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Old 05-23-2009, 10:17 AM   #1
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Need advise installing soffit vent


My house was built in 1949. Originally the only venting was a mushroom other either side of the roof for each knee wall. The soffits are hard-pan and enclosed (under the hard-pan soffiting theres just solid board)

I had a crew come and install a ridge vent this week and I was hoping to simply hole saw a vent into the board above the soffit pan for each bay, cap the holes and install some soffit perf.

Well, now I'm not sure what to do. Each of the birds-mouths are stuffed with some old school loose fill that I moved aside to get a better look at what I'm dealing with. Instead of seeing the top of that board above the hard pan, I'm seeing this:



To help describe... I've pulled the batt back aware the vertical board that is in front of it. the best I can tell, underneath the bat to that board is the drywall ceiling downstairs (I think). Beyond that board (where you can see some tar paper) is another that seems to sit at a 45* angle.

So my question is, how in the heck is this thing built and how do I to vent my soffits? Will I have to hole saw through the board above the hard pan and then hole saw into this angled board as well?

I was going to use a 2" hole saw for each of the 25 or 26 beam pockets. Should this be enough? If it helps, they installed Owens Corning Ventsure [link] [12.5 sq. in. per lineal ft] I would like to make sure that if I'm going through the pains of this to make enough intake, e.g bigger hole, more holes per bay, etc

Heres a snapshot taken from further back so you can see the construction of the eves better:

(the close up picture of the bay is to the left of the one shown center here)

outside view of the soffit:


Any help, diagrams, pictures, etc would be greatly appreciated.

thank you and have a great holiday weekend
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Last edited by scrupul0us; 05-23-2009 at 01:36 PM.
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Old 05-23-2009, 11:27 AM   #2
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Need advise installing soffit vent


Read up @ www.buildingscience.com. A 2" hole per bay is generally not sufficient. You may want to consider installing styrofoam baffle liners every 3 rd rafter space on the underside of your roof to allow an unobstructed air passage up toward your ridge vents.

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Old 05-23-2009, 11:37 AM   #3
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Need advise installing soffit vent


Quote:
Originally Posted by Chemist1961 View Post
Read up @ www.buildingscience.com. A 2" hole per bay is generally not sufficient. You may want to consider installing styrofoam baffle liners every 3 rd rafter space on the underside of your roof to allow an unobstructed air passage up toward your ridge vents.
I have the staple up baffles already purchased for post ventilation installation

As for that website... Maybe it's just me, but I find it tedious to get information there... Searching for 'soffit vent' renders alot of useless results... thats why I came here
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Old 05-23-2009, 01:57 PM   #4
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Need advise installing soffit vent


I would remove the white loose fill with a shop vac and long extension. I would skill saw the soffit out to install 8x16 metal vents (56 NFA), and install the baffles.

http://www.cornerstoneinspectionsdfw...ntilation.html Be safe, G
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Old 05-23-2009, 02:07 PM   #5
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Originally Posted by GBAR in WA View Post
I would remove the white loose fill with a shop vac and long extension. I would skill saw the soffit out to install 8x16 metal vents (56 NFA), and install the baffles.

http://www.cornerstoneinspectionsdfw...ntilation.html Be safe, G
GBAR: thanks for the follow up... that loose fill is pretty packed after all these years so unfortunately its a job for a pair of rubber gloves and full mask respirator

What I'm gathering from your reply, and from what I'm starting to think, that pocket that the loose fill is actually in, is the soffit area and what I think is the top of the sheet rock is the top of the soffit board... I think tomorrow I'll drill a small pilot hole up through the board while my wife keeps and eye out in the attic for it

If it works out that I'm in the clear with a straight shot up, I'll have to borrow a skill saw that can cut a hole that big and that tight to the siding (my jig saw is too big)

Providing an 8x16 is doable, how many should I put in?

Thanks again for the info!
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Old 05-23-2009, 02:48 PM   #6
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Need advise installing soffit vent


Each 8" x 16" provides 56 square inches of NFVA.

You chose, or your contractor chose a very poor ridge vent that only provides 12.5 square inches of NFVA per foot, when the norm is 18 square inches per lineal foot.

With the way your soffits are plugged, I would remove the bottom 3 rows of shingles and cut a 1" wide slot and install the Smart Vent by DCI Products Inc. then you wouldn't have to worry about the debris at the bottom of the soffits.

http://www.dciproducts.com/html/smartvent.htm

If you choose the 8" x 16" vents, I always recommend as continuous intake ventilation as possible, so I would install one in each and every rafter bay.

Ed





"Most people have been taught that warmer air rises and escapes from the high vents, while cooler air enters in lower vents. Thermal buoyancy is a major cause of air leakage from the living space to the attic, but research at the BRC shows that wind is the major force driving air exchange between an attic and the outdoors.
Our research shows that the role of thermal buoyancy in diluting attic air with outdoor air is negligible," says Rose.
This requires rethinking about the design and location of attic vents. For example, some ridge vents may allow air to blow in one side and out the other, without drawing much air from the attic. Rose believes that ridge vents with baffles create better suction to draw air out.

"Rose considers soffit vents to be very important.
"If a roof had only one type of vent device, I would choose soffit vents," he says, "because they work well as inlets and outlets."
There's less problem with rain and snow getting in, because soffit vents point downward. To get maximum protection, locate soffit vents as far out from the wall as possible. If rain or snow blow into the soffit, it's less likely to soak the insulation or drywall."
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Old 05-23-2009, 03:30 PM   #7
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Quote:
Originally Posted by Ed the Roofer View Post
Each 8" x 16" provides 56 square inches of NFVA.

You chose, or your contractor chose a very poor ridge vent that only provides 12.5 square inches of NFVA per foot, when the norm is 18 square inches per lineal foot.

With the way your soffits are plugged, I would remove the bottom 3 rows of shingles and cut a 1" wide slot and install the Smart Vent by DCI Products Inc. then you wouldn't have to worry about the debris at the bottom of the soffits.

http://www.dciproducts.com/html/smartvent.htm

If you choose the 8" x 16" vents, I always recommend as continuous intake ventilation as possible, so I would install one in each and every rafter bay.

Ed
Ed: As is I have ice daming problems so I dont think the smart vent is a good idea... I would much rather spend the time opening up the soffit than cutting into the deck (although the end result of this ventilation project should counteract the issues causing the icing)

thanks to everyone for their helpful insight. Hopefully tomorrows pilot hole test gets me moving in the right direction
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Old 05-24-2009, 07:34 AM   #8
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Need advise installing soffit vent


If you're borrowing a tool anyway, try a Fein or Dremel Multimax for this job. I used mine last weekend ant it makes for a much easier job. No bouncing bladed tips in blind cavities , easy to handle at the top of a ladder
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Old 05-26-2009, 10:09 PM   #9
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just wanted to post an update

i had a chance to make some progress this afternoon... indeed the board above the hard pan was the area that i thought was the top of the drywall (although that really made more sense the more I thought about it)... for the moment I have three 3" holes cut for each bay (i'm 1/4 of the way done) and I've stapled some screening over the holes in the interim to keep bugs out...

I went to the depot to get the vented soffit tray and I guess theres only one standard size they carry and it wouldny suit my needs (depots' is 12' x 12" and I needed anything x 6")... after a quick think I determined I could cut down the 12' length piece on my table saw turn those pieces side ways (now they lock together) and it suits the install rather well (albeit the continuous channel if you will that would run the length of the house is rotated 90*)

what I think I'd like todo is once I get all the holes drilled and I see how the venting is going (how affective it is) I may just slice out that whole 3" gap the length of the house with some form of saw or dremel pro...

as mentioned above, I am removing the loosefill but from the outside (through the hole)... I find this works reasonably well for getting the bulk out and has the added benefit of me not being in the attic with all the dust/insulation flying around

I have made one other observation and that is since this eve was never meant to be vented, my batt insulation can be seen from the holes now (it was ran into that loose fill that occupied the eves) and I wonder if this could be a moisture issue with it being right at the opening? I'm thinking about getting some cheap pine board and cutting it down to the width of the bays and nailing it in to "hold back" the insulation from the holes and then staple up a baffle accordingly to channel air flow... does this seem like a reasonable thing todo?

thanks again

Last edited by scrupul0us; 05-26-2009 at 10:13 PM.
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Old 06-12-2009, 04:19 PM   #10
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Need advise installing soffit vent


Install some picturesof what you did?
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Old 06-12-2009, 04:34 PM   #11
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Need advise installing soffit vent


I've actually only got two bays left that I'm going to finish this weekend. I'll snap some pics and post them
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Old 10-09-2010, 08:57 PM   #12
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Need advise installing soffit vent


I know this thread is from 2008, but I was curious to see if your efforts helped stop your ice dam problems. My situation is exactly the same as your initial posting and my approach is very similar...removing all insulation above the soffit, installing soffit vents and then possibly installing rafter vents that create a void between the soffit and insulation allowing cool air into the attic unobstructed.

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