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Deconstructing Vapor Diffusion for Building Enclosures

Deconstructing Vapor Diffusion for Building Enclosures

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.

Moisture can affect:

The comfort and safety of people in the building
The comfort and safety of people in the building

The comfort and safety of people in the building

The durability of your building enclosure
The durability of your building enclosure

The durability of your building enclosure

The overall performance of the building
The overall performance of the building

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:

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.
1 Minimize or manage wetting sources such as air or water leakage.
1

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.
2 Maximize drying potential by using vapor permeable insulation such as stone wool in the right place.
2

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.
3 Consider climate to ensure correct placement of materials within your wall assembly.
3

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

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