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 Derry 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 Derry
$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 the state’s map records under Derry
Derry has a proper surficial geologic map, published by the New Hampshire Geological Survey in 1985 as GEO-89 at 1:24,000, and it is more detailed than most towns get.
That map records twelve mapped units (New Hampshire Geological Survey, Surficial Geologic Map of the Derry Quadrangle, Rockingham County, Gephart, 1985). Among them are alluvium, swamp deposits and stream terrace deposits from the Holocene, and a set of glacial lake deposits including Glacial Lake Auburn, Glacial Lake Cohas Brook, Glacial Lake Wilson and Glacial Lake Derry, plus the Chester glacial stream deposits.
Glacial lake deposits matter to anybody with a basement. Material that settled out in still water tends to be fine, and fine material holds water rather than letting it pass.
One honest limit, and we would rather state it than gloss it: the Derry quadrangle covers roughly two-thirds of the town, not all of it. So “Derry’s geology is X” is not a sentence anybody should write, including us. Part of the town is on that sheet and part is not.
Soils and how they drain
The USDA NRCS soil survey data for the town is aggregated by dominant component, and that carries its own caveat worth knowing: a component-percentage weighting gives a materially different drainage picture than a dominant-component one. Two legitimate methods, two different numbers. We are not going to pick whichever one sounds better.
Why we lead with the caveats
Because the alternative is a contractor telling you what is under your house based on a map that may not even cover your side of town.
Derry is one of the closest towns to our shop in East Kingston, so we are through there constantly and we are not guessing about the drive. What is under a specific foundation on a specific street is a different question, and the only honest way to answer it is to come and look.
That inspection is free, and you get a written scope out of it rather than a number over the phone.
Glacial lake ground, and what it tends to do
Four of the twelve units on the Derry sheet are glacial lake deposits. Material that settled out of standing water is finer than material dumped by a fast meltwater stream, and fine material is slow to give water up once it has taken it on.
That is a general property of the material, not a prediction about your foundation. Plenty of houses sit on fine ground with dry basements, usually because the water around them has somewhere better to go.
The stream terrace and alluvium units on the same map tell you where water has historically run and left material behind. Those are the low routes through town, and low routes stay low.
What our customers say
Got 2 quotes to encapsulate a dirt floor under my breezeway between my garage and house 603 explained exactly what they were going to do and you and products they were going to use. Pricing was extremely reasonable compared to the other quote that I got. Job was done in a timely fashion. Crew was great. Would highly recommend 603 basement solutions any day
Brian Dean, 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 Derry
- Basement waterproofing in Derry
- 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 Derry
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 Derry and the surrounding towns from our shop in East Kingston, New Hampshire.
Common questions about crawl spaces
- What are the top reasons for immediate house foundation repair and crawl space encapsulation?
- What challenges should I expect fixing squeaky floors in a house with a short crawl space?
- What is the difference between a crawl space and a basement?
- What is the difference between a moisture barrier and a vapor barrier?
- What should the humidity in a crawl space be at different times of year?
- Why, after so many years living without it, is crawl space encapsulation so recommended now, when it lasts 10-15 years and costs half of a foundation repair?
- Can ‘dormant’ mold spores appear and affect a crawl space?
- Can I use plastic sheeting as a vapor barrier?
- Crawl space is infested with mold, how do we go about properly fixing it?
- Does crawl space encapsulation increase home value?
- Does encapsulating a crawl space really work and is it worth the money?
- How does a vapor barrier function?
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- Basement Waterproofing in Derry, NH
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- Foundation Crack Repair in Derry, NH
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