Can I Overvent Soffits


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Old 08-10-20, 06:53 PM
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Can I Overvent Soffits

Is it possible to overvent soffits in my home?

When I go into the attic, I see almost no daylight around the eaves. Since I'll be getting my roof re-shingled, I'd like to install air chutes under the roof deck to ensure that the insulation is kept away from the roof deck to allow my soffit ventilation to be effective.

Q: So should I be installing the air chutes between every pair of roof rafters? Or is that too much soffit ventilation? Currently I have five gable vents and four box vents in a one-story house with about 1800 square feet plus double-detached garage.

Thanks.

Wayne
 
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Old 08-11-20, 04:48 AM
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Are your soffits vented? Roof shingling has nothing to do with anything inside your attic so you don't need to wait for the roofing. Insulation dams are usually installed on every bay to prevent the insulation from blocking the air path.
 
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Old 08-11-20, 07:58 PM
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Yes the soffits are vented. (Aluminum soffits with ventilation holes, no wooden soffits behind the aluminum.)

I'm interested in doing this at the time the roof is replaced because after the old shingles are removed (and before the new installed), we can remove the plywood for easy access to the bays to install the air chutes. If I try to do it at another time, I have to figure out how to get to the eaves from within the attic without screwing up the attic insulation.

Thanks.

Wayne
 
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Old 08-12-20, 04:45 AM
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You are going to strip off the roof sheeting all the way along your roof edge to install insulation baffles??? That will have a significant affect on the cost of your new roof.
 
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Old 08-12-20, 05:35 AM
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Hi, I have been told by roofers that if you have soffit vents then you shouldn’t have gable vents but instead there should be a ridge vent, I had serious mold problems at one point.
do you have blown in insulation now?
Geo
 
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Old 08-12-20, 05:55 AM
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That will have a significant affect on the cost of your new roof.
Well, an insulation guy told me that's the most cost-effective way to get it done. How will it be any easier/cheaper to do it in the attic without destroying the insulation? I live in Canada where we have a LOT of attic insulation (above the tops of the ceiling joists).

I was told to remove the roof plywood at the eaves, nail a 1x2 strip of board to each side of each bay, then staple a styrofoam air chute to the 1x2's to keep the insulation back from the underside of the roof deck. That doesn't really sound like a lot of work, although I'll admit that it could add $1000 or more to the cost. But I don't see how attempting it from within the attic will be easier/cheaper. Or am I missing something?

Actually, I'd prefer to do it myself from within the attic. If done when the roof is done, I pretty much have to get the roofers to do it, since they're not going to wait for me to do the baffle work before they proceed with the shingling. I've thought about removing the lower level of shingles and sheeting myself and doing the baffle work a day or two before the roofers come, but there's some risk there if we get rain, obviously.

The extra cost was part of what motivated my original question re whether I'd be overventing the soffits if I put baffling into every bay. I don't want overkill, but I do think I need to fix my soffit ventilation.

Ventilation expert Joseph Lstiburek says to aim for 60% ventilation at the soffits and 40% in the ridge or roof vents. If I baffle every roof bay at the eaves, I suspect I'll end up with a lot more than 60% at the soffits.
 
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Old 08-12-20, 06:06 AM
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The soffit vents are the intake, the ridge or gable vents are where it exhausts. The soffit vents let cooler air in and forces the hotter air out the ridge/gable.
I don't think the insulation will be a big deal, just fluff it back up on your way out.
 
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Old 08-12-20, 06:09 AM
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I have been told by roofers that if you have soffit vents then you shouldn’t have gable vents but instead there should be a ridge vent
I've had so much conflicting advice from roofers that I don't really take them seriously any more. (Some say no need for more venting, others say add lots more.) Although the garage has roof vents (box vents, not ridge vents), the house itself has only gable vents (five of them). I had a house inspector tell me that there's nothing wrong with the gable vents, although he did recommend adding more roof vents.

I had serious mold problems at one point.
I don't really have a mold problem in my attic. (I've been in the attic to look.) At one corner of the house I can see staining or perhaps even rotting on the underside of the roof deck, but I don't see any other. At that corner I'll definitely want to add air chutes under the roof deck to keep the air flowing from the soffit. Probably one reason I don't have a mold problem is that the attic cavity is huge, so there's lots of volume of air in the attic.

Do you have blown in insulation now?
Yes the house has blown-in, although the attached garage has batting.
 
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Old 08-12-20, 06:15 AM
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just fluff it back up on your way out
The house inspector told me that once the blown-in insulation is compressed, it's difficult to restore it to its previous insulating capacity. It gets c-c-cold here (to minus 40 degrees), so I don't want to mess up my insulation.

I suppose I could use a rake to move it aside, but I'm not sure how well that would work.
 
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Old 08-12-20, 06:22 AM
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How thick is your insulation? would it be worthwhile to blow in more when you get done?
 
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Old 08-12-20, 07:00 AM
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You do not see any evidence of mold in the attic so I would leave well enough alone.
Perhaps just add a couple/few roof vents.

Once blown in insulation is compressed it can be difficult if not impossible to get it fluffed up again.
This depends on the type of insulation.

You see some staining in one corner but that is likely due to a leak.


 
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Old 08-16-20, 06:56 AM
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You see some staining in one corner but that is likely due to a leak.
I think you're right. I went into the attic during a recent rain and noticed a small wet spot on the underside of the deck.

I might need the roofers to replace that corner of the roof deck, at which time they could add a few air chutes to increase air flow there too. Apart from that, yeah, maybe just add a few more roof vents.
 
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Old 08-16-20, 07:01 AM
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Installing the baffles from the inside is the proper way. You could do it yourself and likely have the entire attic reinsulated with blown-in for less than $1,000 (not sure what your square footage is).
 
 

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