Crawlspace...vented, or not vented?

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  #1  
Old 03-13-08, 11:53 AM
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Crawlspace...vented, or not vented?

I spoke to a vendor at the local home & garden show and they were touting the benefits of not having any ventilation in crawl spaces? Said it contributed to moisture and other issues during both summer/winter and was old fashioned conventional wisdom. Had lots of literature supporitng the theory. Almost makes me want to close/block off my vent spaces because it makes sense.

Is this good info, or are they just blowing wind to promote their encapsulated crawlspace products?
 
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Old 03-13-08, 12:01 PM
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Your vendor is a very smart man!
 
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Old 03-13-08, 12:12 PM
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So are you agreeing with that philosophy?
 
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Old 03-13-08, 01:16 PM
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After having just talked about this a couple of weeks ago with a home inspector after finding a little mildew in the crawlspace of the house we were going to buy, I can tell you what he told me. He said that "if it were his house" he would close up the vents.

But you can't just stop there. You need to get some air circulating in the crawlspace too. A vent from the heating system will keep the air from becoming stagnant. Don't just tap into your system anywhere though. You could mess up the balance to the rest of the house.

And a dehumidifier, with a condensate pump plumbed to a drain to get rid of any moisture it draaws out of the air, will take care of any moisture that does creep in from anywhere.

If you do all that you should never have any trouble with moisture (moisture in the air, that is) in the crawlspace.
 
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Old 03-13-08, 01:41 PM
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This article from Building Science Corp. discusses unvented crawlspaces and gives the details, some of which the previous poster already mentioned.

http://www.buildingscience.com/docum...archterm=crawl
 
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Old 03-13-08, 02:28 PM
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Originally Posted by formula1 View Post
This article from Building Science Corp. discusses unvented crawlspaces and gives the details, some of which the previous poster already mentioned.

http://www.buildingscience.com/docum...archterm=crawl
That's a very cool site. It looks like lots of great information. Some of it looks to be over my head, but it looks like great info none-the-less.
 
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Old 03-17-08, 12:01 PM
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Okay but what about the basic choice between closing off existing vents, or simply leaving them be? No conditioners, or gadgets/gizmo's. Without gizmo's, wpould it simplky be best to leave it be or as is?
 
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Old 03-17-08, 01:29 PM
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Wow, what a site. What a cost factor. Condition the air in the crawlspace????!!! Sheesh what a load. It may work in some areas of the country, but you have to move the air in the crawlspace to keep the moist air from getting stagnant and molding. The set up this fine gentleman (and I am not degrading his credentials, please) is proposing would add $20K to the cost of a new house and would run your heat and air conditioner, not to mention a dehumidifier almost constantly to "condition" the air. I have tough enough time conditioning the air where I live, much less where no one lives. 6 mil poly on the ground, open the vents, let the natural breezes move the air with sufficient venting. I said sufficient venting. Putting 2 vents in the foundation is not sufficient. They must be on all sides and be no less than 8 feet apart. We go through this every time someone opens this can of worms. Now, at least, you have an opposing viewpoint. I live in the South and the Southern Building Code adheres to venting the crawlspace, so we are left with little option. Works just fine in our climate. Maybe not in Nova Scotia or New Orleans.
 
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Old 03-17-08, 01:42 PM
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Actually, your furnace and/or A/C unit won't run any longer at all. Unless you put the thermostat in the crawlspace, that is. I'm also assuming you didn't just cut a hole in a supply run somewhere and stick a vent in it. That would draw conditioned air from somewhere else; possibly the room with the thermostat in it. If the vent for the crawlspace were run properly, it shouldn't impact the rest of the system.

Incidentally, I'm talking about a crawlspace that has a concrete floor. I wouldn't consider doing this in a crawlspace with just a dirt floor.
 
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Old 03-17-08, 02:37 PM
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we regularly replaced,,,

static foundation vents w/power'd vents hook'd to a humidistat for auto operation,,, seems to work find down here in ga/sc,,, we also place vapor barriers where none existed previously as part of the project.

completely closing a crawl space's not an option here.
 
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Old 03-17-08, 06:29 PM
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I love this guy!!!
 
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Old 03-18-08, 06:36 AM
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call when you're in marietta,,,

we'll sit on the back deck, lie, spit, & tell stories
 
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Old 03-18-08, 12:21 PM
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Wink

Ill go the other way. For over 40 years now we have closed up and sealed all crawls spaces. Now if a cement floor or dirt They both have to have a 6 mil poly down on the ground there with a 2' over laped and all seams taped. 2" or 3 " Insulation on the walls up to the joist line. Then a block like of R 19 in each joist space up there on the sill plate all around the home. We also put 2 small registers for out and a small return in the duct work for down there. This makes the crawl space work as a heat sink for you year round. Test homes that they had down in Florida show that the sealed up crawl cost about 5% less on fuel bill for heat and cool.
Go to http://aboutsavingheat.com/crawlspace.html
Have gone into many homes and had to rework the crawl space that has gone bad because of the vents. Also have did job's where the floor is made like the outside walls insulation and siding on the bottom With say no walls and open all under the home
 
  #14  
Old 03-19-08, 11:18 AM
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Hmmm, so i guess it's a bit of a crap shoot and every situation is different. So in essence, I can "assume" if I have plenty of crawl-space vents it's maybe best to go ahead and leave them open as long as I have a good vapor barrier down over my dirt floor area (space is flat and about 3-4' high). I also occasionally pop open the crwl-space entrance door and prop a fan in the opening set on high for several hours at a time just for kicks to keep it dry and chase out the occasional musty air, especially during periods of high humidity.
 
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Old 03-19-08, 03:22 PM
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Boater You said everything you need to say. You can not keep mold from growing with open vents in green grass states. Hard to keep crawl dry when you are bringing in 70% RH air. You all ready have some mold because you said it smells musty. You are smelling the spores breaking off the mold.
 
  #16  
Old 03-19-08, 03:45 PM
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Sounds as if there are as many opinions as there are people here.

Just an aside: The Permit office here just recently changed their requirements from vented crawlspaces to non-vented but "properly ventilated". As relayed by the head of the permit office - a simple, small hole in an existing HVAC duct will suffice - providing positive pressure in the enclosed space - thereby reducing humidity/mold/etc... The floor/dirt/gravel has to be covered with a 6 mil poly sheet in this situation.
 
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Old 03-20-08, 11:13 AM
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I'm getting ready to go rent one of those mold misters from THD to set in the space and mist out a couple of gallons for good measure. I bleach-watered the space using a plastic garden sprayer over all the joists etc. last summer in an attmep to cut down on osme of the mustiness that builds up in the back bedrooms when the doors have been closed for a few days.
 
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