Q&A / 

Crawl Space Encapsulation or Not

crawl space vent

This is a typical crawl space vent that’s supposed to allow air into and out of a crawl space. They just don't work. It's like trying to breath through a small cocktail straw. © 2017 Tim Carter

Crawlspace Encapsulation TIPS

DEAR TIM: My head is spinning from all of the conflicting information I'm seeing online about crawl space encapsulation. Should it be done or should I just rely on the traditional vents I have in my foundation? I have a 1,100 square-foot crawl space and the slate floor above is ice cold because there's no insulation. What would you do if this were your home and why? - Richard J., Toledo, OH

DEAR RICHARD: I can understand your frustration. While the Internet is an amazing resource, the barrier to entry with respect to publishing is lower than the bottom of Death Valley. If you can fog a mirror and type on a keyboard, you're capable of posting your opinion about how you think things should be done on the Internet.

Bad JuJu Info

Back before the Internet, traditional book publishers would do a fairly good job of vetting an author before they agreed to publish his work. This filtering process kept much of the erroneous information out of the mainstream.

It was possible to self-publish, but those that chose to do this had a tough time distributing their work. The Internet has removed these barriers and filters.

To stop your head from spinning, let's dive into the science of crawl spaces. I prefer to base my opinions and beliefs on science, not speculation.

Bare Soil

A traditional crawl space under a home consists of soil or sand that was the ground before construction started. Sometimes the topsoil is removed, but what you see is bare soil. I've been in crawlspaces that have had concrete poured on top of the soil or some washed gravel.

Water Vapor Pump

Unless you live in the Atacama Desert, the ground under and around your home contains moisture. This liquid water wants to evaporate and get back up to the atmosphere. If you could see water vapor, you'd see a constant flow of this gas floating up into the air. When it's warm, the flow rate is faster.

Water = Mold

This water vapor, when mixed with wood, is not a good thing. If enough water vapor collects in a crawl space before getting back to the outside atmosphere, it can condense and turn to liquid water again. This water fuels mold growth and fungi growth you might call wood rot.

Old builders knew about this. The best they could do was to provide an escape path of the water vapor to the outside.

Crawl Space Vents

That's what the crawl space vents are for in your foundation. The trouble is, they don't work too well. I've been in crawl spaces when the wind is howling outdoors and barely have felt a puff of air come into an open foundation vent.

Plastic The Answer

Once plastics were gaining traction in the 1960's, thin sheets of vapor barrier were available. While not perfect, they did a magnificent job of blocking the movement of water vapor. Cross laminated vapor barriers that meet or exceed the ASTM E 1745 are some of the best products out there to block water vapor.

Tu-Tuf is an excellent cross-laminated vapor barrier that passes the ASTM E 1745 standard. This is what you want to use to cover the soil in your crawlspace.


An entire industry has evolved in the past fifteen years that specializes in encapsulating crawl spaces so the water vapor stays is the soil. When done correctly, encapsulation is an excellent way to arrest the movement of water vapor from the soil up into your home.

Puffed Barriers

Realize that other gases can escape from the soil under your crawl space and cause any plastic or membrane to puff up like a balloon. Be sure to discuss this possibility with any contractor you're getting bids from.

These same high-performance vapor barriers should be placed under poured concrete basement floors to stop water vapor movement. The same is true for any house that uses a slab-on-grade foundation. Water vapor can and does pass through poured concrete.

Stain Solver Cleaner

Oxygen Bleach

Stain Solver is MADE in the USA with USA ingredients that are food-grade quality. CLICK THE IMAGE to order some NOW.

Once you've encapsulated the soil and stopped the water vapor from entering your crawl space, I'd insulate the floor joists. Be sure there's no mold on the wood.

Clean it off using a Stain Solver.

Stain Solver is a certified organic oxygen bleach that you mix with hot tap water. You stir it until the pure powder dissolves and then pour it into a hand-pump garden sprayer.

Saturate the wood in the crawlspace, and even the soil if you want to get rid of mold and mildew.

Allow it to dry before you insulate. Put fans in the crawlspace to help speed up the drying process.

IMPORTANT TIP: I'd do all this mold remediation before I'd install any encapsulation product or system in the crawl space.

Stop Liquid Water

Some crawl spaces are plagued with standing water or running water in periods of heavy rain. You can stop this water from entering a crawl space by installing one of my linear french drains around the outside of your home.

Linear French Drain DVD

Do your own DIY install of a Linear French Drain with Tim Carter's time-tested methods and materials! CLICK IMAGE TO ORDER NOW!

My college course in hydro-geology taught me how to capture and divert water in the soil. A linear french drain is just a gutter in the ground.

As water passes through the soil sideways through the top soil where there's air, the gravel in the trench captures the water and gravity pulls it down to the perforated drain pipe.

Many homeowners like you have used my technique to dry out their wet basements and crawlspaces. CLICK HERE to get a professional DVD showing you how to STOP water problems in your crawlspace.

Column 1068


34 Responses to Crawl Space Encapsulation or Not

  1. Hi Tim,
    Thanks for the great article about crawl space encapsulation. Guess my wife was right there is a smell coming up through the floor,LOL.
    Now I know what to do about.
    Really appreciate all your help.
    Joe V

  2. Hi Tim,
    If I may share my crawlspace situation with you/others. I have a 4ft high crawlspace, clay earth inside the footer is what the floor is made of. I placed some landscaping membrane down to prevent any rocks from puncturing my next layers of plastic, then 2 layers of heavy construction plastic, then pressure treated lumber 2x4's covered with PT plywood. I painted the plywood with enamel floor paint. I wasn't expecting it to happen, but mildew bloomed and the smell was horrible. I have no ventilation in this crawlspace. I tried to run a dehumidifier, but it did nothing but absorb some air moisture and run pretty much constantly. After it burned up and having high electrical bills, I thought of something else. I cut a 6"x8" hole in the floor over the crawlspace area on 1 end and covered the hole with an attractive 'cold air return grill'. On the far end, I drilled a 4" hole in the foundation of the crawlspace and installed a bath fan in the crawlspace ceiling joists and exhausted it out the hole in the foundation to the outside. Air from my living space is drawn down into the crawlspace and crosses the entire crawlspace and is exhausted out of the house. I sanitized the entire crawlspace and I have had no more issues with mildew. Yes, it is sucking heated air out of my home in the winter time, but having no smells/mildew in my crawlspace which I use for storage is worth it to me. I have usable storage space now for seasonal items without any fear of items being ruined by mildew. No smells enter my room over my crawlspace either.

    • I would suggest: Using an exhaust fan that's typically made for radon evacuation rather than a bath fan unless it's designed for 24-7 operation (like radon fans).

      If anyone stores anything in a crawl space it should be limited to non-organic items and stored in sealed plastic tubs or containers.

      No paper/printed material of any kind. One may have conditioned their crawl space but also ensure that it's free of vermin and animal intrusion as well.

  3. Hi Tim,
    Interesting story. It should be code to encapsulate crawl spaces in this day and age. I found 10'' of water in my crawl space because I lost power.
    I have a backhoe and dug a 5 foot deep trench with drainage to the river front making sure I was high enough not to get back flow when the river is at flood stage. I added a check valve to keep critters out. The concrete contractor did not put down a proper vapor barrier. I had to bring in 14 ton of fines gravel and then encapsulate with a fiberglass liner. The 2005 code called for mechanical venting. They cut a 6'' hole in the utility room by the furnace and cut a diffuser in the crawl space main duct. Before my work I thought I had wall leaks from all the condensed water on the perimeter joist board. I put in an extra sump pump with my first attempts and tied them to a separate 4'' line to the river but the 4'' fabric covered drain catches all the water and will run for months in the Spring down my boat ramp. I now have a dry storage crawl space and run a humidifier timed for 8 hours a day during the humid months for good measure. I researched on the Web and read that up to 12 gallons of moisture can come into a gravel crawl space everyday. For me encapsulation was the only thing that made sense.
    Thanks to your videos I tackled building out my raw attic space. You have the best videos.

  4. Tim, do you have any suggestions for mold remediation in basements that already have a poured concrete floor (which probably was done improperly)?

  5. My wife and I have been gathering quotes to complete an crawlspace encapsulation project – the issue has been is that there has been little product comparisons on the actual vapor barrier products. Do you have any opinions on the various 16-20mil products? I’ve read about Cleanspace, WhiteCap, Crawlspace 1800, Silverback. The various companies all do the marketing on why you should select the one they're selling.

    The reason why I ask is to ensure that we’re not installing an inferior product, one that emits VOC’s (if this is a problem?), if anti-microbrial or fire retardant treatments contained in the plastic present health risks. There is very little information on the web comparing products or providing recommendations (other than those that are being sold by a franchisee for example)

    I've found surprisingly little objective product comparisons on the web. Thanks so much for your help.

    • Hello found your web site accidentally very informative. I have a dirt crawlspace 7' by 12' which is under the kitchen, there are no outside vents. The crawl space is open on one end to a finished concrete basement, the crawl space is dry and no mold. I did a radon test in the crawl space, came back at 29.6. My question is would a 45mil rubber fish pond liner be as equal or better than the plastic liners? Thank you for your time!

  6. Interesting but only historically to me. Down here in the SE Texas swamp, everything is on a slab so we do not have crawl spaces. Back in a previous life in the 1950's, the dirt floor crawl space was critical as that was our version of a root cellar. I was the one who had to crawl under and lay out the newly dug potatoes in a single layer and then go into pick up 2 or 3 for mom to bake for Sunday dinner.

  7. Wow!!! I can't believe it. I had a perfect score. It is making my day. I was so sure that I am not going to get one answer correct.

  8. I'm having a nightmare with an encapsulation project. We had our crawlspace encapsulated in Jan because every summer the warm air would hit our cool ductwork and cause condensation and moisture and then mold. So the crawlspace was encapsulated by a professional company and they put in a dehumidifier, and they finished the adjacent room. Now this summer, we started having water drip through our first floor ceiling. We had a plumber come in think it was a plumbing issue. He opened up the ceiling and to our horror our ductwork is condensating all throughout our home. Now since this has happened all summer, we have several area of drywall and mold issues and now our hardwood floor needs replaced. The company that did the work is stating the dehumidifier is putting off so much heat it's going through the floor boards and creating the heat between the floors and then the condensation. They said we may need to run a hvac line in there. What is your suggestion?

    • Kim,

      I read your post and am having nearly the same problem. We haven't encapsulated yet, but the cupping of my new hardwood floors is driving me insane. Have you found a solution

      • If both you and Kim are having condensing issues on metal ductwork, then the humidity inside the home is too high. Period.

        In Kim's case her AC unit may be sized too LARGE and is short cycling NOT running long enough to extract the moisture in the air.

        Yours is doing it because of all the reasons in the above column.

  9. The house we own now had a very wet crawl space. The workmen always commented about the standing water. So we decided to encapsulate it.
    Now it's clean, dry and pure white and the workmen comment on how nice it is.
    The wood floors, however, began creaking not long after we encapsulated our crawl. My husband stapled the floor in numerous places, stopping the squeaks. Just goes to show, if it's not one thing it's another!

  10. This article opened my eyes to a lot!!! I have a crawl space with vents and the main components to the HVAC system are under there. I refuse to go...I don't like the space but to know what damage it could potentially do is amazing.

    The quiz was fun and I got 5/5...w00t!!!

    I need to get some quotes to take care of my home.

    THANKS TIM for the awakening!!!

  11. Hi Tim,
    I've got another troubled encapsulation project for you. I had a vented crawl that had no moisture problems, but the first floor in winter was like an ice rink. So we had the crawl encapsulated. They put 15 mil poly on the floor, insulated the foundation with foam boards, and installed a register vent in the duct running through the crawl to condition it. Now, seven months later, we have a serious odor coming up through the floor vents and the wood in the crawl stinks. How common is this? The installer says we have to run the AC much more than we need to stay comfortable in our home, or we'll have this problem. Seriously considering sealing the register vent in the crawl and reinstalling vents. We'd rather have a cold floor than a rotting crawlspace. Otherwise, it's good money after bad installing a dehumidifier and, I guess, an exhaust fan (after sealing off the register vent). What do you think? We're in southern Indiana, so it's not South Carolina or Georgia (yet). Thanks, Joe

    • It sounds like the encapsulation was not done right. When it is and the right products are used, the relative humidity in the space should be at 40 percent or lower.

      Check the relative humidity. You really need to do a phone consult with me. Look above in my shopping cart.

  12. Tim,
    Post-encapsulation, are there problems with too little humidity for hardwood floors? We are in the Deep South, and our only concern with encapsulation in our remodel (after getting over sticker shock) is that we may end up with problems with drying out the heart pine and oak floors that have survived in the house for the last 100 years.

  13. I built my home in 2005 and the contractor encapsulated the crawlspace. Annual inspection by my exterminating company keep commenting they can't fully check for termites due to this. Today a new person from the company that has been doing this inspection came by and handed me a note that states "Wait...Don't Encapsulate. Don't allow other companies to VOID your termite warranty. Full encapsulation may restrict effective inspections, treatments and the sale of your home." It went on to say they could evaluate my home's health and prescribe the best treatment. He said they would be contacting me and he mentioned something about a control bond. What's going on?

  14. Hi, We had our crawl space encapsulated 2 years ago when we bought our house. It was built in 1976 and had a little mold on the joists in the crawl. The week after we encaped a smell started coming up in the 3 rooms above the crawl. The company came out and put in a radon mitigation system under the liner with a fan shooting the pulled air outside. This did nothing to the smell. It gives me a headache when I go into those rooms. I can hardly smell it in the crawl space itself but can smell it in the fan that goes outside. We are completely lost....we have tried everything. The company that installed this is saying that none of it is their fault. We just want the smell to go away.

  15. Hi Tim,
    We are so glad to see this article on crawlspace encapsulation. We live in E. TX and have been struggling with excess moisture under our pier & beam home for some time. We have installed a French drain on the uphill side as well as addressing the gutter downspout drainage. All of this has helped but we still have a humid house.

    Terminix is offering two options: crawlspace encapsulation (~$10k) and Vapo Check (which is a vapor barrier that is placed on the floor of the crawlspace) (~$3000). Obviously, they are doing the hard sell on the encapsulation! This includes a dehumidifier that has a one year warranty. Our experience is dehumidifiers don’t last. It appears from some of your other readers that they are having the same experience. They also want $200/year to some out and check the dehumidifier and liner seals, change the filter and drains, record updated moisture readings and change the batteries in your monitor.

    So, we would like your opinion on having polyisonene sprayed on the underside of the floor (that is, the ceiling of the crawlspace) and installing powered vent fans. We have also found that basic crawlspace vents don’t work!

    If crawlspace encapsulation is the only way to solve this issue, do you have any tips on finding a reputable installer? We saw that one reader had this done and still have issues. You thought that the encapsulation had not been installed correctly (#11, Joe, October 2016). Of course, the installer disagrees! Another reader claims that their house cannot be inspected for termites due to the encapsulation. Holy cow, it’s our termite company that is offering this!!!

    Any additional information is helpful!
    Cheryl & Phil

    • I too use Terminix, but am having another contractor encapsulate my walk-in crawl space. My encapsulation is costing $4,900 for 1000 sq ft. 20 mil nylon reinforced 7 layer barrier on the ground and 10 mil barrier on the foundation walls. The top of the wall barrier is 3 inches below the sill to allow for termite inspections. The cost includes a commercial grade dehydrator with a 5 year warranty. If I want to pay for an annual maintenance plan the cost is $125. I think your quote from Terminix is too high.

  16. Tim,
    I live in Virginia and have a home built in 1956 with a crawl space. I recently had an inspector come out because of a refinance. He had a guy with him he was training. While under my house I was sitting in my Den and happened to hear their conversation below me. The inspector said at one point “I’m going to give this guy a clean inspection, but I’m going to sell him a full encapsulation.” I listened intently to him explain the sales tactics they we going to use on me. I. E. excessive moisture, humidity, air quality etcetera. They laid out an estimate of $5800 for full encapsulation. I paid them for the inspection and thanked them for the estimate. My question to you is this. If my home has been fine without “Crawl Space Encapsulation” for 62 years why should I need it now?

  17. Wow, I am lost on what to do. We are facing encapsulation now as well. I want to know if we have French drains installed with a sump pump along with a good vapor barrier would this be sufficient to reduce humidity levels that are acceptable? I live in Alabama

  18. I am in need of some guidance. My family and I recently moved into a home originally build in 1924. Since the first day we moved in I have noticed it had an "old house smell" and when it rains the smell becomes particularly noticeable. I went down to the basement and noticed along one of the duct work lines condensation. I am concerned possible mold/mildew growth from the condensation in the basement could be causing the smell, causing structural damage to our home or cause breathing issues in the future. I have been looking into encapsulating our basement; however, I am unsure if this is the route I should take. It is also quite expensive. I would appreciate any advice you could offer. Thank you.

  19. I live in Northern Ohio and had my crawlspace encapsulated this fall. It was a relatively dry crawlspace with no water intrustion. They first installed a black hard plastic over the stone then followed up with heavy duty 20mm material running up the walls. After that they spray foamed all the exterior walls. I have 2 of these crawl spaces on each side of my basement they’re approx 20x20. On the one side I’ve noticed that the membrane will bulge up like there is air trapped under it. The other side does not do this. It eventually dissipates with time. It seems to be related to either high winds or massive temperature drops. The first time it was the polar vortex and temps went down to -10. The second time wasn’t so cold but very windy. Not sure what was going on, I initially suspected it was significant ground gas but the fact that it’s not happening on the other side I’m not so sure anymore. Any thoughts?

  20. I live on a lake, have a 5 ft. crawl under my house. I have 4 sump pumps placed in my crawl which are drained out into the lake. If we get a lot of rain and the lake raises we will get water in the crawl, the crawl floor is about at lake level at normal pool. The sumps do a good job removing the water but some standing pools will remain until they drain to the sump wells. Can a crawl space with this issue be incapsulated?

  21. Just watched your video about crawl space encapsulation. You stated when these were installed properly they would prevent moisture from entering the crawl space. But then you go on to talk about possibly needing a dehumidifier. Why would one be needed if there's no moisture entering the crawl space. If it's due to faulty encapsulation instalation isn't the answer to have the contractor come back to correct their work rather than put a band-aide on it?

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