Short answer: crawl space insulation slows heat loss through the floor or the crawl space walls. Encapsulation closes the crawl space off from the ground and the outdoors: a sealed vapor barrier over the dirt and up the walls, with vents and gaps sealed, so the space stays drier. Many crawl spaces need both, but in the right order. Standing water, leaks and drainage problems have to be fixed before either one goes in.
I'm Joe Giordano. Since 2004 I've been in a lot of crawl spaces across Nassau and Suffolk, from older ranches to beach houses on Fire Island. Here's how I explain the difference to homeowners.
What does crawl space insulation do?
Insulation slows heat moving between your living space and the crawl space. It goes in one of two places:
- Under the floor, between the floor joists. This treats the crawl space as outside. It's common in vented crawl spaces.
- On the crawl space walls and rim joists. This treats the crawl space as part of the house. It only works if the crawl space is also sealed from outside air and ground moisture.
Floor insulation in a damp, vented crawl space is a common problem. Batts sag, soak up moisture and fall down. If that's what you see under your house, insulation alone won't fix it.
What is crawl space encapsulation?
Encapsulation turns a damp, vented crawl space into a closed one. A typical scope includes:
- A heavy vapor barrier over the ground, with overlapped and sealed seams
- The barrier run up the foundation walls and sealed
- Vents and other openings to the outside sealed
- Air sealing and insulation at the rim joists and walls
- A way to keep the air dry
That last item matters. A sealed crawl space can't just be closed up and forgotten. The Residential Code of New York State has specific requirements for unvented crawl spaces, including a sealed ground cover and a way to exhaust, condition or dehumidify the air. If that means a dehumidifier, HVAC change or drainage work, that's work for the right trade, and I'll tell you so up front.
How do I know which one my crawl space needs?
Here's how I sort it out on a visit:
- Dry dirt floor, sound insulation, warm floors. You may need nothing, or just air sealing at the rim joists.
- Cold floors, but the crawl space is dry. Floor or wall insulation, plus air sealing, may be enough.
- Musty smell, damp soil, sagging or wet insulation. Moisture control comes first. That usually means a vapor barrier at minimum, and often full encapsulation.
- Standing water or active leaks. Stop. Drainage, gutters, grading or plumbing need to be fixed before insulation work makes sense.
EPA puts it simply: "the key to mold control is moisture control" (EPA mold and moisture guide). If there's visible mold, cleanup comes before insulation. See EPA's mold cleanup guidance.
Is a vapor barrier the same as encapsulation?
No. A ground vapor barrier is one part of encapsulation. Laying plastic on the dirt helps a vented crawl space by cutting the moisture coming up from the soil, and sometimes that's the right first step. Full encapsulation also seals the walls, vents and openings and deals with the air. We do both. The right choice depends on what's going on under your house.
Which insulation works in a crawl space?
It depends on where it goes. Rigid foam board and closed-cell spray foam hold up well on foundation walls and rim joists because they don't soak up water. Floor insulation between joists has to be properly supported and kept dry. I explain the trade-offs between foam and other materials in cellulose vs spray foam. For basements, see our basement insulation page.
What happens at the free estimate?
I go into the crawl space and the attic, because air moving up through the house connects the two. I measure, look at the soil, walls, framing and existing insulation, check for signs of water, and use a thermal camera to find where heat is escaping. Then I tell you what I'd do, in what order, and which parts belong to another trade.
Frequently asked questions
Does encapsulation help with musty smells?
Damp crawl space air often finds its way into the house. Sealing out ground moisture and outside air, and keeping the air dry, addresses the usual source. A leak or mold problem still has to be fixed on its own.
Should I close my crawl space vents?
Only as part of a complete encapsulation that also deals with ground moisture and keeps the air dry. Closing the vents on a damp crawl space without the rest can make moisture worse.
Do you do crawl spaces on Fire Island and Shelter Island?
Yes. Older beach houses and island homes often sit on piers or have open or vented crawl spaces, and we take the ferry for these jobs. See Fire Island and Shelter Island.
Where else do you work?
All of Nassau and Suffolk, including Brookhaven, Islip, Smithtown and Riverhead. See our service areas.
Have Joe take a look
Call or text me at (631) 492-0214, Monday to Saturday, 7 AM to 7 PM. I answer my own calls and texts and call back the same day. You can also book a free estimate or read more about our crawl space insulation and encapsulation work.