Water sitting on crawl space vapor barrier


Are there any guidelines being used to determine if any amount of water sitting on a crawl space vapor barrier is too much? My mother has a house that is only 5 years old and it seems like every time I go under there I find some pockets of water sitting on the vapor barrier. It does seem like there is more this year than last year and I’m guessing that could be due to the excess rainfall we’ve had this year here in the Northeast. I only see one place around the outside of the foundation where the grade is actually sloping toward the house, yet I see the water in quite a few places inside the crawl space. No evidence of any plumbing leaks of any kind anywhere.

Please advise,


That is way too much, check the drainage system. Also Clear plastic is not to be used.

You should also have a concern for mold. I looked at a house last fall that had standing water in the crawl and the underside of the flooring and joists were covered in mold.

Says who?

I’ve been building homes for 3 decades and never heard that…6mil poly yes…color requirement…don’t think so.

As to the problem at hand…you have 3 options.

  1. positive drain system (cheapest)
  2. sump pump (should have alarm when power is shut down)
  3. encapsulation system. (most expensive but most effective)
    (I’ve done all three)


I never heard of that either Jeff.

And here is a 10 mil product similar to what we use.

One of the most difficult decisions you can be faced with is trying to compare products as “true” alternatives to each other. Thankfully, testing procedures allow you the ability to compare physical properties side by side. W. R. MEADOWS, the originator of below-slab vapor protection, is concerned that confusing information is being provided to you, the specifier. If you design it, you own it, so you need to trust the companies you’re dealing with.
**FACT: **
There are two vapor retarder specifications with very different performance requirements. They are ASTM 1745 Class A, B, and C for plastic film vapor retarders and the more stringent (lower perm rating) ASTM 1993 specification for critical area use.
Be wary of download specifications that pit an ASTM 1745 material against a material that meets the more stringent ASTM 1993 specification. The ASTM 1993 material is 150 times more effective at stopping water vapor. Confusing? You decide – it’s your building … forever.

This is the cadillac of the systems, but most norally, the standard is clear 6 mil poly with all penatrations sealed and edges seal.
Above proves to be a water problem more that moisture, so that has to be address first as you well pointed out. :):smiley:

If your local code permits it great, not here. Black is to be used. Think we all know why.

Well Darren, I will be the first to ask why. Always willing to learn new stuff. :):smiley:

I don’t know why either…I mostly see clear poly here

These are the only differences I can make heads or tails from it.
Please advise on any new information that might have lapse me.
Always open to learn new things about products of my everyday usage.

From this Old House;

Option: Install a clear polyethylene vapor retarder
Most plastic barrier films are either clear polyethylene, black polyethylene,cross-laminated polyethylene, or reinforced polyethylene.

The most basic ofthese materials, clear polyethylene, is also the most economical. Available in4-, 6-, and 10-mil thicknesses, it is best suited for interior wall applicationsover framing and insulation.

As clear poly’s content is up to 80 percent “reprocessed” material,it is also an environmentally sustainable choice.
The high recycled contentcomes at a cost: its quality can be uneven and it generally has poor tear andpuncture resistance.
Clear poly should never be used for exterior applicationsor applications with more than limited exposure to sunlight.
Clear poly isavailable in widths of 4 to 32 feet in 100-foot long rolls. As with allpolyethylene vapor retarders, for horizontal application over wood framing,staples are most often used. For maximum effectiveness, joints should be kept toa minimum and seams should be lapped and taped.

Relatively inexpensive and easy to install. In more severeheating climates, the use of interior polyethylene films is most effective andis practical where interior finish surfaces are removed. Being transparent,attachments to framing members are simplified, as is the installation ofwallboard material over the polyethylene, because the studs are visible.

Limited tear and puncture resistance. Clear poly must beinstalled with care to avoid damage. All penetrations such as electricaljunction boxes must be taped and sealed to ensure effectiveness.
Clear poly canbe used only in instances where wall finishes and surfaces have been removed,fully exposing wall framing.

Option: Install a black polyethylene vapor retarder
Black polyethylene is nearly identical to clear poly, except for the additionof carbon black to the composition as a Ultraviolet inhibitor.
This permits theuse of the polyethylene where some limited exposure to sunlight is required,such as at exterior wall surfaces.
Black polyethylene strength characteristicsare similar to clear poly, with low tear and puncture resistance.

For exterior wall surface applications in hot, humid, coolingclimates, black UV protected poly films can provide superior vapor retarderperformance.

Limited tear and puncture resistance. Unreinforced black polymust be installed with care to avoid damage.
Its opaque nature makesinstallation more difficult by obscuring underlying framing, sheathing, andother components. Joints and seams must be lapped and taped for fulleffectiveness. Installation is limited to conditions where siding has been fullyremoved and attachment directly to exterior sheathing can be made.

Option: Install a cross-laminated polyethylene orfiber-reinforced polyethylene vapor barrier
Compared with standard polyethylene, high-density cross-laminated poly andfiber-reinforced poly are both specialty products manufactured for applicationswhere higher strength is required.
For retrofitting over rough, irregularsurfaces, such as solid board sheathing, both products would be less susceptableto tearing or puncture by lifted nail heads, splinters, or exposed sharp corneredges.
Either product would also be appropriate where rough handling and adversesite conditions are expected.

Stronger than standard poly, reinforced and laminated materialcan withstand more adverse site conditions and rough handling. The reinforcedand laminated products are typically rated for limited UV exposure for exterioruse and situations where the installation of siding and coverings is delayed.Black reinforced and laminated poly can be used as the required weather barrierunder exterior siding and cladding.

Higher initial cost compared to standard black poly.Application is limited to conditions where siding and exterior wall coveringshave been removed. Seams must be lapped and sealed for full effectiveness.

Glad to hear about addittional pros and cons.:):smiley:

Hey Marcel,

It looks simliar, at least concept wise, as what I have used except we don’t do the gravel…I use rock dust (sand) simply because its easier to spread and is easy on materials and more son on my knees. We install a 20 mil reinforced product, take it as well, install 2 inch styrofoam board (clued and nailed) and then run the 20 mil up that as well, leaving at least 6 - 8 inches of the top portion of the block wall visible in order to check for pests (termites)…and of course we cover up the foundation vents and introduce condition air which precludes the use of insulation in the floor.

Here in the Carolinas, even when the poly is done correctly, the humid air can still wreck havoc by entry through the foundation vents.

Ideally its best to stop the moisture from entering through the foundation in the first place but many builders simply refuse to stop it at its source (extra $$$$) or more often fail to properly install french drains in the first place which leads to what Stephen has posted.

Ditto what Marcel said… I am waiting with baited breath.

(If I was clear plastic I would be contacting my lawyer with a discrimination lawsuit forth coming…:mrgreen:…)

That was funny Jeff.

Now we can’t even work in a garden and shout out for the most common tool of all without being sued for discrimination. The “hoe”
And in the electrical field, the “Dykes”

That reminds me about the gardener that got fired at the White House. He was going around asking if people had seen the hoe and spade. :stuck_out_tongue:

Back on topic:

Clear and black are what we see.

Why not clear?

Screw the poly right now, you’ve got major exterior drainage issues…

It allows vegetation growth.


I haven’t experienced that in our dark spaces. We’re mostly sand around here, too, so not any moisture to speak of.

That looks more like a pool liner, not a vapor barrier…

The only reason I can think of for using black is because the clear stuff deteriorates in UV light - but in a crawl space??

As for water, I tell clients that there is never an acceptable amount of water in a crawl space. It should be dry - period. In the humid south, water can frequently be found on the vapor barrier below HVAC ducts in the summer (cooling season) due to leaking ducts. Cold air + moist air= condensation. It is a great way to identify leaking ducts.:mrgreen: