent openings and adding vent covers to the wood, then replacing the vinyl with the perforated kind? If there is insulation all the way to the end of the rafter bay, how do I deal with that?
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Old 07-28-2017, 03:58 PM   #6
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Re: Attic ventilation


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Originally Posted by ksguy View Post


As for adding soffit vents. I wish I could say how hard it is, but I'm not really sure. We have vinyl siding and the soffits also have the vinyl over them. I haven't peeked in there but I do not believe the plywood soffit boards underneath have vents cut in them but I know the vinyl is not the perforated vent kind. I'm also not certain whether the insulation in the attic goes all the way to the roof sheathing on the end of the rafter bays or leaves an air gap - if it does go to the end, I'm not sure I can get to it to pull it away due to the slope of the roof.

Does adding soffit vents with vinyl entail pulling the vinyl, cutting the standard vent openings and adding vent covers to the wood, then replacing the vinyl with the perforated kind? If there is insulation all the way to the end of the rafter bay, how do I deal with that?
From inside the attic with a flashlight you might be able to see if the insulation is right up to the roof deck. with stick you might be able to feel if there is a solid block over the wall, blocking the space.

Then we can talk about the bad news.
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Old 07-28-2017, 04:00 PM   #7
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Re: Attic ventilation


You need to get in the attic with a good light and see if the insulation goes into the soffit bay. If it does, you'd clean it out and install a styrofoam baffle to give the intake air non restricted access to the attic.
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Old 07-28-2017, 04:02 PM   #8
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Re: Attic ventilation


I'll be home from work in about an hour. I'll snag a picture of the fascia/soffit areas on the front and back of the house, then see what I can see in the attic. Will post pics.
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Old 07-28-2017, 04:07 PM   #9
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Re: Attic ventilation


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Originally Posted by ksguy View Post
I'll be home from work in about an hour. I'll snag a picture of the fascia/soffit areas on the front and back of the house, then see what I can see in the attic. Will post pics.
Don't forget the water bottle and towel.
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Old 07-28-2017, 04:07 PM   #10
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Re: Attic ventilation


A piece of plywood across several joists (I like to use 2 to leap frog them as needed) will let you crawl around up there, watch your head for nails.

There are several ways the eaves/soffits could have been constructed so taking a look with pictures will be a big help.

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Old 07-28-2017, 04:09 PM   #11
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Re: Attic ventilation


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Don't forget the water bottle and towel.
LOL, I have an old t-shirt that I cut into strips years ago to wear as a sweat-soaker-upper on my head or I'd be drenched in under a minute.
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Old 07-28-2017, 05:27 PM   #12
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Here are some shots of the outside. Front of the house on the side with the attic over living space has a gable end so no soffits and no vent up there. I've taken a picture of the side with the vent, and a shot of the soffits on the back of the house. Looks like the gable vent is smaller than I remembered.

And before anyone mentions it, yes the tree touches the fascia, and I'm trimming it this weekend. :-)
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Attic ventilation-20170728_171000_1501280765990.jpg   Attic ventilation-20170728_170940_1501280781633.jpg  
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Old 07-28-2017, 05:55 PM   #13
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Re: Attic ventilation


The good news is you do have an overhang and those vinyl panels should come out, the pros will know how. Next is to determine if there is an air path from soffit to attic.

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Old 07-31-2017, 10:50 AM   #14
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Re: Attic ventilation


OK, I did not get a chance to get up into the attic to see how far out the insulation goes, or if there are blocks at the end. Too much other work to do over the weekend.

I did get a chance to check the vinyl soffit panels, and they do have plywood soffit boards under them. Removing the vinyl is straight forward and I can get the vented panels easily enough from one of the local big-box stores. When I get to the point of adding the vents, do I have to completely remove the entire wooden panels, or is it acceptable to just cut out long strips of the soffit board with the circular saw set just deep enough to penetrate the plywood? I ask because it looks like the retention channels for the vinyl soffit are nailed to this existing plywood and I'd rather not have to mess with removing them if I can avoid it.
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Old 07-31-2017, 11:06 AM   #15
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Re: Attic ventilation


Just a few good sized hole in the plywood would do it. As long as it is a common area below the tails of the rafters. When we build houses really close together, all the venting is supplied from the front and back of the house and the soffets are just like yours.
So does that roof wrap around the front and back where you might find vents? Often it is just a little skirt roof.
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