Crawl space encapsulation: what to know

What the job involves, what changes the price, and what to ask a pro.

What crawl space encapsulation is

Crawl space encapsulation seals a crawl space with a heavy vapor barrier on the floor and walls, closes the vents, adds drainage or a dehumidifier and insulates the walls or rim joists. The goal is to control moisture and improve the air quality below the house. The work is done by a contractor who first finds the moisture sources.

Signs you need it

  • The crawl space floor is damp, has standing water after rain, or shows mold and wood rot on the joists
  • You smell mustiness in the rooms above the crawl space, especially in the summer or during humid weather
  • Floors above the crawl space are cold, bouncy or sloped, and the insulation between the joists is sagging or wet
  • The crawl space vents are open to outside air that is humid, and the floor has bare dirt with no barrier
  • Your heating or cooling bills rise, and the ducts or the air handler run in the crawl space with high humidity

What the pro does

  • The contractor inspects the crawl space for moisture sources, including ground water, leaks, condensation and poor grading
  • They correct the sources they find, such as a leaking plumbing line or a downspout that drains into the crawl space
  • They clean the crawl space of debris, old insulation and any wet materials, and remove the materials that cannot be kept
  • They install a heavy vapor barrier over the floor and seal it up the walls to the rim joist, with the seams taped
  • They close or seal the foundation vents, add a drain or a sump if water is present, and install a dehumidifier when the design calls for one
  • They insulate the rim joists and the walls, and check the work for gaps, drainage and airflow before they finish

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Size of the crawl space, its height and the number of access points
  • Condition of the existing floor and walls, including standing water, rot or old insulation
  • Vapor barrier thickness and the number of seams and penetrations to seal
  • Drainage or sump installation needed to handle ground water
  • Dehumidifier and its wiring, which may need a licensed electrician if the unit is hardwired
  • Insulation type and the amount needed on the rim joists and the walls
  • Repairs to framing, plumbing or ducts found during the work

What a written quote should spell out

  • Crawl space size and the area to be covered by the vapor barrier
  • Vapor barrier material, its thickness and how it is sealed at the walls and the piers
  • Vent closure method and the air sealing included
  • Drainage, sump or dehumidifier scope, with the electrical work listed separately
  • Insulation on the rim joists and walls, with the material and the thickness
  • Moisture source repairs included or listed separately, and the warranty terms

Questions to ask before you hire

  • What moisture sources did you find, and which ones must be fixed before the encapsulation?
  • What thickness is the vapor barrier, and how are the seams and the piers sealed?
  • Do you close the vents, and how do you provide the crawl space with air if it needs it?
  • Is a dehumidifier included, and who makes its electrical connection?
  • What drainage do you install if there is standing water, and where does it discharge?
  • How will you check the work after the encapsulation is complete?
  • Who checks the joists and sill plates for rot before the barrier covers them, and what happens if rot is found?

Red flags

  • They lay plastic sheeting on the dirt and call it a vapor barrier
  • They seal the vents without finding and fixing the moisture source
  • They install a dehumidifier without a drain or a plan for the water it collects
  • They do not inspect the framing or the wood for rot before they cover it

What you can do yourself

You can keep the crawl space access clear, check for standing water after rain, and note any wet spots, sagging insulation or musty smells. You can also fix a leaking outdoor faucet or extend the downspouts away from the foundation. Do not install a vapor barrier, seal the vents, or work in the crawl space with damaged or moldy materials yourself. Call a licensed contractor to inspect and encapsulate the space.

Licenses and permits

Crawl space encapsulation is commonly done by licensed contractors, and any hardwired dehumidifier or drainage pump is often required to be connected by a licensed electrician. Some areas require permits for the work. Check with your state or local licensing agency and your local building department for the rules that apply to the crawl space.

Crawl space encapsulation questions

Should I close the crawl space vents?

It depends on the climate, the drainage and the design. Closing vents usually works best with a vapor barrier and a dehumidifier. Ask the contractor how the space will be kept dry and whether the design calls for a conditioned approach.

Does encapsulation fix mold in the crawl space?

It helps by controlling moisture, but existing growth must be dealt with first. Ask the contractor to inspect for growth, remove wet materials and fix the source before the barrier goes down.

Will encapsulation lower my energy bills?

It can reduce the moisture load and help the floors feel warmer, which may affect heating and cooling use. The amount depends on the home, the equipment and the insulation, so ask the contractor for their basis.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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