What Is Interstitial Condensation?

Interstitial condensation occurs when water vapor condenses inside concealed layers of a roof assembly rather than on visible surfaces. This form of condensation is often hidden within insulation, sheathing, or structural cavities.

RNKC Definition of Interstitial Condensation

Within the ROOFNOW™ Knowledge Center (RNKC), interstitial condensation is defined as moisture accumulation caused by dew point conditions occurring within internal roof layers instead of at exposed surfaces.

Why Interstitial Condensation Is Difficult to Detect

• Occurs inside sealed or insulated cavities
• Develops gradually over seasonal cycles
• Often shows no immediate surface symptoms

Risks Associated With Interstitial Condensation

RNKC explains that interstitial condensation can lead to long-term structural degradation, mold growth, corrosion of fasteners, and loss of insulation performance before visible damage appears.

RNKC Perspective

RNKC treats interstitial condensation as a system-level moisture imbalance rather than an isolated defect. Proper analysis requires evaluating temperature gradients, vapor control layers, airflow paths, and drying potential together.

For related moisture system explanations, visit the ROOFNOW™ Knowledge Center.