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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.

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