Moisture migration in the walls, floors, and ceilings of buildings is controlled by vapor barriers or vapor retarders. Explain the difference between the two, and discuss which is more suitable for use in the walls of residential buildings.

To understand the difference between vapor barriers and vapor retarders, let's first define what vapor barriers are. Vapor barriers are materials that are specifically designed to prevent water vapor from diffusing through a building's walls, floors, or ceilings. They are made of impermeable materials like plastic, foil-faced insulation or, in some cases, a combination of materials. A vapor barrier should have a low permeability rating, typically 0.1 perm or lower.

Vapor retarders, on the other hand, are materials that only slow down the diffusion of water vapor through building materials like walls, floors, and ceilings. Unlike vapor barriers, vapor retarders are not completely impermeable to water vapor. They are made of more permeable materials like building paper, house wrap, or certain types of coated insulation. Vapor retarders typically have a somewhat higher permeability rating (around 1 perm) than vapor barriers.

The main difference between vapor barriers and vapor retarders is their permeability to water vapor. Vapor barriers are more effective at stopping water vapor from infiltrating a building's structure, while vapor retarders only slow down the process. In some cases, depending on the climate and the construction of a building, a vapor retarder might be enough to protect the structure from moisture damage, while in more humid or wet conditions, a vapor barrier might be required to provide adequate protection.

Now that we understand the difference between vapor barriers and vapor retarders, let's discuss which one is more suitable for use in the walls of residential buildings. In general, both vapor barriers and vapor retarders can be used in residential buildings, but the choice depends on several factors, including local climate and building design. In colder climates, where the main concern is preventing the warm, moist indoor air from condensing on cold surfaces inside the walls, floors, and ceilings, a vapor barrier will typically provide better protection. This prevents moisture from getting trapped in building materials leading to mold, rot, and reduced insulation effectiveness. However, in areas with mixed or warmer climates, a vapor retarder may be more appropriate due to its ability to allow some moisture to escape from the building's structure. This can help prevent trapping moisture inside the walls, which, if left unresolved, may cause similar issues to those faced in colder climates.

To sum up, the difference between vapor barriers and vapor retarders lies in their permeability to water vapor. Vapor barriers are impermeable, while vapor retarders offer partial resistance to moisture migration. Depending on the location, climate, and specific building design, either a vapor barrier or a vapor retarder can be more suitable for use in the walls of residential buildings. In cold climates, a vapor barrier is likely to provide better protection against moisture issues, while in mixed or warmer climates, a vapor retarder might be more appropriate.