Free calculator
Crawl Space Encapsulation Calculator
Enter the crawl space size, wall height, piers and vents. Get the square feet of vapor barrier, the seam tape, butyl tape and fasteners, the dehumidifier a sealed crawl space needs, and the DIY materials cost against a professional install.
Updated Nov 12, 2026
- Answer a few questions
- See the math behind every number
- Get models that actually fit
Every encapsulation part this tool can recommend
Barrier rolls by thickness, tapes, fasteners and vent covers. Dehumidifiers come from the dehumidifier sizer's list of crawl space units.
AlorAir 10 mil Crawl Space Vapor Barrier, 10 x 100 ft
- 10 x 100 ft
- Black/white panda film
A 10 mil black and white polyethylene ground cover for a crawl space you rarely go into.
- 10 mil polyethylene
- 1,000 sq ft per roll
- Black side down, white side up for light
- Thinner film tears easier under knees and storage
About $129.99 at AlorAir, checked Nov 12, 2026
Check price at AlorAirPaid link. We earn a commission at no cost to you.
AlorAir 12 mil Crawl Space Vapor Barrier, 10 x 100 ft
- 10 x 100 ft
- Black/white panda film
A 12 mil black and white polyethylene barrier for floors and walls in a crawl space you service once or twice a year.
- 12 mil polyethylene
- 1,000 sq ft per roll
- Reinforced, anti-aging additives (maker)
- Not woven; heavy storage or daily crawling calls for 20 mil
About $192.99 at AlorAir, checked Nov 12, 2026
Check price at AlorAirPaid link. We earn a commission at no cost to you.
Crawldryer 20 mil Crawl Space Vapor Barrier, 10 x 100 ft
- 10 x 100 ft
- White LDPE
A 20 mil white polyethylene barrier for a crawl space you store things in or crawl through often.
- 20 mil (0.02 in) polyethylene
- 1,000 sq ft per roll
- White surface brightens the space
- Heavy roll, harder to fold around piers
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
SUYISH Double Sided Butyl Sealant Tape, 2 in x 90 ft
- 2 in wide
- Double sided
Double sided butyl strip that seals the top edge of the barrier to the foundation wall.
- Double sided
- Sticks to unprimed concrete and block (maker)
- Rated 0 to 250 F
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
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Taiyin Christmas Tree Vapor Barrier Fasteners, 1 3/8 in (150)
- 1 3/8 in long
- White nylon
Push-in nylon fasteners that pin the barrier to the wall through a 1/4 in drilled hole.
- 150 pieces
- 1 in head
- Fits a 1/4 in hole
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
OKQX Christmas Tree Vapor Barrier Fasteners, 1 3/8 in (300)
- 1 3/8 in long
- Black polyethylene
A 300 pack of push-in fasteners for a long foundation perimeter.
- 300 pieces
- 1 in head, 1/4 in shaft
- Made for 6 to 20 mil barriers (maker)
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
RTTHEL Vapor Barrier Seam Tape, 4 in x 180 ft (3 rolls)
- 4 in wide
- 9 mil
- 3 rolls
White polyethylene tape for the overlapped seams and pier wraps of a crawl space barrier.
- 540 ft total in 3 rolls
- 4 in wide, 9 mil
- Bonds to plastic, wood and concrete (maker)
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Kensal Home Solid Crawl Space Vent Cover, fits 8 x 16 in openings
- Solid ABS
- Non-opening
A solid, non-opening ABS cover that closes a standard 8 x 16 in foundation vent for good.
- Solid ABS, no damper to leak
- Fits most 8 x 16 in openings
- Room inside for a foam insulation insert
- Fasteners or adhesive not included
- Measure first: other vent sizes need another cover
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Some of these links pay us a commission and some do not; each card says which. Commissions do not affect which models the tool picks or how it ranks them. See our disclosure.
How this calculator works
- Floor. 10 ft wide strips run the long way, lapped 12 in (the code minimum is 6 in), with the last strip cut to width. Ground cover only adds 12 in up every wall.
- Walls and piers. Sealing covers each wall from 3 in below the sill to the floor, with a 12 in lap onto the floor barrier. Piers are wrapped as 16 in square blocks, full height when sealed and 12 in when not.
- Waste and tape. 10 percent extra barrier for cutting. Seam tape covers every lap, the wall-to-floor seam, the corners and the pier wraps. Butyl runs the full top edge, with a fastener every 18 in.
- Dehumidifier. Sealed crawl spaces get the dehumidifier sizer's AHAM chart for your floor area and dampness, filtered to crawl space units the maker rates for your area. With no drain, the cheapest installed choice wins, counting an add-on pump where a unit lacks one.
- Cost. Materials are the parts list at current prices. The installed range is $3 to $7 per sq ft of floor, from This Old House's 2026 cost guide.
Worked examples
40 x 30 ft crawl space, 3 ft walls, sealed
- 40 x 30 ft, 3 ft walls, 8 piers, 6 vents
- Seal it, serviced once or twice a year (12 mil)
- Always musty, must pump the water out
About 2,171 sq ft of 12 mil barrier (3 rolls), 374 ft of seam tape, 196 ft of butyl tape, 126 fasteners and 6 vent covers.
The floor takes 4 strips of 10 ft roll lapped 12 in (1,320 sq ft), the walls 525 sq ft from 3 in below the sill with a 12 in lap onto the floor, and the pier wraps 128 sq ft; plus 10 percent for cutting. The sealed 1,200 sq ft needs a crawl space dehumidifier the maker rates for at least that area, and with no drain a built-in pump. Installers typically charge $3,600 to $8,400 for this floor.
50 x 28 ft crawl space, ground cover only
- 50 x 28 ft, 2.5 ft walls, 10 piers, 8 vents
- Ground cover only, almost never entered (10 mil)
About 1,952 sq ft of 10 mil barrier (2 rolls), 247 ft of seam tape, 225 ft of butyl tape and 144 fasteners. No dehumidifier.
Each strip runs 52 ft so it turns 12 in up the end walls, and the 4 strips cover 30 ft across so they turn up the side walls too, which is twice the code's 6 in minimum. The vents stay open, so the space is not dehumidified; the cover stops ground moisture, the vents handle the rest.
60 x 35 ft crawl space, 4 ft walls, wet, used for storage
- 60 x 35 ft, 4 ft walls, 14 piers, 10 vents
- Seal it, used for storage (20 mil)
- Wet spots, floor drain nearby
About 3,838 sq ft of 20 mil barrier (4 rolls), 571 ft of seam tape, 285 ft of butyl, 183 fasteners, 10 vent covers and 34 pints a day of drying.
2,100 sq ft at the wet line of the AHAM chart needs 34 pints a day. Two 60 pint crawl space units, one at each end, cover it for less than one 100 pint unit and dry a long space more evenly. Walls this tall are often insulated too; foam board goes on before the barrier. Installers typically charge $6,300 to $14,700 here.
Frequently asked questions
How much vapor barrier do I need for my crawl space?
About 1.4 times the floor area for ground cover only (12 inch laps, 12 inches up each wall and cutting waste), and about 1.8 times if you seal the walls and piers too. A 40 x 30 ft crawl space with 3 ft walls and 8 piers takes about 1,668 sq ft as ground cover or 2,171 sq ft sealed.
What thickness vapor barrier is best for a crawl space?
12 mil for a crawl space someone goes into once or twice a year, 20 mil if you store things there or crawl through often, and 10 mil only where nobody goes. Thicker film resists tears from knees, tools and rocks. Some local codes call for an ASTM E1745 Class A barrier, which plain thin poly usually is not, so check yours.
How much does crawl space encapsulation cost?
This Old House puts professional encapsulation at $3 to $7 per sq ft, up to about $10 with serious moisture problems, around $5,500 for a typical project. DIY materials are mostly the barrier and the dehumidifier; the calculator prices both for your size.
How much should the vapor barrier overlap?
The code minimum is 6 inches, taped. We plan a 12 inch overlap, the common practice, which leaves room to tape the seam without the film pulling apart. Edges go at least 6 inches up the wall and are attached and sealed to it.
Do I need a dehumidifier after encapsulating my crawl space?
A sealed crawl space has to be conditioned somehow. The IRC accepts a dehumidifier sized to the maker's specs, continuous exhaust at 1 cfm per 50 sq ft, or a conditioned air supply at the same rate. A dehumidifier is the usual choice for an existing home.
Should I close the crawl space vents?
Only if you seal the whole crawl space and condition it. A sealed crawl space with open vents pulls in humid summer air. If you only lay ground cover, leave the vents open.
Do vapor barriers go up the walls?
Yes. Even ground cover goes at least 6 inches up the wall by code; we plan 12. Full encapsulation covers the whole wall to about 3 inches below the wood sill, leaving the sill visible for termite inspection.
Can I encapsulate a crawl space myself?
Yes, if you can work on your knees for a few days. The steps are clearing debris, fixing standing water, laying the floor strips with lapped and taped seams, running butyl and fasteners along the walls, wrapping piers, closing the vents and setting the dehumidifier on risers.
Marcus Reed
Founder and Editor, CrunchYourDollars
Marcus Reed builds the sizing tools on CrunchYourDollars. He is a software engineer with a long-running PC hardware and power supply habit, which is where the watts, watt-hours and surge math on this site comes from. Product specs are pulled from manufacturer data sheets, electricity rates from the U.S. Energy Information Administration, and water chemistry rules from the Water Quality Association. He is not a licensed electrician or plumber: the tools show the math and the matching models so you can make the call, and anything involving your electrical panel should be checked by a licensed pro.
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