Role of Vapor Barrier in Wood-Frame Stucco Wall in Various North American Climates: Observations from Hygrothermal Simulation

This 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. For this purpose, the wall is subjected to the exterior weather conditions of six different North American geographic locations and three different interior climatic conditions. Seven different vapor diffusion strategies, generated by varying the water vapor permeance of the vapor barrier, installed outboard of the interior finish, have been studied to generate critical understanding on the role of vapor barrier in the wood-frame stucco walls.The outputs from the simulations have been analyzed with the help of a novel moisture response indicator called RHT index. Simulation results indicate that the vapor transmission characteristics of the vapor barrier, in terms of water vapor permeance, play a very important role in the overall moisture response of the wood-frame stucco wall. A very high or low vapor permeance of the vapor barrier does not produce the optimum moisture management strategy for the wood-frame stucco wall. Moreover, simulation results indicate that the removal of vapor barrier from the wall system can result in a heightened moisture response and a considerable accumulation of moisture in the interior gypsum board that may lead to severe consequences in particular, the premature deterioration of the interior facing gypsum board.It has also been observed from the simulation outputs that the optimum vapor diffusion strategy, that of limiting the vapor permeance of the vapor barrier, is not a function of interior climatic conditions considered in this study. It is hoped that the results reported in this paper will shed some light on a number of concerns raised in recent years on the role of vapor barrier in wood-frame stucco wall construction.On examine dans ce document le r\uf4le que joue le pare-vapeur dans les murs ext\ue9rieurs en stucco \ue0 ossature de bois, au moyen d?un outil de simulation hygrothermique bidimensionnel nomm\ue9 hygIRC-2D. \uc0 cette fin, le mur est soumis aux conditions climatiques de six (6) emplacements g\ue9ographiques diff\ue9rents d?Am\ue9rique du Nord ainsi qu?\ue0 trois (3) types de conditions ambiantes (int\ue9rieures) distincts. On a \ue9tudi\ue9 sept (7) strat\ue9gies diff\ue9rentes de diffusion de la vapeur, obtenues par variation de l?indice d?hydrofugation du pare-vapeur, install\ue9 \ue0 l?ext\ue9rieur du rev\ueatement int\ue9rieur, afin de d\ue9gager une compr\ue9hension critique du r\uf4le du pare-vapeur dans les murs de stucco \ue0 ossature de bois.Les rendements des simulations ont \ue9t\ue9 analys\ue9s \ue0 l?aide d?un indicateur de performance hygrom\ue9trique de conception novatrice appel\ue9 indice HRT (humidit\ue9 relative et temp\ue9rature). Les r\ue9sultats des simulations indiquent que les caract\ue9ristiques de transmission de vapeur du pare-vapeur, en termes de perm\ue9abilit\ue9 \ue0 la vapeur d?eau, ont une incidence tr\ue8s importante sur la performance \ue0 l?humidit\ue9 globale des murs de stucco \ue0 ossature de bois. Une perm\ue9abilit\ue9 \ue0 la vapeur soit tr\ue8s \ue9lev\ue9e, soit faible du pare-vapeur n?engendre pas une strat\ue9gie de contr\uf4le de l?humidit\ue9 optimale pour ce type de mur. En outre, les r\ue9sultats des simulations r\ue9v\ue8lent que l?enl\ue8vement du pare-vapeur du syst\ue8me de mur peut accro\ueetre la sensibilit\ue9 \ue0 l?humidit\ue9 et causer une accumulation d?humidit\ue9 consid\ue9rable dans les plaques de pl\ue2tre pouvant entra\ueener de graves cons\ue9quences, notamment une d\ue9t\ue9rioration pr\ue9matur\ue9e des plaques du rev\ueatement int\ue9rieur.Les rendements des simulations nous ont \ue9galement permis d?observer que la strat\ue9gie optimale de diffusion de la vapeur, soit celle consistant \ue0 limiter l?indice d?hydrofugation du pare-vapeur, n?est pas fonction des conditions ambiantes (int\ue9rieures) prises en compte dans le cadre de cette \ue9tude.Nous esp\ue9rons que les r\ue9sultats dont ce document fait \ue9tat permettront de mieux cerner plusieurs des questions qui ont \ue9t\ue9 soulev\ue9es ces derni\ue8res ann\ue9es concernant le r\uf4le exact que joue le pare-vapeur dans les constructions \ue0 murs de stucco \ue0 ossature de bois.Peer reviewed: YesNRC publication: Ye