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Old 01-21-2013, 09:36 PM   #1
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Venting a concrete basement crawl space?


Does an unheated concrete crawl space need vents open in the winter?

My home has a full basement that is unfinished with a concrete floor, and then the house had an addition put on and the foundation below that addition has a crawl space with a concrete floor, but it is only about 4+ feet tall. So if you are in the basement of the house, you have a step up into the basement area underneath the addition.

It gets super cold in there in the winter, and we store stuff down there so I was thinking of closing the vents. I read that many people debate on keeping the vents open versus closed. What's the right answer?

Right now it is connected to the basement, but I have a door in-between so I typically keep it closed to keep the cold out.

Overhead is insulated for the floor of the addition above. The walls are concrete block, and the floor is too. It is below the grade other than about a foot or so that he addition sits on.

We are in Connecticut so its gets super cold, and super hot.

Can I close the vents or will it cause mold to form from the cold/hot of the seasons?

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Old 01-21-2013, 09:44 PM   #2
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Venting a concrete basement crawl space?


They should have been closed as soon as it started getting cold out unless you want frozen pipes and cold floors.
Post a picture of the vents you have now, You may be able to replace them with automatic opening vents and never have to touch them again.
Just knock your out with a maul and slide the new ones in.
http://www.ebay.com/itm/Solar-Tek-Au...item4ac049a10a

You may need a dehumidifyer in the basement.

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Old 01-21-2013, 10:19 PM   #3
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Venting a concrete basement crawl space?


It is my understanding that crawl spaces are not vented. Every house is a living being and it seems like you need to figure out what works best.
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Old 01-21-2013, 10:23 PM   #4
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Venting a concrete basement crawl space?


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Originally Posted by joecaption View Post
They should have been closed as soon as it started getting cold out unless you want frozen pipes and cold floors.
Post a picture of the vents you have now, You may be able to replace them with automatic opening vents and never have to touch them again.
Just knock your out with a maul and slide the new ones in.
http://www.ebay.com/itm/Solar-Tek-Au...item4ac049a10a

You may need a dehumidifyer in the basement.

Thanks for the input so far. There is no plumbing under this portion of the basement since it is only an addition that has no bathroom, just one large room so there is no worry of frozen pipes.

Currently there are 2 vents, one on the side, and another on the opposite side of where the addition connects to the house. They are the plain metal type that has a screen and the bars that you can slide open and closed. It looks sort of like this:


I looked all around for those automatic vents in local stores and couldn't find them, should have checked eBay.

Seems like there are a lot of people that are hell bent on them being vented, and others say it doesn't matter. Since I don't have a dirt floor, my guess is that it will probably be better off with an automatic one that opens or closes, or just have it closed off and then monitor the humidity.
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Old 01-21-2013, 10:48 PM   #5
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Venting a concrete basement crawl space?


Any Lowes Home Depot, local lumber or building supply should have them.
I keep hearing over and over about venting or not venting.
I've worked for many years on mostly older home where the insurace companys would make the homeowner seal up the crawl spaces if there was ballon framing.
The house was fine before it got closed up, I know because I inspected it long before being closed up.
Go back years later and the mold and fungus everywhere.
I've seen 7 year old houses built with no vents at all and we had to change out most of the floor joist because of fungus.
There may be differant conditions in other areas of the contry but around here there not even going to give you a permit with out including vents.

Those vent you have will just pop right out with a big hammer and a flat bar to snap off the top part.
I've done a 1200 sq. ft. house by myself in under an hour.
I have a system, I buy them by the case, I get out of the truck with the box and walk around the house and drop one in front of each vent, Next circle I remove the old ones, one more time and install the new ones. Then use the empty box to pick up the trash.
Only trick is to make sure there right side up, and do not over tighten the screws of the louvers bind up.
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Old 01-21-2013, 10:56 PM   #6
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Venting a concrete basement crawl space?


I close mine the minute cold weather shows up. I keep them open in warm weather. I have four two on back two on side. Mine have a push lever in the middle to push open from outside.
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Old 01-21-2013, 11:06 PM   #7
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Venting a concrete basement crawl space?


If you look up the CFM ratings on both style vent the auto opening of have much higher CFM.
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Old 01-21-2013, 11:09 PM   #8
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Venting a concrete basement crawl space?


Thanks for the tips and input.

Sounds like at the minimum I should be manually opening and closing them for winter/summer.

I'm going to measure the vent and see if it is a standard size, and if so i'll probably get the automatic vents.
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Old 01-22-2013, 03:48 AM   #9
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Venting a concrete basement crawl space?


There are two new theories on venting a cinder-block crawlspace. One says install fans like this. http://www.rewci.com/underaire-crawl...-two-fans.html

Another says no vents. Just an air handler. Fresh-air in stall air out.

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Old 01-22-2013, 06:36 AM   #10
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Venting a concrete basement crawl space?


In my area vents are code required for crawl spaces. A minimum of two on opposite walls and they must be within three feet of an outside corner. The only exception is if the crawl space is conditioned, in which case the walls must meet the minimum insulation standard.
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Old 01-22-2013, 06:45 AM   #11
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Venting a concrete basement crawl space?


Quote:
Originally Posted by paintdrying View Post
It is my understanding that crawl spaces are not vented. Every house is a living being and it seems like you need to figure out what works best.
Your understanding is incorrect. Code in many places (including where I live) requires crawl spaces to be vented. But some locations do not.
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Old 01-22-2013, 10:45 PM   #12
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Venting a concrete basement crawl space?


Your location is under the 2003 IBC; http://publicecodes.cyberregs.com/ic..._12_par006.htm

http://publicecodes.cyberregs.com/ic..._12_par007.htm

Either/or; http://publicecodes.cyberregs.com/ic..._12_par008.htm


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Old 01-24-2013, 08:51 PM   #13
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Venting a concrete basement crawl space?


I had the same question as you did a few years ago. As I have HVAC ducting and copper water lines running in there I was always worried that the pipes would freeze. I bought enough insulation to install between the floor joists and was researching the proper method of installation (vapor barrier vs none, etc) and learned that vented crawl spaces are no longer considered the proper way to deal with crawl spaces. I ended up sealing the two vents with insulating foam boards which I caulked around the perimeter, per the recommendations of the link below. Check out this link from Building Science for the complete report.

http://www.buildingscience.com/docum...nd-crawlspaces

Ever since I insulated the rim joists and closed off the vents, the temperature in the crawl space remains constant all year round at about 62 degrees. Right now it is 18 degrees outside in the Chicago area and the crawl space is currently at 60 degrees (I have a remote thermometer probe in the crawl space that I can check here at my computer work area). I ended up using the newly purchased insulation up in the attic. My crawl space is about three feet below grade with about a foot above, with a concrete floor. The attached pic shows the rigid foam on the rim joists prior to caulking the edges. Amazing how much cold air would come through that area prior to the rigid foam being added.
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Venting a concrete basement crawl space?-rigid-foam-rim-joist.jpg  

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Old 01-24-2013, 09:44 PM   #14
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Venting a concrete basement crawl space?


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Originally Posted by Dave Sal View Post
I had the same question as you did a few years ago. As I have HVAC ducting and copper water lines running in there I was always worried that the pipes would freeze. I bought enough insulation to install between the floor joists and was researching the proper method of installation (vapor barrier vs none, etc) and learned that vented crawl spaces are no longer considered the proper way to deal with crawl spaces. I ended up sealing the two vents with insulating foam boards which I caulked around the perimeter, per the recommendations of the link below. Check out this link from Building Science for the complete report.

http://www.buildingscience.com/docum...nd-crawlspaces

Ever since I insulated the rim joists and closed off the vents, the temperature in the crawl space remains constant all year round at about 62 degrees. Right now it is 18 degrees outside in the Chicago area and the crawl space is currently at 60 degrees (I have a remote thermometer probe in the crawl space that I can check here at my computer work area). I ended up using the newly purchased insulation up in the attic. My crawl space is about three feet below grade with about a foot above, with a concrete floor. The attached pic shows the rigid foam on the rim joists prior to caulking the edges. Amazing how much cold air would come through that area prior to the rigid foam being added.
Great tips! Sounds like your scenario is almost identical to mine, except I don't have the HVAC and pipes. Maybe i'll try to insulate like you did. I have insulation already in the upper bays, but the end caps can probably benefit from some like you have installed. Thanks for the added info, and that link.
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Old 01-25-2013, 10:49 PM   #15
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Venting a concrete basement crawl space?


If your crawl space has a vapor barrier on the floor, it should be a 'conditioned' area. This means that it is not vented outside, the foundation walls are insulated with at least R12 insulation.
It is to have both a heat supply and a cold return!

I converted mine in 1999 and its been drier than the desert down there since.

Outside humid air is the source of moisture. This moisture will cause mold.

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