This article discusses the use of ground covers to control crawl space moisture.

We explain how moisture moves from soil below the crawl space up into the building, how to select and install a plastic vapor barrier, where to put the plastic, and handling crawl space water, moisture, or humidity.

We also discuss the use of spray foam as a crawl space moisture barrier.

Crawl Space Ground Covers to Help Control Crawl Space Moisture

Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Our page top photo shows a wet, flooding crawl space in which a poly barrier and gravel had been placed on the crawl space floor.

[Click to enlarge any image]

Those wet concrete blocks in our page top photograph are diagnostic: water was still entering the crawl space through the foundation wall, ponding on to of the gravel-covered plastic "moisture barrier". Here we explain why the good idea of covering the floor of a dirt crawl space may not be enough to stop a building moisture and mold problem.

Readers dealing with damp or wet crawl spaces should start reading
at CRAWL SPACE DRYOUT PROCEDURES.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

How Best to Control Crawl Space Moisture

Question:

I read your article "Controlling Moisture in Houses" (Solar Age 1/84), but it did not touch on this particular wet crawl space problem. I am having trouble controlling moisture in a crawl space. I believe that the house is over a wet-weather spring. -- Virginia Riffee, Georgetown KY

Answer:

According to researchers Charles Jennings and Thomas Moody, who worked on TVA's weatherization program, installing a crawl space ground cover can reduce moisture from capillary rise by up to 90 percent.

Below we have updated the original 1984 article to add more effective steps besides just installing a ground cover -- DF.

Sketch (above left) showing the effects of covering a dirt floor in a crawl space is courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Carson Dunlop's comment that a dirt crawl can contribute several gallons of moisture per day into a home is the best case. If the crawl area is actually wet from surface runoff, roof spillage, ground water, or plumbing leaks, the amount of water pumped into the home can be much larger and more harmful.

How to Place Polyethylene Ground Cover in a Crawl Space

Heavy polyethylene plastic sheeting works well since it resists deterioration by mold. Covering the poly with one or more inches of sand or smooth rounded gravel will protect it from occasional trampling.

In new construction, where the polyethylene overlaps on the ground it should be overlapped by at least two feet, or sealed using a caulk or sealant that will adhere to the poly, and the poly should be carried up the walls several inches or more, at least to grade line - a height equal to the height of soil outside.

Some installers use a sealant caulk or furring strips to secure the poly to the building foundation wall.

We do not like to staple the poly to the sill plate on top of the foundation wall as doing so can in some areas provide a ready path for termite attack. For this reason we exercise similar care when insulating a crawl space foundation wall interior.-- DF

In building retrofit installations of crawl space moisture barriers, Jennings and Moody recommend leaving about 20 percent of the ground uncovered so that the structure is not subjected to undue shrinkage and movement. In particularly wet spaces, they suggest first covering 50 percent, then finishing up to 80 percent of the ground area in 10 percent increments every 4 to 6 weeks to reduce "moisture shock".

[This was 1984 vintage advice. Our building inspection and testing experience in the ensuing decades indicates that covering 100 % of a dirt crawl space floor with 6-mil poly, sealed as we described above, is the most effective practice and can substantially reduce unwanted building moisture and mold problems. -- DF]

Should Crawl Space Ventilation Be Included in a Crawl Space Dryout Scheme?

In the original 1984 Solar Age article, the same experts were recommending what was conventional crawl space ventilation wisdom - specifications that were consistent with building codes:

1984 crawl space advice:

"A ground cover should be used in conjunction with ventilation.

The HUD standard [1984] typical of others, recommended four crawl space vents with a total minimum free vent equal to 1/150 of the crawl space floor area if there is a ground cover, 1/1500 with the ground uncovered. For best results, place two vents each on opposing walls."

Our photo shows a severe and problematic mold contamination on the underside of the first floor of a building constructed over a wet crawl space.

Ventilation had not helped one bit to avoid this problem.

Current Best Practices Crawl Space Moisture Control Advice

Conventional best practice crawl space moisture control has shifted from that 1984 view.

Experts observed that crawl space venting was not effective in many instances, for example depending on wind direction as well as the source and amount of crawl space water or moisture, crawl space vents were simply ineffective.

In some instances, such as blowing warm high-moisture laden air into a cool crawl space in summer months in some climates greatly increased the level of crawl space moisture and condensation, making crawl space moisture worse rather than better.

Our crawl space photo (left) shows that poly was placed on the dirt floor of the crawl area and a heat source was provided, salvaging an old radiator.

We'd have preferred to see the poly extending up the crawl space walls a foot or so.

But we notice that this crawl space looks dry: there are not mold nor moisture stains on the floor framing overhead, and no leak stains on the crawl space foundation wall.

Below we summarize the best way to avoid wet or damp crawl space problems under buildings. If your crawl area is already wet or damp, also

see CRAWL SPACE DRYOUT - home.

Current best practice in controlling crawl space moisture involves:

• Seal the crawl space from outdoor air -
  
  close off those crawl space vents - and convert the crawl space to conditioned space, providing a small amount of heat where climate dictates, to help keep the area dry and above freezing.
  
  See CRAWL SPACE VENTILATION CODES for details.
• Identify and cure sources of crawl space moisture
  
  such as roof drainage spilling around the foundation. In roughly 90 % of inspections performed by experts, we find that wet or moldy crawl spaces or basements that had been blamed on "high water table", "rising damp", or "built over a spring" were actually being caused by gutter and downspout defects, perhaps combined with in-slope grade that concentrated roof drainage right against the building foundation.
  
  Our page top photo shows that water was entering the building crawl area through the foundation wall - see those wet blocks along the bottom of the wall?
• Use a moisture barrier such as 6-mil poly continuously over the crawl space floor
  
  and lower crawl space walls, up to grade level, sealed as we described above. In new construction the poly may be installed under a crawl space slab or gravel. In crawl spaces that are rarely entered, placing sand or gravel over the poly is probably not necessary, and its use can hide depressions in the poly that may actually be holding ponding water on top of the poly in some cases.
• Inspect the crawl space periodically,
  
  at least once a year, to be sure that the poly moisture barrier is working as intended. As we just suggested, an outside water leak, such as roof spillage entering through a foundation wall, or an inside water source such as from a leaky plumbing supply or drain pipe, can place water on top of your crawl space poly moisture barrier, leading to a costly building moisture and mold problem.
  
  At CRAWL SPACE DRYOUT - home we show photos of just this problem. -- DF

Remember these are minimum values for average conditions. Your building may need special measures. If, after identifying and fixing outside sources of a wet or damp crawl space, you still find high water levels right under the crawl space floor, you may want to install a sump pump as well.

The question-and-answer article about use of a plastic barrier on crawl space floors to control crawl space moisture and mold, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

The link to the original Q&A article in PDF form immediately below is preceded by an expanded/updated online version of this article.

• Moist Crawl Space - Q&A on use of ground covers to control crawl space moisture - PDF version, use your browser's back button to return to this page

This article series describes the steps needed to get into, inspect, clean, and then dry out a building crawl space. We give a step by step crawl space entry, inspection, cleanout, dryout and keep dry guide explains how to get into or inspect a crawl space even if there is no ready access, how to assess crawl space conditions, how to stop water that is entering the crawl area, how to dry out the space, how to clean up and if necessary disinfect or sanitize the crawl space, and how to keep out crawl space water and moisture in the future.

Using Spray Foam as a Crawl Space Moisture Barrier

Spraying foam insulation in a dirt floor crawl space - spray foam directly onto the dirt?

I recently purchased a house with a crawl space, The crawl space had foam board on the wall poly on the floor tapped about 5-6" up the walls and bat insulation stuffed in the rim joust.

I called around and found a spray foam company that says they have had a really good experiance spraying the rim joust and down the walls and across the dirt floor (yes I said dirt floor) he said it locks out any moisture pests and mold, he recommended filling in the vents with the foam that was cut out originally (basically putting back in the cut out pieces that were just laying down there, So I put all the foam cut outs back in and removed all the bat insulation and removed all the poly that was on the floor.

His company came in and sprayed the rim joust all the way around and down the walls and across the floor.

(it looks like a big bath tube now, The first year Prior foam the house was so cold the furnace ran like 10 min shut off for 5 min and turned right back on, around 130.00 a month in the winter months, After foam the furnace runs like 5-8 min and is off for alot longer bills dropped to around 60.00 a month.

Do you have any comments on the foam being sprayed directly on the dirt, I have had no problems except for the flash floods we had 2 weeks ago (NORTHERN MINNESOTA) so much water collected under the foam it cracked in the low spot next to the sump pump and flooded a little but I am positive it was due to the sump pump crapping out.

But I went to the local hardware store and bought spray foam in a can and fixed the crack and its all sealed up again.

I have looked every where for comments on spraying the dirt floor again just looking for comments on this. - (July 4, 2012) Spray foam

Reply: cost benefits of spray foam vs. simple plastic poly on a crawl space floor?

Well that's one I've not heard before: direct foam application to a dirt floor. I suppose a closed cell foam might act like a poly vapor barrier but I wonder about the durabilty of a foamed dirt floor as well as access to run wires, fix a sump, or remove water below. The experts I've read never proposed such a measure; See Shipston's patent (2010).

Christian (2011), writing for the Oak Ridge National Lab certainly does not contemplate foaming dirt floors and instead agrees with my view on use of a vapor retarder (plastic):

Exposed earth in crawlspace is covered with Class I vapor retarder overlapped and taped at seams. - Christian (2011) p. 10.

The first priority is to solve the bulk water drainage flowing through the crawl space - Christian (2011) p. 34.

These citations may be helpful:

Spraying foam as insulation or barrier material

• Christian, Jeffrey E., and Kathy Gant. "Spray Foam in Accessible Spaces: Best Practices and Case Studies for Retrofit in Mixed-Humid Climates." UT_Battelle for the U.S. Department of Energy, Oak Ridge National Laboratory, ORNL/TM-2011/437 (2011). Excerpt:
  This report will look at areas to consider for spray foam application and discuss the types of spray foams available and their uses. A number of case studies are presented to show the effectiveness of this retrofit in existing houses based on performance data.
• Gibson, Scott. "Air and Vapor Barriers." Fine Homebuilding 4, no. 94 (1994): 48-53.
• Lubeck, Aaron, and Francis Conlin. "Efficiency and comfort through deep energy retrofits: Balancing energy and moisture management." Journal of Green Building 5, no. 3 (2010): 3-15.
• Shipston, Lorri B., and Mark Pavlansky. "Crawl space encapsulation system." U.S. Patent 7,735,271, issued June 15, 2010.
  
  Abstract: A system for forming an insulating vapor barrier in a building is especially suited for forming an insulating vapor barrier in a crawl space beneath a building. The system includes a series of separate vapor barrier panels that can be attached around a wall. A ground level vapor barrier can be sealed to the insulating vapor barrier panels, which can be sealed to each other and along a top edge to the wall.
  
  The individual vapor barrier panels include an insulating foam member with a vapor resistant liner laminated thereto and extending beyond the edges of the insulating foam member to provide space for securing and sealing multiple vapor barrier panels to form a continuous insulating vapor barrier. Mechanical or hook and loop fasteners can be provided to secure the top edges of the vapor barrier liners to the wall and bottom edges to a ground liner.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Is it OK if the crawl space dirt floor is not well sealed?

I live just North of Myrtle Beach SC one mile from the ocean. The crawl space has been encapsulated, but the 6ml poly on the sandy ground was not sealed with caulk or tape at the seams. And the poly is held down with roofing nails with washers. The joints overlap only a few inches. The poly comes up the walls and support columns two feet. All the wall vents have been sealed. There is a dehumidifier with a pump that keeps the space consistently at 55% RH.

Is there a reason to be concerned about the floor covering not being sealed properly other than that the dehumidifier maybe runs longer than if properly sealed? 5anks On 2020-08-16 by Kris F I

Reply by (mod) NO

Kris, if there is moisture coming up into the crawl space due to poor or incomplete vapor barrier placement over a dirt crawl space floor the risk is that the moisture can, in some seasons, overwhelm your dehumidifier and lead to mold contamination or may invite insect pests.

Reader opinion about crawl space venting SNAFUs

well mobile homes and doublewides are planets apart from your , reg. stick built, plus if you have wood skirting, the amount of passive air vents, could easly double, and then some, , also with high humidity, and rain falls, and so, many more vents, are being installed, and also another floor vapor barrier over the old one, ,, which is a yeomans job, , major job, with all the wood skirting , still up, and the width of 28 ft. x 6i8 ft., length, , and anchor straps, and the piers, in the way, , with work lights, and knee and elbow pads, a head cap covering your ears and head from spiders, ect., sharp rocks under the old plastic floor liner, and only enough crawlspace for , in some spots, less than, 15 inches between you and the steel I beam frame,

I know ive done it, now I have to go in and redo the vapor retardant floor barrier, thoughout, , much better than the clowns that installed it , when we bought it, , ive by hand , pick axe and shovel, dug a outside trench, 2 ft. wide by 1.5 indeep approx., in hard rock clay, and swung the ditch around to the side of yard where the ground starts to slope, away, for rain runoff, plus installed gutters with long extenders, and pitch, with there own trenches, to keep all roof water away from foundation, under crawlspace, but the wood skirting , needs even more vents, and a better liner for dirt floor, ,

the moisture is from sweating, due to humid summers in mo., , you cannot use a dehumidifier in a situation like this even if you could afford one for 1904 sq. ft. or so space, because, , they are too damn tall to get them inside in the center of the crawl, plus what about draining it out?, ,

no one , I mean no one is going to crawl in every other day of there life, to drain it out, they just aint practical, , cost a ton of money, , so are exhaust fan vents, if , you don't do everything else first right anyway, and then youd have to know where to place the one , or two, exhaust fan vents, for proper, locations, and you only have 2 outlet plugs under there plus running your elec. bills up , more every 2-3 seasons of the year, now if we finally get enough venting done, and still moisture, then the vapor barrier needs installed, , ,,

6 inch up all walls, and 1 ft. overlays , , we aint gonna do no stapling, or sealtapes, just overlays, , best as we can, this is a major job as it is, and ,also you want pest control acsess to interior as well as exterior, , bottom of wood skirting, , every year, , the clay soil, exposure there would be minimal, , beyond all this if we still have too much moisture under there, then we might have to close some of the vents, with , pieces of thick pond liner stapled over certain vents., these are 8x 16 inch alum. soffit vents, once cut out from wood skirting , leaving 1 inch on all sides for screws are really, 6x 14, ,

so you see , the vents, and cutouts, are , less than the required 1 ft. per 150 ft. of crawlspace, , im discusted by the lack of real info., , plus , some parts , the height of crawl is higher than , the rest, , , so no one wants to help calculate, the height, into it, for venting purposes, we do know that wood skirting , requires even more venting than traditional skirting, if some one could tell us , how to factor in the height, into the math for crawlspace feet, I could get the measuring tape, from points inside, and outside, section by section where height changes, and figure out, each section, by legnth ect., and finally calculate it , real close, , ,

now those are the 3 things it could be, if after all this, and still too much moisture, well, , that means well need expensive steel siding skirting , cause we aint buying cheap love skirting, like cement board, that it came with, or vinyl love, , , I believe we can fix this , and thanks for all the info., but really your not talking to mobile home owners, , for crawls, , and there are no standards that are followed in America, for these mobile home gypsy dealers, installers, , , ,

on pest control we do it yearly, and sometimes twice yearly, we also installed a pond liner around entire perimeter of wood skirting sides, to keep rainwater there from , rotting the skirting, that's where I do thepest control, lifting the pondliner up, and spraying against termites ect., , the steel j channel is 1 inch high, that's it, all skirting is way too close to the dirt ground, no standards, no knowledge, no caring , we all do the best we can by gods grace and info., is surely lacking., please talk about mobile and doublewides here, ours has the top vapor , belly wrap, thank god, we already got screwed by our dealer, on many things, , from poor land slope, , to bad liner crawl install, , ,

cheapo love cement board skirting, and other things, and the factory screwed us on the roof, 13 years, it had staples , showing and even nails showing, slap job from factory, then when we had to switch insurance companies, because , out insurer at the time, was reorganizing or something we had to scramble and get another mobile home type ins., and we thought we had real roof replacement on our policy, but didn't, so we had to pay over 8500 dollars, and , you have to get a indapendant contractor, not the companies, to do this, only a qualified little guy with knowledge, ,

ou cannot reroof over, the trusses are too thin for the weight, and , always need a tearoff, why its so high., , , plus we needed more roof vents, than the love factory gave, , we have no , long ridge vent there, most don't, , , and under the vinyl siding on these things, there is no synthetic, water barrier, installed, so its just the vinyl siding, installed correctly or not between you and disaster, , , ,

weve had to redo and come out of our pockets on the 2 sides of vinyl siding, where the dealers, gypsies, installed at the marriage lines, , and our installer got shocked by elec current, of 110 amp., where the factory apes, had the wires running on the outside, of the walls, , behind the foam boards, , where you cannot see, behind, so he was nailing into the studs there were he was supposed to to install the vinyl, and hit a live line, on both side of home, thank god it was only 110 not 220, , everyone knows elec lines go inside home, , , ok?, this is just some of the stuff goes on with mobile homes, doublewides, ect., , ,

you work all your life and buy a home you think , and lookout, the headaches are just beginning., , most mobile homes doublewides do not have tyvek, or nothing, behind vinyl, , period, no standards at the factory, ,

whatever they want to do and get away with, the factory was in boaz. Alabama, and 5 years after we bought ours, , new, the factory closed, I wonder why, , champion homes bought the homes from them, that remained, I will give the name here cause I don't care, homes of legend, mobile homes in boaz Alabama, , , awful, construction sloppy at the factory, use the cheapest, products they can get and the workers, probably minumun wage, and mad, so no care how they install things, plus no oversight , from supervisors, like the elec.,

name of the jerk dealer, was jim l. Williamson, , again im using names cause I don't care, hes a fraud, , so was homes of legend, yeah, legend of love, anyway, were doin everything we can and shouldn't have to, but that is the way it is , no standards, and I mean the newer ones, , there never was any standards on the older ones , and the new standards mean nothing in the realworld., , , America the ripoff, no matter what you buy.thanks for letting me vent, no pun intended. On 2019-05-30 by ruth d.

On 2019-05-28 - by (mod) -

Everything you're saying sounds reasonable. I'm assuming that you've tried and ventilation and heat to see if you could speed up and finish off an mvoc off gas problem. Before buying any paint be sure to talk to the manufacturer about the coating that is already on the floor to be sure that it will bond successfully. Also I'm disappointed that a sealant didn't stop off-gassing from the floor which in turn makes me want to repeat the smell patch on maybe wood framing and subflooring overhead or any insulation that may be in the area.

On 2019-05-28 by Anonymous

Yes, I will confirm sealant options with Behr prior to proceeding with a sealant on top of the epoxy. I will also ask about trying a third coat of the epoxy as a first step - the recommendation is to only put down two coats. I expect this is for a more typical situation to ensure water vapour can permeate from the concrete. Also, good point about the overhead subfloor. This has all been dusted and HEPA vacuumed as part of the remediation, however no effort was made to seal it. I sure hope that wont be necessary. The smell swatch test should provide an indication if it is.

Crawlspace mold questions coming from a northern climate

Anonymous by private email asked:

Two Mold related questions coming from a northern climate (4 seasons, with cold winters and hot, humid summers).

Q1. Follow-up to your reader (July 2012) who used closed-cell spray foam on a dirt crawl space floor ?

SITUATION: I rent a cottage and am helping the owner address a moisture/mold issue in the crawl space. The crawl space has an irregular (not flat) dirt floor with rock jutting up in many places. A local jack-of-all-trades contractor is recommending spray foam for the floor, walls and headers; he states he's previously done this successfully on dirt floors.

I haven't found any reference to creating a moisture barrier by spray foaming a dirt floor; other than from your reader from July 2012 (see below). Any updates about this approach? I'm apprehensive if only because it doesn't seem to be a typical approach and I don't want u to be the ginny-pigs.

The only mechanicals in the crawl space are a hot water tank and pump for in-take of lake water. There is some water puddling in one corner of the 1500 sq ft basement that will be addressed, the moisture Barrie installed and then remediation of the moldy joists and electrical wiring.

Q2. Post-remediation Mold smell - how to address mvoc off gassing from concrete basement floor:

SITUATION: Over the past 18 months we have addressed a mold issue in ou basem including: fixing wall cracks where moisture was entering, removing smelly drywall and fibre glass insulation, adding a moisture barrier of closed cell spray foam to walls and headers and running two de-humidifiers to keep the moisture level under control.

We also used a Zinsser shellac-based odor sealer on the underside of wooden steps, AFM Safecoat on the wooden 2x4 framing and Behr 1 part epoxy on the floor (2,000 sq ft). Smell got progressively better and after all these actions was eventually gone (February/March).

BUT, now it's May, the environmental conditions have changed and the moldy/gassy smell is back. Given the basement is dry (~50% RH) I'm assuming the smell is off gassing from somewhere and I assume it's the floor (since the concrete floor is porous and the 1-part epoxy paint is gas permeable). I'm currently doing your smell test with foil and paper towel taped to the floor to test this assumption.

QUESTION: How can I clean the epoxy acrylic painted floor to purge the concert of mvocs (TSP alternative? ) and/or can I better seal the mvoc off gassing from the floor? The situation is significant as the smell is making the house uninhabitable without having open windows and constant fresh air.

I'm not sure where to turn - even knowing what kind of 'expert' to contact isn't clear. NOTE: because the basement is below grade the temperature doesn't allow me to open windows without the RH jumping above 60%. I will try an HEPA air scrubber but don't see that being a cure. Vacuuming with a HEPA vac has been inefffective. On 2019-05-27 - by Anon-

Moderator Reply:

You could spray closed cell foam on a crawl space floor - I think almost nobody does it because it's a pretty expensive alternative to 6-mil poly + cleaning the roof gutters. I'd prefer to spend on

- de-watering the crawl space

- removing any mold contamination

- laying down a properly-placed and sealed plastic moisture barrier (watch out some plastics also smell horrible from offgassing, especially in a confined space - might even be unsafe to breathe

- converting the crawl area to a dry, warmed, conditioned space if at all possible, such as by

- sealing air leaks such as at the rim joist

- insulating at least the perimeter

The floor doesn't have to be level to put down poly but you do need to consider where water might collect - under plastic is ok, on top of it means the installation made a mistdake.

Consider how irritating it'd be if the floor is foamed, now harder than ever to access, and somebody has to get in there to install a sump.

Consider too how irritating it'd be to spray foam the floor, then discover you have to pay someone still more to squeeze over the foam through tighter spaces to do necessary mold remediation on all of those exposed wood surfaces or perhaps remove moldy insulation.

At InspecApedia.com you'll want to read the CRAWLSPACE DRYOUT articles.

About heating costs, most house heat loss is up and out - through air leaks at windows, doors, attics. Heat loss "down" into a crawl area is usually considerably less.
But still, fixing drafts, stopping water entry, converting the crawl area to a closed, conditioned space, is current "Best Practice".

About continued odor off-gassing from concrete, if cleaning, ventilating, and drying out an area over a smelly concrete slab don't fix that problem - as it may not - you may need to seal the slab with an odor-sealant paint such as is used by fire restoration companies. Some mold fungicidal paints can also work.

But before more paint coatings let's ask: did someone run an ozone generator in that space? Over-dosing with ozone can itself oxidize building materials and lead to a troubling chemical odor problem. You can find OZONE WARNINGS in the ARTICLE INDEX along with more mold cleanup and crawlspace dryout articles.

Followup by Anonymous

2 THANK-YOUs:
Follow-up to questions Q1 and Q2. FIRST, thank-you for responding and so promptly to my questions! I'm very impressed.

And regarding Q2 a SECOND thank-you as I able to use the smell patch test on your site to narrow down and confirm the source of our problem ( https://inspectapedia.com/odor_diagnosis/Smell_Patch_Test.php ) I assessed various locations in the basement and it clearly identified the concrete floor as the source.

This has saved me at least $250.00 for an IAQ inspector I had spoken to come and inspect our house. Per your response, the basement has not had an ozone generator so, the smell must be related to mvocs from prior to the mold remediation that were absorbed into the porous concrete and are now off-gassing.

On the advice of another IAQ inspector I had hoped the 1-part Behr epoxy would help seal and prevent odors from the concrete but this theory has been proved wrong. I don't believe I have any option but to put down a clear odor sealing product over the Behr epoxy.

Fortunately I don't have a problem with water vapour seaping through the concrete (based on taping saran squares to the floor and checking for condensation under the saran) so sealing the concrete should be ok. Can't wait to get this done and get the smell out of our home. FYI I will look at smoke door sealing products from Fosters, Recon (Fiberlok) and Sentinel etc. to determine what is available locally as well as what is effective and reasonably priced.

 

Would it be foolish to spend a few hundred dollars on materials to DIY “most” of the dirt covering rather than thousands on a complete fix?

Thanks Dan. A full encapsulation seems likely to be expensive (especially if it’ll need repair after we eventually fix the skirting around the house), but I can reach most of the crawl space easily.

Would it be foolish to spend a few hundred dollars on materials to DIY “most” of the dirt covering rather than thousands on a complete fix?

We haven’t seen evidence of bulk water or mold problems; the house just gets humid and the clay soil stays damp for a long time after it rains. On 2019-04-28 by Chris

Reply by (mod) - No, it's sensible IF you can access the area safely.

No, it's sensible IF you can access the area safely.

Watch out: I did the very same thing in a horribly tight crawl space in a 1920's Poughkeepsie home, crawling into the space, unfolding and smoothing out 6-mil clear polyethylene sheeting as I went ahead - making the crawl easier.

I pushed the poly everywhere I could reach, made it flat, ran it a foot or so up walls, and made sure there would be no areas that would puddle if water got into the space.

I figured I was reducing the rate of moisture movement into the space and thus reducing moisture movement up into the home from the crawl - possible mold issues - even though there were some spots I couldn't even reach using a long stick to push poly ahead.

But

Watch out: I was sickened by fumes off-gassing from the polyethylene sheeting itself.

After that nauseating job I made sure to smell the poly before buying it and also to air it out outside in sunlight.

I don't know if I was breathing respiratory irritants or carcinogens or other toxins. In 2013 Mülhaupt (2013) pointed out that there was actually rather little research on the respiratory hazards of offgassing from such material. But the very next year just such hazards were cited by another researcher (Meng 2014).

Research on Toxic or Hazardous Offgassing from Polythylene Sheeting

• Lithner, Delilah, Åke Larsson, and Göran Dave. "Environmental and health hazard ranking and assessment of plastic polymers based on chemical composition." Science of the Total Environment 409, no. 18 (2011): 3309-3324.
• Mülhaupt, Rolf. "Green polymer chemistry and bio‐based plastics: dreams and reality." Macromolecular Chemistry and Physics 214, no. 2 (2013): 159-174.
  
• Meng, Tingzhu Teresa. "Volatile organic compounds of polyethylene vinyl acetate plastic are toxic to living organisms." The Journal of toxicological sciences 39, no. 5 (2014): 795-802.
  Abstract:
  
  Volatile organic compounds (VOCs) in polyvinyl chloride (PVC) plastic products readily evaporate; as a result, hazardous gases enter the ecosystem, and cause cancer in humans and other animals. Polyethylene vinyl acetate (PEVA) plastic has recently become a popular alternative to PVC since it is chlorine-free.
  
  In order to determine whether PEVA is harmful to humans, this research employed the freshwater oligochaete Lumbriculus variegatus as a model to compare their oxygen intakes while they were exposed to the original stock solutions of PEVA, PVC or distilled water at a different length of time for one day, four days or eight days.
  
  During the exposure periods, the oxygen intakes in both PEVA and PVC groups were much higher than in the distilled water group, indicating that VOCs in both PEVA and PVC were toxins that stressed L. variegatus. Furthermore, none of the worms fully recovered during the24-hr recovery period.
  
  Additionally, the L. variegatus did not clump together tightly after four or eight days’ exposure to either of the two types of plastic solutions, which meant that both PEVA and PVC negatively affected the social behaviors of these blackworms.
  
  The LD50 tests also supported the observations above.
  
  For the first time, our results have shown that PEVA plastic has adverse effects on living organisms, and therefore it is not a safe alternative to PVC.
  
  Further studies should identify specific compounds causing the adverse effects, and determine whether toxic effect occurs in more complex organisms, especially humans.
  

...

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