3.5.2 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 90.1-2013.
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 D) 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.

90.1-2019

For use with Standard 90.1-2019, construction assemblies for the proposed design shall be created by selecting from a library of building construction layers in Standard 90.1-2019, Appendix A. The software shall specify all composite layers that consist of both framing and insulation and shall use established methods defined in the Standard 90.1- 2019 Appendix A or the ASHRAE Handbook of Fundamentals for calculating effective R-values of composite layers

*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 Building	Not applicable

*Specification Method*
Applicability	All projects
Definition	The method of describing a construction assembly. The simpler method is to describe the U-factor of the construction assembly, which can account for thermal bridging and other factors. However, this method does not account for the time delay of heat transfer through the construction assembly. 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. For below-grade constructions, a C-factor can be specified; for slab-on-grade constructions, an F-factor is specified.
Units	List: layers, U-factor, C-factor, F-factor, R-value
Input Restrictions	The layers method shall be used for all constructions except for metal building or similar constructions with negligible thermal mass may use the U-factor method
Baseline Building	Construction assembly for the baseline building will be defined in layers

*Layers*
Applicability	All construction assemblies that use the layers method of specification
Definition	A structured list of material names that describe a construction assembly, beginning with the exterior finish and progressing through the assembly to the interior finish. Materials are described in Section 3.5.2
Units	List: layers of construction assembly
Input Restrictions	The user is required to describe all layers in the actual assembly and model the proposed design based on the layer descriptions
Baseline Building	See building descriptors for roofs, exterior walls, exterior floors, doors, fenestration, and below-grade walls