Crawl space encapsulation cost

Encapsulating a crawl space costs $3 to $10 per square foot, so a 1,200 square foot crawl space is $3,600 to $12,000, with the national average around $5,500. Labour is 50% to 70% of it, because the work happens on hands and knees in a space three feet high.

Encapsulation means sealing the crawl space from the ground and the outside air: a heavy vapour barrier over the soil and up the walls, vents closed, and usually a dehumidifier to hold the humidity down.

What it costs

Mould remediation is the item that turns a $5,500 job into a $10,000 one, and it is common in exactly the crawl spaces that need encapsulating.

Why vented crawl spaces stopped making sense

For decades, code required crawl space vents, on the theory that outside air would dry the space out.

In humid climates it does the opposite. Warm, moist summer air enters the vents, meets the cool surfaces of the crawl space, and condenses. The vents are actively delivering water. That is why so many vented crawl spaces in the south have soaked insulation hanging out of the joists and mould on the framing.

Modern codes recognise sealed and conditioned crawl spaces as an alternative, and in humid regions encapsulation is generally the better approach. In a genuinely dry climate the argument is much weaker, and encapsulation there is often selling a solution to a problem the house does not have.

What it actually fixes

Humidity in the house. Air moves upward through a house, so much of what you breathe on the ground floor came through the crawl space first. Sealing it cuts musty smells and lowers indoor humidity measurably.

Mould and rot in the framing. Wood needs sustained moisture to rot. Take the moisture away and the process stops.

Cold floors. A sealed, insulated crawl space is meaningfully warmer underfoot than a vented one.

Pests. Sealing the space removes the entry routes and the damp habitat.

Duct and pipe losses. Ductwork in a vented crawl space is losing heat to outdoors. Once the space is inside the envelope, it is not.

What it does not fix: standing water. Encapsulation is a vapour control measure. Water entering the crawl space needs drainage and a sump first, and a barrier laid over a wet crawl space traps the water underneath it.

What a proper job includes

• Clearing debris, old insulation and any standing water
• Treating and removing mould before covering anything
• A drainage system and sump, where water enters
• A vapour barrier of at least 12 mil, and 20 mil where anyone will crawl on it
• The barrier running up the walls and sealed to them, with a termite inspection gap left where local code requires one
• Seams overlapped and taped, not merely laid alongside
• Vents sealed, and the rim joist air-sealed and insulated
• A dehumidifier with a drain, or conditioned air supplied from the HVAC system
• The barrier sealed around piers and penetrations

The two most commonly skipped items are the wall termination and the dehumidifier. A barrier lying loose on the soil with the walls untouched is not encapsulation; it is a ground cover, and it costs a third as much and does a third as much.

Is it worth it

In a humid climate with a damp crawl space, yes. It stops rot in the structure, which is the expensive failure, and the indoor air improvement is immediately noticeable to most people.

Energy savings are real but modest, typically 5% to 15% on heating and cooling, and most of that comes from bringing the ducts inside the envelope rather than from the barrier itself. Payback on energy alone is 10 to 20 years. Buy it for the structure and the air, not the utility bill.

In a dry climate with a dry crawl space, the case is thin.

Frequently asked questions

Can I do it myself?

Partly. Laying and taping a barrier is achievable if you are willing to spend days in a three foot space, and it saves most of the labour. Drainage, mould remediation and the dehumidifier are not DIY. The unpleasantness of the work is the main reason the labour costs what it does.

How long does it take?

Two to five days for a typical crawl space. Longer with drainage work or mould remediation beforehand.

Do I still need the vents?

No. Sealing them is part of the point, and modern codes permit a sealed crawl space provided it is conditioned or dehumidified. Some jurisdictions require a specific approach; a contractor working locally will know.

Will it fix a standing water problem?

No. Fix the water first with grading, gutters, a footing drain or a sump. A barrier over standing water hides it and rots the framing anyway.

Does it help with radon?

It can reduce it, because the barrier restricts soil gas entry, but it is not a radon system and it should not be sold as one. If radon is a concern, test, and fit a proper sub-slab depressurisation system at $800 to $2,500.