INTRODUCTION/BACKGROUND
The literature review identified much information relevant to the development of the guidelines,
including many examples of thermal envelope defects. Research was identified in the area of
calculation and modeling that has enabled the quantification of the effects of thermal defects on
envelope heat transfer rates. The review identified several principles for the design and
construction of building envelopes that avoid the occurrence of thermal defects. Many design
details were identified that provide effective alternatives to the details that result in these defects.
The main conclusions of the literature review include the determination that thermal defects have
significant detrimental effects on energy consumption, thermal comfort and material performance.
Publications that identify these defects and present alternative designs have been limited to specific
buildings and specific envelope components. There are no thorough presentations of thermal
envelope defects, poor design details or alternative designs for the great variety of building
envelope constructions. This is the information that the thermal envelope guidelines are intended to
present, and this information exists primarily in the practical experience of design and construction
professionals.
The literature review also examined existing standards and construction guidance documents for
information on thermal envelope integrity. Most of these documents contain general information on
design principles and construction techniques or guidance on the selection of U-values and glazing
systems. While some of these documents recognize the importance of thermal envelope defects,
they do not emphasize the importance of these problems or contain the information or design
details necessary to construct building envelopes that avoid these defects. Construction
handbooks cover many important areas of envelope design, but do not generally address issues of
thermal defects and air leakage and do not provide the design details necessary to avoid these
defects. Construction guides that were developed specifically to promote energy conserving
designs address insulation levels, thermal mass, fenestration and materials, but generally not
thermal defects. In some cases they mention the importance of controlling infiltration and avoiding
thermal bridges, but do not indicate how to design and construct an envelope that actually achieves
these goals. The sections on the thermal envelope within the energy standards developed by GSA,
ASHRAE and DOE concentrate on insulation levels and fenestration systems. While they refer to
the importance of thermal bridges and air leakage, they do not contain sufficient criteria for their
control.
During the literature review and the subsequent development of the guidelines, several documents
were identified of particular relevance. Several years ago Owens/Corning Fiberglas developed a
design guide, currently out of print, containing many design details for walls, roofs and envelope
intersections. The guide is very good on insulation system continuity, but does not deal with air
leakage and air barrier systems. Steven Winter Associates recently developed a catalog of twenty-
one thermal bridges commonly found in commercial building envelopes, including proposed
alternative constructions in each case. A recent book by Brand is another good source of
information, containing design details developed to explicitly avoid thermal defects.
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