Crawl Space Ninja Show

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

• Michael Church, Founder of Crawl Space Ninja • Season 2025 • Episode 3

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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.

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

Schedule a consultation: https://buymeacoffee.com/csninja/extras

Need help: https://crawlspaceninja.com or https://diy.crawlspaceninja.com

Speaker 1:

Hey there, michael Church with CrawlSpaceNinjacom, and we get questions a lot about how much vapor barrier do I need to encapsulate my crawl space? Well, if you're a DIYer, you're going to want to watch this video. I'm going to show you how to calculate exactly how much vapor barrier you are going to need, and be sure to stay tuned to the end, because I've got a special ebook that we're going to give away and I want to tell you how to get it. Thanks again for watching. Okay, so let's jump right in. Basically, what I wanna show you here is, if you are trying to figure out how much vapor barrier you need, there's a few things that you need to pay attention to, and hopefully these pictures will help me explain. First of all, I want you to notice that the ground is not level in this picture. Okay, so anytime you're dealing with uneven or unlevel ground, you're going to use more vapor barrier, okay, so if you've got a lot of this going on in your crawl space, you need to pay attention to this. Now, what you can do is, if you want to level it all out, you can get some pea gravel maybe, or some three-quarter inch stone and fill in these little areas around the pillar and that'll help level it out and help save a little bit of the vapor barrier and even probably make it easier on you to install. But I want you to notice something else about this is this particular situation there was water percolating up around the pillar, so this crawl space needed a trench and sump pump installed, and this is another picture of it here. So if you got these low valleys in between these pillars, it's a good place for water to move, and sometimes just adding some gravel, some pea gravel, something like that, to raise these valleys up and make it level, is going to keep that water from sitting in these valleys and moving it hopefully to the outside where you've got a trench and sump pump if you're taking on a lot of standing water. So just keep that in mind.

Speaker 1:

The other thing you got to look at is how large are your pillars. These are your basic eight inch block doubled up, so it's 16 around, and then it's eight high and eight high, so it's 16. So typically we go about two feet high. Sometimes it will go higher if the crawl space is really tall. So these are some things you've got to figure out is calculate 16 by 16 by 16 by 16 by 24. And that will give you some parameters as far as that goes. So if you do that calculation, 16 on each of the four sides, by two feet tall you're looking at each side, is going to take up approximately three square feet. So if you've got four sides, that is about 12 square feet of vapor barrier without any excess, without going down in here or anything like that. So if we said that each pillar is, say, 30 square feet, that is a good indication of how much vapor barrier you would need for each pillar. So if you have 10 pillars, that's 300 square feet. So let's move on to the next slide Right here.

Speaker 1:

I want to show you a couple things. Number one this is the old vapor barrier. See how it was not. The plastic was not overlapped and it was not taped. So you know, make sure that you overlap and tape the plastic in the crawl space to keep it from coming apart. The more people over the years that crawl on the vapor barrier, the more it is going to separate. So we recommend a 9 to 12 inch overlap. If you're using it as a radon barrier, you have to go a minimum of 12 inches and you also have to use a polyurethane sealant to join the bottom and the top piece. So if you're doing a radon system, make sure you check with your local radon codes for that situation. But if you're not doing a radon system, 9 to 12 inches with just your basic seam tape is all you need, and that's going to be most people Over here.

Speaker 1:

You've got what appears to be a two-foot wall. Actually that's a shadow, so you've got probably closer to a three-foot wall on this side, 30 inches of wall. So if you've got mud caked up around the edge, that tells me that water is probably coming through the foundation, again, good chance that we're going to need to put in a trench along this wall that leads to a sump pump. But you got to take this wall into consideration. So if you're going 30 inches high to cover all this up, all that has to be calculated as well. So I'm just showing you some basic things that you need to look at inside the crawl space whenever you're trying to figure out how much vapor barrier you are going to need.

Speaker 1:

Some people decide not to take the vapor barrier up the wall. As you can see, they stopped it right here. This is not a good idea in this case, or this case because you can see the water coming through the cinder block. This has got efflorescence and different things getting going here, so there's a lot of hydrostatic pressure behind this wall pushing water through. And what that's going to do? If you don't put the vapor barrier up the block, it's going to make your dehumidifier run harder in the summertime, in your wet season, because your crawl space humidity is increasing. The other thing to look out for is these little intrusions, or outcroppings, depending on where you're at. These add to the square footage of the vapor barrier because you've got to make this turn here, here, here and here, so they can't all be perfectly rectangular or square, so just keep that sort of thing in mind. So let's go to the next slide and we'll try to do a calculation for you on how much vapor barrier you're going to need.

Speaker 1:

Now, this is a 2048 square foot crawl space with six pillars, and we're going to pretend that these pillars are square, even though they're not in the picture, and they are 16 by 16 by 16 by 16 and we're gonna go two feet high. So we got 30 square feet is our calculation for each pillar. Okay, you got 30 square feet, so that's going to be 30 times 6 is what is that? 180 square feet. There we go. I still learn something, or remember from math class. Okay, so we got 180 square feet of Let me see if I get my pen here got 180 square feet For the pillars, okay, and then we've got this wall is 32 feet and this wall is 64 feet.

Speaker 1:

So what you're going to do there is you need to calculate how tall the wall is. So let's say it's a four foot wall. We got 32 times four. So this wall is going to be 128 square feet. This wall is going to be 128 square feet. This was going to be 128 square feet and they were also going, and what I did was I took the the length times the height. So we got four feet times 64 feet. This wall is 256 square feet and this wall is 256. Now remember that this wall, for example, our north wall could be seven feet tall and our south wall could be two feet tall. So just keep that in mind. But basically it's length times height and that gives you the square footage of the wall. Footage of the wall, okay, and then the floor is 2048. So 2048 square feet. So we're going to take that number 2048 plus 256 plus 256. That covers the north and south walls plus 128 plus 128. That covers the east and west walls, plus 180 square feet for the pillars. So we're looking at a grand total, if everything goes perfect, of 2,996 square feet.

Speaker 1:

Ok, so here's what you've got to remember, though You're going to probably overlap here and here you're going to have an overlap, okay. So I would probably get an extra thousand square feet of plastic. So, in other words, this crawl space would probably need 4,000 square feet of plastic, need 4,000 square feet of plastic to do this job. Oops, that's 400. 4,000 square feet of plastic. So, anyway, you're going to have a lot of cuts. Sometimes you're going to have a pillar here, you may have one over here.

Speaker 1:

Crawl spaces are always going to be crazy. But the point is and you may want to go higher than two feet, remember that 30 square foot per pillar is only going two feet tall, and what I mean by that is, if you look at this one, we actually went higher than two feet, okay. So here that's probably a three-foot tall pillar. The wall is taller. We had to go over the foam board here, which makes more slack in it, and you can see, it's kind of hard to get it perfectly straight. So you've got a lot of gaps and things like that in the plastic. Here's a tape seam. Here there's probably another one. 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.

Speaker 1:

So, as you can imagine by me saying that you need 4,000 square feet in this photo and this example, I would rather you get a little bit too much vapor barrier and then maybe put an extra layer around the door. So if, if your door is like right here, maybe this little section where people are going to be crawling in and out of the most, you put an extra layer underneath the main part. So that way you're doubling up in this area to give your knees and everything a little bit of extra cushion and give that vapor barrier, that high traffic area right there, a little bit of extra protection. So if you get too much, that's one thing you can do with. The extra vapor barrier is put this in your high traffic area. If your HVAC unit is over here and your HVAC person has to climb over here to get to it, you could, you know, put a little extra vapor barrier in this whole area here to give your, your heating and air company a little less wear and tear on that plastic. So, anyway, I hope this helps. And again, take a look, this is a before and this is an after. So I hope this helps.

Speaker 1:

I hope you like this video down below and let me know if you have any questions. And stay tuned for a little special I wanted to tell you about. Well, I hope that helped you figure out how much vapor barrier you're going to need for your crawl space encapsulation, and about that e-book that I mentioned in the beginning. If you'll check out the links below in the description, we're going to link you to our free crawl space encapsulation homeowner's guide. So if you get a chance to go down there, it'll take you right to the website. It'll have some tips and tricks in there for you to know how to encapsulate your crawlspace properly, and also some inspection tips and even a coupon on there about how to save on any of the DIY products that you order through our website. So thanks again for watching. My name is Michael Church with CrawlSpaceNinjacom, and I hope you make it a happy and blessed day. Thanks so much.