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Old 03-19-2012, 12:52 AM   #31
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ridge vent, gable, moisture in the attic


Seal the joint to drywall at the lights, IC need no covers: http://www.finehomebuilding.com/PDF/Free/021105092.pdf

http://www.bpi.org/Web%20Download/In...V1.3_DRAFT.pdf

http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

http://www.google.com/url?sa=t&sourc...O842EQ&cad=rja

That should hold you for the next few nights....

Gary

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Old 03-21-2012, 08:41 PM   #32
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Originally Posted by Windows on Wash View Post
You should always shoot for 2:1 soffit (intake) to ridge (exhaust) ratio.

Air sealing the attic floor will help control condensation movement as well.
where did this info come from. My understanding was to have a balanced vented area. Basic physics... one CFM in will means one CFM out. so if you are allowing twice as much in, where does it go?
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Old 03-21-2012, 08:46 PM   #33
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i even get this one. having more intake than exhaust is not only recommended via some of the links above. it prevents negative pressure in the attic from too much exhaust which would suck from the easiest source...that can be the house. other unsealed areas, you name it. from what i gather is the idea is to have enough soffit that the ridge exhaust can easily pull on the soffit. being right at 1:1 gives you no wiggle room if anything gets blocked. my own home is going to come in at 1.4:1 which should be open, breezy and prevent high humidity conditions up there.

i've been adding 50-100sq in of intake per day in my free time and i literally have watched the humidity meter drop a few % each day
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Old 03-21-2012, 08:51 PM   #34
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ridge vent, gable, moisture in the attic


Joe Lstiburek

He typically aims for a 60/40 split on intake vs. exhaust.

He always preaches to aim high on the intake side. Intake air is more often overlooked or obstructed, creating an imbalance the other way. If there is too much exhaust, you just drive stack pressure and air loss from the envelope.

Intake air is also a bit more difficult to get right in most cases vs. just about anyone can easily add in additional ridge vent or box vents to make up for lack of exhaust air.

Most of the homes that I go into with persistent venting issue are lacking intake volume or have obstructed some aspect of it.
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Old 03-21-2012, 09:09 PM   #35
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okay I can accept that one. Reason is more of a practical one due to the vast lack of attention to details of the construction industry in general. However you can also go overboard. If you pressurize the attic space you drive heated air in the summer into the conditioned space below. The ideal is one to one! And completely sealing the attic floor is far more critical than attic venting in most climate zones.
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Old 03-21-2012, 10:50 PM   #36
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In post 29, I showed our (U.S.) codes are allowing for 50-60% soffit over exhaust, any more than that and you create the possibility of air in one soffit---out the soffit right next to it. No reason to go up if the resistance is less down below. Here is the idea: 10-15 % (or 55-58%) more soffit than exhaust is recommended here, pp. 615: http://books.google.com/books?id=Z8a...0vents&f=false

Many won't achieve those figures as WoW said, much easier than crawling at the soffits- especially for us old guys....There is not much research on the percentages ratio with test results, I'm still looking...

Gary
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Old 03-22-2012, 09:18 AM   #37
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ridge vent, gable, moisture in the attic


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okay I can accept that one. Reason is more of a practical one due to the vast lack of attention to details of the construction industry in general. However you can also go overboard. If you pressurize the attic space you drive heated air in the summer into the conditioned space below. The ideal is one to one! And completely sealing the attic floor is far more critical than attic venting in most climate zones.
Convection will probably always steer a negative pressure even the the presence of a slightly overbalanced intake:exhaust ratio.

Stack pressures during what the the more problematic venting seasons (winter) are already in effect in the home and pushing warm, moist air up into the attic.

In those cases I would always prefer a slightly overbalanced intake vs. exhaust if I am going to err on one side or the other.

Air sealing is first and foremost and that is why I mention it in nearly every discussion about ventilation. It will nearly always mitigate or completely eliminate the needs for modification.
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Old 03-27-2012, 02:17 AM   #38
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well, it's been a little over a week since i did everything that was mentioned. couple cans of spray foam and hvac tape did wonders sealing the attic floor. had a couple really big home to attic vents, one being that bathroom vent, second being from the kitchen. the cutout for the exhaust vent had a good 3/8" all around going directly to the attic. that's on a...what...8" pipe so that's a good amount of air. anyway. with the gable closed down and sealing done along with a whopping 98 more 2.5" holes in the soffits {hole sawed 6-7 -2.5" holes in each soffit i chose} the air feels about the same up there as it does outside and get this...the mold is dying on its own. some areas that had grey splotches starting are either gone totally or shrinking. i microban'd the worst areas but the minor areas appear to be dying on their own with the food source cut off

for reference a 2.5" hole is 5sq/in
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Old 03-27-2012, 05:35 AM   #39
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Glad you took the time to read all the confusing opinions on how to fix this issue. But you did it and it is working. Good job!
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Old 03-27-2012, 07:41 AM   #40
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for reference a 2.5" hole is 5sq/in
Yeah - rounded up. But the resulting NET area is reduced significantly when an insect screen or louvers are added.

Glad your solution is working.
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Old 03-27-2012, 02:26 PM   #41
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Yeah - rounded up. But the resulting NET area is reduced significantly when an insect screen or louvers are added.

Glad your solution is working.
i figured it would be, i used the chicken wire style 22 by 3.5" slide in grills they had at lowes to cover the holes and aimed for a 1.5 to 1 intake to exhaust ratio just for this very reason.

which again, i'm glad you guys pointed out was the smart play. had i just read the instructions and went with 1:1 when the screens and any debris get factored in i would certainly have more exhaust than intake. great setup for a turbocharged car, not so much for an attic

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