The design of energy-efficient, comfortable and long-lasting buildings must include restrictive barriers that protect the building envelope from air, water, condensation, movement and energy loss.
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- Air: Prevent excessive air infiltration
- Water: Resist liquid water penetration
- Condensation: Resist condensation within the wall system
- Movement: Accommodate differential movement (caused by moisture, seasonal or daily temperature shifts and structural movement)
- Energy conservation: Resist thermal transfer through convection, conduction, and radiation
Achieving these functions in new construction and renovation projects requires a clear understanding of the differences between air, moisture, vapor and weather barriers. Here are four simple comparisons between barrier types and materials:
1. Air Barrier vs. Vapor Barrier
- Vapor barriers restrict water vapor migration by limiting the flow of water vapor (diffusion) through materials.
- Air barriers, however, limit air migration by restricting air through a material.
2. Moisture Barrier vs. Vapor Barrier
- Moisture barriers are usually installed on the warm side of the wall. In warm climates the vapor barrier is placed on the exterior, while in colder climates the vapor barrier is placed on the interior, to prevent water and vapor from entering the wall cavity.
- Vapor barriers are installed inside the frame, between the studs and drywall, stopping vapor from the house's interior from infiltrating the wall system and condensing on the warm side of the insulation.
3. Weather Barrier vs. Vapor Barrier
- Weather barriers stop moisture, rain and wind from passing through the building envelope. However, they also allow water infiltrating the wall system to dry out quickly.
- Properly installed vapor barriers can also act as air and water barriers. They would then be considered a non-permeable air barrier.
4. Spray-Applied vs. Sheet Applied Air Barrier
Air, Moisture, Vapor and Weather Barriers
Tremco Construction Products Group offers a wide range of air, moisture, vapor and weather barriers that builders and architects can use to ensure moisture-resistant, vapor-resistant and airtight building envelopes. Read on to learn more about these specific building materials.
Air Barriers
What Is an Air Barrier?
Air barriers form a continuous plane around a structure to stop uncontrolled air movement in and out of the building envelope. Air leakage accounts for up to 100 times more moisture infiltration than diffusion.
A high-quality air barrier limits heat losses and gains through convection, conduction and radiation.
- Thermal convection happens when heat energy from a warmer area flows to a cooler place by moving fluids, usually gas and liquids.
- Thermal conduction occurs when hot molecules move towards colder molecules. The effective R-value of a wall system represents its resistance to conduction.
- Thermal radiation transfers heat from warmer spaces to cooler spots by electromagnetic waves, mainly the sun&#;s radiation.
When tested according to ASTM E , an air barrier's air permeance should not surpass 0.02 L/(s·m²) at a pressure difference of 75 Pa (or 0.004 cfm/ft2 at a pressure difference of 1.56 lb/ft2).
Air permeance represents the amount of air that moves through a material. In contrast, air leakage flows through holes and gaps.
Why Building Envelopes Need an Air Barrier
Air barriers regulate the indoor climate by stopping airflow between the exterior and interior of a building. In addition, air barriers prevent air-transported moisture from flowing to the interior of a wall system. Controlling air and preventing moisture infiltration:
- Reduces building energy usage, saves money and protects the environment.
- Minimizes moisture in the wall cavity, stopping the growth of structurally damaging rot and mildew.
- Improves indoor air quality by preventing the growth of unhealthy mold.
- Enhances occupant comfort and productivity by stabilizing temperatures and eliminating drafts.
Types of Air Barriers
Builders often install air barriers on the external side of the wall assembly to keep unconditioned air out of the wall cavity, which is the area between the inner and outer wall. A quality air barrier should provide continuity, structural support, air impermeability and durability regardless of the type. Air barrier types include:
- Permeable and impermeable air barriers
- Spray foam barriers
- Mechanically adhered sheet membranes
- Self-adhered sheet membranes
- Fluid-applied membranes (including spray and roll-applied products) installed on the job site or in a factory setting
Air Barrier Standards for Commercial Buildings
Section C402.5.1 of the International Building Code (IBC) demands a continuous air barrier for commercial structures, except climate zone 2B, throughout the building envelope.
Air Barrier Standards for Residential Structures
Section R402.4.1.1 of the International Residential Code (IRC) instructs to apply a continuous air barrier in a building envelope and sealing breaks for joints in the air barrier. IRCs apply to detached one-and-two family townhouses and dwellings not exceeding three stories above grade plane in height. Additionally, they must provide a separate means of egress with accessory structures not exceeding three stories above grade in height.
Moisture Barriers
What Is a Moisture Barrier?
Moisture barriers, or water/weather resistant barriers, in residential construction are applied over the exterior sheathing and are usually vapor permeable to prevent trapping moisture vapor in the wall cavity. Waterproofing membranes are used in below grade construction to protect the foundation from moisture.
Why Above Grade Building Envelopes Need Moisture Barriers
Above-grade moisture barriers seal against water infiltration to protect the building envelope's integrity and improve the safety and comfort of the occupants. Specifically, building envelopes need moisture barriers because they:
- Provide waterproofing that stops soil moisture from intruding into the building envelope.
- Reduce moisture and condensation in the wall cavity, leading to unhealthy and structurally damaging mold.
- Limit exposure to moisture that can decrease the thermal efficiency and R-value of the building thermal barrier.
- Provide termite and pest prevention by eliminating moisture that attracts pests.
- Protect against hydrostatic pressure, forcing water through porous concrete below-grade walls, which is particularly vital in areas with high water tables and excessive rain.
Below-Grade Moisture Barriers
Below-grade moisture barriers typically involve applying a sheet or liquid-applied membrane to the below-grade walls as positive, negative or blind side waterproofing:
- Positive side waterproofing is installed post-construction and requires access to the exterior side of the building before the ground is filled in around it.
- Negative side waterproofing is applied post-construction on the inside of the structure.
- Blindside waterproofing is when the foundational walls are put into place after the waterproofing systems are already established.
Waterproofing Membrane Types
Manufacturers produce commercial waterproofing membranes in many types, sizes and thicknesses. However, builders typically use liquid-applied waterproofing membranes or pre-formed sheets.
- Liquid-applied waterproofing membranes that one can spray, roll or brush onto the surface.
- Polyurethane membrane
- EPDM membrane
- Polymer-modified bituminous membrane
- Sheet-based membranes, typically made with bituminous materials, come in rolls that a contractor can unroll and attach to a solid surface.
- EPDM sheets
- Self-adhesive modified bituminous membrane
- Polymer-modified bitumen membrane
Moisture Barrier Standards
The IRC R406 and the IBC specify the conditions requiring waterproofing or damp proofing:
- The IRC and IBC require waterproofing in areas with severe soil water and high water table conditions.
- The IRC and IBC mandate damp proofing from the top of the footing to the finished grade for concrete or masonry below-grade walls retaining earth and including below-grade interior floors and spaces.
Vapor Barriers
What Is a Vapor Barrier?
Vapor barriers dampproof a structure to combat moisture and prevent water vapor inside the building from moving throughout the structure and permeating the walls and insulation.
Waterproofing vs. Dampproofing
The American Concrete Institute (ACI 515.1R-85) defines waterproofing as treating a structure or surface to resist water intrusion under hydrostatic pressure. In contrast, they define dampproofing as treating a surface or structure to resist water intrusion without hydrostatic pressure.
Specifically, vapor barriers stop vapor diffusion, which happens when moisture flows from an area of higher moisture concentration towards a space of lower concentration. It can also occur when moisture flows from a hotter to a cooler place within a building material, like insulation. Vapor barriers stop diffusion, while vapor retarders only slow vapor diffusion.
The ASTM E96 desiccant method determines a building material's ability to limit moisture from passing through it, giving it a vapor retarder (barrier) class:
- Class I vapor barrier (0.1 perms or less)
- Class II vapor retarder (0.1 < perm <1.0 perm)
- Class III vapor retarder (1.0 < perm <10 perm)
Why Do Building Envelopes Need Vapor Barriers?
Buildings prone to direct contact with water require a vapor barrier. However, your local building inspection offices can provide guidance on using vapor barriers. Building envelopes need vapor barriers to:
- Keep air from leaking out of the building
- Reduce building energy usage
- Improve occupant comfort
- Enhance indoor air quality
Above-Grade Vapor Barriers
Most building experts recommend applying vapor barriers on the side of the wall experiencing the more hot and moist conditions &#; the inner surface in cooler climates and the outer surface in humid, hot climates. Examples of vapor barrier applications include:
- Placing polyethylene plastic vapor barriers between the interior wallboard and insulation in frigid climates to manage moisture accumulation.
- Placing a vapor barrier in high-humidity spaces like spas, bathrooms, greenhouses, and rooms or swimming pools helps control condensation.
- An exterior vapor barrier in humid and hot climates can help stop outside humidity from infiltrating the walls.
Below-Grade Vapor Barriers
- Below-grade walls and floor slabs transfer ground moisture through concrete walls and slabs. Therefore, place a vapor barrier against the concrete surface to prevent moisture infiltration before installing wood framing.
- A polyethylene moisture barrier over the exposed dirt in crawl spaces will help manage moisture infiltration.
Types of Vapor Barriers
Manufacturers commonly make vapor barriers out of water-resistant materials, including:
- Extruded polystyrene or foil-faced foam board insulation
- Sheet-type roofing membranes
- Aluminum sheets or paper-backed aluminum
- Polyethylene plastic sheets
- Exterior-grade plywood
Code Requirements for Vapor Barriers
The need for a vapor barrier on a building's interior or exterior depends on the climate zone. The IRC R702.7 and the IBC .3 mandate Class I or II vapor barriers and retarders on the interior of frame walls in climate zones Marine 4 and 5, 6, 7 and 8. However, climate zones 1, 2 and 3 do not require vapor retarders and barriers.
Weather Barrier
What Is a Weather Barrier?
The AAMA (American Architectural Manufacturers Association) defines a weather barrier as a surface or a wall responsible for stopping air and water infiltration to the building's interior, protecting the building and its occupants from damaging and unhealthy mold and rot.
Placing a weather barrier over the sheathing and behind the siding allows moisture that infiltrates the wall system to dry out quickly. Vital components of a high-quality WRB include high tear strength, durability, ultraviolet resistance and straightforward installation.
Weather Barriers vs. Water Barriers
- Weather-resistant barriers stop the passage of bulk water, vapor and air from infiltrating the walls and roof.
- Water-resistant barriers offer only a continuous water-resistant barrier under the exterior wall veneer.
Why Building Envelopes Need Weather Barriers
Today&#;s building envelope designs require permeable weather barriers. Weather barriers protect a building against moisture-laden air and water infiltration which shields the structure and its occupants from unhealthy mold and rot.
Permeable weather barriers also protect against condensation because they allow moisture that accumulates in the wall system to escape. High-quality permeable weather barriers resist air, moisture and vapor by creating energy-efficient, healthy, long-lasting and comfortable buildings.
Weather Barrier Codes
The WRB must also comply with the IBC .2 requirements for water resistance and vapor permeability and the International Residential Code for water resistance (IRC R703.1.1).
The Importance of Air, Moisture, Vapor and Weather Barriers
Properly applied air, moisture, vapor and weather barriers help contractors and architects create energy-efficient, comfortable, safe and long-lasting buildings. Furthermore, air, vapor and moisture-resistant systems that feature high-quality products can contribute toward code-compliant, sustainable construction.
Understanding the similarities and differences between vapor and moisture barriers can help builders and designers minimize moisture infiltration into building envelopes.
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Similarity Between Moisture Barrier vs. Vapor Barrier
Vapor and moisture barriers aim to keep moisture (in vapor or liquid form) out of the building envelope. Manufacturers use different materials to make various types of moisture and vapor barriers.
The International Residential Code categorizes these moisture and vapor barriers based on their permeability as determined by the ASTM E96 desiccant method. The method determines a building product's ability to limit moisture from passing through it, and gives it a vapor barrier or retarder class:
Class I vapor barriers (0.1 perms or less) have the lowest permeability and include glass, sheet metal, polyethylene sheets, and rubber membranes.
Class II vapor retarders (0.1 < perm <1.0 perm) include extruded polystyrene, 30-pound asphalt-coated paper, plywood, and bitumen-coated kraft paper.
Class III vapor retarders (1.0 < perm <10 perms) include gypsum board, cellulose insulation, concrete block, house wrap, and board lumber.
Main Differences Between Vapor vs. Moisture Barrier or Basement Moisture Barrier vs. Vapor Barrier
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The main differences between moisture and vapor barrier products come from their permeability and application:
Vapor permeable or impermeable moisture barriers (Class II and III) install on the wall's exterior to stop bulk water from infiltrating the wall cavity while also allowing water vapor within the cavity to pass outside, which helps to dry out the wall assembly.
Vapor impermeable vapor barriers typically install on the inside of the frame, between the studs and drywall, to stop vapor from the structure's interior from infiltrating the wall cavity through diffusion and condensing on the warm side of the insulation.
NOTE: Because airflow contains 50 to 100 times more moisture than that carried by vapor diffusion, a building envelope needs a superior air barrier system, like that offered by Polyguard, to minimize infiltration and accumulation of moisture in the wall cavity.
What Are Moisture Barriers?
Moisture barriers apply over the exterior sheathing to prevent trapping moisture vapor in the above-grade wall system. Likewise, below-grade moisture barriers protect the foundation from moisture.
Why Above-Grade Building Envelopes Need Moisture Barriers
Above-grade moisture barriers protect against water intrusion to protect the building envelope's integrity and improve the comfort and safety of the occupants. Moisture barriers provide several significant benefits to a building envelope:
Minimize moisture exposure that can reduce the building thermal barrier's thermal efficiency and R-value
Provide waterproofing that prevents soil moisture from infiltrating the building envelope
Provide termite and pest prevention by eliminating moisture that attracts pests
Lessen moisture and condensation in the wall system that can cause structurally damaging and unhealthy mold
Protect against hydrostatic pressure that can force water through porous concrete below-grade walls. (Hydrostatic pressure is of particular concern in regions with excessive rain and high water tables.)
What Are Below-Grade Moisture Barriers?
Below-grade moisture barriers usually involve applying a liquid or sheet-applied membrane to the below-grade walls as negative, positive, or blind side waterproofing:
Builders use negative side waterproofing post-construction on the interior of the structure.
Builders install positive side waterproofing post-construction and require access to the building's exterior before filling the ground around it.
Blindside waterproofing involves installing the waterproofing system before constructing the foundation walls.
Moisture Barrier Types
Manufacturers offer commercial moisture barrier membranes in various types, thicknesses, and sizes. However, builders often prefer pre-formed sheets or liquid-applied moisture barrier membranes:
Liquid-applied moisture barrier that brushes, rolls, or sprays onto the surface
Self-adhesive modified bituminous membrane
EPDM membrane
Polyurethane membrane
Polymer-modified bitumen membrane
Sheet-based membranes are typically made with bituminous materials and come in rolls that a contractor can unroll and attach to a solid surface.
What Is a Vapor Barrier?
Vapor barriers dampproof a building to combat moisture and stop water vapor inside the structure from moving throughout the building and permeating the insulation and walls.
Waterproofing vs. Dampproofing
The American Concrete Institute Guide to the Use of Waterproofing, Dampproofing, Protective, and Decorative Barrier Systems for Concrete (ACI 515.1R-85) defines waterproofing as &#;treating a surface or structure to resist water infiltration under hydrostatic pressure.&#; In contrast, they define dampproofing as &#;treating a surface or structure to resist water intrusion without hydrostatic pressure.&#;
Vapor barriers prevent vapor diffusion, which occurs when moisture flows from an area of higher moisture concentration toward a space of lower concentration. Vapor diffusion can also happen when moisture flows from a warmer to a cooler place within a building material, like insulation. Vapor barriers stop diffusion, while vapor retarders only slow vapor diffusion.
Why Do Building Envelopes Need Vapor Barriers?
Structures in direct contact with water need a vapor barrier. Your local building inspection offices can furnish guidance on using vapor barriers. Building envelopes need vapor barriers in order to:
Lower building energy usage
Improve indoor air quality
Keep air from leaking out of the building
Enhance occupant comfort
Do You Need a Vapor Barrier?
Polyguard suggests you contact your building inspection office for local guidance on vapor barriers.
Vapor diffusion represents the smallest amount of moisture transfer into a wall system compared to air movement, liquid flow, and capillary suction. Therefore, effectively stopping moisture from infiltrating and accumulating in the wall system requires an application of a high-performing, complete moisture and air system like those offered by Polyguard Building Solutions.
Below-Grade Vapor Barriers
Below-grade walls and floor slabs transfer soil moisture through concrete slabs and walls. Placing a vapor barrier against the concrete surface will prevent moisture infiltration before installing wood framing.
A polyethylene moisture barrier over the exposed ground in crawl spaces will help control moisture infiltration.
Above-Grade Vapor Barriers
Building scientists recommend applying vapor barriers on the side of the wall that experiences the moistest and hottest conditions &#; the outer surface in humid, hot climates and the inner surface in cooler climates. Vapor barrier applications typically include:
An exterior vapor barrier in hot and humid climates can help prevent outside humidity from entering the walls.
Placing polyethylene plastic vapor barriers between the insulation and interior wallboard in cold climates can control moisture accumulation.
Placing a vapor barrier in high-humidity spaces like bathrooms, spas, greenhouses, or swimming pools helps manage condensation.
Types of Vapor Barriers
Manufacturers generally make vapor barriers out of water-resistant products, including:
Exterior-grade plywood
Aluminum sheets or paper-backed aluminum
Extruded polystyrene or foil-faced foam board insulation
Polyethylene plastic sheets
Sheet-type roofing membranes
Code Requirements for Vapor Barriers
The climate zone mandates the need for a vapor barrier on a building's exterior or interior. The IBC .3 and IRC R702.7 mandate Class I or II vapor barriers and retarders on the interior of frame walls in climate zones Marine 4 through 8. Climate zones 1 through 3 do not require vapor barriers and retarders.
Waterproofing Systems
Polyguard provides quality protection against air and moisture infiltration for below- and above-wall assemblies to ensure a high-performing building envelope and the long-term integrity of the structure. Polyguard&#;s moisture and air barrier systems include air barriers, liquid flashings, below-grade waterproofing systems, and door and window sheet flashings.
Polyguard Air Barriers
For more than ten years, Polyguard has successfully waterproofed above-grade residential walls in moist-hot climate zones 1, 2, and 3A with their non-permeable, self-adhering Aluma Flash&#; Plus weather-resistant barriers. Polyguard also supplies permeable Blue Barrier&#; Liquid Wrap for applying over surfaces and substrates like exterior gypsum, OSB, and plywood.
UV-2 40
Straightforward and quick to apply, chemical- and sunlight-resistant UV-2 40 effectively adheres when applied according to the manufacturer&#;s performance and installation requirements. UV-2 40 is a 40-mil rubberized asphalt waterproofing membrane, laminated to two high-strength polyethylene films, with a top protective aluminum layer &#; which makes it a strong waterproofing product. Additionally, the aluminum surface of durable UV-2 40 works efficiently with higher exposure structures because it reflects heat, which lowers energy use.
Polyguard Below-Grade Waterproofing Systems
Home Stretch&#; ICF Waterproofing Membrane
Polyguard specifically engineered and designed Home Stretch&#; ICF Waterproofing Membranes for insulated concrete form (ICF) walls. However, it also provides a superior waterproofing choice for CMU (concrete masonry unit), poured foundation walls, and other crucial waterproofing applications or protection against hydrostatic pressure.
To produce a complete waterproofing system for your ICF, poured concrete, or CMU, below-grade wall, Polyguard suggests using Home Stretch&#; in combination with:
Polyguard Quick Grip
Home Stretch&#; Detail Tape
Blue Barrier&#; Gap Filler
Polyflow 10
Totalflow End Outlet
Stretch Flex
&#;&#;Home Stretch&#; Water-Based Liquid Adhesive
Polyguard Liquid Flashing Products
Polyguard also offers waterproof barrier systems for windows, doors, penetrations, and gaps:
Simple to roller apply Polyguard Blue Barrier&#; Flash &#;N Wrap is a liquid window and door flashing that replaces traditional window tapes. It can also be a permeable air barrier for thin building envelope applications.
All-purpose, trowel-grade, fluid-applied Polyguard Blue Barrier&#; Liquid Flashing trowel-grade creates a weather-resistant, fully adhered waterproof barrier system around windows and doors.
Polyguard BB GF fills the gaps or treats pipes and penetrations before applying Blue Barrier&#; Liquid Wrap or Blue Barrier .
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Polyguard Window and Door Sheet Flashing Products
Polyguard also has five unique window and door flashings: WS20 Flashing, Butyl Flash&#;&#;, Aluma Flash&#;, UV2-40, and Elastiflash.
Preserve Your Structure&#;s Integrity with Polyguard Air and Moisture Barrier Systems
Vapor and moisture barriers both protect a building&#;s integrity by preventing moisture accumulation within the wall cavity, which can lead to structurally damaging mold.
A building&#;s design must also include a high-quality air and moisture barrier, like Polyguard Air and Moisture Barrier Systems, to stop the significant infiltration of moisture through airflow. A Polyguard Air and Moisture Barrier System, applied from the top down to its foundation, will protect a building&#;s integrity and air quality, reduce repair and maintenance bills, and significantly lessen energy use and moisture-related problems.
Get in touch with our Polyguard professionals today for more about vapor vs. moisture barriers and how Polyguard products can help achieve optimum moisture resistance for your home or building&#;s design!
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