# Crawl Space Vapor Barrier Thickness: 6, 12 or 20 Mil?

> Whether to use 6, 12 or 20 mil vapor barrier in a crawl space, what the mil rating does and does not tell you, and why reinforcement matters more.

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# What Thickness Vapor Barrier Does a Crawl Space Need?

Reference What Thickness Vapor Barrier Does a Crawl Space Need? The number on the box is not the specification. Updated 2 August 2026 Use reinforced 12–20 mil for a crawl space anyone enters. 6 mil unreinforced builder sheet is not suitable at any price. Reinforcement matters more than thickness: reinforced 12 mil outlasts unreinforced 20 mil, because the scrim layer stops a puncture becoming a tear.

## What a mil actually is

A mil is one thousandth of an inch. A 12 mil liner is 0.012 inches thick. On its own that number tells you about material volume and very little about whether the sheet survives service. Puncture resistance and tensile strength are the properties that matter, and ASTM E1745 sets minimums for both alongside permeance.

## Choosing by how the space is used

The realistic question is how often someone will be down there and on what surface. 6 mil unreinforced — not suitable for a crawl space 10–12 mil reinforced — occasional service access, smooth ground 16 mil reinforced — regular access, equipment to maintain 20 mil reinforced — frequent access, storage use, or sharp/rocky ground

## The bottom line

Reinforced 12 mil meeting ASTM E1745 is the sensible default for most Wilmington crawl spaces. Step up to 20 mil if the space gets used rather than just inspected. For a number against your own crawl space, use the cost estimator , or call (910) 886-2018 and we will come and measure it. Get an exact quote A free on-site measure beats any online range. Website What do you need? Select a service… Crawl Space Encapsulation Crawl Space Insulation Crawl Space Waterproofing Crawl Space Mold Removal Crawl Space Vapor Barrier Installation Crawl Space Dehumidifier Installation Crawl Space Drainage Crawl Space Sump Pump Installation Crawl Space French Drain Crawl Space Cleanup Crawl Space Structural Repair Sagging Floor Repair Crawl Space Door Replacement Flood Vent Installation Not sure — I need someone to look ZIP code Continue Your name Phone What are you seeing? (optional) Back Request my inspection Got it — your request is in. We'll be in touch with a quote. Related service Crawl Space Vapor Barrier Installation Related guides How to Choose the Best Vapor Barrier for a Crawl Space Vapor Barrier for a Crawl Space: Spec and Standards What Crawl Space Humidity Level Should You Aim For? Common Encapsulated Crawl Space Problems How Long Does Crawl Space Encapsulation Last? All guides → , not a heading: this is a CTA, not a section of the document outline. --> Get your crawl space measured and priced Free on-site inspection across Wilmington and New Hanover, Brunswick and Pender counties. Free quotes within 24 hours. Call (910) 886-2018 Get a free quote

## Questions

Is 20 mil vapor barrier worth the extra cost? In a crawl space with equipment to service or regular access, yes. In one that gets entered once a year, reinforced 12 mil is the proportionate choice. Can I double up 6 mil instead of using 12 mil? No. Two unreinforced layers still have no scrim, still tear, and now have a moisture plane trapped between them.