In New Hampshire, professional crawl space encapsulation runs $3,000 to $25,000. Where your job lands in that range comes down to five things: the size of the crawl space, the thickness of the vapor barrier, whether you need drainage and a sump, whether you add a radon fan, and the shape the space is in before we start.
That’s a wide band on purpose. A small, dry crawl space with good access is a different job from a large, wet one with rotting wood and elevated radon. No honest contractor can hand you a flat number without getting under the house first. Below is exactly what moves the price, what the number covers, and what it doesn’t.
What crawl space encapsulation costs in New Hampshire
603’s NH range for a full crawl space encapsulation is $3,000 to $25,000. That covers the spread from a straightforward seal-up of a small, dry space to a full system in a large crawl space that needs drainage, moisture control, and prep work before the barrier ever goes down.
We don’t quote a flat price over the phone, and you should be wary of anyone who does. The cost depends on what we find when we open the space — access, moisture source, and condition all move the number. That’s why we start every job with a free inspection.
What moves a job within that range
Five factors decide where a crawl space lands between $3,000 and $25,000. Here’s how each one works.
Square footage and layout
The bigger the footprint, the more vapor barrier, matting, and labor it takes — that’s the obvious half. The less obvious half is layout. A crawl space you can stand up in is fast to work. One with 24 inches of headroom, a dirt floor, multiple piers, ductwork, and pipes to seal around takes far longer to do right. Tight access and obstructions raise the cost even when the square footage is small.
Vapor-barrier thickness (mil)
“Mil” means one thousandth of an inch — it’s how vapor barriers are graded. Thicker liner resists punctures, lasts longer, and costs more. Building code sets a floor here: the International Residential Code (IRC R408.2) requires at least a 6-mil Class I vapor retarder over the exposed earth in an unvented crawl space.
603 builds well above that minimum. Our encapsulation uses a 12-mil vapor barrier on the walls and a 20-mil vapor barrier on the floor — the 20-mil floor liner takes the foot traffic and abuse, so it’s the heaviest grade. A thicker, more durable system costs more upfront than a thin code-minimum liner, and it’s the difference between a barrier that lasts and one you re-do.
Drainage matting and a sump pump
If water gets into the crawl space, sealing it in is the wrong move — you have to give it somewhere to go. We run dimpled drainage matting underneath the 20-mil floor barrier; the channels route any groundwater to a sump pump that pumps it out.
This is one of the biggest swing factors in the whole quote. A genuinely dry crawl space may not need the matting-and-sump layer at all. A wet one does, and that’s added material and labor. Whether your space needs it is one of the main things the inspection settles.
A dehumidifier
A sealed crawl space still needs its air managed, so a dehumidifier is part of a fully encapsulated system. It keeps humidity down once the space is closed off, which is what stops condensation, musty air, and the mold that grows in damp insulation and wood.
A radon fan add-on
Radon is a real consideration in a New Hampshire crawl space. The EPA estimates radon causes about 21,000 lung-cancer deaths a year in the U.S. and is the leading cause of lung cancer among people who’ve never smoked. The EPA recommends fixing a home when radon measures 4 pCi/L or higher. And this isn’t a national average problem you can wave off — the EPA’s Map of Radon Zones puts every New Hampshire county, including Rockingham County, where we do most of our work, in Zone 1, the highest-potential category, meaning the predicted average indoor level is above that 4 pCi/L action level.
If a radon test comes back elevated, a mitigation fan ties into the sealed crawl space to vent it. That’s a separate add-on, not part of the base encapsulation number — more on that below.
The condition it’s in before we start
A clean, dry, empty crawl space is ready for barrier. A space with standing water, an old failed liner, mold, rotted wood, or debris needs prep first — pump it out, clear it, address the moisture source. That prep is real work, and it’s why two crawl spaces of the same size can quote very differently.
What the price covers
A 603 crawl space encapsulation is a full sealed system, not a sheet of plastic. The price covers:
- 12-mil vapor barrier on the walls
- 20-mil vapor barrier on the floor — the heavier grade, where the wear happens
- Dimpled drainage matting under the floor barrier, where the space needs it, routing water to the sump
- All seams sealed with spray-foam insulation, so the envelope is actually closed
- A dehumidifier to manage humidity in the sealed space
- A sump pump to clear any water the matting collects
The encapsulation carries a 25-year warranty covering the liner, the wall barriers, and the workmanship. That’s the figure to anchor on. (The dehumidifier and sump system carry their own manufacturer-based terms.)
What’s usually not included
Knowing what isn’t in the encapsulation number is just as useful as knowing what is. These are priced separately:
- Structural repairs. A rotting sill plate, failing lally columns, or sagging floor framing are structural jobs, not encapsulation. If we find them, we’ll tell you and quote them on their own — they’re not folded into the barrier price.
- Radon testing and mitigation. A radon test runs $50, and a mitigation fan is an add-on, not baked into the base encapsulation. We don’t pad the number with a radon system you may not need until we’ve tested. If you do need one, radon mitigation is its own line — typically $1,950 to $2,250.
- Finishing the space. Turning a crawl space into usable, finished living area is a different project.
And if the inspection shows you don’t need the full system yet, we’ll say so. We’d rather give you the honest version than sell you a layer you don’t need.
Why a real quote needs an inspection
You can’t price a crawl space from a phone call or a photo. The three things that decide the cost — how the space accesses, where the moisture is coming from, and what condition the wood and floor are in — can only be read in person. That’s the whole reason the inspection exists.
So we do it free. A 603 inspection comes with a free, written estimate, and we get the quote back to you within 24 hours. You’ll know exactly what your crawl space needs and what it costs before you commit to anything.
Frequently Asked Questions
How much does crawl space encapsulation cost in New Hampshire?
603’s NH range for a professional crawl space encapsulation is $3,000 to $25,000. The spread reflects everything from a small, dry, easy-access space to a large, wet one that needs drainage, a sump, and prep work before the barrier goes in.
Why is there such a big range in encapsulation prices?
Five factors move the number: the square footage and layout of the space, the thickness of the vapor barrier, whether you need drainage matting and a sump pump, whether a radon fan gets added, and the condition the crawl space is in before work starts. A small dry space and a large wet one are different jobs.
What’s included in a professional crawl space encapsulation?
A 603 encapsulation is a full sealed system: a 12-mil vapor barrier on the walls, a 20-mil vapor barrier on the floor, dimpled drainage matting under the floor barrier where it’s needed, all seams sealed with spray-foam insulation, a dehumidifier, and a sump pump. It carries a 25-year warranty on the liner, wall barriers, and workmanship.
Does crawl space encapsulation include radon mitigation?
No. A radon test runs $50, and a mitigation fan is a separate add-on, not part of the base encapsulation price. New Hampshire crawl spaces often need it — the EPA places every NH county, including Rockingham, in its highest radon-potential zone — but we only add it if a test shows your levels are elevated.
Is a thicker vapor barrier worth the extra cost?
Code only requires a 6-mil minimum vapor barrier over the earth in a sealed crawl space. 603 runs a 12-mil liner on the walls and a 20-mil liner on the floor because a thicker barrier resists punctures and lasts. It costs more upfront than a code-minimum liner, but it’s the difference between a system that holds and one you re-do.
Why can’t 603 give a price over the phone?
Because the cost depends on what’s under your house. Access, the source of the moisture, and the condition of the wood and floor all move the number, and none of them can be read over the phone. That’s why we start with a free inspection and a free written estimate, with the quote back to you within 24 hours.
Ready to find out what your crawl space needs?
If your crawl space is damp, musty, or you just want it sealed up for good, we’ll come take a look. The inspection is free, the written estimate is free, and you’ll have your quote within 24 hours — no pressure, no flat phone-quote guesswork, just an honest read of what your home needs. 603 Basement Solutions has handled crawl spaces in homes across the Seacoast and Rockingham County, and we’ll tell you straight whether you need the full system or not.
