Key concepts in sustainable building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 83

Figure 3. How vapour permeability works in a hempcrete wall.
In Figure 1, all the materials are vapour permeable, so any moisture that enters the wall
(whether from rising damp, rain, or internal sources such as cooking) is allowed to leave
again by natural evaporation before any ill effects are caused.