Deconstructing Vapor Diffusion for Building Enclosures

Moisture can affect:

 The durability of your building enclosure

The overall performance of the building.


This is how vapor typically moves:


This movement directly influences the placement of the materials within your wall assembly. Improper placement can lead to:

What is vapor diffusion?

Vapor diffusion is the movement of water vapor molecules through porous materials as a result of vapor pressure differences. It’s one of four critical elements that affects the success of your building enclosure.

Vapor diffusion is generally thought of as a negative process but in reality it’s an important drying mechanism that can be used as part of the solution.

Don’t trap moisture; allow it to dry.

Here’s how:

Minimize or manage wetting sources such as air or water leakage.

Maximize drying potential by using vapor permeable insulation such as stone wool in the right place.

Consider climate to ensure correct placement of materials within your wall assembly.

Expert Tip:

Stone wool vapor permeable insulation allows for greater outward drying than vapor impermeable insulation such as foam plastics.

Don’t let vapor diffusion negatively impact your building enclosures.

Learn more by viewing our Vapor Diffusion and Condensation Control for Commercial Wall Assemblies guide:

Download our guide


COMFORTBOARD™ 110 is a rigid, high density, non-combustible, stone wool insulation board designed for use as an exterior continuous insulation in commercial applications

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CAVITYROCK® is a semi-rigid insulation board designed for exterior cavity wall and rainscreen applications

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