The Importance of Capillary Breaks in Residential Construction
Capillary breaks are one of the most important components of a properly designed building envelope. They prevent liquid moisture from moving through porous building materials such as concrete, masonry, brick, mortar, wood, and certain insulation materials.
Without effective capillary breaks, moisture can migrate from the soil, foundation, masonry, and other wet materials into the home's structural components, contributing to deterioration, elevated moisture levels, mold growth, and reduced building durability.
What is capillary action?
Capillary action, also called capillary suction or wicking, occurs when liquid water moves through small interconnected pores in building materials. Water can move upward, horizontally, or downward, depending on the material's pore structure and moisture conditions.
For example, a concrete foundation can absorb groundwater and transport moisture upward into a wood sill plate if there is no effective capillary break separating the two materials.
A capillary break interrupts this liquid-water pathway using a nonabsorbent material, a properly detailed membrane, or an air gap.
Important distinction: A capillary break controls liquid water movement. It does not necessarily stop water vapor diffusion, air leakage, or water under hydrostatic pressure. These require additional moisture-control measures.
- Foundation capillary breaks