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Old 03-15-2012, 06:15 AM   #16
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ridge vent, gable, moisture in the attic


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the only head scratcher i have with the soffit venting is how to. the soffits are nailed inside the wall so i can't get at the sinkers holding the 2x4. i could use a 2.5" hole saw and burn a bunch of 2.5" holes along the soffits. it's just if i do that, how to get the screen behind them, it's a bit too tight to crawl up to with a staple gun.
1st, air seal the ceiling.

2nd, as WOW advised, do some measuring and calculating and verify that you actually need more intake vent. If you do, use a reciprocating saw and remove the blocks you want to vent. Cut new blocks with vent holes and install the screen and paint them on the ground. Install them by nailing through the rafters from the other side.

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Old 03-15-2012, 08:48 AM   #17
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1st, air seal the ceiling.

2nd, as WOW advised, do some measuring and calculating and verify that you actually need more intake vent. If you do, use a reciprocating saw and remove the blocks you want to vent. Cut new blocks with vent holes and install the screen and paint them on the ground. Install them by nailing through the rafters from the other side.
Good idea right there.
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Old 03-15-2012, 11:43 PM   #18
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ridge vent, gable, moisture in the attic


spent an hour or so studying roof ventilation. correct me if i'm wrong but,

1. the ridge vent acts as a suction device pulling air up, if the soffits are unable to supply enough air it draws from the easiest source. my loose bathroom vent being the #1 reason i have a few mold blotches, even without the fan on negative pressure was pulling it up.

2. adding soffit venting will reduce the negative pressure in the attic and make it less likely to draw on the multiple cracks and crevices in the ceiling that could pump conditioned air into the attic. it will also lower my heat bill since i won't be sucking heat up the top

3. use bleach or some type of mold killing product to scrub spots, then fog the attic with microban. was considering using my auto paint gun with a fine tip and a lot of air pressure to shoot a couple gallons of microban on the osb. at the moment the only traces of mold are on the osb or upper joists.

and of course seal every place i possibly can along the ceiling. was thinking of buying some pink 1/2" foam insulation and duck taping together boxes to slip over the canister lights
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Old 03-16-2012, 05:38 AM   #19
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ridge vent, gable, moisture in the attic


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spent an hour or so studying roof ventilation. correct me if i'm wrong but,

1. the ridge vent acts as a suction device pulling air up, if the soffits are unable to supply enough air it draws from the easiest source. my loose bathroom vent being the #1 reason i have a few mold blotches, even without the fan on negative pressure was pulling it up.

2. adding soffit venting will reduce the negative pressure in the attic and make it less likely to draw on the multiple cracks and crevices in the ceiling that could pump conditioned air into the attic. it will also lower my heat bill since i won't be sucking heat up the top

3. use bleach or some type of mold killing product to scrub spots, then fog the attic with microban. was considering using my auto paint gun with a fine tip and a lot of air pressure to shoot a couple gallons of microban on the osb. at the moment the only traces of mold are on the osb or upper joists.

and of course seal every place i possibly can along the ceiling. was thinking of buying some pink 1/2" foam insulation and duck taping together boxes to slip over the canister lights

The purple quote is kind of, but not exactly, true. Tinkering with the venting before air sealing is treating the symptom instead of the disease. The conditioned air is mostly being pushed rather than pulled. If you have a forced air heating system, the house interior will be somewhat pressurized when it's running, forcing moisture laden conditioned air into the attic. Opening and closing interior doors causes localized pressurization. Weather related pressure drops can cause conditioned air to migrate. Think of the sum of the openings through the ceiling as a partialy open window. Each hole around a wire you seal closes that open window a little.

The blue quote is a good idea. Check to see if the cans are IC (insulation contact) rated. As cheap as can lights are, it might be worthwhile to swap them for ICs if they're not and add some insulation to your attic after you air seal.
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Old 03-17-2012, 04:12 AM   #20
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ridge vent, gable, moisture in the attic


was working on this earlier today. the single gable end vent i had was turned into an intake by my ridge. you can literally see the water/mold path follow the airflow from the gable.

i'm going to try and find a cheap humidity meter tomorrow to leave up there and borrow one of the industrial dehumidifiers from my partner {used for flood jobs}

80% of the mold up there is within a few feet of that gable vent. there was a little around the bathroom vent but nothing like around the gable area.
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Old 03-18-2012, 12:26 AM   #21
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doing the math on ridge to soffit venting. earlier today i found these at lowes, claim a maximum 27sq/in for flow {brown grates} along with basic 3" hole vents

the problem i have is that i forgot how to figure sq/in. i plan on using a 3" hole saw to put holes in the soffits then silicone these screens over say...4 of them.

a 3" circle has a 1.5" radius and a 9.424 circumference along with a total area of 7.068 but i totally forgot how to transform this into sq/in to get an idea of how much i'll need to get that ridge vent working efficiently

also worth noting he humidity is down to 40% ish and holding

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Old 03-18-2012, 06:28 AM   #22
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doing the math on ridge to soffit venting. earlier today i found these at lowes, claim a maximum 27sq/in for flow {brown grates} along with basic 3" hole vents

the problem i have is that i forgot how to figure sq/in. i plan on using a 3" hole saw to put holes in the soffits then silicone these screens over say...4 of them.

a 3" circle has a 1.5" radius and a 9.424 circumference along with a total area of 7.068 but i totally forgot how to transform this into sq/in to get an idea of how much i'll need to get that ridge vent working efficiently

also worth noting he humidity is down to 40% ish and holding

Do you mean convert to SQ FT? Divide by 144. Each 3" rd hole will give you 7/144=.05 sq ft. Gonna be doing a lot of drilling.
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Old 03-18-2012, 01:23 PM   #23
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well, i already have a good chunk of soffit venting, just need to add more. from what i gather i need to be at 1:1 intake/exhaust and being 2:1 favoring the soffit isn't a bad idea when possible

just realized area is sq/in since it's the total area of the circle. my ridge vent flows 32sq/in every 2 feet which would mean 5 of those 3" holes would be 35 sq/in
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Old 03-18-2012, 01:44 PM   #24
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ridge vent, gable, moisture in the attic


If your gable end vent is located close to one of the roof box vents, that may be short-circuiting the ventilation at that end of the attic. I would make sure I had enough square inches of net ventilation area of roof box vents, and then seal the second gable end vent.

And I agree with Mr. W.O.W, about the benefit of providing more than ample low venting.
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Old 03-18-2012, 02:02 PM   #25
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If your gable end vent is located close to one of the roof box vents, that may be short-circuiting the ventilation at that end of the attic. I would make sure I had enough square inches of net ventilation area of roof box vents, and then seal the second gable end vent.

And I agree with Mr. W.O.W, about the benefit of providing more than ample low venting.
what>?

roof box vents? like for the bathroom? those were sealed. the moisture problem was obvious when i looked in the daylight. the gable vent became an intake for the ridge vent and drew in a lot of moisture. humidity dropped rapidly the second i sealed that off.

just curious but did you read the thread? you keep referring to "roof box vents" what i have is



last question for someone who will know but when ridge vent is quoted at 16sq/in/ft in flow is that on each side of it or total? if it's total my intake calc's will be a lot easier to arrive at
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Old 03-18-2012, 02:47 PM   #26
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It's total.
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Old 03-18-2012, 06:24 PM   #27
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check out my site on condensation
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Last edited by beenthere; 05-14-2013 at 05:56 AM. Reason: Removed link to his company
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Old 03-18-2012, 10:08 PM   #28
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check out my site on condensation
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more or less what i've been lead to believe so far.

seal the attic deck. spray foam the can lights or build enclosures around them. hvac tape the bathroom vents, spray foam the wire holes. equalize soffit and ridge vent sq/in favoring more on the soffit.

i'm just happy i caught it before it really started to mold the wood. the few grey spots i have more or less melt the second you spray them with microban

turning my bathroom vent and gable into intakes were ugh...............i have no idea how that was ever overlooked in the first place
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Old 03-18-2012, 11:15 PM   #29
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If the soffit vents are substantially more than the exhaust vents, the air could move from one soffit vent to another close by rather than to the ridge vent. This is why there are limits on the percentage system. The soffit air feeds the ridge vent. The new “I” codes reflect this by limiting soffit at 50-60% maximum, more than exhaust: http://publicecodes.citation.com/ico...006_par001.htm

Regardless, you are under your own State Energy Code of balanced system with intake, exhaust to use the 1/300 rule. If adding more soffit venting percentage past 50%, be sure to meet the 1/300 rule first. “Ventilation in attics
“The attic ventilation requirement is one square foot of net
free vent area per 150 square feet of ceiling. This is often
abbreviated as 1/150. If half the vents are placed low, at the
eaves, and half the vents are placed high, at the ridge or
gable end, the vent to ceiling ratio may be reduced to 1/300.” “Flat ceiling insulation” – just above Fig. 1: http://www.cbs.state.or.us/external/...ResPub_all.pdf

To clarify: meet your 50/50 rule for 1/300 first; then add additional soffit venting to get your greater soffit percentage.

10-15 % (or 55-58%) more soffit than exhaust is recommended here, pp. 615: http://books.google.com/books?id=Z8a...0vents&f=false

2:1 is here: http://www.inspectapedia.com/interiors/atticcond10.htm
BSC recommends 60/40 best: http://www.buildingscience.com/docum...n-roof-venting
From the picture, it appears your ridge vent doesn’t have baffles, which are much better by giving you negative pressure (suction): http://oikos.com/esb/30/atticvent.html

http://www.buildsite.com/dbderived/a...rived20936.pdf

The circular vent Net Free Ventilation Area (NFVA) is minus the screening and louvers: (1.735 NFVA) https://ventmastersstore.com/shop/3-...ack-p-128.html

May need to re-figure your NFVA: http://www.airvent.com/homeowner/pro...it-specs.shtml

Gary
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Old 03-18-2012, 11:25 PM   #30
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i don't have the cool baffled ridge vent but boy do i ever relate to

Quote:
The ratio of soffit intake to roof outlet should be at least 2:1 to avoid unnecessary these heat losses from the building. A serious error is a roof outlet vent net free area that exceeds the air inlets at lower roof edges or eaves. When this occurs in a climate where building heating is needed during part of the year, warm air leaking into the attic or roof space and exiting at the ridge vent (or other vents high on the roof) creates a convection air current that draws excessive heat out of the building during the heating season, leading to unnecessarily high heating costs.
as it sits now i have somewhere close to .6sq/in of intake for every 1 sq/in of exhaust. your links and others have made me realize what seems so obvious now, the ridge IS venting and is pulling air from the easiest source. it's why the gable end turned into an intake when it was open and why i need to seal my attic deck and add more intake. i added about 50sq/in of intake today and will continue to do so until i get to at least 1.1sq/in of intake for every 1sq/in of exhaust. i'm not sure i can achieve 2:1 but i think 1.5-1 could be in the cards

thanks again for the links i will read through them all

oh, for my IC rated can lights, is spray foaming around the loose edge between it and the sheetrock okay or does each canister require a box or foam baffle to be placed over it?

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