Does encapsulating a crawl space really work and is it worth the money?

Yes, encapsulating a crawl space works, and for a damp or musty crawl it is worth the money. Sealing the crawl off from the ground and the outside air stops the moisture, clears the smell upstairs, and keeps the framing from rotting on a slow clock. Encapsulation runs $3,000 to $25,000 in New Hampshire, and the price tracks the size of the crawl and how much prep it needs first. If your crawl is already dry with no odor, you may not need it yet.

That is the short answer. Here is what is actually going on down there.

Why the crawl goes bad in the first place

Most crawl spaces sit on disturbed backfill. That is the looser soil the builder put back when the foundation went in. It drains slowly and holds water. So after a hard rain or a spring thaw, water pools right at the foundation and works its way in. NH frost heave makes it worse, pushing on the walls all winter.

Then the dirt floor does its part. Bare soil gives off moisture all day. That moisture rises into the joists and the subfloor, and eventually into the rooms above. You smell it before you see it. Musty air. A cold floor. Sometimes mold on the framing, or rodents and bugs making a home out of the mess.

Does sealing it actually fix that?

It does, when the work is done right. Encapsulation is not a sheet of plastic thrown on the dirt. Here is the full system we put in:

• A 12-mil wall vapor barrier up the foundation walls.
• A 20-mil floor vapor barrier across the dirt.
• Dimpled drainage matting under the floor barrier so any water has a path to follow.
• Spray foam to seal the seams.
• A dehumidifier to hold the space dry year round.
• A sump to handle water if the crawl takes any.

Put all that together and the crawl becomes a sealed, dry room. The barrier is rated tough enough to crawl on and move around in. The moisture that was feeding your house gets cut off at the source. That is why it works. You sealed the water out.

This is different from our Forever Dry System, which is a basement job. Crawl spaces get encapsulation.

What drives the cost

The biggest factor is the footprint. A bigger crawl is more area to cover, so it sits higher in the $3,000 to $25,000 range. After that:

• Headroom. A tight crawl is slower and harder to work in.
• Standing water or a wet floor, which leans on the sump and matting more.
• Old junk, debris, or a torn-up vapor barrier from a past job we have to pull out first.
• Whether you want radon handled at the same time.

We give you the number after we see it. The free inspection is how we know which of these apply to your house, and we get the written quote back to you within 24 hours.

Is it worth the money?

For a lot of homes, the moisture is the whole problem. Seal the crawl and the musty smell upstairs goes away, the floors feel warmer, and the framing stops rotting. The Department of Energy notes that up to about a third of a home’s heat loss can come through an uninsulated foundation or crawl, so a sealed crawl can take some load off your heating bill through a NH winter.

If your crawl is already dry, with a sound vapor barrier and no smell, you may not need this yet. We will tell you that to your face. Encapsulation earns its keep when there is real moisture, an odor, or framing starting to suffer. If you have got soft floors over the crawl, the fix might be added support, not the full barrier. We will sort out which is which when we are down there.

One more thing. If you have a dirt or fieldstone crawl and a radon reading, ask us about a sub-membrane radon system while we are in there. It pairs well with the same barrier work, so you only open up the crawl once.

Crawl encapsulation carries a 25-year warranty on our work, and the wall vapor barrier is backed 25 years too. The sump system is covered 3 years, and the dehumidifier 5 years. Trusted by 5,000+ homeowners in New England, and we are BBB A+ accredited, licensed and insured.

Talk to us

Call us at 603-610-1770 or book your free inspection. We will crawl the space, tell you what it needs and what it does not, and send a written quote within 24 hours.

Want more on the parts of the job? See crawl space services, radon mitigation, supplemental support, and the 603 guarantee. If your problem is really a basement, start with basement waterproofing instead.

Related questions

How long does an encapsulated crawl space last? The work carries a 25-year warranty, and the wall vapor barrier is backed 25 years too. The dehumidifier is covered 5 years and the sump system 3 years. Done right and left sealed, the crawl stays dry. The warranty transfers, but it is conditional. It voids if another contractor or homeowner touches our work.

Does encapsulation lower my heating bill? It can help. The Department of Energy notes up to about a third of a home’s heat loss can come through an uninsulated foundation or crawl. Sealing the crawl and adding a dehumidifier stops cold, damp air from working into the floors above, so your heat does not fight as hard in a NH winter.

Will encapsulation fix a radon problem? Not by itself. Sealing helps, but a high radon reading needs an active system. For a dirt or fieldstone crawl we install a sub-membrane depressurization system. Radon mitigation runs $900 to $6,000, and most homes land around $1,950 to $2,250, and a test is $50, credited toward the job if you move ahead. EPA says to fix at 4.0 pCi/L and to consider fixing between 2 and 4.

Is exterior digging a better way to keep the crawl dry? In our field experience, no. Exterior excavation jobs tend to fail in a couple of years and cost more to do. The durable fix for water is interior drainage and a sealed crawl.