6.5.2 Construction Assemblies

Assembly Name
Applicability	All projects
Definition	The name of a construction assembly that describes a roof, wall, or floor assembly. The name generally needs to be unique so it can be referenced precisely by surfaces.
Units	Text, unique
Input Restrictions	Construction name is a required input.
Baseline Rules	Not applicable

Specification Method
Applicability	All projects
Definition	The method of describing a construction assembly. The more simple method is to describe the U-factor of the construction assembly which can account for thermal bridging and other factors. However with this method, the time delay of heat transfer through the construction assembly is not accounted for. Generally, with the U-factor method, heat transfer is assumed to occur instantly. The more complex method is to describe the construction assembly as a series of layers, each layer representing a material. With this method, heat transfer is delayed in accord with the thermal mass and other properties of the assembly.
Units	List: choices are U-factor or Layers
Input Restrictions	The layers method shall be used for all constructions except for metal building or similar constructions with negligible thermal mass.
Baseline Rules	For each construction, the proposed design specification method shall be used.

U-factor
Applicability	All construction assemblies that are specified by a U-factor
Definition	The steady state rate of heat transfer through a construction assembly
Units	Btu/h-ft²-°F
Input Restrictions	U-factors should be consistent with values in Appendix A of ASHRAE Standard 90.1-2007.
Baseline Rules	Not applicable

Layers
Applicability	All construction assemblies that use the layers method of specification
Definition	A structured list of pairs of material names that describe a construction assembly, beginning with exterior finish and progressing through to the interior finish. Material names must be from the standard list (Appendix E) or defined (see above).
Units	Data structure: construction assembly
Input Restrictions	The user is required to describe all layers in the actual roof assembly and the proposed design will be modeled as input by the user.
Baseline Rules	See building descriptors for roofs, walls, and floors.

U-factor Derating Factor
Applicability	All construction assemblies that use the layers method of specification
Definition	A derating factor to account for thermal bridges and other non-homogeneous construction features. The factor is a multiplier on the U-factor such that a value greater than one increases heat losses and gains. The layers method assumes that all layers are completely homogeneous and that there are no thermal bridges or other features that would increase heat gain or loss.
Units	Unitless
Input Restrictions	Default is 1.2 (120%). Minimum value is 1.0 and maximum value is 3.0.
Baseline Rules	The baseline building shall use a derating factor of 1.0, e.g. no derating.