http://www.buildingscience.com daily 1 2010-01-26T02:05:02Z http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers The function of a vapor barrier is to retard the migration of water vapor. Where it is located in an assembly and its permeability is a function of climate, the characteristics of the materials that comprise the assembly and the interior conditions. Vapor barriers are not typically intended to retard the migration of air. That is the function of air barriers. No publisher Joseph Lstiburek Building Science Digests are information articles intended for professionals. The author and the publisher of this article have used their best efforts to provide accurate and authoritative information in regard to the subject matter covered. The author and publisher make no warranty of any kind, expressed or implied, with regard to the information contained in this article. The information presented in this article must be used with care by professionals who understand the implications of what they are doing. If professional advice or other expert assistance is required, the services of a competent professional shall be sought. The author and publisher shall not be liable in the event of incidental or consequential damages in connection with, or arising from, the use of the information contained within this Building Science Digest enclosure-Wall assembly guidance-Enclosure design principles comp-walls moisture-Drainage plane moisture-Vapor Permeance resources-vapor-barrier-code-changes doc-Digest moisture-Drying residential ventilation guidance-Roof design enclosure-Roof assembly guidance-Wall design moisture-Diffusion/Vapor Pressure comp-roofs 2013-03-20T20:26:19Z BSC Article http://www.buildingscience.com/documents/information-sheets/info-sheet-310-vapor-control-layer-recommendations The current International Residential Code (IRC 2009) provides excellent guidance for the installation of vapor control layers. No publisher Building Science Corporation resources-vapor-barrier-code-changes doc-InformationSheet Building America IRC climate-Building design and climate 2013-04-09T17:28:00Z BSC Article http://www.buildingscience.com/documents/information-sheets/vapor-open-assemblies Vapor barriers were originally intended to prevent assemblies from getting wet. Incorrect use of vapor barriers is leading to an increase in moisture-related problems. No publisher Building Science Corporation drying resources-vapor-barrier-code-changes doc-InformationSheet Building America vapor barrier climate-Building design and climate 2013-04-09T17:30:02Z BSC Article http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers Most of us are not aware of just how differently these two barriers work in building assemblies. This article makes the differences as clear as the polyethylene film that should (or more likely should NOT) be in your walls. No publisher Joseph Lstiburek enclosure-Wall assembly guidance-Enclosure design principles moisture-Diffusion/Vapor Pressure airflow-Physics of Air Movement resources-vapor-barrier-code-changes moisture-Vapor Permeance moisture-Convection/Air barriers enclosure-Roof assembly doc-Report airflow-Airtightness/Air barrier vapor barrier 2013-04-16T21:26:13Z BSC File http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design Good design and practice involve controlling the wetting of building assemblies from both the exterior and interior and different climates require different approaches. No publisher Joseph Lstiburek enclosure-Wall assembly moisture-Diffusion/Vapor Pressure resources-technical doc-Report resources-vapor-barrier-code-changes guidance-Wall design vapor barrier 2013-04-16T22:25:47Z BSC File http://www.buildingscience.com/documents/reports/rr-1101-influence-low-permeance-vapor-barriers-roof-wall-performance Low-permeance vapor barriers are widely used on the interior of wall and roof systems in large parts of North America. Many codes and standards imply or even state that low-permeance vapor barriers should be used in all cold regions as well as many moderate climate zones. The influence of vapor barriers on the hygrothermal performance of wall and roof systems is a function of exterior climate, interior climate, solar absorptance, rainwater absorption, and the vapor and thermal resistance of all of the layers in the system. 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. This paper will examine the role of vapor barriers on hygrothermal performance with the aid of simple and transparent diffusion calculations supported by measurements from full-scale natural exposure monitoring. The phenomenon of summertime condensation, the drying of roofs and walls, and multiple vapor barrier layers will be explored. The importance of properly assessing both the interior and exterior climate will be discussed. Vapor diffusion control strategies will be presented. No publisher John Straube resources-vapor-barrier-code-changes ASHRAE 2013-03-02T02:57:30Z BSC File