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Abstract
Simultaneous experiments on the moisture behaviorof six low slope roof systems were performed in a climate simulator. The systems were composed of a self drying design over a coventional metal deck, a self drying design over a significanlty more permeable slotted metal deck, and four other sytems over conventional metal decks; a systems typical of U.S. construction with a liquid water permeable vapor retarder, a system typical of European construction with a ilquid water permeable vapor retarder, a top ventilated systems with a polyethylene vapor retarder, and an impermeable ocntrol sytsem with apolyethylene vapor retarder. The total weight of each test panel was measured and recorded continuously, along with temperatures and heat fluxes to compare the behavior ot he various systems. We imposed steady-state temeratures from hot summer to cold winter conditions to obtain the R-values of the construction dry insulations to each panel. Temperature cycles typical of hotsummer days to cold winter conditions to obtain the r-values were hen imposed above the construction assembly to obtain baseline diurnal performance. Enough water was added under the membrane of each sytem to saturate a layer of blotting paper. During the repeated diurnal cycles typical of hot summer days, the self-drying design over the slotted deck dried fastest, followed by the European constrccuion with a liquied water permeable vapor retarder, then the self drying design over the solid deck. When water was added to the systems, the lower membrane of the top ventilated system had bee slit in several places and this system dried at a slow rate. JWhen the lower membrane was removed completely, the top ventilated system dried as fast as the self drying design over the solid deck. The control system and the U.s. construction with a iquid water permeable vapor retarder dried slowly at about the same rate. We applied a one dimensional thermal and hygric model. The solid and slotted deck were assumed to differ only in water vapor permeance. A model was not attempted for the top ventilated ystem. The 1-D model predicted very well that slow rates of wetting in the winter cycles and both the slow then fast rates of drying in the summer cycles before and water addition; howerver, it overpredicted the drying rate for the U.s. construction with a liquid water permeable vapor retarder.
Simultaneous experiments on the moisture behaviorof six low slope roof systems were performed in a climate simulator. The systems were composed of a self drying design over a coventional metal deck, a self drying design over a significanlty more permeable slotted metal deck, and four other sytems over conventional metal decks; a systems typical of U.S. construction with a liquid water permeable vapor retarder, a system typical of European construction with a ilquid water permeable vapor retarder, a top ventilated systems with a polyethylene vapor retarder, and an impermeable ocntrol sytsem with apolyethylene vapor retarder. The total weight of each test panel was measured and recorded continuously, along with temperatures and heat fluxes to compare the behavior ot he various systems. We imposed steady-state temeratures from hot summer to cold winter conditions to obtain the R-values of the construction dry insulations to each panel. Temperature cycles typical of hotsummer days to cold winter conditions to obtain the r-values were hen imposed above the construction assembly to obtain baseline diurnal performance. Enough water was added under the membrane of each sytem to saturate a layer of blotting paper. During the repeated diurnal cycles typical of hot summer days, the self-drying design over the slotted deck dried fastest, followed by the European constrccuion with a liquied water permeable vapor retarder, then the self drying design over the solid deck. When water was added to the systems, the lower membrane of the top ventilated system had bee slit in several places and this system dried at a slow rate. JWhen the lower membrane was removed completely, the top ventilated system dried as fast as the self drying design over the solid deck. The control system and the U.s. construction with a iquid water permeable vapor retarder dried slowly at about the same rate. We applied a one dimensional thermal and hygric model. The solid and slotted deck were assumed to differ only in water vapor permeance. A model was not attempted for the top ventilated ystem. The 1-D model predicted very well that slow rates of wetting in the winter cycles and both the slow then fast rates of drying in the summer cycles before and water addition; howerver, it overpredicted the drying rate for the U.s. construction with a liquid water permeable vapor retarder.
Date
12/1998
12/1998
Author(s)
A Desjarlais; T Petrie; P Childs; J Atchley
A Desjarlais; T Petrie; P Childs; J Atchley
Page(s)
41-54
41-54
Source
Oak Ridge National Lab
Oak Ridge National Lab
Keyword(s)
self drying roof; moisture; steep slope; vapor retarder
self drying roof; moisture; steep slope; vapor retarder