R value
a measurement of heat resistance (the higher, the better). R value = the number 1 divided by the U value.
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rafter
the structural main "rib" of a glazed structure available in straight and bent.
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rail
a horizontal sash member.
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receptor
framing system consisting of two snap-together extrusions used to contain a window frame head and jambs in a masonry type opening. It allows for deflection and inconsistencies in the openings.
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reflective glass
glass with metallic coatings applied onto or into the glass surface to reduce solar radiant energy and visible light transmission.
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ridge
an extrusion at the top of the structure which all sloping rafters marry into.
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