Crawl Space Ventilation

baston-bobSeptember 27, 2009

I have an addition on my house, heated space that has a crawl space under it, 8'x24' poured foundation on four sides. The only opening is about 2.5'x2.5' and I was told by home energy tech that it ok to close the opening with a sheet of plywood and NO vent opening as long as the dirt floor was all covered with sheet plastic.

The tech said that it will save energy in the house with the crawl space closed up, keeping the crawl space cooler in the summer and warmer in the winter. Also he said cement walls would disperse any small amount of moisture down there. I'm old school and thought there always needs to be some venting. I did cover the dirt floor, close up the opening with no vent grate, any thoughts?

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He's right. You would benefit even more if insulation were included. Where depends on your climate.

This site has links to many documents detailing the best approaches. (See particularly the link "Closed Crawlspaces do Double Duty.") Advanced Energy has partnered with the DOE in developing and researching energy efficient crawlspace design.

See, also the Building Science Corp. document linked below.

Here is a link that might be useful: Conditioned Crawl Spaces

    Bookmark   September 28, 2009 at 9:52AM
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I've been researching and reading about related recommendations since I bought my home 10 years ago.. and I have an opening from my basement into the crawl space - which is about 4-8" in size - SURROUNDING THE HEAT VENT (as it goes to that room). Since the room - built above a slab which was the original garage - was cooler in winter - I had two small screen vents installed to two opposite ends (in the masonry foundation) which I understood were to provide better air flow and moderate temperatures. 'No change.

My current question is how can you see/find out what is in there - insulation - plastic - whatever - as the house was orig built in 1948, etc? I have copied the links referred to above, but would like to know/understand what I'm dealing with better, to start with, if possible.

Thank you in advance for any information or advice that may help -


    Bookmark   September 30, 2009 at 4:39PM
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The room above the former garage slab is cooler in winter because the floor is likely not insulated/sealed properly. Adding vents to the crawl space certainly doesn't help.

No access to the crawl space means you're just going to have to use a powerful flashlight. You could also use miniature remote camera systems. (Link for illustration only.) I have no personal experience with them.

I've seen those "Flip This" house shows where the renovation included some poor guy sliding in on his back on the dirt past dead varmints in what looked like an 18" crawl space. Not me!

    Bookmark   October 2, 2009 at 5:21PM
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Thank you. I've tried the best flashlight I could find and still can't see much of anything. I expect the floor isn't insulated - and I'll seal the vents I had put in back up again. There's some old insulation hanging around the heat air vents going into the space: I've been afraid to seal that up too much - but from what I read in the links you posted - it should only help. There's a red pine wood floor in the room above and I hate to have to cover it all up with carpet!

    Bookmark   October 3, 2009 at 9:55AM
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QUOTE-Posted by worthy, "He's right. You would benefit even more if insulation were included. Where depends on your climate."

I have insulation between the floor joists above the crawl space. The tech said not to insulate the walls of the crawl space, just cover the floor with sheet plastic.

    Bookmark   October 3, 2009 at 5:00PM
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I live in a Double wide mobile home and my family and I are sick seems more than normal. Starting to think something in / around our house is making us sick. We keep our house liveable clean. I put in a whole house heat exchange ventilation system and a 4 inch allergen filter in our heating/cooling system. Air got a little better but we still get sinus infections often. I'm working on a project to vent the crawlspace air through none load bearing walls via multiple 2" conduit pipes. These pipes that will be spaced throughout the house will have 1/4 inch wire mass to block unwanted rodents but won't restrict air flow. The attic will be forced vented with two 1600 cfm roof power vents. I'm thinking that this will create a negative air pressure in both the crawlspace and the attic thus stopping air from unwanted areas entering the living space. Our house has already been sealed tight from a project to reduce our power bill years earlier. The crawlspace will have self opening wall vents and we were thinking of partly sealing the eaves vents to force more air from the crawlspace through the attic. The foundation vents will open at 40 degrees and I was thinking of setting one roof vent to start at 50 degrees and the other at maybe 60 to 80 degrees. I know that the air under the house is cooler and warmer air flowing there will release moisture creating higher moisture in the crawlspace but I was thinking if we get more air flow maybe this will correct inself some. I was wanting any comments pros and cons of this idea. I lived in this mobile home many years without brick underpining and didn't have half the problems we now have. Our sinus problems got worst when we sealed our home to save on energy. I don't want to go back to $400 a month power bills but don't want to stay sick either. We live in South Carolina so winters are mild and summers hot.

    Bookmark   April 9, 2011 at 10:39PM
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As I understand it, what you're proposing makes no sense and, having read the literature, you know it and yet you persist.

I have extreme allergies to fur and feathers, so I appreciate your desperation. Perhaps the problem is not the crawl but elsewhere--such as water damage leading to mould growth in the walls or attic or sub-floor structure.

    Bookmark   April 10, 2011 at 5:42PM
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