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Basics & Theory

Architect Magazine: Overview Of Weather, Vapour, Air Barriers
Architect Magazine describes how weather, vapor, and air barriers protect buildings and their occupants, and when each should be used.

Building Green: How Smart Vapor Retarders Work
Building Green describes smart vapor retarders that retard vapor diffusion in less-humid conditions while allowing drying when conditions are more humid.

Building Green: Overview Of Smart Vapor Retarders
Building Green describes new smart vapor retarders that block most vapor diffusion when you want to eliminate risk of condensation, but allow vapor flow when you want drying potential.

Building Science: Double Play with Water Control & Air Control Layers
Building Science Corporation describes how the failure of either a water control layer or air control layer can lead to loss or severe damage to equipment or property.

Building Science: Vapor Permeance Of Some Building Materials
Building Science says good design and practice involve controlling the wetting of building assemblies from both the exterior and interior and different climates require different approaches. This chart lists some common vapor permeance characteristics of some common building materials.

Canadian Contractor: Difference Between Vapour Barrier & Vapour Retarder
Canadian Contractor says there appears to be confusion between the terms vapour barrier (VB) and vapour retarder (VR). The term vapour barrier should be reserved to referencing a barrier that essentially does not allow water vapour to pass, and is designated as vapour impermeable. In contrast, a vapour retarder should be used to describe a barrier that has some level of vapour permeance.

Energy Vanguard: Air Barriers, Vapor Barriers, Drainage Planes
Energy Vanguard describes air barriers, vapor barriers, and drainage planes and how they do different jobs.

Energy Vanguard: Types Of Vapor Barriers
Energy Vanguard defines types of vapor barriers including impermeable, semi-impermeable, semi-permeable, and permeable.

Energy Vanguard: What Happens When You Put A Plastic Vapor Barrier In Your Wall
Energy Vanguard explains what happens in a wall cavity with and without a plastic vapor barrier installed.

GBA: All About Water-Resistive Barriers
Green Building Advisor describes how to choose between asphalt felt, Grade D building paper, housewrap, and a few exotic WRBs.

GBA: Comparison Of Air Barrier & Vapor Barrier
Green Building Advisor online podcast by Dr. Joe Lstiburek offers a simple comparison between air barriers and vapor barriers, and warns that we need to worry more about airtightness if we want to keep our homes healthy and dry.

GBA: Vapor Retarders & Vapor Barriers
Green Building Advisor describes vapor retarders and vapor barriers, and answers persistent questions about vapor diffusion.

ICAA: Types & Placement Of Vapour Retarders
Insulation Contractors Association of America technical bulletin provides an overview of the use, types, and placement of vapour retarders. (PDF)

IRC: Types & Selection Of Vapour Barriers
Canadian Institute for Research in Construction building digest explains types and selection of vapour barriers for exterior walls, ceilings, & roofs. 1960 (PDF)

US DOE: Vapor Barriers & Diffusion Retarders
U.S. Department of Energy covers vapour barriers and diffusion retarders, what are they, where they go, how important are they, and links to more information.
Information Sources

Building Science: Expert Discussions On Vapor Barriers
Building Science says the building science community has long known that interior vapor barriers are unnecessary and even harmful in some assemblies, but some codes still require them. In this expert conversation they we discuss sections of the Canadian building code and how its requirements are influencing US practices.

Building Science: Reports On Vapour Barrier Guidance
Building Science offers articles and information about vapoor barriers including Understanding Vapor Barriers, Air Barriers vs. Vapor Barriers, Vapor Barriers and Wall Design, The Influence of Low-Permeance Vapor Barriers on Roof and Wall Performance, Vapor Open Assemblies and Vapor Control Layer Recommendations.
Issues & Performance

Building Science: Innovative Passive Ventilation Water-Resistive Barriers
Building Science paper Innovative Passive Ventilation Water-Resistive Barriers and How They Work investigates the hygrothermal performance of wall assemblies with brick veneer cladding as well as manufactured adhered stone veneer with two different types of water resistive barriers.

Building Science: Water-Resistive Barrier Performance In Hot-Humid Climates
Building Science research project evaluated performance of typical residential wall systems that incorporate water-resistive barriers with a range of vapor permeability. These systems included both absorbent and nonabsorbent claddings in hot-humid climates for direct comparison. This paper describes the test design, the test facility construction and installation, and the resulting data.

CUFCA: Spray Polyurethane Foam Meets Code Requirement For Vapour Barrier
Canadian Urethane Foam Contractors Association research demonstrated ability of typical framed walls using spray polyurethane foam insulation, with and without additional vapor barrier layers, to meet National Building Code of Canada requirements. (PDF)

Energy Vanguard: Does Your Water Resistive Barrier Really Resist Water?
Energy Vanguard says a water resistive barrier provides protection against water damage for water that gets behind the cladding of a building. But what if it doesn't really resist water?

Fine Homebuilding: Drainable Housewrap Fire Risk Depends on Gap Size
Fine Homebuilding discusses whether or not the tiny air gap in water-resistive barriers is large enough to feed a flame.

GBA: How To Deal With Vapor Barrier Code Edict
Green Building Advisor provides a solution for when a local code inspector insists on an interior polyethylene vapor barrier.

APA: Water Vapor Permeance of Wood Structural Panels
Engineered Wood Association document addresses water vapor permeance of structural wood panels, vapor retarders and their role in wall-system design. Free site registration required.

BC Housing: Online Video On Building Smart With Air & Vapour Barriers
BC Housing online video of their workshop Building Smart with Air and Vapour Barriers covers building science principles, design considerations and practical installation details related to the use of air and vapour barriers in single and multi-unit residential buildings. Speakers examine the challenges and options for improving the durability, safety, comfort and energy efficiency of buildings through the effective use of barrier materials.

Building Science: Chubby Checker & Fat Man Do Permeance
Building Science says vapor permeance needs to be re-thought, as vapor transmission at the exterior of a wall assembly is not always straightforward. We have to worry about how much can get out as well as how much can get in. And things change as thermal resistance goes up and air leakage goes down.

Building Science: Double Vapor Barrier = Double Toil & Trouble
Building Science says Canadian walls dried to both the outside and the inside, but that all changed when we started putting plastic on the inside of walls and began to put impermeable insulating sheathing on the outside. We started to have double vapor barriers.

Building Science: Flow-Through Wall Assemblies & Vapour Barriers
Building Science says a wall is supposed to keep the outside out and the inside in. That is the way things are supposed to work. The premise relating to the vapor control layer in the perfect wall is that it is for all intents and purposes completely impermeable, a true vapor barrier. But do we even need the vapor control layer at all?

Building Science: Holes & Leaks
Building Science says to claim that something that has holes in it can act as a water control layer is a pretty interesting argument. It is both true and untrue.

Building Science: How Come Double Vapor Barriers Work?
Building Science describes why, in some assemblies, double vapour barriers are actually a pretty good idea. The most famous of them all is a classic compact flat roof. The roof membrane on the top is clearly a vapor barrier, and the membrane on the bottom is also a vapor barrier. The bottom membrane's primary function is that of an air barrier but it's material characteristics are such that historically it has also been a vapor barrier.

Building Science: Influence Of Low-Permeance Vapor Barriers On Roof & Wall Performance
Building Science paper describes how, in many practical situations, a low-permeance vapor barrier will not improve hygrothermal performance and may in fact increase the likelihood of damaging condensation or trap moisture in the system. (PDF)

Building Science: Understanding Vapor Barriers
Building Science digest describes the function of a vapor barrier, where it is located in an assembly, its permeability, and characteristics of materials that comprise the assembly and the interior conditions.

Building Science: Vapor Open Assemblies
Building Science describes how vapor barriers were originally intended to prevent assemblies from getting wet, and incorrect use of vapor barriers is leading to an increase in moisture-related problems.

CMHC: Where Polyethylene Is Appropriate As Air & Vapour Barrier
CMHC research illustrates where polyethylene is appropriate for air/vapour barriers and where other vapour barrier materials might be preferable. It identifies situations in which performance could be improved, and provides information on general approaches to help mitigate performance concerns. (PDF)

Fine Homebuilding: Water-Resistive Barriers
Fine Homebuilding describes options for this water-impermeable layer beneath the siding that protects walls from rain and snow, and often functions as a building's air barrier.

GBA: Choosing & Using Water-Resistive Barriers
Green Building Advisor online video Water-Resistive Barriers describes how they keep water out of your walls, as well as cost and installation details.

GBA: Choosing The Right Water-Resistive Barrier
Green Building Advisor discusses whether there are times when a rubberized asphalt membrane makes more sense than ordinary plastic housewrap.

GBA: Do I Need a Vapor Barrier?
Green Building Advisor online video tackles one of the most commonly asked building science questions on GBA and beyond. Do I Need a Vapor Barrier?

GBA: Do I Need A Vapor Retarder?
Green Building Advisor says if your wall doesn’t have a vapor retarder, there is no need to worry. Builders worry way too much about vapor diffusion and vapor retarders. It’s actually very rare for a building to have a problem caused by vapor diffusion.

GBA: How To Combine Board & Batten Siding With Exterior Rigid Foam
Green Building Advisor Q & A says exterior foam helps minimize thermal bridging and improve energy efficiency, and discusses how to keep costs down and avoid moisture problems.

GBA: Reviving An Old Debate On Vapor Barriers
Green Building Advisor says evidence suggests that interior polyethylene vapor barriers can cause problems, but architects still specify them.

GBA: Using Rigid Foam As A Water-Resistive Barrier
Green Building Advisor describes some pros, cons, and considerations for using foam as a water resistive barrier.

GBA: Vapor Barriers May Or May Not Be A Good Thing
Green Building Advisor discussion says vapor barriers are supposed to stop vapor diffusion through roofs, walls, and floors, but they can also can trap moisture, causing rot and mold.

GBA: Vapor Barriers Redux
Green Building Advisor discusses whether there are any risks if you build an exterior wall without an interior polyethylene vapor retarder.

GBA: When Sunshine Drives Moisture Into Walls
Green Building Advisor says because of inward solar vapor drive, vapor diffusion from the outside inward is often more worrisome than vapor diffusion from the inside outward. So you need a good vapor barrier strategy.

IRC: Role Of Vapor Barrier In Wood-Frame Stucco Wall
Canadian Institute for Research in Construction research paper investigates the role of the vapor barrier in exterior wood-frame stucco walls with the help of a two dimensional hygrothermal simulation tool, hygIRC-2D. (PDF)

WoodWorks: Integrated Air & Water Barrier Systems
WoodWorks online course presentation Integrated Air & Water Barrier Systems provides guidance for architects, specifiers, waterproofing contractors, and other professionals considering use and advantages in the selection or specification of air and water barriers for the design and installation of integrated structural panel and air and water barrier systems. Topics covered include an introduction to air and water barriers, structural panels, code requirements when designing for energy code compliance, and common design and installation practices and techniques. (PDF)
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