Sunroom Crawl Space Insulation and Encapsulation in Greenwich
1 / 5Illustrative recreation of the crawl space before encapsulation, aged batting insulation over an open fieldstone wall, labeled as a recreation and not a photo of this project
See How the Work Was Done
Opens with a labeled illustrative recreation of the original state. Every other frame is a real install-day photo from this Greenwich sunroom crawl space: the fieldstone foundation, the sealed rim, and the 12 mil membrane being fitted.
What Happened
The crawl space under this Greenwich, CT sunroom is the kind of space most homeowners never see: a tight cavity walled by the original rubble fieldstone foundation, with batting insulation that had been absorbing crawl space moisture for years. The homeowner wanted the space cleaned out and properly sealed, not patched. The crew worked the full sequence in a single day. The old batting and accumulated debris came out first and were hauled away. With the framing and stone exposed, the rim joists and the open joints in the foundation stone were spot-sealed with foam sealant to cut air movement through the assembly. New R-21 mineral wool went into the rim joists, fitted tight to the floor line and held with tension-rod supports. Then the encapsulation layer went up: 12 mil white poly across the crawl space walls, and a floor system of dimple matting under 12 mil poly with the seams taped. The photos on this page were taken mid-install, as the membrane was being fitted against the fieldstone, which is exactly the stage where the quality of the seal is decided.
Scope of Damage
Aged Batting Insulation
ModerateThe existing batting had spent years absorbing crawl space moisture. All of it was removed from the sunroom crawl space and hauled away with the accumulated debris.
Fieldstone Foundation Walls
ModerateThe rubble stone construction leaves irregular joints that leak air and moisture. Open joints at the rim and stone were spot-sealed with foam sealant before the membrane went on.
Rim Joists
ModerateThe band of framing where the floor system meets the foundation was uninsulated once the old batting came out. R-21 mineral wool was fitted tight to the floor line with tension-rod supports.
How We Solved It
- 1
Tear-Out and Haul-Away
The existing batting insulation and debris were removed from the sunroom crawl space and hauled off site, leaving the framing and fieldstone exposed for sealing.
- 2
Air Sealing
Rim joists and the open joints in the foundation stone were spot-sealed with foam sealant, closing the gaps that let outside air and ground moisture move through the assembly.
- 3
Rim Joist Insulation
R-21 mineral wool was installed in the rim joists and fitted tight to the floor line, secured with tension-rod supports so it stays in contact with the framing.
- 4
Wall Encapsulation
12 mil white encapsulation poly was fitted across the crawl space walls, shaped around the irregular fieldstone rather than bridged over it.
- 5
Floor System and Cleanup
Dimple matting went down first, then 12 mil poly with the seams taped, and the work area was cleaned up before the crew left.
Tools & Equipment Used
Questions Homeowners Ask
Can a crawl space with a fieldstone foundation be encapsulated?
Yes, and this Greenwich sunroom is a working example. Fieldstone needs more preparation than poured concrete: the open joints between stones are spot-sealed with foam sealant first, then the encapsulation poly is fitted to the irregular surface rather than stretched flat across it. The result is a sealed liner that follows the real shape of the wall.
Why remove the old batting insulation before encapsulating?
Batting that has spent years in a damp crawl space holds moisture and whatever has grown in it. Sealing it inside a new encapsulation traps that load against the framing. On this project all of the existing batting and debris came out and was hauled away before any sealing or new insulation went in.
What is dimple matting and why does it go under the floor poly?
Dimple matting is a dimpled plastic drainage layer laid on the crawl space floor before the vapor barrier. The dimples create an air gap that lets any ground moisture drain and equalize instead of pooling directly against the poly, and they protect the barrier from the rough surface below. The 12 mil poly goes over it with taped seams.
Why insulate the rim joists in a crawl space?
The rim joist is the band of framing where the floor system meets the foundation, and it is one of the biggest heat-loss paths in an older home. On this project R-21 mineral wool was fitted tight to the floor line with tension-rod supports after the rim was air sealed, so the sunroom floor above stays warmer and the assembly stays drier.
How much does crawl space encapsulation cost in Connecticut?
Full crawl space encapsulation in Connecticut typically runs $3,000 to $15,000 depending on the size of the space, the foundation type, and how much cleanup and insulation work comes first. A compact sunroom crawl space with a fieldstone foundation, like this Greenwich project, sits toward the lower end of that range. A free on-site assessment is how the number gets real.
How long does a sunroom crawl space encapsulation take?
This Greenwich project was completed in one working day: tear-out and haul-away of the old batting, air sealing, R-21 rim joist insulation, wall poly, and the dimple matting floor system. Larger crawl spaces or jobs that need rodent cleanup or mold remediation first typically run three to five days.
