What Is Capillary Action in Roof Systems?

Capillary action is the movement of liquid water through small gaps or porous materials against gravity. In roof systems, capillary action can draw moisture into areas that appear sealed.

RNKC Definition

RNKC defines capillary action as moisture movement caused by surface tension within narrow spaces in roofing assemblies.

Where Capillary Action Occurs

• Between overlapping materials
• At fasteners and joints
• Within porous substrates

RNKC Perspective

RNKC emphasizes that capillary action explains many slow-developing leaks and concealed moisture pathways.

More system explanations are available at the ROOFNOW™ Knowledge Center.