Crawlspace
Encapsulation in
Boulder, Colorado

Why Boulder Crawlspaces Stay Wet

Boulder's geography works against crawlspaces. The city sits at the base of the foothills, so spring snowmelt moves through the ground on its way down. Much of the area has expansive clay soil that holds water against foundations rather than letting it drain away. Established neighborhoods have mature landscaping and decades of irrigation adding to the load.

On top of that, most Boulder homes older than the last couple of decades were built with vented crawlspaces. The theory was that open foundation vents would let the space dry out. In practice, warm humid air enters a cool crawlspace, hits cold surfaces, and condenses. The vents make the problem worse, not better.

The result is what we find under a lot of Boulder houses: exposed damp soil, fiberglass batts sagging out of the joists or lying on the ground, rusted duct work, dark staining on the framing, and a musty smell that migrates up into the living space through the stack effect.

What We Do About It in Boulder

• Diagnose the water first. Clay soil and runoff mean liquid water is often part of the picture. Drainage and a sump come before sealing anything.
• Full cleanout. Old barrier, failed insulation, debris, and anything organic gets removed and bagged out.
• Treat the framing. Borate treatment on wood that has seen sustained moisture, and structural repair or sistering where decay has set in.
• Seal the ground and walls. Heavy-duty reinforced vapor barrier across the floor and up the foundation walls, all seams taped.
• Close and insulate the vents. Foam board and spray foam permanently seal the foundation vents.
• Insulate the walls, not the floor. Closed-cell foam on the foundation walls and rim joists brings the crawlspace inside your thermal envelope.
• Control humidity. A properly sized dehumidifier with automatic drainage keeps it dry permanently.

Boulder Homeowner Questions