Heating and cooling
Crawl space insulation cost
A 1,200 sq ft crawl space is about $1,988 to insulate the traditional way — batts between the floor joists, a vapor barrier on the ground, the vents left open — and about $6,365 to seal: a reinforced liner over the ground and up the walls, R-10 foam on the walls, the vents closed and a dehumidifier. The first is right where the air is dry; the second is the one that lasts where it is not, because vented batts hold the summer moisture and fall in ten years. This prices both on the same space, by the climate zone that sets the R and the height that sets the hours.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-23 · Nothing you type leaves your browser
Crawl space insulation cost calculator
The space, the climate, and which way to do it
Two ways: batts in the floor with the vents open, or the space sealed with a liner, foam on the walls and a dehumidifier. The vapor barrier on the ground goes under both.
The footprint over the crawl.
Left blank: a square, 416 sq ft of wall.
Room to kneel.
A reinforced liner over the ground and up the walls, taped at the seams; foam board on the foundation walls; the vents sealed; and a dehumidifier or a trickle of house air to keep it dry. The space becomes part of the house, and the floor above it stops being cold.
R-10 on the walls.
String-reinforced, white, and it takes being crawled on. The usual liner for a sealed crawl.
Bare earth.
Crawl-rated, with a condensate pump.
Dry ground.
A crew, per square foot, with the height factored in.
Used only to pick a regional labour rate. It stays in your browser.
Sealed crawl
$6,365
$5 per sq ft of floor · 1,826 sq ft of liner · R-10 walls · 37.4 h
Sealed, and why it costs more
The liner goes over the ground and up the walls, the foam goes on the walls, the vents close and the dehumidifier keeps it dry: $6,365 against $2,394 for batts in the floor. It costs more because it does more — the floor above stops being cold, the ducts stop sweating, and the space stops growing mould.
Under both
The vapor barrier is the job.
Bare earth puts gallons of water a day into a crawl space as vapor, and it goes up into the joists, the subfloor and the ducts. A liner over every square foot of ground, lapped and taped, is the first thing under either approach — $986 here — and a crawl with insulation and no barrier is insulation getting wet.
One crawl space, two ways
Batts in the floor with the vents open, or sealed with the liner up the walls.
What the crew charges for
- 1,826 sq ft of 12 mil reinforced liner liner, floor and walls
String-reinforced, white, and it takes being crawled on. The usual liner for a sealed crawl.$822 - Seam tape, mastic and wall fasteners
Every seam taped, the liner glued and pinned to the wall a foot up, every pier wrapped.$164 - R-10 foam board on 381 sq ft of wall
Glued and pinned to the foundation wall, stopped 3 in below the sill for the termite inspection gap.$610 - 17 vents sealed
Foam board and sealant from inside, a cover outside.$544 - Crawl-rated dehumidifier, installed
A crawl-rated unit with a condensate pump to a drain, hung from the joists. A sealed crawl without one is a sealed crawl that grows mould on the joists.$1,610 - 37.4 crew hours, on their backs
A crawl space is worked on the back and the knees, and every square foot of it is crawled to twice. Under two feet of clearance nothing is quick.$2,615
What it costs
National average. 1,200 sq ft of crawl space, 36 in high, sealed crawl, climate zone 4, with a dehumidifier. Not included: mould remediation on the joists, a drainage tile or grading outside, radon mitigation, or a new access hatch.
The attic above the house is the other half of the envelope, on the insulation page; standing water in a crawl usually starts at the gutters and the grading, which are cheaper than a sump.
Worth knowing
- 1,200 sq ft of ground and 416 sq ft of wall, 36 in high. The liner covers the floor and runs up the wall — 1,826 sq ft with the overlaps — and 381 sq ft of wall gets R-10 foam board, stopped 3 in below the sill so a termite inspector can see the top of the wall.
- Sealed is $6,365 against $2,394 for batts in the floor with the vents open. It costs more because it does more: the floor above stops being cold, the ducts under the house stop sweating, and the space stops growing mould — in a humid climate, batts in a vented crawl hold the moisture and fall in ten years, and the sealed crawl is the one that lasts.
On this page — 5 sections
Two ways, and the air decides
The short version
- Vented, batts in the floor: $1,988. Sealed, liner and foam on the walls: $6,365. Same 1,200 sq ft.
- The vapor barrier goes under both. Bare earth puts gallons of water a day into the space.
- Humid air: seal it. Vented batts hold the summer moisture and fall in ten years.
- A sealed crawl needs a dehumidifier, about $1,350, or it grows mould.
A crawl space is done one of two ways. The traditional one leaves the foundation vents open, puts batts between the floor joists above, and lets outside air move through. It is cheap and it works where the air is dry. Where summers are humid, the air coming through the vents is warm and wet, it meets joists cooled by the air-conditioned floor above, it condenses, and the batts hold the water until they fall — which is the crawl space found ten years later with the insulation on the ground and the joists black.
The other way seals it: a reinforced liner over the ground and a foot up the walls, foam board on the foundation walls, the vents closed, and a dehumidifier to keep it dry. The space becomes part of the house. It costs about two and a half times as much, and it is the one that lasts.
| Vented — batts in the floor | Sealed — liner and foam on the walls | |
|---|---|---|
| Where it works | Dry climates | Humid climates, and anywhere with ducts down there |
| Insulation | R-25 batts, 1,200 sq ft of floor | R-10 foam, 381 sq ft of wall |
| The liner | 6 mil on the ground, 1,308 sq ft | 12 mil up the walls, 1,826 sq ft |
| 1,200 sq ft, zone 4 | $1,988 | $6,365 |
| Per square foot | $1.66 | $5.3 |
| Lasts | Ten years in a humid climate | The liner's life: 20 to 30 years |
MaterialsEstimator, Crawl space insulation and encapsulation price survey · checked 2026-09-23
The vapor barrier is the job
Bare earth under a house gives off water as vapor all day, every day — gallons of it — and it rises into the joists, the subfloor, the insulation and the ducts. The plastic over the ground is what stops it, and it goes under both approaches: 6 mil builder’s plastic, lapped and taped, in a vented crawl; a 12 or 20 mil reinforced liner, run up the walls and sealed at every seam, in a sealed one. A crawl with insulation and no barrier is insulation getting wet from below.
The code says the same thing from the other side: a vented crawl with a Class I vapor retarder on the ground can cut its vent area by ten times, because most of what the vents were there to carry away was coming out of the ground.
$218
6 mil, on the ground
1,308 sq ft with laps
$986
12 mil, up the walls
1,826 sq ft, taped
$1,350
Crawl dehumidifier
With a condensate pump
35%
Under 24 in
On every hour
International Code Council, IRC R408 — Under-floor space: ventilation, vapor retarders and unvented crawl spaces (2021) · checked 2026-09-23
The climate zone sets the R
For a vented crawl the insulation is in the floor above, and the Department of Energy wants R-13 in the hot zones, R-25 in zone 4 and R-30 in the cold. For a sealed crawl it is on the walls, and there zones 1 and 2 need nothing — the liner and the closed vents are the job — zone 3 wants R-5, zone 4 R-10, and zone 5 up R-15, which is three inches of foam board glued to the foundation wall and stopped 3 in short of the sill so a termite inspector can still see the top of the wall.
| Climate zone | Vented: floor R | Vented, 1,200 sq ft | Sealed: wall R | Sealed, 1,200 sq ft |
|---|---|---|---|---|
| Zone 2 | R-13 | $1,686 | none | $5,260 |
| Zone 3 | R-19 | $1,837 | R-5 | $6,060 |
| Zone 4 | R-25 | $1,988 | R-10 | $6,365 |
| Zone 5 | R-30 | $2,114 | R-15 | $6,670 |
| Zone 6 | R-30 | $2,114 | R-15 | $6,670 |
| Zone 7 | R-38 | $2,316 | R-15 | $6,670 |
36 in high, bare ground, a 12 mil liner and a dehumidifier on the sealed side. The sealed price barely moves with the zone; the liner and the labour are most of it.
U.S. Department of Energy, Recommended insulation levels by climate zone · checked 2026-09-17
Before anyone goes under
On the list
- The clearance at the lowest point. Under 24 in is a different price, and under 18 some crews decline.
- What is there now: bare ground, old plastic, or batts hanging wet. Wet batts decide the approach.
- Standing water after rain: a sump first, and the gutters and grading outside looked at.
- The climate zone, for the R on the floor or the walls.
- Ducts down there? Then seal it — sweating ducts in a vented crawl are wet insulation and lost cooling.
- A drain or a route outside for the dehumidifier's condensate.
- Foam stopped three inches below the sill: the termite gap. Ask, or the pest company will.
What goes wrong
01Batts in a humid vented crawl
Summer air through the vents condenses on the cold joists; the batts hold it and fall in ten years, and the joists go black.
Instead — Seal it: $6,365 against $1,988, once.
02Insulation with no vapor barrier
The ground puts gallons of water a day into the space, and the insulation is the first thing it wets.
Instead — Plastic over every square foot of ground, lapped and taped, under either approach.
03Sealing without a dehumidifier
A sealed box with damp ground under a liner and no way out for the moisture grows mould on the joists.
Instead — A crawl-rated dehumidifier with a condensate pump, about $1,350, or a trickle of house air.
04A liner over standing water
A pond with a lid. The water is still there, under the plastic, feeding the walls.
Instead — A sump and a pump first — $950 — and the gutters and grading outside fixed.
05Foam board to the top of the wall
Termites tube up the foundation behind it unseen, and the pest company voids the warranty.
Instead — Foam stopped 3 in below the sill, bare concrete above.
066 mil plastic in a sealed crawl
It tears on the first knee and silts in a year; a sealed crawl is crawled through for service for decades.
Instead — 12 mil reinforced at least — $233 more than 6 mil on this space — or 20 mil to outlast the house.
07Batts compressed to fit or paper down
Squashed batts lose most of their R; paper facing the crawl traps moisture against the subfloor.
Instead — Paper up against the subfloor, full thickness, wire rods every 18 in.
08Ignoring the rim joist
It is where the air leaks in a vented crawl and the cold comes through in a sealed one, and batts do not seal it.
Instead — Foam board cut to each bay, or spray foam, along the whole rim.
- 01Measure the floor and the heightThe footprint over the crawl, and the clearance from the ground to the joists at the lowest point. Under two feet changes the price.
- 02Look at what is thereBare ground, old plastic, or batts hanging wet. Wet batts are the evidence that the vented approach was not working here.
- 03Find the climate zoneZones 1 and 2 need no wall insulation at all; zone 4 wants R-10 on the walls or R-25 in the floor; zone 6 and up R-15 or R-30.
- 04Choose the approach by the airDry climate: batts in the floor with the vents open. Humid: sealed, with a liner up the walls and a dehumidifier.
- 05Check for waterStanding water after rain is a sump and a look at the gutters, before any liner.
- 06Count the vapor barrier under bothFloor area plus a foot up the walls for a sealed crawl, plus 15 per cent for the laps. It is the job.
The attic is where most of the heat leaves and where insulation is cheapest per point of R — priced by the inch and the zone on the insulation page.
The other end of the house- Vented crawl space
- The traditional kind: vents in the foundation wall, insulation between the floor joists above, and outside air moving through. Right where the air is dry.
- Sealed or encapsulated crawl
- The vents closed, a liner over the ground and up the walls, insulation on the walls, and the air kept dry by a dehumidifier or a trickle from the house. The space becomes part of the house.
- Vapor barrier
- The plastic over the ground that stops the earth's moisture rising into the space. Under both approaches; without it, the joists and the insulation get wet.
- Class I vapor retarder
- The code's name for a liner that all but stops vapor — polyethylene 6 mil and up. What lets a vented crawl cut its vent area to 1/1,500.
- Liner mil
- Thickness in thousandths of an inch. 6 mil is builder's plastic; 12 mil reinforced takes being crawled on; 20 mil outlasts the house.
- Foam board
- Rigid XPS or polyiso glued to the foundation wall in a sealed crawl, about R-5 an inch, stopped short of the sill for the termite gap.
- Termite inspection gap
- The top 3 in of the foundation wall left bare above the foam, so an inspector can see termite tubes. The code asks for it and pest companies insist.
- Rim joist
- The joist at the edge of the floor, sitting on the sill. Where the air leaks in a vented crawl, and insulated separately.
- Condensate pump
- The small pump that sends a dehumidifier's water to a drain or outside. Without a drain in the crawl, it is not optional.
- Climate zone
- The IECC's 1 (hot) to 8 (arctic). It sets the floor R-value for a vented crawl and the wall R-value for a sealed one.
- Sump
- A pit and pump at the low point, for a crawl where water stands after rain. Before anything is sealed over it.
- Tight crawl
- Under 24 in of clearance. Everything is done lying down, at 35 per cent on the hours, and some crews will not go under 18.
Common questions
- How much does it cost to insulate a crawl space?
- Two answers. Batts between the floor joists with the vents left open, over a vapor barrier on the ground: about $1,988 for a 1,200 sq ft crawl, or $1.66 a square foot. The space sealed — a 12 mil liner over the ground and up the walls, R-10 foam on the walls, 17 vents closed and a dehumidifier — about $6,365, or $5.3 a square foot. The first is right where the air is dry; the second where it is not.
- How much does crawl space encapsulation cost?
- About $6,365 for 1,200 sq ft in climate zone 4 — $5.3 a square foot — with a 12 mil reinforced liner, foam board on the walls, the vents sealed and a crawl-rated dehumidifier. A 20 mil liner is $6,913; in zone 2, with no wall insulation needed, $5,260; in zone 6 with R-15 walls, $6,670. Under 24 in of clearance, with old batts to remove first, $8,125.
- How much does a crawl space vapor barrier cost?
- The 6 mil plastic that meets the code is about $218 in material for 1,200 sq ft, laid over the ground and lapped — most of the $1,988 vented-crawl job is the batts and the crawling. A 12 mil reinforced liner for a sealed crawl, run up the walls and taped at every seam, is $986 in material; the difference is the liner you can crawl on for twenty years.
- Should I insulate the floor or the walls?
- The floor if the crawl stays vented; the walls if it is sealed. Where the air is dry, batts in the floor with the vents open work and cost $1,988. Where summers are humid, vented air condenses on the cold joists, the batts hold the water and fall in ten years, and the sealed crawl — walls insulated, vents closed, dehumidifier — is the one that lasts: $6,365. Wet batts hanging from the joists now are the evidence.
- Does a sealed crawl space need a dehumidifier?
- Yes, or a trickle of conditioned air from the house. A sealed space with damp ground under a liner and no way for moisture to leave grows mould on the joists. A crawl-rated unit with a condensate pump is about $1,350 — $6,365 with against $4,755 without — and it runs a few hours a day in summer.
- What R-value does a crawl space need?
- By climate zone. For a vented crawl, the floor above it: R-13 in zone 2, R-25 in zone 4, R-30 in zone 6. For a sealed crawl, the walls: R-0 in zone 2, R-5 in zone 3, R-10 in zone 4, R-15 in zone 5, R-15 from zone 5 up. Zones 1 and 2 need nothing on the walls; the liner and the closed vents are the job there.
- What if there is water in the crawl space?
- A sump pit and pump at the low point before anything is sealed over it — about $950, $7,315 all in — and a look at where it comes from, which is nearly always the gutters and the grading outside, and cheaper to fix there. A liner over standing water is a pond with a lid.
- Can I encapsulate a crawl space myself?
- The materials are about $3,490 for 1,200 sq ft with a dehumidifier, or $848 for the vented approach with batts. The work is 37 hours on your back with a headlamp: the liner laid from the far corner to the hatch, seams taped as you go, foam board glued and pinned to the walls, vents foamed shut. A respirator, coveralls, and somebody at the hatch. Under two feet of clearance, it is a job people abandon halfway.
- What about the termite gap?
- Foam on the foundation wall stops 3 in below the sill, leaving bare concrete an inspector can see termite tubes on. The code asks for it and pest companies refuse to warrant a crawl without it; a crew that foams to the sill has taken a shortcut that shows.
- Is encapsulation worth it?
- Where the air is humid, yes, and not for the energy first: for the floor that stops being cold, the ducts that stop sweating, the mould that stops growing, and the smell that leaves the house. The energy saving is real and modest. Where the air is dry, a vented crawl with batts and a good vapor barrier does the job for $1,988 and the extra $4,377 buys little.
- How long does a crawl space liner last?
- 6 mil plastic about 8 years — it tears and silts; 12 mil reinforced about 20; 20 mil 30 or more. The foam on the walls outlasts all of them. Batts in a vented crawl in a humid climate, about ten, and then they are on the ground.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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