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August 26, 11:58 PM [GMT -5]

Thank you everyone, this gives me an idea on what to do. The moisture is causing mold to come int my closet and back of house. I just dont have a large budget to pay a company. I am a female, i want to do this my self. It just Gross me out to have to go into my crawl space. Its earth and about two feet high only

May 27, 1:47 PM [GMT -5]

ThomasBrown asks a number of very good questions and raises a number of issues involved with crawlspace vapor barriers and encapsulation. I work for a company that’s been dealing with crawlspaces in the humid southeast (www.yourcrawlspace.com) for more than a decade and maybe I can help.

There are many good articles written by “experts” on crawlspace vapor barriers and crawlspace encapsulation on the web. The EPA (http://www.epa.gov/indoorairplus/technical/moisture/1_4.html)
and the DOE (http://energy.gov/energysaver/articles/moisture-control) have some very good information. The best information is from Advanced Energy, a nonprofit who did much of the early research on crawlspace encapsulation. This link is one of many and leads to links with even more information. (http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Closed%20Crawl%20Spaces_An%20Introduction%20for%20the%20Southeast.pdf).

The experts tell us that in most cases crawlspace moisture does not come from the soil or foundation walls. It is the result of warm moist air entering the crawlspace through the vents and condensing on the cooler crawlspace surfaces (framing, HVAC ducts, insulation, etc.) much like a cold iced tea glass will sweat on your kitchen table in the summer. In most of the country, crawlspace encapsulation is the only solution. The time and material cost for encapsulation vs. a quality vapor barrier is not that much different, so it makes sense to me to do the encapsulation.

With regard to ThomasBrown’s specific question, first of all, one day is not enough time to budget for this job. It takes an experienced crew of two or three, two or three days to do this kind of job right. Proper preparation alone can take a day.

Six mil plastic may be appropriate for covering firewood but it’s not the best choice for a crawlspace vapor barrier. What you’ll buy in your local hardware store tears easily and is not treated to be ultraviolet light tolerant. It will become brittle and crack in a matter of just a few years. As ThomasBrown is discovering, this is not a job you want to repeat in just a few years. Yes, reinforced and ultraviolet light tolerant vapor barriers are more expensive but they will last the life of the house. If you intend to live in your house for more than another five years, using inexpensive plastic is penny wise but pound foolish. Quality vapor barriers are sold in more manageable dimensions – generally ten to twelve foot widths. It is also easier to cut the material outside in the yard than in the crawlspace. Shop around. There are a lot of quality vapor barriers available.

If you install a quality, reinforced vapor barrier, there will be no need to put cement (I assume you mean concrete) on top of the vapor barrier.

The experts also agree that it’s necessary to attach and seal the vapor barrier to the foundation wall. This is a requirement of the international energy code that most states have adopted. That is problematic. No adhesive will attach a plastic vapor barrier to a concrete foundation so most reputable contractors use a combination of Tapcon screws, Hilti Guns, Ramset nailers, plastic anchors pushed into predrilled holes, or hand-driven concrete nails in combination with furring strips, caulks, expensive tapes, mastic tapes, or liquid mastics. As ThomasBrown is discovering, not a simple task in a two foot crawlspace.

The only alternative is a patented wall vapor barrier called the Crawl Curtain that was developed to attach and seal to a foundation wall with adhesive. It can save hours (even days) in the typical confined crawlspace vapor barrier installation. The Crawl Curtain is sold in various widths including a two foot width appropriate for sealing piers. We’ve tried all the alternatives and the Crawl Curtain is the only one that works.

The two-by sitting flat on your foundation wall is called a sill plate and the vertical two by ten or two by twelve is your rim joist. Most building codes require that the wall vapor barrier be installed four or six inches below the sill plate, exposing a little bit at the top of the foundation wall. This is to allow for termite inspections. If you are going to install rigid insulation (foam board) come down another inch or two with the vapor barrier. Foam board is very light-weight so a small bead of foam board adhesive above the vapor barrier will hold the insulation in place. The experts recommend insulating the walls of an encapsulated crawlspace. Since your floor is already insulated and is in good shape, leave it in place, even if insulating the walls. Be sure your wall insulation is low VOC and fire retardant.

One of the comments here expressed concern about wicking behind the rigid insulation. Building codes require the insulation start four to six inches below the sill plate and terminate four to six inches above the floor to prevent wicking.

Finally, if installing just a quality vapor barrier, I recommend attaching and sealing the vapor barrier to the foundation wall twelve inches above outside grade.

April 13, 10:37 PM [GMT -5]

I am working on this project now. I bought the 6 mil plastic, but I hear of 20 mil plastic which isn't at the local hardware store. Dealing with the 6 mil plastic is rough. It is 20 feet wide and costs $ 98 for 100 feet. That will cover the crawl space. I have so much work just to get to how I adhere the plastic up the wall on cement blocks. I insulated the floors; that part is complete. I have the wires and flex pipes for HVAC taken care of. I have removed the 50-year old plastic which also was 6 mil best I can tell. I have removed the debris from the basement. Each sentence here on this post is a day's work by itself. This is an unreal amount of work. I had to stop and go to hardware store to buy goggles that wrap my eyes because all the goggles I have I used outside with the weed-eater and tools like that and I cannot see under there. I have installed light fixtures throughout the crawl space. I still need a flashlight with me during the bright sunny days under there. I am just whining. Need to vent.

Your 1st step is excellent. I have done that, but you telling me I should have done that, is a reinforcement you are starting off on the right track.

2nd Step. How am I supposed to fasten the 6 mil paper to concrete blocks ? Why 6 " up " I think how far up depends on how high the vents are. Vents are most important. I cannot imagine the cost of having a self-contained system for the 60-years this crawl space has existed to-date. And, what happens with such a system when it fails in the 60 years ? Landscape fabric stakes to hold it down is a great concept too. I have no idea what it is, where I get it, what I am asking for, and why I would want to purposely punch holes in a $ 100 sheet of plastic I have already purchased and starting working with now. Great Scott is it rough dealing with 20' x 100'. You cut off 10 feet off the roll and you have 10' x 20'. I have to deal with the support columns in the middle of the home. I see folks go up the support columns with the 6 mil plastic. I have no concept of how they do that when you look at their completed task. I see this as a 3 month project since I have a day-job obviously and have the do this Saturday and Sunday mornings only. In fact, it is Spring now and I have mowing, weeding, grass seeding, planting, trench composting, hedge trimming, car washing, Spring home cleaning, painting, and oh by the way, that assumes there is nothing that goes wrong requiring me to work on that too. Projects such as this one require as much thought ahead of time, as can be contemplated. I do not wish to re-do this work again in the next 60 years. So, what I am doing now is for the next guy, since I will not outlive this project's lifetime. The workers in the last 50 years have totally destroyed the vapor barrier. It's useless now.

Mine is dirt. I wonder if folks aren't giving advice for cement crawl spaces ?

Should I stop and put some cement on the top of the dirt first ? That would be very hard to crawl on the next 50 years, no matter how smooth I can make it down there now.

My crawl space is like 2 feet dirt to top. I have no room to work. Pictures I see are 4 feet crawl spaces. I would die to have even a 3 feet crawl space.

Should I stop and dig it out to 4 feet ?

I'd love to do that too.

Cover exposed foundation walls with 1-1/2 in. of rigid, moisture-proof insulation. How do I do that ? What is that ?

I do not know what a rim joist is or rigid insulation, either.

Termite barrier ? This is the 1st I've heard of that. I had termite actual treatment again since the home is 60 years old. I've done that now 3 times. I have thought about spraying for bugs down there while I am there, not sure before or after I put the plastic in ?

Great article. I could spend as much time addressing my questions from it, as it allows me to do the whole job.

1 Day.

Not if it was a 5 feet by 5 feet space, could I accomplish the tasks.

I think I am in a half the home's width concept right now. I've got the materials. I have no idea where to start. None. But, I don't have thousands to pay a company to come do a half-way job and leave me with decisions I'd like to make myself.

February 02, 9:48 PM [GMT -5]

We had moisture problems in the summer. I took digital pictures & one showed water streaming off a vent. We have now sealed up all the vents (as recommended), replaced our older unit, replaced all the ductwork (they now have an open vent or two in the crawlspace), wore protective masks & etc and scrubbed off mold with tea tree oil & reapplied the tea tree oil as
a preventive for further mold & have had a vapor barrier installed on the foundation floor which was overlapped & sealed with Mastic. After research, we decided to seal the brick & masonary foundation walls with Radon Seal (masonary) and LastiSeal (brick) & hope we won't need further insulation on the walls. We figured if it prevented water from coming in basement walls it should prevent moisture from coming from the masonary & bricks. Hope this helps.

July 03, 11:03 AM [GMT -5]

not yet done. very helpful

March 27, 8:19 PM [GMT -5]

Working on insulation at the moment, then come back with vapor barrier. My crawlspace has a sump pump, and moisture runs by block foundation to sump pump, so not sure system will work for me. Thinking of using 1 x 4s attached below vents, and keeping the space vented.

Any suggestions on screws to use to hold the vapor barrier and 1 by 4s?

February 14, 12:53 PM [GMT -5]

For the most thorough website to answer all your questions pertaining to crawlspaces visit http://crawlspaceinfo.com This is the most helpful site that i have found.

August 03, 4:18 PM [GMT -5]

I understand that the ISO boards are great in R per inch, (what is shown against the concrete) but that they can wick up water. For that reason would extruded polystyrene be a better choice?

June 18, 9:47 PM [GMT -5]

My contractor says that the ground level under the crawl space should be ABOVE the outside ground level. Is this correct? The photo clearly shows the the crawl space ground level is BELOW the outside ground level.

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How to Install a Vapor Barrier in a Crawlspace

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