Thermal bridges in roofs made of wood and light-gauge steel profiles
- Oak Ridge National Lab., TN (United States). Building Technology Center
Experimental measurements and three-dimensional thermal modeling were undertaken for several configurations of wood and metal truss roofs. The main goal of this work was to estimate the real effects of thermal shorts generated by wooden or metal structural components of roofs. The connection between roofs and walls is an important detail that needs to be considered to design thermally efficient roofs. It was found that, even for wooden roof structures, this detail has a significant impact on the overall thermal performance of the building envelope. Experiments were done on half the actual top of a single-wide manufactured home in a large-scale climate simulator. They showed that, despite the use of high levels of insulation in the attic, the measured overall thermal performance of the roof system can be significantly lower than that through the center of the cavity. Several configurations with different insulations were examined, including ones using thin, powder-filled evacuated panels (PEPs) with high R-values. Three-dimensional thermal modeling, proven on wood- and metal-framed walls, was used to analyze the effect of thermal bridges and underinsulation. For wooden roof structures, replacement of the traditional roof/wall details by ones that are more thermally efficient can reduce local heat losses by about 10%. The same modeling techniques were used on details specific to roofs with metal infrastructures. For metal roof constructions where highly conductive metal profiles are used, R-value for the insulation can be even more extreme than that with wooden structures. Several reasons are apparent, the most significant of which is thermal bridges created by the structural elements. Most of these bridges have a complicated three-dimensional character. In metal constructions, local temperature gradients can be enhanced by strong thermal bridges and underinsulation. Thermal bridges generated by metal components of roofs can reduce the effective R-value of the structure by 50% to 75% of the nominal R-value of the insulation material used in the center of the cavity.
- OSTI ID:
- 345258
- Report Number(s):
- CONF-9702141-; TRN: IM9922%%191
- Resource Relation:
- Conference: American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) winter meeting, Philadelphia, PA (United States), 24-28 Feb 1997; Other Information: PBD: 1997; Related Information: Is Part Of ASHRAE transactions: Technical and symposium papers, 1997. Volume 103, Part 1; PB: 1136 p.
- Country of Publication:
- United States
- Language:
- English
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