From Ground to Wall: A Complete Guide to Calculating Crawl Space Vapor Barrier Needs

NOTE: This may be more helpful if the video is watched: https://youtu.be/sp7-O9YFTpo. Wondering exactly how much vapor barrier you need for your crawl space project? Stop guessing and start calculating with precision.

Michael Church of CrawlSpaceNinja.com dives into the often-overlooked science of vapor barrier measurement that can make or break your DIY crawl space encapsulation. Far from a simple floor measurement, proper calculation involves accounting for uneven ground, support pillars, and foundation walls—factors that can add hundreds or even thousands of square feet to your material requirements.

Through real-world examples and visual demonstrations, Michael walks viewers through a foolproof method for determining vapor barrier needs. Learn why those depressions around support pillars matter, how to calculate the extra material needed for proper seam overlaps, and why those white mineral deposits on your foundation walls are signaling moisture problems that require special consideration.

The most eye-opening revelation? A typical 2,048 square foot crawl space with standard support pillars and 4-foot walls actually needs closer to 4,000 square feet of vapor barrier when properly installed. This crucial buffer prevents the frustration of running short mid-project while allowing strategic reinforcement in high-traffic areas that experience the most wear and tear.

Whether you're planning your first encapsulation project or wondering why your previous attempt failed to control moisture, this step-by-step guide provides the calculation framework every homeowner needs. Download the free Crawl Space Encapsulation Homeowner's Guide mentioned in the video to access additional installation tips, inspection checklists, and special discounts on DIY materials that will help you complete your project with professional-grade results.

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Check out Michael's book, "Crawl Space Repair Myths-Busted" now available on Amazon!

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Episode Transcript

Speaker 1 (00:00):
Hey there, michael Church with CrawlSpaceNinjacom,
and we get questions a lot abouthow much vapor barrier do I
need to encapsulate my crawlspace?
Well, if you're a DIYer, you'regoing to want to watch this
video.
I'm going to show you how tocalculate exactly how much vapor
barrier you are going to need,and be sure to stay tuned to the
end, because I've got a specialebook that we're going to give

(00:23):
away and I want to tell you howto get it.
Thanks again for watching.
Okay, so let's jump right in.
Basically, what I wanna showyou here is, if you are trying

(00:46):
to figure out how much vaporbarrier you need, there's a few
things that you need to payattention to, and hopefully
these pictures will help meexplain.
First of all, I want you tonotice that the ground is not
level in this picture.
Okay, so anytime you're dealingwith uneven or unlevel ground,
you're going to use more vaporbarrier, okay, so if you've got

(01:08):
a lot of this going on in yourcrawl space, you need to pay
attention to this.
Now, what you can do is, if youwant to level it all out, you
can get some pea gravel maybe,or some three-quarter inch stone
and fill in these little areasaround the pillar and that'll
help level it out and help savea little bit of the vapor
barrier and even probably makeit easier on you to install.

(01:29):
But I want you to noticesomething else about this is
this particular situation therewas water percolating up around
the pillar, so this crawl spaceneeded a trench and sump pump
installed, and this is anotherpicture of it here.
So if you got these low valleysin between these pillars, it's
a good place for water to move,and sometimes just adding some

(01:52):
gravel, some pea gravel,something like that, to raise
these valleys up and make itlevel, is going to keep that
water from sitting in thesevalleys and moving it hopefully
to the outside where you've gota trench and sump pump if you're
taking on a lot of standingwater.
So just keep that in mind.
The other thing you got to lookat is how large are your pillars
.
These are your basic eight inchblock doubled up, so it's 16

(02:18):
around, and then it's eight highand eight high, so it's 16.
So typically we go about twofeet high.
Sometimes it will go higher ifthe crawl space is really tall.
So these are some things you'vegot to figure out is calculate
16 by 16 by 16 by 16 by 24.
And that will give you someparameters as far as that goes.

(02:42):
So if you do that calculation,16 on each of the four sides, by
two feet tall you're looking ateach side, is going to take up
approximately three square feet.
So if you've got four sides,that is about 12 square feet of

(03:02):
vapor barrier without any excess, without going down in here or
anything like that.
So if we said that each pillaris, say, 30 square feet, that is
a good indication of how muchvapor barrier you would need for
each pillar.
So if you have 10 pillars,that's 300 square feet.

(03:23):
So let's move on to the nextslide Right here.
I want to show you a couplethings.
Number one this is the oldvapor barrier.
See how it was not.
The plastic was not overlappedand it was not taped.
So you know, make sure that youoverlap and tape the plastic in
the crawl space to keep it fromcoming apart.

(03:45):
The more people over the yearsthat crawl on the vapor barrier,
the more it is going toseparate.
So we recommend a 9 to 12 inchoverlap.
If you're using it as a radonbarrier, you have to go a
minimum of 12 inches and youalso have to use a polyurethane
sealant to join the bottom andthe top piece.

(04:08):
So if you're doing a radonsystem, make sure you check with
your local radon codes for thatsituation.
But if you're not doing a radonsystem, 9 to 12 inches with
just your basic seam tape is allyou need, and that's going to
be most people Over here.
You've got what appears to be atwo-foot wall.

(04:28):
Actually that's a shadow, soyou've got probably closer to a
three-foot wall on this side, 30inches of wall.
So if you've got mud caked uparound the edge, that tells me
that water is probably comingthrough the foundation, again,
good chance that we're going toneed to put in a trench along

(04:48):
this wall that leads to a sumppump.
But you got to take this wallinto consideration.
So if you're going 30 incheshigh to cover all this up, all
that has to be calculated aswell.
So I'm just showing you somebasic things that you need to
look at inside the crawl spacewhenever you're trying to figure
out how much vapor barrier youare going to need.

(05:12):
Some people decide not to takethe vapor barrier up the wall.
As you can see, they stopped itright here.
This is not a good idea in thiscase, or this case because you
can see the water coming throughthe cinder block.
This has got efflorescence anddifferent things getting going
here, so there's a lot ofhydrostatic pressure behind this

(05:32):
wall pushing water through.
And what that's going to do?
If you don't put the vaporbarrier up the block, it's going
to make your dehumidifier runharder in the summertime, in
your wet season, because yourcrawl space humidity is
increasing.
The other thing to look out foris these little intrusions, or
outcroppings, depending on whereyou're at.
These add to the square footageof the vapor barrier because

(05:57):
you've got to make this turnhere, here, here and here, so
they can't all be perfectlyrectangular or square, so just
keep that sort of thing in mind.
So let's go to the next slideand we'll try to do a
calculation for you on how muchvapor barrier you're going to
need.
Now, this is a 2048 square footcrawl space with six pillars,

(06:18):
and we're going to pretend thatthese pillars are square, even
though they're not in thepicture, and they are 16 by 16
by 16 by 16 and we're gonna gotwo feet high.
So we got 30 square feet is ourcalculation for each pillar.
Okay, you got 30 square feet,so that's going to be 30 times 6

(06:40):
is what is that?
180 square feet.
There we go.
I still learn something, orremember from math class.
Okay, so we got 180 square feetof Let me see if I get my pen
here got 180 square feet For thepillars, okay, and then we've

(07:03):
got this wall is 32 feet andthis wall is 64 feet.
So what you're going to do thereis you need to calculate how
tall the wall is.
So let's say it's a four footwall.
We got 32 times four.
So this wall is going to be 128square feet.

(07:24):
This wall is going to be 128square feet.
This was going to be 128 squarefeet and they were also going,
and what I did was I took thethe length times the height.
So we got four feet times 64feet.
This wall is 256 square feetand this wall is 256.

(07:48):
Now remember that this wall,for example, our north wall
could be seven feet tall and oursouth wall could be two feet
tall.
So just keep that in mind.
But basically it's length timesheight and that gives you the
square footage of the wall.
Footage of the wall, okay, andthen the floor is 2048.

(08:14):
So 2048 square feet.
So we're going to take thatnumber 2048 plus 256 plus 256.
That covers the north and southwalls plus 128 plus 128.
That covers the east and westwalls, plus 180 square feet for
the pillars.
So we're looking at a grandtotal, if everything goes

(08:34):
perfect, of 2,996 square feet.
Ok, so here's what you've got toremember, though You're going
to probably overlap here andhere you're going to have an

(08:58):
overlap, okay.
So I would probably get anextra thousand square feet of
plastic.
So, in other words, this crawlspace would probably need 4,000
square feet of plastic, need4,000 square feet of plastic to

(09:20):
do this job.
Oops, that's 400.
4,000 square feet of plastic.
So, anyway, you're going tohave a lot of cuts.
Sometimes you're going to havea pillar here, you may have one
over here.
Crawl spaces are always going tobe crazy.
But the point is and you maywant to go higher than two feet,
remember that 30 square footper pillar is only going two

(09:41):
feet tall, and what I mean bythat is, if you look at this one
, we actually went higher thantwo feet, okay.
So here that's probably athree-foot tall pillar.
The wall is taller.
We had to go over the foamboard here, which makes more
slack in it, and you can see,it's kind of hard to get it

(10:02):
perfectly straight.
So you've got a lot of gaps andthings like that in the plastic
.
Here's a tape seam.
Here there's probably anotherone.
Here's a tape seam.
This has all been taped.
There's probably tape seams.
Here's a tape scene.
This is all been taped.
There's probably tape, seems,here along this area.
So, as you can imagine by mesaying that you need 4,000

(10:24):
square feet in this photo andthis example, I would rather you
get a little bit too much vaporbarrier and then maybe put an
extra layer around the door.
So if, if your door is likeright here, maybe this little
section where people are goingto be crawling in and out of the
most, you put an extra layerunderneath the main part.
So that way you're doubling upin this area to give your knees

(10:46):
and everything a little bit ofextra cushion and give that
vapor barrier, that high trafficarea right there, a little bit
of extra protection.
So if you get too much, that'sone thing you can do with.
The extra vapor barrier is putthis in your high traffic area.
If your HVAC unit is over hereand your HVAC person has to
climb over here to get to it,you could, you know, put a

(11:06):
little extra vapor barrier inthis whole area here to give
your, your heating and aircompany a little less wear and
tear on that plastic.
So, anyway, I hope this helps.
And again, take a look, this isa before and this is an after.
So I hope this helps.
I hope you like this video downbelow and let me know if you

(11:26):
have any questions.
And stay tuned for a littlespecial I wanted to tell you
about.
Well, I hope that helped youfigure out how much vapor
barrier you're going to need foryour crawl space encapsulation,
and about that e-book that Imentioned in the beginning.
If you'll check out the linksbelow in the description, we're
going to link you to our freecrawl space encapsulation

(11:50):
homeowner's guide.
So if you get a chance to godown there, it'll take you right
to the website.
It'll have some tips and tricksin there for you to know how to
encapsulate your crawlspaceproperly, and also some
inspection tips and even acoupon on there about how to
save on any of the DIY productsthat you order through our
website.
So thanks again for watching.

(12:11):
My name is Michael Church withCrawlSpaceNinjacom, and I hope
you make it a happy and blessedday.
Thanks so much.