Liner rolls, seam and butyl tape, termination bar and dehumidifier for a sealed crawlspace.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ Fix standing or actively flowing water before you encapsulate — a liner and dehumidifier manage humidity, not a flood. If the space floods or stays wet in a rainy season, install a French drain or a sump pump first; see the French Drain Builder or Sump Pump Builder.
⚠ Closing 4 foundation vents changes how the space breathes. Most codes that allow closed vents (commonly a version of IRC R408.3) require either a continuously running exhaust fan or a mechanical dehumidifier in place of passive ventilation — check your local code before sealing every vent shut.
| Membrane & Fabric | $517–$699 |
| Drainage | $408–$552 |
| Finishing & Sealant | $271–$367 |
| Insulation | $61–$83 |
| Fasteners & Hardware | $37–$51 |
| Total | $1,295–$1,751 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
About this calculator
Give the Crawlspace Encapsulation Calculator your crawlspace's floor length and width, the average wall height you're wrapping the liner up to, and how many support piers stand in the space, and it lays out a full sealed-crawlspace takeoff: reinforced poly liner sized to the floor plus the wall wrap-up, seam and butyl tape, a termination bar and drive pins to anchor the liner at the foundation, and a dehumidifier sized to the space.
Pick a liner thickness from 6 to 20 mil, and toggle vent covers, an access-door weatherstrip kit and a floor drainage mat for a wetter site. This is a moisture-control envelope, not a thermal one — pair it with the Insulation Calculator if you're also insulating the rim joists or subfloor. Closing foundation vents changes how the space needs to breathe, so check your local code (IRC R408) before sealing every vent shut.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
Address any standing or actively flowing water with grading, a French drain or a sump pump first — a liner traps water it doesn't stop, so the drainage work always comes before the encapsulation.
Remove debris, old insulation and anything touching the dirt, and knock down high spots that could puncture the liner. Note where piers, ductwork and plumbing will need the liner cut and sealed around them.
Fit foam covers into the foundation vents you're closing per your local code, and weatherstrip the access hatch so it seals into the same closed system.
Fasten the termination bar around the full perimeter at your wrap-up height, driving pins into the foundation wall on a clean, brushed ledge so the fasteners hold.
Run liner strips across the floor at the roll's full width, overlapping each seam by several inches and taping every seam as you go.
Bring the liner up the foundation walls to the termination bar, bedding the top edge in butyl tape underneath the bar, and wrap each support pier separately, taping it to the floor liner.
Go back over the whole space and tape any remaining seams, pier wraps and pipe or duct penetrations — a sealed system is only as good as its weakest gap.
Install the dehumidifier with its condensate line run to a drain or sump, set it to hold 50–55% relative humidity, and check back after a few days to confirm it's cycling normally.
Equip the job
Hand-picked categories that match the shopping list above. Links open a current selection so you can compare brands and prices.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
As an Amazon Associate I earn from qualifying purchases. We may also earn from other retailer links here. This doesn’t change your price and helps keep these planners free.
Keep planning
Interior & Finishing
Answers
A full encapsulation seals the crawlspace off from ground moisture and outside air: a reinforced poly liner covers the dirt floor and wraps up the foundation walls to a termination bar, every seam and penetration gets taped, the foundation vents are covered or closed, and a dehumidifier keeps the sealed space at a target relative humidity. It's different from just laying plastic on the ground — the wall wrap-up, the mechanical termination at the top edge, and the vent and air-sealing work are what actually stop the space from tracking humid outside air and soil moisture into the floor above.
Sealing the vents is central to encapsulation — an open-vented crawlspace pulls in warm, humid outside air that condenses on the cooler foundation walls and framing, which is the opposite of what you want once the liner is down. Most jurisdictions that allow closed vents require it under a specific code path, commonly a version of IRC R408.3, that calls for either a continuously running exhaust fan or a mechanical dehumidifier sized to the space instead of passive ventilation. Confirm your local code before sealing every vent, and budget for the dehumidifier either way — it isn't optional once air can no longer exchange freely.
6 mil poly is the bare minimum and tears easily around piers, ductwork and foot traffic, so most encapsulation jobs use at least 10 mil reinforced liner. 12 mil holds up well in crawlspaces you'll actually walk through for storage or utility access, and 20 mil heavy-reinforced liner is worth the extra cost in wet, rocky, or frequently-serviced spaces where punctures are likely. The calculator prices whichever grade you pick, but going thinner than 10 mil to save money on a space with real foot traffic usually means a puncture and a redo within a few years.
Yes — sealing the liner and closing the vents stops new moisture from entering through the ground and the air, but it doesn't remove the humidity already in the space or generated by the house above (plumbing, HVAC ducts, seasonal swings). A crawlspace-rated dehumidifier with a condensate drain keeps relative humidity around 50–55%, which is the range that actually stops mold growth and wood rot. Skipping it after doing all the liner and sealing work is the most common reason an otherwise good encapsulation still smells musty a year later.
Yes, always. A vapor barrier and dehumidifier manage humidity and slow moisture migration through the soil, but neither one moves standing or actively flowing water — if your crawlspace floods or has a wet season, that has to be solved first with grading, a French drain, or an interior perimeter drain to a sump pump. Encapsulating over a space that still floods just traps water under an expensive liner where you can't see it, and the pump and drain still need to be installed before the liner goes down, not after.