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Sensitivity of Low Sloped Roofs Designs to Initial Water and Air Leakage
Abstract
Liquid water in low sloped roofs almost
always causes problems. Roofs are
designed only to control the migration of
vapor, if at all. Small amounts of water
leakage/penetration, may cause mold
growth or catastrophic corrosion in current
roofs systems. In a recent paper by the
authors the effect of exterior surface
emissive and absorptive properties was
found to have a significant effect on the
moisture performance of a roof that had a
leak. Depending on the surface
characteristics, roof systems can be
designed to effectively manage water
penetration, but at an energy cost. In the
roofs system examined previously, air
leakage was not included.
In the present study, the authors reinvestigated
the effect of water penetration
and the influence of air leakage on the
hygrothermal performance of a few
selected roofs. The drying potential of a
groove ventilated roof is examined. The
performance concept is based on the fact
that warming up of air in the groove
increases it's ability to transport moisture
to the outside. Solar radiation raises the
temperature of air in the grooves and on
average, during a sunny summer day 0.5 L
of water can be ventilated out of the roof
per 1m width of the roof.
In this paper, one climatic condition was
investigated; a hot and humid Climate
representative of Houston, TX. The
specific questions that the paper addresses
are: What are the vapor and liquid control
dynamic involved in the moisture
migration of a roof in Houston TX? and
how does airflow influence the
performance of a roof that is initially wet ?
A state-of-the-art numerical model was
used to address these issues. Results
showed that the drying potential depends
on the ventilation rates. The roof system
with ventilation grooves dried out faster
from the initially wet stage than the roof
without the ventilation grooves. The total
increase in heat loss of the roof was found
to be between 0 - 5 % depending on the
thickness of the insulation. The ventilation
can cool down the temperature of the roof
in the middle of a hot and sunny day thus
reducing the heat load to the inside.
Citation
Karagiozis, A.; Desjarlais, A.; Salonvaara, M. (2002). Sensitivity of Low Sloped Roofs Designs to Initial Water and Air Leakage. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /4593.