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Before You Buy: Compare Cost Per Square Foot of Crawl Space Vapor Barriers

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Comparing online costs of vapor barriers for your crawl space project can be easy and effective. Using the following tips that Contractors use every day will make your comparison-shopping even more effective.

  1. Develop your installation strategy to determine your roll size combination before you shop.
  2. Look beyond the price of a roll, focus on square foot prices when comparing costs.
  3. Keep your focus on the overall project cost, not the price of one item.
  4. Know how to find the good stuff, comparing fabric weight to determine if you are getting the best value.

1. No one wants to purchase too little or way too much material. Thinking through how you want to install the vapor barriers can help you decide what combination of roll sizes will work best for your project. (See our project-planning guide for more information.)

Rules of thumb from the Pro’s: The fewer seams the better. Don’t put seams in the corner or at the floor cove (where wall and floor meet). Use seams to make difficult areas easier. Add 1’ overlap to every seam — from each side.

2. Shop like a pro. After you layout the project, it’s time to get the best project price. There is no standard size when it comes to rolls of vapor material, so Contractors who buy these products every week look beyond the roll price and compare the price per square foot.

Roll Sizeft2/RollCost/RollCost/ft2
CS-DIY6’ x 100’600$30551¢/ft2
11.5’ x 100’1150$51545¢/ft2
23.5’ x 50’1175$52545¢/ft2
Competitor “A”6’ x 50’300$17558¢/ft2
12′ x 110’1320$66050¢/ft2
24′ x 50’1200$66055¢/ft2
Competitor “B”6’ x 50’300$16555¢/ft2
6’ x 100’600$29750¢/ft2
12’ x 100’1200$57548¢/ft2

3. Don’t lose sight of the forest over a couple of trees. Find a fair and dependable supplier who is price competitive and work with them. All suppliers have a pricing strategy. No one is giving away anything for free and staying in business. Look at the complete package price, delivered to your home. Don’t forget our 6×100 is now free shipping!

4. Finally, finding the good stuff. Everyone claims to have the best products. But, all 20 mil vapor barriers are not the same. Not by a long shot.

The skinny on liner thickness. Plastic film and sheeting is measured in mil’s, 1/1000th of an inch. 20 mil is 20/1000ths of an inch thick. While ASTM D6988-13 sets thickness measuring standards for the entire plastic’s industry, just like with lumber, this is a nominal measurement. The entire surface area of a 20 mil vapor barrier is not actually 20 mil. And, manufacturing methods can make a big difference in durability. For crawl space liners, we believe that weight, expressed as pounds per thousand square feet (MSF) and/or ounces per square yard, CBR Puncture Resistance, reported as lbf (foot pounds), and perm rating – vapor transportation rate measured in grains/(ft²·hr·in Hg) – are the important numbers. Even if you don’t understand how they are calculated, we can all compare numbers. Look for the higher number when comparing Weight and CBR Puncture Resistance, and the lower perm numbers.

Thickness, NominalWeightCBR Puncture ResistancePERM Rating Imperial*
6 mil 0.15 mm4.9 oz/yd²208 lbf0.042 PERMS
12 mil 0.30 mm7.9 oz./yd²276 lbf0.023 PERMS
20 mil 0.51 mm14 oz./yd²340 lbf0.019 PERM

* The imperial calculation of perms is based on a square foot fabric sample; metric [g/(24hr·m²·mm Hg)] is based on a square meter of fabric. The metric method results in a much lower number. Make sure comparisons are made on the same scale. The 12 mil sited above has an Imperial rating of 0.023 perms and a metric rating of 0.015 perms.

It’s All About the Fold!

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After you stopped laughing at the contractor’s price to encapsulate your crawl space, you planned your DIY project by researching and ordering materials, and now you are ready to start the work.  A few hours spent preparing the crawl space and another hour preparing your materials outside the crawl space will save you twice the amount of time in the end.

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  1. Empty the crawl space. Really, everything but the furnace and pressure tank.
    1. Are you going to insulate the band board/rim joist area with spray foam? Do it as part of the clean out.  You don’t want spray foam all over your new liner.
    2. Clean it all out. Every piece of carpet and length of old door stop, the boxes, everything. You might be thinking, “it’s not going to be that big of a deal to move that small pile so I can put the liner there.”  It will add an hour, maybe more, and you will end up moving it 10 times.
    3. Leveling gravel is hard work. You should do it before you start installing liner.  The alternative is to get halfway done, rip out what you have already installed, level the gravel, and then start over.  It’s your call.  Thinking it won’t make that big of a difference?  Yeah, it will.
    4. Keep the crawlspace empty until you are finished. If you drag your rolls of liner and a box of project supplies into the crawlspace and start unrolling the liner, your project is doomed.  A roll of 20 Mil 12’ x 100’ weighs about 125lbs.  Most manufactures fold liner by length and width to produce manageable sized rolls.  Keep everything for the project outside near the crawlspace entry until it is needed.
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  1. It’s all about the fold! Cut your liner into sections and fold them so you can simply unfold them into place.
    1. Completely unroll and unfold your floor liner in a large open space like the lawn or driveway.
    2. Following your design plan, cut the floor liner into sections.
    3. With a section fully laid out, fold each long side over 1’. This is 1’ overlap that will go up the side wall or over/under the previous/ next section of floor liner.
    4. Next fold the 1’ wall overlaps at each end.
    5. Next, fold the width of the material in half, leading edge over the immediate seam edge.
    6. Finally, fan fold the length with the far end of the crawlspace on the bottom and the end closest to the entry on top. (I like to run two or three rings of cheap packing tape around each bundle to keep it folded and manageable)
    7. Label the section just in case your helper gets them out of order or turned over.

The goal is to have material ready.  Grab the next section, take it to the far end, unfold it easily and completely, double check your alignment, and double seal the seam.  Next section.  By folding all your 1’ wall and floor overlaps, lining up the next section is easy from the start.

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  1. A little comfort goes a long way. And, so does a little dirt management.
    1. If you are installing drainage mat under your liner, over gravel or dirt, install it first. Kneeling or crab-walking for the next few hours will be much easier on drainage mat then on gravel!  (Note:  The wall liner will go under the drainage mat.  But that is easy to do by just pulling up the edge of the mat and tucking the liner down flat.)
    2. You want the finished project to look great. So, if you don’t want to spend hours cleaning the liner after the install, a little dirt management goes a long way.  Most professional installers wear a disposable suit and boot covers until the drainage mat is installed so they can work on the liner in clean clothes and shoes.  Since you are at home, change your clothes and shoes.  Trust me, the white liners look great…  unless they are covered by dirt and dirty boot prints.
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