Encapsulation seals a crawl space off from the ground. Liner on the dirt floor, barrier up the walls, the whole thing tied together and sealed, and a way to control the moisture that is already in there. In Nashua it usually runs $3,000 to $25,000, quoted in writing after we look at it.
How do you know your crawl space needs it?
You usually smell it before you see it. That damp, closed-up smell in the room above the crawl is air coming up out of the crawl, because that is what air does in a house. It moves up.
Other things we get called for:
- Floors above the crawl that feel cold or springy
- Condensation on ductwork or pipes down there
- Rot at the bottom of framing, or fungus growing on joists
- Mice, red squirrels, anything that found a way in and stayed
- A dirt floor that is damp to the touch even in a dry stretch
An unhealthy crawl space will rot your house from the inside out. It is not the kind of thing that holds steady and waits for you.
What actually goes in
A real encapsulation is not a sheet of plastic thrown on the dirt. Ours is a liner across the full floor, barrier run up the foundation walls, everything lapped and sealed so there is no open seam, and moisture control sized for the space. We spec a heavier liner on the floor than on the walls, because the floor is what gets walked on when somebody has to get down there to run a wire in ten years.
If there is standing water, that gets solved first. Sealing a wet crawl just traps the water on the inside of a nice new liner.
What it costs in Nashua
$3,000 to $25,000, and that is a wide range because crawl spaces are wildly different from each other. What moves your number:
- Square footage. The single biggest driver.
- Headroom and access. A crawl you can sit up in is a different job from one somebody has to army-crawl through with materials.
- What is down there now. Old insulation falling out of the joists, debris, a previous half-attempt at a vapor barrier. It all has to come out first.
- Whether there is water to deal with. Drainage or a pump adds to it.
- Rot. If framing is gone, that is structural work and it happens before the liner.
We give you a written number after somebody has been in the crawl. Not before.
The warranty
Crawl space encapsulation carries a 25 year warranty on the liner, the wall barriers and the workmanship. Dehumidification carries 5 years per the manufacturer terms.
One thing worth knowing: if somebody else later fastens into a sealed wall and puts holes through the barrier, that damage is not covered. Tell whoever works down there next that there is a system on those walls.
Questions we get
Should I just add vents instead?
Venting a crawl space in New England means inviting in humid summer air that then condenses on cool surfaces. Sealing is the approach we use.
Do I need a dehumidifier too?
Usually yes for a full encapsulation, because sealing controls where moisture comes from but does not remove what is already in the air. We size it to the space.
Can I do part of it now?
Yes, and people do. Tell us the whole plan so we do the first part in a way that does not have to be undone.
How long does it take?
Most crawls are a day or two once we start. Rot repair or drainage adds time.
What you are seeing, and what it usually means
| What you notice | What it usually points to | What we normally do |
|---|---|---|
| Musty smell in the rooms above | Crawl air moving up into the house | Seal the crawl, then control the moisture left in it |
| Cold or springy floors | Insulation failed, or framing has softened | Check the framing first, insulate after the seal |
| Condensation on ducts and pipes | Humid air meeting cold surfaces | Dehumidification sized to the space |
| Damp dirt floor in a dry spell | Ground moisture coming up continuously | Full floor liner, lapped and sealed to the walls |
| Standing water after rain | Water entering, not just vapour | Drainage or a pump before anything gets sealed |
| Fungus or soft spots on joists | Rot, which is structural | Repair the framing first. Sealing over rot hides it |
How the job runs
Somebody comes out and gets into the crawl. Not a look through the hatch with a torch, actually in there, because you cannot see the far corners from the opening and the far corners are usually where the trouble is.
Then you get a written scope. What is coming out, what is going in, what it costs. If there is rot or standing water, that is its own line and its own sequence, because sealing over either one just hides it under a new liner.
On the day, the old material comes out first. Debris, fallen insulation, whatever the last owner left. The liner goes down across the full floor, runs up the walls, and every seam gets lapped and sealed. Then the moisture control goes in and gets set.
Most crawls are a day or two. Rot repair or drainage adds to that, and we will tell you which one you are before we start rather than after.
What Nashua’s own records say about water
Nashua does not guess about this, and neither should we. The city keeps its own numbers, and they are worth knowing before you spend money on a basement.
Roughly 20 percent of the city runs on combined sewers, which carry sewage and stormwater in the same pipe, and the city notes that some of those sewers date back to the 1880s (City of Nashua Stormwater Funding Feasibility Study, 2011). The drainage network they are attached to is large: 8,069 catch basins, 130 miles of drainage pipe, 807 outfalls, and about 400 catch basins cleaned a year, which is roughly five percent of them.
The city also names the places that give trouble. Old Maid’s Brook at Shelley Drive and Browning Avenue “currently overtops the road creating a hazard.” Harris Brook at Northeastern Boulevard does the same. Manchester and Charlotte floods “due to a lack of a drainage system” (same study, capital improvement list).
And when it rains hard here, basements are what fills. In the 11 September 2023 event, Nashua Emergency Management recorded about a dozen reports of flooded basements, with 2 to 6 inches of rain reported between Hollis, Nashua and Hudson (City of Nashua Hazard Mitigation Plan Update, 2024).
The ground under the city
Four watersheds sit inside Nashua, all draining to the Merrimack, and the city’s floodplains run with Pennichuck, Hale, Hassel and Salmon Brooks as well as the two rivers (Nashua Natural Resources Inventory and Conservation Plan, 2006). The land falls from Gilboa Hill at 426 feet to about 90 feet at the Merrimack in the southeast corner.
Gilboa Hill is not just high ground. The USGS records it as one of several thick-till-cored drumlins in the area. Till is dense, mixed glacial material, and it drains slowly. Down near the rivers the soils are different again, with Windsor and Hinckley types among the largest mapped units in this survey area (NRCS soil survey NH601).
So a house on Gilboa and a house off Main Dunstable can have genuinely different water behaving genuinely differently, in the same city, in the same storm.
That is the regional picture. It is not a reading of your lot, and we are not going to pretend it is. Two houses on one street can sit on different material. The free inspection is where we find out which one you have.
Flood insurance and the streets that carry water
Nashua joined the National Flood Insurance Program on 15 June 1979, and as of January 2017 held 155 policies in force against $43,548,100 of insurance, with 31 paid losses. The NOAA gauge on the Merrimack at Nashua sets minor flood stage at 18 feet and records a crest of 41.3 feet in March 1936.
Several road crossings sit inside the floodway itself: Main Street at the Nashua River, Allds Street at Salmon Brook, Manchester Street at a floodway crossing, with Pine Hill Road inside the 0.2 percent floodplain. Salmon Brook, which takes in Hassell, Old Maid’s and Hale Brooks over its 6.5 miles, is listed impaired for E. coli with the source recorded as illicit connections to storm sewers.
None of that is a verdict on a specific street. It is the shape of how this city moves water, and it is the background we are working against when we look at a basement here.
What our customers say
We had basement encapsulation and radon mitigation completed from 603 basements and are very happy with the results. The entire process was great from the consultation/quote through the completion of the job. They answered all of my questions about anything basement related and also were reasonably priced. We have a continuous radon detector and our numbers reduced from 18 to less than 2! We have another basement project to do later this year and will no doubt use them again! Thank you 603 basements!
SHAUNA MULLENIX, Google review, 5 stars
That is one of more than 240 Google reviews. We would rather you read them than take our word for anything on this page.
Related pages for Nashua
- Basement waterproofing in Nashua
- Crawl space services
- Crawl space encapsulation cost
- Every town we cover
- Who you would actually be dealing with
- Basement waterproofing
- Straight answers to basement questions
Book a free inspection in Nashua
Somebody comes out, looks at the actual space, and tells you straight what it needs and what it does not. You get a written number for a defined scope. No two hour pitch, because we would rather be at the next house.
If you are looking for a team that isn’t going to treat you like another number, we would be happy to give you an estimate free of charge. We don’t cut corners. We stand behind our work. We care.
Call 603-610-1770 or book your free inspection. We cover Nashua and the surrounding towns from our shop in East Kingston, New Hampshire.
Common questions about crawl spaces
- Does encapsulating a crawl space really work and is it worth the money?
- How does a vapor barrier function?
- How imperative is it that a house is anchored to a crawl space?
- How much does it cost to encapsulate the crawl space for a 3,000 sq ft house? Is it worth it?
- How much wood moisture in your crawl space can you tolerate
- How to get rid of moisture in a crawl space
- I had my crawl space encapsulated and outside vents sealed. Why have my radon levels gone up?
- I was told of an add-on for my crawl space encapsulation: insulation under the 20 mil white casing. Is that preferred?
- If a house already has a vapor barrier, is there a need for another one?
- If the humidity in your crawl space is 60-70% but in your house it’s lower, do you still need to fix the crawl space?
- Is a little water in a crawl space normal?
- Is a vapor barrier necessary under the subfloor?
More 603 services in Nashua
- Basement Waterproofing in Nashua, NH
- Foundation Crack Repair in Nashua, NH
- Radon Mitigation in Nashua, NH
