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 MIL-HDBK-1001/5A
factor, overall thermal transmittance, the R-value for either
materials or constructions must first be evaluated because, by
definition, the evaluated because, by definition, the U-factor is
the reciprocal of the R-value.
Thermal shock. Stress-producing phenomenon resulting from sudden
temperature drop in a roof membrane when, for example, a rain
shower follows brilliant sunshine.
Thermal shock factor (TSF). Mathematical expression for
calculating the theoretical temperature drop required to split a
rigidly held membrane sample under tensile constructive stress.
(TSF = tensile strength at 0 divided by load strain modules at 0F
times coefficient of expansion in temperature range of 0 to 30
degrees F.)
Thermal transmittance (U-factor). The time rate of heat flow per
unit area under steady conditions from the fluid on the warm side
of a barrier to the fluid on the cold side, per unit temperature
difference between the two fluids. It is evaluated by first
evaluating the R-value and then computing its reciprocal.
Thermoplastic. Changing viscosity under thermal cycling (fluid
when heated, solid when cooled).
Thermosetting. Hardening permanently when heated, owing to
cross-linking of polymeric resins into a rigid matrix.
Through-wall flashing. Water-resistant membrane or material
assembly extending through a wall's horizontal cross section, and
designed to direct flow through the wall toward the exterior.
Tiles. Roofing tiles are produced by baking plates of molded
clay into tile, with density determined by the length of time
heated and by heating temperatures. Clay tile offers a wide
range of design possibilities for residential roofs due to the
variety of tiles available, i.e. roll tile and flat tile.
U-factor.
See Thermal transmittance.
Vapor barrier.
See Vapor Retarder.
Vapor migration. Flow of water vapor from a region of high vapor
pressure to a region of lower vapor pressure.
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