What is a Class 2 vapor retarder

Class II vapor retarders are typically Kraft paper (Kraft-faced insulation). The permeance of Kraft paper increases to Class III levels at higher relative humidity (from 0.3 up to 3 perms). … Typical perm ratings for common building materials are shown in Table 2. Permeance typically decreases with increasing thickness.

What is a Class I or II vapor retarder?

Class I – Very low permeability vapor retarders – rated at 0.1 perms or less. … Class II – Low permeability vapor retarders – rated greater than 0.1 perms and less than or equal to 1.0 perms. The kraft facing on batts qualify as a Class II vapor retarder.

What is a class one vapor retarder?

A Class I vapor retarder is a material with a permeance less than 0.1. … Permeance, for example, is the amount of moisture vapor that can pass from one side of an object (in this case a plastic liner/sheet) to the other.

What is a Class 2 Vapour barrier?

CLASS 2 (MEDIUM) VAPOUR BARRIER. CLASS 4 (LOW) VAPOUR BARRIER. CLIMATE CONSIDERATION. Recommended for warmer climates where lower insulation values are used. Recommended for tropical climate zones.

How many vapor retarder classes are there?

When we start to look at categorizing vapor retarders, materials can be separated into three general classes based on their permeance and are defined in the International Building Code (IBC). This covers most materials that are usually referred to as vapor barriers.

What is a good vapor retarder?

To be considered a vapor retarder, the material should have a permeance or “perm” rating less than 1.0 as tested in accordance with ASTM E-96. The lower the perm rating, the better the ability of the material to control the diffusion of water vapor.

What is a good perm rating?

A perm rating of less than 0.1 is considered a Class I impermeable vapor retarder (which is also considered a vapor barrier); perm rating between 0.1 and 1 is considered a Class II semi-permeable vapor retarder; a perm rating between 1 and 10 is a Class III permeable vapor retarder; and a perm rating greater than 10 is …

Do I need a vapor barrier on exterior walls?

If the area spends a bit more time in the warmer months, install the vapor barrier at the exterior. … This is another humid climate, so vapor barriers are often required in most areas. Because it is mostly hot and very humid outside the building, the vapor barrier should be installed on the exterior of the insulation.

What is the best Vapour barrier?

Elastomeric coatings.
Aluminum foil.
Paper-backed aluminum.
Polyethylene plastic sheet.
Asphalt-coated Kraft paper.
Metallized film.
Vapour retarder paints.
Extruded polystyrene or foil-faced foam board insulation.

What is a vapor retarder in insulation?

A vapor retarder is defined as a material or system that adequately retards the transmission of water vapor under specific conditions. … The kraft facing on insulation is a vapor retarder. It can reduce moisture movement through your walls, floors, and ceilings.

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What is vapor retarder used for?

Water Resistive Barriers 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 an example of a class 3 vapor retarder?

Examples include unfaced expanded polystyrene, fiber faced polyisocyanurate and asphalt-backed kraft paper facing on fiber glass batt insulation. Class III vapor retarders have a permeance rating between 1 perm and 10 perms and are considered semi-permeable.

What is concrete vapor retarder?

Vapor retarders are materials that will minimize the transmission of water vapor from the sub-slab support system into a concrete slab. Vapor retarders are typically specified according to ASTM E 1745 and have a permeance of less than 0.3 US perms (0.2 metric perms), when tested by ASTM E 96.

Is plywood a vapor retarder?

Latex painted gypsum board (one coat of latex paint) is a Class III vapor retarder. Plywood sheathing and oriented strand board (OSB) have perm values of greater than 1 perm when using the wet cup test. … Therefore, a kraft-faced batt (Class II vapor retarder) is required on the interior of this assembly.

Are vapor barriers bad?

Vapor barriers are supposed to stop vapor diffusion through roofs, walls, and floors. But they can also can trap moisture, causing rot and mold. Where moisture comes from: Water vapor can be forced into wall assemblies from the warm side of the house.

What does vapor diffusion mean?

Vapor diffusion is the movement of water vapor molecules through porous materials as a result of vapor pressure differences. … Stone wool vapor permeable insulation allows for greater outward drying than vapor impermeable insulation such as foam plastics.

What is the perm rating of 4 mil poly?

One of the lowest perm ratings for a building material is polyethylene sheeting at . 04-. 06 perms for 4-6 mil poly. In comparison, raw drywall has a perm rating of 40.

What is the perm rating of Tyvek?

Tyvek® HomeWrap® is not surfactant resistant. Tyvek® HomeWrap® has a perm rating of 56 US Perms, much higher than the recommended perm rating.

What is the perm rating of drywall?

Gypsum drywall, for example, has a perm rating of about 50, while 1-mm-thick foil sheeting has a perm rating of about zero. Almost as good at 0.06–and cheaper and easier to install than foil–is 6-mm-thick polyethylene sheeting. Any barrier rated 1 or less is considered a viable vapor barrier.

Is vapor retarder the same as vapor barrier?

“Vapor retarder” is the term used to describe materials of varying types and classifications which impede the infiltration of water vapor into a structure. Often the term “vapor barrier” will be used interchangeably with the term “vapor retarder,” with no repercussions.

Do I need a vapour barrier in Canada?

Understanding vapor barriers: The National Building Code of Canada stipulates that for residential buildings, a vapour barrier must have a water vapour permeance of less than 60 ng/Pa*s*m2 or 1.0 Perm.

What mil plastic should be used for a vapor barrier?

Crawlspace Vapor Barrier Materials Reinforced polyethylene plastic sheeting (poly) comes in a variety of thicknesses and strengths. A 6 mil thick poly is commonly used as a vapor barrier and offers short-term savings to the homeowner.

Should I put a vapor barrier on my ceiling?

All attics — vented or unvented — should have an air barrier (a properly detailed airtight drywall ceiling, for example) regardless of climate. Omitting a ceiling vapor barrier by arguing that “you have to let the moisture escape” or “because the house has to breathe out the top” is actually correct, in a way.

How thick should a vapor barrier be?

Vapor barriers should be at least 6 mil in thickness to effectively cover the area and create a moisture barrier. Triangle Crawl Space Solutions uses both a 6 mil material for simple vapor barrier installation and a thicker more durable 12 mil vapor barrier material depending on the budget and needs of the home.

Can foil backed plasterboard be used as a vapour barrier?

Foil backed plasterboard’s are the same as a standard plasterboard, except for a thin layer of foil that is applied to the back of the board. This foil sheet acts as a vapour barrier, it is intended to stop moisture from penetrating through the boards.

Is sheetrock a vapor barrier?

The permeance of unpainted drywall is very high, generally between 20 and 90, so it’s not a vapor retarder at all. Meanwhile, air leakage through a 1 square inch hole in a sheet of drywall allows 30 quarts of water vapor to pass through the drywall under the same conditions.

Is 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.

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.

Should you put vapor barrier basement walls?

It provides the best coverage and R-value and and functions as a moisture barrier in and of itself. … But if you use fiberglass insulation batts, then a moisture barrier will prevent water and moisture from entering your walls and creating mold and mildew.

Should I put plastic over insulation?

Without a vapor barrier in place, condensation inside the walls could ruin the insulation and promote the growth of harmful mold and bacteria. Plastic, specifically 6-mil polyethylene plastic, is the most commonly used vapor barrier.