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Old 10-31-2012, 01:20 PM   #1
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Crawl space vent and mold question


I have a dirt crawl space that is vented, typical where I live in Southern California. I notice that inside my home, there is mild mildew/mold on the plaster walls. I use damp rid near the problem areas and it has helped but not 100% effective.

I noticed that the walls that have the issue are near the vented crawl space areas. I am not a rocket scientist but I think the humidity and draft is coming through those vents and affecting my inner walls.

I have read on the building science website that a completed crawl space is recommended, closed vents and vapor barrier. My only reluctance is that pricing maybe out of my affordable range and if only one area is not sealed correctly, there can be humidity locked in that space.

I was wondering what my options would be otherwise?

I was thinking maybe keep the vents open and possibly look into closed spray foam under the floor boards and over the joists?

Maybe just spray foam the areas near the open vents only?

Any suggestions would be greatly appreciated.

Thank you.

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Old 10-31-2012, 03:04 PM   #2
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Crawl space vent and mold question


Is there a 6 mil. vaper barrier on the ground under the house?
Has the crawl space been air sealed? (sealing up all the holes where plumbing and wiring was run thorugh the bottom plates)
Insulated the rim joist?

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Old 10-31-2012, 03:39 PM   #3
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Crawl space vent and mold question


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Originally Posted by joecaption View Post
Is there a 6 mil. vaper barrier on the ground under the house?
Has the crawl space been air sealed? (sealing up all the holes where plumbing and wiring was run thorugh the bottom plates)
Insulated the rim joist?
there is nothing in the crawl space besides what was there when the home was built originally in 1954.

there is just exposed floor boards, a slab foundation, dirt floor, and crawl space vents. no insulation and no vapor barrier. I wondering what I need to do to get rid of the mold from forming?
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Old 10-31-2012, 05:13 PM   #4
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Crawl space vent and mold question


Really need your location/ PLease go back and edit your profile.
Without that vaper barrier all the moisture that rises is going eight up into the home.
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Old 10-31-2012, 05:52 PM   #5
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Southern California. Listed in first post.

Put a vapor barrier on the floor and seal it to the wall. Insulate the crawl space wall and seal up the crawl to create a conditioned space.
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Old 10-31-2012, 06:01 PM   #6
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Originally Posted by Windows on Wash View Post
Southern California. Listed in first post.

Put a vapor barrier on the floor and seal it to the wall. Insulate the crawl space wall and seal up the crawl to create a conditioned space.
so a conditioned crawl space would be the best route? i would imagine there would be no need to spray foam the floor boards and joists then?

thanks.
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Old 10-31-2012, 11:22 PM   #7
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You are correct.

Move you insulation and air barrier layer to the outside stem wall and then just condition the space after you put down the vapor barrier on the floor.
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Old 11-02-2012, 10:41 PM   #8
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Crawl space vent and mold question


Conditioning; http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf

Termites, local AHJ will know: http://www.termites101.org/termite-b...ites-by-region

Radon: http://energy.cr.usgs.gov/radon/rnus.html

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Old 11-07-2012, 01:53 PM   #9
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Crawl space vent and mold question


I got one quote to condition my 1140 sq foot crawl space and it came out to 7k. That would include labor and materials to lay down 20mil vapor barrier, close off all vents, and insulation the foundation walls. He also mentioned a possible need for a dehumidifier but cost additional to the original quote.

That is way out of my budget. I am looking into a cheaper route.

I also got a quote for closed cell spray foam on the sub floors only at two inches thick for 2k. That is more in my range but I am a bit concerned.

I read the excellent article on the building science website and they recommended at least three inches of closed cell foam along with the joists if not a pier type constructed crawl space.

My crawl space is all vented and maybe about three feet in height. I wanted to know if you guys would agree that a closed cell spray foam on sub floors ONLY at three inches thick and leave all the vents kept open would be fine? My may concern is dew forming on the joists in the future.

Just some pertinent background, I do not have the pier construction crawl space, all my crawl space vents are currently all open with about three feet of space to crawl, and I live about two miles from the ocean in Southern California.

Thanks for you time.
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Old 11-07-2012, 09:34 PM   #10
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I presume you were referring to this article; http://www.buildingscience.com/docum...n-crawlspaces/

If so, notice no vinyl flooring above the foil-faced Polyiso. Your floor requirements for Zone 3 are R-19. Eg.- San Diego: You could use cavity R-13 batts with 1/2" Foamboard and not see any condensation or thermal bridging on the joists until 59%RH. With 1" f.b., at 70* inside, the joists would be safe at 64%RH in the crawl space. OR, add some housewrap on the joists after installing R-19 cavity insulation, no worries about vinyl above, and good for 50%RH in the crawl (air seal any wiring/plumbing holes in the sub-flooring first). The housewrap will stop all drafts if carefully installed. Foamboard/canned foam the rims, regardless; http://www.buildingscience.com/docum...l_seal_rev.pdf

As the rims in older/newer houses (if solid wood) change size with the moisture change in the air, pp. 51; http://books.google.com/books?id=iwS...joists&f=false

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Old 11-07-2012, 09:47 PM   #11
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Jim....chances are you are pretty close to me.....

Let me guess.....your house was built in the 50's? And the mold is on a North facing wall?

Just so you know....there is NO insulation in those walls. the only 'vapor barrier' is the tar paper between the stucco and studs.

I would not waste any money on trying to condition your crawl space...the humidity in our area is not enough of an issue. I live 4 miles from the beach....deal with the marine layer nightly.....we 'used' to have a mold problem on one back wall....but it was a north facing wall....the issue was not the crawl space....

The walls are pretty much sealed from the crawl space. All of your wiring is going to be in the attic.

Assuming all of the above is correct for your house....about the only solution will be to yank off the dry wall....insulate and re-drywall. As it was explained to me...once you get mold....you never really get rid of it....just make it dormate....
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Old 11-07-2012, 11:52 PM   #12
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Quote:
Originally Posted by GBR in WA View Post
I presume you were referring to this article; http://www.buildingscience.com/docum...n-crawlspaces/

If so, notice no vinyl flooring above the foil-faced Polyiso. Your floor requirements for Zone 3 are R-19. Eg.- San Diego: You could use cavity R-13 batts with 1/2" Foamboard and not see any condensation or thermal bridging on the joists until 59%RH. With 1" f.b., at 70* inside, the joists would be safe at 64%RH in the crawl space. OR, add some housewrap on the joists after installing R-19 cavity insulation, no worries about vinyl above, and good for 50%RH in the crawl (air seal any wiring/plumbing holes in the sub-flooring first). The housewrap will stop all drafts if carefully installed. Foamboard/canned foam the rims, regardless; http://www.buildingscience.com/docum...l_seal_rev.pdf

As the rims in older/newer houses (if solid wood) change size with the moisture change in the air, pp. 51; http://books.google.com/books?id=iwS...joists&f=false

Gary
yes, that was the exact article i read. it confused the heck out of me the first read. i'm still not 100% in what it states is the best methods and which are OK.

thanks for the relative humidity breakdown. from what you are telling me, the best route to take is the 1" foam boards because they take higher RH levels. should i housewarp the joists anyways with the 1" foam boards? i would imagine it would keep the joists closer to the subfloor temperature?

I live in redondo beach which is about two hours north of san diego. the relative humidity and weather is more or less the same in the southern california region though.

thanks again for the info.

Last edited by jimleahman; 11-08-2012 at 12:10 AM.
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Old 11-08-2012, 12:04 AM   #13
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Originally Posted by ddawg16 View Post
Jim....chances are you are pretty close to me.....

Let me guess.....your house was built in the 50's? And the mold is on a North facing wall?

Just so you know....there is NO insulation in those walls. the only 'vapor barrier' is the tar paper between the stucco and studs.

I would not waste any money on trying to condition your crawl space...the humidity in our area is not enough of an issue. I live 4 miles from the beach....deal with the marine layer nightly.....we 'used' to have a mold problem on one back wall....but it was a north facing wall....the issue was not the crawl space....

The walls are pretty much sealed from the crawl space. All of your wiring is going to be in the attic.

Assuming all of the above is correct for your house....about the only solution will be to yank off the dry wall....insulate and re-drywall. As it was explained to me...once you get mold....you never really get rid of it....just make it dormate....
i live in redondo beach. and yes, the home was built in 1954 with plaster walls and an "air" barrier within the walls. i have read that back then, they thought the "air" provided enough insulation. boy, that was wrong.

the north facing walls tend to be more of an issue but the other sides get the mildew as well if furniture or anything leans against the wall and doesn't let it "breathe." The problem is all along the walls where the crawl space vents are located. so it leads me to think that the draft is coming through subfloor/rim joists and causing humidity to be high in the walls inside my home that are adjacent to the crawl space vents. but yes, the north facing is more of an issue and i am glad you brought that up because i never thought about that.

i have a friend that lives a few blocks from me that had the same issue. he pulled down the plaster and took a look inside and he said there was no mold inside. he said it was all a surface issue. he put fiberglass batts in between the joists and he said the problem went away. i just didn't want batts if it was going to collect moisture because it renders it useless and ends up being mold candy later on. my friend looked in his crawl space and he says it is fine thus far. been about a year.

I have somewhat slowed the mildew formation down by using damp rid near the most problematic walls but it doesn;t solve the problem completely. i want a more permanent solution because it is occurring mostly in my kid's room.

thanks for the info.
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Old 11-08-2012, 03:00 PM   #14
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Crawl space vent and mold question


Jim....I live right down the road from you.......as in....near El Camino College.....

I don't think you need to do anything with your crawl space.

The mold issue we had was caused by furnature up against the wall. Where ever there was furnature against the wall...we had mold.

Let me guess....your also still using the in floor heater? Half in the hallway...other half in a main room?

We installed forced air heating about 6 years ago and that pretty much took care of the issue.

Moot issue now....the back half of the house is gone now.....click on the link in my signature and you will see why.....

In fact...drive down Manhattan Beach...and you will see my house...stop by...have a beer...
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Old 11-08-2012, 03:19 PM   #15
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ddawg16 - That sounds about right, forced air heating solves more than people initially realize.

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