How do smart vapor retarders work?

When the air is humid in the summer, the moisture penetrates through the pores into the building interior, allowing building materials to dry out. If the relative humidity decreases, the pores close up again, and the smart vapor retarder then acts as a barrier to moisture.

How does a smart vapor barrier work?

When the air or the building materials adjacent to a smart vapor retarder get more humid, however, the membrane becomes more vapor-open — in other words, its vapor permeance increases. Under dry conditions, it acts like a vapor retarder; while under humid conditions, it opens up and allows moisture to pass through it.

What is the purpose of a vapor retarder?

An air barrier/vapor retarder attempts to accomplish water vapor diffusion and air movement control with one material. This type of material is most appropriate for southern climates where keeping humid outdoor air from entering the building cavities is critical during the cooling season.

What is a good vapor retarder?

Vapor Retarders in Warm Climate Zones 1, 2, 3, and 4

NAIMA recommends using either a Class II or III vapor retarder in these warmer climate zones and avoid the use of Class I (very low perm) vapor retarders. Kraft-faced batts can be installed in all climate zones.

Do interior walls need vapor barrier?

Normally interior walls do not require a vapor barrier, but there are some situations where it is highly recommended. Interior bathroom and kitchen walls, for example, are areas where there is great benefit to installing a vapor barrier. Bathrooms and kitchens produce an enormous amount of water vapor daily.

Do I need a Vapour barrier in Canada?

…vapour barrier is required in addition to spray foam. Building codes change and can vary by region, so confirm this locally, but currently The National Building Code in Canada for example allows foam insulation without fire protection on crawlspace walls that are less than 5 feet in height.

Do I need a vapor retarder?

If you live in a mixed climate – hot and humid with several heating months in the winter, you probably need a vapor retarder. Specifically, if you live in climate zones 4C (marine), 5, 6, 7 and 8.

Do I need a vapor barrier or retarder?

In a hot, humid climate, it’s recommended that a vapor retarder be placed at the exterior. In hot, dry climates, a vapor retarder is not required. Again, it is still necessary to check on local building codes to ensure you remain compliant in your building processes.

Is Tyvek A vapor retarder?

No, DuPont™ Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.

Where should vapor barrier be installed?

Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates.

What happens if you don’t use vapor barrier?

If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface, moisture problems can occur. Of course, you can have moisture problems here even without the exterior vapor barrier because of what Bill Rose calls the rule of material wetting.

Do vapor barriers cause mold?

The Problem With Vapor Barriers

This can lead to significant moisture problems and mold; problems occur when walls get wet during construction or more often throughout the home’s life.

Can I use plastic sheeting as a vapor barrier?

In simple terms, a vapor barrier is a material that won’t allow moisture to pass through it, such as plastic sheeting. A very simple experiment to show how a vapor barrier works is to lay a plastic garbage bag down on some damp soil.

Is drywall a vapor retarder?

Painted drywall should not be considered a Class III vapor retarder unless the paint is rated/tested at ≤10 perms – standard paint should be considered vapor permeable (not a vapor retarder). Wall components have vapor retarding characteristics that can affect moisture migration.

What is the difference between a vapor barrier and a moisture barrier?

Moisture barriers function to help in preventing water from entering inside of the wall cavity. On the other hand, vapor barriers basically prevent water vapor from the interior of the house to filter through the wall and condense on the warm side of the insulation.

Can you use house wrap as a vapor barrier?

For example, House wrap by itself is not an air barrier, it is a vapor barrier. However, IF installed properly, which is rare, with taped seams, bottom, top edges, and no tears, it acts as an air barrier. So primarily it acts as a vapor barrier, but installed properly can do both; vapor barrier and air barrier.

Can I use TARP as vapor barrier?

Lay a heavy plastic tarp — 6 mil or thicker — over the entire area. If you must use multiple sheets, overlap them by at least 2 feet. Use stones to hold the plastic down. The plastic acts as a vapor barrier, eliminating much of the migration of water vapor from the ground to the crawl space.

Is the paper on insulation a vapor barrier?

Vapor Blockers

Vapor barriers—sheets of plastic or kraft paper—keep water vapor out of the wall cavity, so the insulation stays dry. Not every type of insulation needs a vapor barrier. But if it does, the barrier should face inside in northern, heating climates, and outside in humid southern climates.

Is Tyvek air or Vapour barrier?

Is DuPont™ Tyvek® a vapor barrier? No, DuPont™ Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.

Can you put tar paper under Tyvek?

When it gets to tar paper, Tyvek, etc… these items are not impermeable (aka *Vapor Retarders) as they allow vapor to flow through them. (*We will discuss this more in another piece on “perms”) So having two layers of Tyvek or where you place Tyvek over tar paper is allowable / should not cause issues.

Can roofing felt be used as a Vapour barrier?

This makes felt a great performer for walls where there is a good chance of water intrusion. When it gets wet, it can easily dry out and let vapor pass through it.

Does Tyvek breathe both ways?

Tyvek® HomeWrap®, Tyvek® StuccoWrap®, Tyvek® DrainWrap™ and Tyvek® CommercialWrap® are equally effective in both directions and the logo may be on the inside or outside.