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What a Crawl Space Vapor Barrier Does

The ground under your house gives off water vapor all the time, even when the soil looks dry. In a crawl space that vapor rises into the framing, the insulation and the air, and it ends up in your house. A vapor barrier is a heavy plastic liner that covers the ground and blocks that vapor.

In North Carolina, summers are humid, and the ground under a house stays damp for much of the year. A vapor barrier is one of the simplest and most effective ways to cut the moisture that reaches your floor system.

Vapor Barrier vs. Full Encapsulation

A basic vapor barrier is laid over the dirt floor. It stops much of the ground moisture, but if the walls and vents are still open, humid outside air can keep moving through the space.

Full encapsulation carries the liner up the foundation walls and across piers, seals the seams and closes the vents. That is a sealed system rather than a covered floor. Many homes need encapsulation for lasting results, and some only need a barrier on the floor. We inspect and tell you which fits your crawl space. See crawl space encapsulation for the full system.

How Thick Should the Liner Be?

Building codes set a minimum thickness for ground covers, and it is thin. Liners used for encapsulation are usually much thicker, because a crawl space gets foot traffic, equipment, and pipes and ducts that rub against it. Thicker, reinforced liners resist tears and punctures.

We use a heavy-duty liner and tell you its specification in your estimate. Ask any company for the thickness in writing before you compare prices.

How We Install a Vapor Barrier

  • Inspect. We check for standing water, wet insulation, mold and wood damage.
  • Prepare. We clear debris and level the ground so the liner lies flat.
  • Address water. If water collects, we deal with drainage or a sump pump first.
  • Lay the liner. We cover the full floor and fit the liner around piers and posts.
  • Seal. We overlap and seal seams, and seal the liner to the walls or piers.
  • Review. We walk you through the finished space and what to watch for.

Signs You Need a Vapor Barrier

  • Bare dirt in the crawl space, or an old torn or bunched plastic sheet
  • A musty smell in the house that gets stronger on humid days
  • Damp, sagging or discolored insulation under the floor
  • Mold or mildew on the joists, subfloor or ducts
  • Cold or damp floors, or floors that feel soft
  • Condensation on ducts and pipes in the crawl space

Vapor Barrier Installation Cost

A floor-only vapor barrier costs less than full encapsulation. Full crawl space encapsulation for Triangle homeowners typically costs $3,500 to $7,500, with a full range of $1,500 to $15,000, or about $2.50 to $4.00 per square foot.

The price depends on square footage, liner thickness, obstacles such as piers, the condition of the space and whether you add a dehumidifier or drainage. We quote both options after we see the space, so you can compare. We offer flexible financing options for qualifying homeowners; terms depend on the lender and your approval.

Common Vapor Barrier Mistakes

A vapor barrier only works if it is installed as a system. These are the mistakes we see most often in Triangle crawl spaces:

  • Thin plastic that tears. Thin sheeting rips when anyone crawls on it or when pipes shift.
  • Not covering the full floor. A liner that stops short of the walls leaves bare soil that keeps releasing vapor.
  • Unsealed seams. Seams that only overlap let vapor and air through.
  • Covering standing water. Water trapped under a liner has nowhere to go and can damage the framing.
  • Leaving the vents open. Humid air keeps coming in over the top of the liner.
  • Wet insulation left in place. Damp insulation holds moisture against the floor above it.

What Happens If Mold Is Already There?

A vapor barrier prevents new mold by controlling moisture, but it does not remove mold that has already grown. Existing mold should be removed first. See mold removal in Raleigh.

Vapor Barrier Installation by City

Pick your city for local information and a free estimate.

Crawl Space Encapsulation Apex, NC
Crawl Space Encapsulation Cary, NC
Crawl Space Encapsulation Charlotte, NC
Crawl Space Encapsulation Clayton, NC
Crawl Space Encapsulation Concord, NC
Crawl Space Encapsulation Fuquay-Varina, NC
Crawl Space Encapsulation Garner, NC
Crawl Space Encapsulation Holly Springs, NC
Crawl Space Encapsulation Knightdale, NC
Crawl Space Encapsulation Raleigh, NC
Crawl Space Encapsulation Wake Forest, NC
Crawl Space Encapsulation Zebulon, NC

Also see: Crawl space dehumidifiers, Crawl space moisture control , sump pump services and mold removal.

Vapor Barrier Installation: Frequently Asked Questions

A floor-only barrier costs less than full encapsulation. Full encapsulation for Triangle homeowners typically costs $3,500 to $7,500, with a range of $1,500 to $15,000, depending on size, condition and the work needed. We give a free estimate.

No. A vapor barrier covers the ground. Encapsulation also seals the walls, piers and vents so the crawl space is a closed, conditioned space.

A heavy-duty liner can last many years if it is not torn. The lifespan depends on the liner quality, foot traffic and how it was installed and sealed.

If the insulation is wet, moldy or has fallen, it usually has to come out. Dry insulation in good condition may stay. We check during the inspection.

No. Standing water has to be dealt with first, usually with drainage or a sump pump. Covering it does not solve the problem.

We serve Raleigh, Cary, Apex, Garner, Wake Forest, Knightdale, Zebulon, Clayton, Holly Springs, Fuquay-Varina and the Charlotte area. See the city links on this page, or send your address.

It helps prevent new mold by cutting ground moisture. For best results it is combined with sealed vents and humidity control. It does not remove mold that is already there.

Yes, we offer flexible financing options for qualifying homeowners. Ask when you request your free estimate. Terms depend on the lender and your approval.

Get a Free Vapor Barrier Installation Estimate

Request an estimate or call (704) 727-4344.

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