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.