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Old 01-12-2010, 11:41 AM   #1
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Installing a Vapor Barrier into existing crawl space


About 1/4 of my basement is exposed dirt and needs a vapor barrier installed into it. I have the plastic (6 mil) to lay in, but I'm not sure to to secure it so it doesn't just all end up sliding down to the low end of the space. I've done some browsing online and what I've seen has the seams taped and the plastic bolted to the wall using 2x4's to secure it. In an existing construction is this the best method to attach it? I have also read something about using plastic garden stakes as intermediary fasteners. I know the amount of vapor lost through the holes created by the stakes is minimal - I just don't know if there is a better way to go about it.

In the near future I (or someone) will need to get up in the space to re-wire somethings and I don't want to have to re-install the plastic every time the crawl space is used.

In short -

Tape? What kind of tape should i use?
Fastening to the wall in some way - how?
Intermediary anchoring of some sort?

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Old 01-12-2010, 02:21 PM   #2
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Installing a Vapor Barrier into existing crawl space


I would like to know this also have the same thing.

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Old 01-12-2010, 02:46 PM   #3
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Installing a Vapor Barrier into existing crawl space


I do not have the book in front of me

But the book

Foundations and Concrete Work - put out by Taunton Press
Revised Edition

There is a whole chapter about sealing up a crawl space.

The best I can remember they used a tapcon type screw and screwed it into the sill wall.

I am sure you can find or by the article at Finehomebuilding.com

They are the affilate of the book

I think the chapter name was "Sealing a Crawl Space"

It was detailed and would recommend reading it. I will read it again when I get home this evening and post on it.
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Old 01-12-2010, 02:53 PM   #4
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Installing a Vapor Barrier into existing crawl space


http://www.finehomebuilding.com/how-...42&ac=ts&ra=fp

there's the article but it requires a paid membership

I'll keep digging around to see if I can find some more info. Thanks for the info on the site though - it looks like a good one!

edit: http://www.crawl-space.com/PDF/FH_sealingcrawlspace.pdf and there's the article! gogo google! (if for some reason linking that is against ToS I'll happily remove it!)

Last edited by cellophane; 01-12-2010 at 02:57 PM.
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Old 01-14-2010, 03:29 PM   #5
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Installing a Vapor Barrier into existing crawl space


I've done mine, and here are my suggestions: Forget the 6 mil poly from the home center, and buy a real Vapor Barrior.

I purchased Stego Wrap (online from Hvacquick.com) (I have no interest in either the manufacturer or vendor), after much research.

It's available in 15 or 20 mil...I used the 15. It's thick enough and strong enough to stay in place on its own. I used the Stego Tape to seal overlaps.

This stuff is not a vapor retarder...it's a barrior. Moisture cannot get through. I cannot speak highly enough of this material.

No matter what you use, you only want to do this job once. It's a pain...so do it right the first time, IMO

Rod
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Old 01-14-2010, 07:47 PM   #6
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Installing a Vapor Barrier into existing crawl space


I know a guy who paid good money to get a real opinion. I got to listen in for free.

The certified professional said to use "just plastic." Overlap it a foot or so. No need to tape. Let it lap up the sides of any posts or what have you.

The idea is to stop 99.999% of the moisture, not 100%.

And where we live there's a ton of moisture. Probably more than almost anywhere else in the 49 states not counting the island.

I'm getting ready to do this very job myself. I got a roll of plastic that's 8x400, because I've got posts on roughly 8' centers, so I can just pull the plastic up between the posts and cut it off. Then move to the next section.
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Old 01-14-2010, 08:00 PM   #7
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Installing a Vapor Barrier into existing crawl space


You absolutely do want to seal the overlap and seal the seams and affix the sheeting to the crawl space walls. There are many ways to do that. I've seen everything from construction adhesive to the 2xlumber fastened to the walls. The construction adhesive will work, but will fail if it is subjected to repeated pulling. If you are not using that crawl space for anything and are not getting into it frequently, then the adhesive can work. The whole purpose of a vapor barrier is to stop vapor which rises or diffuses from the high concentration, (the soil or gravel under it), to the lower concentration, the ambient air in the crawl space. If you don't implement this source control of water vapor it can condensate in the flooring or floor insulation (if the crawl is unconditioned) and ruin it. It can also be absorbed into the floor covering (wood, carpet pad, carpet, etc) and damage or distort it. This water vapor can also be the culprit or at least a contributing factor to condensation on the warm side of the windows in the winter.
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Old 01-14-2010, 08:46 PM   #8
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Installing a Vapor Barrier into existing crawl space


I suggest using Acoustical Sealant as a caulk against the wall, cover it with the poly, then a batten ( 1x4 or 2x4) over it (nailed/screwed in).
The Acoustical Sealant will 'seal' the poly very well. It is messy. Be careful using it.
And yes, tape the joints/seams in the poly as well as any post openings where you need to have the poly around.
Also, consider placing sand over top of the poly to hold it in place. not gravel. screened sand.
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Old 01-14-2010, 09:11 PM   #9
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Installing a Vapor Barrier into existing crawl space


"so it doesn't just all end up sliding down to the low end of the space." ------ dig some level spots, filling sand bags to put there after the plastic is spread, leaving enough looseness to move somewhat. 4 mill plastic is a vapor barrier, as is 6 mill, just one will rip or tear easily. If in a termite area, recommend not running it up the wall more than 12", or can't see their tunnels. If any mold, the solution is: http://www.buildingscience.com/docum...n-crawlspaces/

Be safe, Gary
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Old 01-14-2010, 11:18 PM   #10
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Installing a Vapor Barrier into existing crawl space


Quote:
Originally Posted by pyper View Post
I know a guy who paid good money to get a real opinion. I got to listen in for free.

The certified professional said to use "just plastic." Overlap it a foot or so. No need to tape. Let it lap up the sides of any posts or what have you.

The idea is to stop 99.999% of the moisture, not 100%.

And where we live there's a ton of moisture. Probably more than almost anywhere else in the 49 states not counting the island.

I'm getting ready to do this very job myself. I got a roll of plastic that's 8x400, because I've got posts on roughly 8' centers, so I can just pull the plastic up between the posts and cut it off. Then move to the next section.
This is just my opinion, and I'm no expert. But When you want to seal to keep out moister or whatever it sounds silly to me that you wouldn't actually seal it, just overlap it. Again I could be wrong, but him saying just use plastic doesn't sound right.
Different types of plastic I would think would break down faster over time and would stand up differently when being moved around. ( Because the fella said that he would need access from time to time. ) So I think the min. would be the 6" .
Not sealing the joints would be like, when you put your left overs in the fridge laying the plastic over it but not wrapping it under the plate, or around the cover of the bowl I would think. The food inside stays fresh longer if you wrap it.

The reason your post caught my eye was that I went into city hall and was asking about Vapour barrier. I was insulating a place and it was my first project. I had two contractors give me different info. One said the use the 6 mill and the other said don't waist your money, get the cheaper stuff. I always want to save money, but I didn't want to waist the money I had already spent on the insulations etc. just to save $50 on plastic. Cityhall, building inspector said code was 6 mill and the other plastic I was told about he wouldn't wrap in sandwich in. So that has stuck with me all these years.

I would check with your local city hall. You can call them or go in and see them. You know that they will know the answer to your questions and if they don't they can find the correct answer. They don't charge you money to get the answers.
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Old 01-15-2010, 05:00 AM   #11
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Installing a Vapor Barrier into existing crawl space


If the OP wishes to do much moving around after placing the plastic, he will be sorely disappointed if using untaped 6 mil. Ask me how I know.

Pyper: Certified Professional? He may have many abilities, but who provided his certification in this area? What he recommended is not what the latest studies show to be the proper way to do this.

Sure, the way he described will slow down vapor transmission. But as one who has spent hours in a 16" tall area, I want to only do it once

Rod
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Old 01-15-2010, 08:43 AM   #12
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Installing a Vapor Barrier into existing crawl space


Quote:
Originally Posted by RoyalAcresRod View Post
But as one who has spent hours in a 16" tall area, I want to only do it once
my thoughts exactly. although its more than 16" high - its an odd little condition... i'll try and get some pictures over lunch. it is actually part of the basement that isnt concreted in, no idea why not however so it does receive some ambient conditioning.

back to the original thought - is there a specific type of tape to use? the article in fine home building uses tyvek tape, just not sure if there is another type or brand to look out for if i cant find that.

i appreciate the input so far.
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Old 01-15-2010, 08:59 AM   #13
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Installing a Vapor Barrier into existing crawl space


This paper is the latest and most comprehensive research on closed crawl spaces:

http://www.advancedenergy.org/buildi...0Southeast.pdf

Now, if one lives in the area of the country without much humidity, a ventilated crawl space may do just fine. I live in Oklahoma, and had many of the problems outlined in the research, particularly:

In the summer, when it's 95 degrees and 80-90% humidity, air would flow into the crawl space. Of course, in there the temperature is much lower, 75-80 degrees, and with a dew point in the same range.

So of course the incoming sir would lose it's moisture....and my pipes and framing members would be dripping with water...a perfect place for mold and wood-destroying organisms.

My A/C would work overtime trying to get all the humidity out of the house.

I can now keep my thermostat at a higher temperature in the summer, and be just as comfortable. And the musty smells in my 50-year-old home are gone.

Will the 6 mil poly help? Sure. But with the Stego Wrap and Stego Tape, I can slide around under the house with ease....it will not move. I'm doing some rewiring down there, and it makes it so much more comfortable. But even without the tape, it will stay in place due to its thickness.

Again, I have no financial intererst in this product. Other materials to consider are pool liner....and there's one site on the net (can't recall it presently) that sells the material that many firms who do this type of work use.

Rod
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Old 01-15-2010, 11:19 AM   #14
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Installing a Vapor Barrier into existing crawl space


Quote:
Originally Posted by RoyalAcresRod View Post


Pyper: Certified Professional? He may have many abilities, but who provided his certification in this area? What he recommended is not what the latest studies show to be the proper way to do this.

Sure, the way he described will slow down vapor transmission. But as one who has spent hours in a 16" tall area, I want to only do it once

Rod
The American Board of Industrial Hygiene. He was called in specifically to devise a mold remediation protocol that involved a vented crawlspace in the South. The original poster doesn't mention if his crawlspace is vented or not, or if he's in the South or not.

If it is vented then you're still going to get moisture in the crawl space because it's going to come in through the vents -- all the moisture barrier is going to do is to make it so you're not appreciably adding to it. The difference between 99.9% effective and 100% effective isn't going to make much difference in an application like this.

Now if it's a non-vented crawl space that would be something different. I've never met anyone who had a non-vented crawlspace in the south, reading the PDF you linked will be useful. Maybe I'll change my plans. Thanks!
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Old 01-15-2010, 11:33 AM   #15
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Installing a Vapor Barrier into existing crawl space


I was too quick to doubt your professional's certification...my apologies!

However, he may not be up on the latest info on closed crawls. The document I linked earlier is 75 pages...here's a 4-page summary:

http://www.advancedenergy.org/buildi...0Reference.pdf

In any event, I have closed mine, and this weekend am installing a dampered HVAC duct as decsribed in the pdfs. I'm perhaps going to install also a de-humidifier...we'll see.

The pdf is quite an interesting read...they even built and instrumented a number of homes to not only test the concept, but to also find the energy consumption and humidity differences between wall and joist insulation.

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