INTERSTITIAL MOSITURE

The problem of interstitial moisture—moisture that forms or migrates within walls, roofs, or other concealed building assemblies—is very widespread, especially in modern high-performance buildings. Here’s how it breaks down:

What Is Interstitial Moisture?

It’s moisture that accumulates inside the layers of a building assembly, often due to vapor diffusion, air leakage, or temperature differentials that cause condensation within walls—not on surfaces.

How Widespread Is It?

Extremely. It affects:

Commercial Buildings

• Glass curtain walls, EIFS, metal panel systems, and even “high-performance” facades often suffer from hidden condensation—especially where insulation is not continuous and airflow is limited.
• LEED and Passive House projects may ironically be at higher risk due to tighter envelopes and more vapor-impermeable layers.

Residential Buildings

• Common in wood-frame construction, particularly in cold climates or when interior humidity is high.
• Retrofits (e.g., adding spray foam or airtight barriers) often trap vapor in unintended places, causing mold and rot.

Older Buildings

• Brick cavity walls and early curtain wall systems weren’t designed to handle vapor from within. These often have decades of hidden damage.

Hot-Humid & Mixed Climates

• Especially severe in the southeastern U.S., Gulf Coast, and Asia where cool, dry interiors meet hot, humid exteriors. Vapor moves inward and condenses behind finishes.

Evidence of Scale

• ASHRAE, NIBS, and DOE all cite interstitial condensation as a top hidden threat to energy efficiency and durability.
• A 2018 study by Building Science Corporation found that in many airtight buildings with no intentional airflow behind facades, over 40% had signs of hidden moisture accumulation.
• Insurance claims for mold and water damage often trace back to vapor accumulation, not leaks.

Why It’s a Big Deal

• Invisible damage: Mold, rot, corrosion often go unnoticed until there’s structural or IAQ (indoor air quality) failure.
• Undermines insulation: Wet insulation has virtually no R-value.
• Legal risk: Building owners and contractors are increasingly liable for mold-related health claims.
• Energy waste: Trapped moisture increases HVAC load and reduces material performance.

Why PortalWall® Matters

Your system’s airflow-enabled cavity and dew-point-aware design directly address this problem—where most facades simply trap it.