6.8 Thermal Bridges

To learn how to use THERM software developed by Lawrence Berkeley National Laboratory (LBNL) to calculate thermal bridges, an introductory training package may be purchased from the THERM Introduction page on the PHIUS website.

PHIUS has created a Psi-Value Calculator Template for consultants to use to document and calculate a project’s thermal bridges.

Negative Thermal Bridges: If accounting for any negative thermal bridges, all thermal bridges in the project must be calculated, no matter how small. In general, we recommend against taking negative thermal bridges in the design phase, and only using these as a “last line of defense”.

Temperature Zone Assignments in WUFI Passive

WUFI Passive Attachment	Temperature conditions in psi-value calculation
	Interior (68F)	Exterior (14F)	Ground (41F)
Ambient	x	x
Perimeter	x	x	x
Basement Floor	x		x

• Ambient: Use this selection for thermal bridges occurring above grade. Only two temperatures will be used in the THERM/psi value calculation -- ambient and interior. 
• Perimeter: Use this selection for thermal bridges occurring at grade. In this case, there will be three temperature zones used in the THERM calculation -- ambient, ground, and interior. 
• Ground Floor: Use this selection for thermal bridges below grade. Only two temperatures will be used in the THERM calculation -- ground and interior. 

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