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Old 01-30-2011, 05:17 PM   #1
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Drilling holes to vent soffits?


We recently hired a contractor to install vented soffits in our 1940s house, and I have some concerns that there's still not enough ventilation.

The original soffits were just solid boards covered with white aluminum. The contractors ended up taking off the old aluminum panels, then drilled 1" holes about a foot apart in the board (picture below), and put continuous vented panels (looks like Durabuilt) back in place.

My searches haven't turned up much about this method, and it seems like most advice is to put in a bunch of individual rectangular vents instead of continuous panels. One post I saw said that drilling the small holes would better preserve the structural integrity of the roof, but I didn't think that soffits were load-bearing pieces.

Any opinions? Is a single 1" hole per linear foot really enough to do anything? There are spots of daylight visible in the attic now, but there's no way it could be enough to balance the exhaust (there's a continuous ridge vent, and also gable vents that I plan to block off once I know the soffits are working). For now I'm going to just leave it as is and see if the ice dams improve, but do you think I could/should drill more holes in the future if needed?



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Old 01-30-2011, 06:20 PM   #2
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Drilling holes to vent soffits?


Gary is going to kill me but...

are you haveing any issues that you think may be cause by lack of venting?

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Old 01-30-2011, 08:21 PM   #3
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Drilling holes to vent soffits?


I'm gonna beat up on ya a little till gary gets here

You need at least as much intake at the soffit as you have exhaust at the ridge, otherwise you risk pulling conditioned air from other gaps in the envelope between the living space and attic. Not only could the continuous ridge vent cost you money in wasted energy, but if you're in ice dam country the ridge vent with insufficient eave intake could also make you more prone to those.

So jessc, are we in ice dam country, or are we not? Shall we move on with making it optimal either way?
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Old 01-30-2011, 08:46 PM   #4
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Drilling holes to vent soffits?


Sorry Tom, couldn't wait on this one....

"and see if the ice dams improve, but do you think I could/should drill more holes in the future if needed?"---- I doubt they will improve....

The 1" holes are the same as a square 3/4"+ hole. You need a 1" slot every lineal foot, or another contractor. Actually, the slot would not be enough if covered by perforated panels, unless they were 24" deep from fascia to house as they only draw 4.68 NFVA per foot; http://files.buildsite.com/dbderived...rived92755.pdf

The only way to get the NFVA required to balance the exhaust and stop the ice dams is continuous soffit venting, rated at 9 NFVA per foot, along with the other side's soffit, matches the ridge vent (18NFVA). Air seal the attic, http://www.familyhandyman.com/DIY-Pr...s/Step-By-Step
foam board above the exterior walls, http://www.homeenergy.org/archive/he...96/961110.html
and then close the gable vents, only if the soffit NFVA is below the exhaust NFVA; http://www.airvent.com/homeowner/pro...it-specs.shtml With more exhaust than intake, indoor air will supply the ridge rather than soffits.

If the perf's are installed over any size holes, you will be 75% short of the required NFVA (if the soffit depth is 6").

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Old 01-30-2011, 09:01 PM   #5
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Drilling holes to vent soffits?


oh man
did i choke on that one or what?
i didn't even see the ice dam thing

oh well...to air is human
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Old 01-31-2011, 12:30 AM   #6
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Drilling holes to vent soffits?


Thanks for the replies, everyone.

I had no idea the perforated panel NFA was so low. The contractors didn't provide any specs on the stuff they installed, and I can see why now. With 6" soffits, it's absolutely impossible for those panels to ever allow enough intake, even if there weren't any boards above them at all.

So it seems like my best bet is to either put in some 16x4 vents (26 sq in NFA) every few feet, or else cut a long strip out of the the soffit board and install 9 sq in/ft NFA continuous vents.

Also, Gary, you said "close the gable vents, only if the soffit NFVA is below the exhaust NFVA". Did you mean "only if the soffit NFVA is above the exhaust NFVA"?
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Old 01-31-2011, 07:02 AM   #7
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Drilling holes to vent soffits?


you need to understand however that the vinyl soffit system is not by means an air tight system,air will easily flow around the panels

just measuring air movement thru the holes in the panel is not a true measurement as to how these panels are typically installed
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Old 01-31-2011, 07:03 AM   #8
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double post
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Old 01-31-2011, 09:06 AM   #9
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Drilling holes to vent soffits?


I don't understand why the contractor drilled holes at all.
Take a jig saw and cut each of those holes to with in a 1" or so of the truss on either side, than widen the slot to at least 2".
Cover it with continuous soffit vents.

(That's assuming those holes were drilled center of each truss, which they should have at least known to do that, i would hope anyhow.)
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Old 01-31-2011, 04:14 PM   #10
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Drilling holes to vent soffits?


Quote:
Originally Posted by Slyfox View Post
I don't understand why the contractor drilled holes at all.
Take a jig saw and cut each of those holes to with in a 1" or so of the truss on either side, than widen the slot to at least 2".
Cover it with continuous soffit vents.

(That's assuming those holes were drilled center of each truss, which they should have at least known to do that, i would hope anyhow.)
x2

All they did is start your cut.
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Old 01-31-2011, 11:40 PM   #11
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Drilling holes to vent soffits?


"So it seems like my best bet is to either put in some 16x4 vents (26 sq in NFA) every few feet, or else cut a long strip out of the the soffit board and install 9 sq in/ft NFA continuous vents." ----------- The idea is to vent every rafter bay as that is where most of the heated air escapes from the room below. Wire and pipe holes let air through. Convective loops from low density insulation, batt and loose fill in walls deposit the heat to the top plate, rafter and ceiling joist ends, right at the thinnest insulation coverage areas = over the exterior walls. This also happens to be the exact place the cold outside air enters first…… Ice dams form here because of explained reasons (location). If you vent only 4-5’, only that area would get air movement, doing nothing for the spaces in-between.

”Also, Gary, you said "close the gable vents, only if the soffit NFVA is below the exhaust NFVA". Did you mean "only if the soffit NFVA is above the exhaust NFVA"?" ------
The soffit vents need to be equal to, or slightly more than the exhaust vents. Otherwise you will have a negative pressure that would draw on the leaks in the house = stack effect pulling air from the basement or crawl, possibly back-drafting any gas appliances below. To me, the gable vents are exhaust vents, not intake, so long as they are 3’ above the soffit vents. A balanced system is needed, read pages 615 and 616 here; http://books.google.com/books?id=Z8a...0vents&f=false

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Old 02-01-2011, 06:31 AM   #12
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Drilling holes to vent soffits?


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Originally Posted by GBR in WA View Post
To me, the gable vents are exhaust vents, not intake, so long as they are 3 above the soffit vents.
Gary
Unless they are three feet below the ridge (which I can't imagine the bottom of a gable vent not being), in which case they short circuit the soffit->ridge stack effect and do become intakes. Even that is preferable, IMHO, to leaving the soffit vents as is and blocking the gables- which will as you mentioned result in conditioned air in the attic.

@jessc:
Cut the slot out as mentioned by slyfox from end to end,
install continuous vented soffit end to end,
from the attic install foam baffles from the box store all the way down into the soffit,
support the baffle with a pc of fiberglass insulation that fills the void between top plate and decking tightly,
do this to every single rafter bay,
blow in the field insulation to the recommended r value making sure it doesn't go down into the baffles while getting it as thick as you can near the eaves,
check that the decking near the ridge was cut to manufacturer specs, and reference the distance of cut sq inches versus what the vinyl soffit NFA is,
if more exhaust than intake> some ridge vent needs to blocked off either from the inside or out,

now you can safely block the block the gable vents.
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Old 02-01-2011, 11:24 PM   #13
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Drilling holes to vent soffits?


jmiller- That plan makes sense. I may also add foam boards near the eaves, since the roof pitch is kind of low to get a ton of insulation in there.

Thanks again everyone for the advice and all the links. I'm glad I'm not crazy for questioning what the contractors did.
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Old 02-05-2011, 10:35 PM   #14
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Drilling holes to vent soffits?


“Unless they are three feet below the ridge (which I can't imagine the bottom of a gable vent not being), in which case they short circuit the soffit->ridge stack effect and do become intakes.’ ----- I think they would still act as exhaust because the soffit intakes are 3’ below those. The only case for gables acting as intakes is: 1. if they are less than 3’ higher than soffit vents. 2. if the outside siding is in full sun to heat the wall, 3. if the prevailing wind is directly toward the gable end. Siteing research testing would be great, but there is minimal. (Other than ridge vent manufactures claims) I enjoyed this article, still researching their exhaust vents; http://www.savenrg.com/venting.htm

Check your ridge vent to make sure you are getting the maximum amount of NFVA possible, as Jmiller said, every ” makes a difference; http://en.allexperts.com/q/Roofing-1...able-Vents.htm

You want to use rigid foam board at the exterior walls not fiberglass rolled up to hold the baffle up. The baffles should be stapled to the roof sheathing, the roll of f.g. will not stop the air from the soffits and will create a thermal wick between the roof and the outside wall for ice dams. http://www.diychatroom.com/f98/how-b...ulation-90438/
Buy the wind-blocker; http://www.adoproducts.com/wind.html
Or, use the plastic baffles from HD with built-in wind blockers; http://www.bergerbuildingproducts.co...sAccuvent.html

Let us know how it turns out…….

Gary
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Old 03-29-2011, 08:38 AM   #15
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Drilling holes to vent soffits?


Quote:
Originally Posted by jessc View Post
We recently hired a contractor to install vented soffits in our 1940s house, and I have some concerns that there's still not enough ventilation.

The original soffits were just solid boards covered with white aluminum. The contractors ended up taking off the old aluminum panels, then drilled 1" holes about a foot apart in the board (picture below), and put continuous vented panels (looks like Durabuilt) back in place.

My searches haven't turned up much about this method, and it seems like most advice is to put in a bunch of individual rectangular vents instead of continuous panels. One post I saw said that drilling the small holes would better preserve the structural integrity of the roof, but I didn't think that soffits were load-bearing pieces.

Any opinions? Is a single 1" hole per linear foot really enough to do anything? There are spots of daylight visible in the attic now, but there's no way it could be enough to balance the exhaust (there's a continuous ridge vent, and also gable vents that I plan to block off once I know the soffits are working). For now I'm going to just leave it as is and see if the ice dams improve, but do you think I could/should drill more holes in the future if needed?


You made a nice spot for wasp to live

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