3.5.5.Floors

Applicability

All walls, optional input

Definition

A unique name or code that relates the exterior wall to the design documents. This is an optional input since there are other acceptable ways to key surfaces to the construction documents.

Units

Text: unique

Input Restrictions

None

Baseline Building

None

Applicability

All wall surfaces, optional

Definition

One of four categories of above-grade wall assemblies used to determine minimum insulation requirements for walls. The four wall type categories are as follows:

a. Mass walls

b. Metal building walls

c. Steel framed walls

d. Wood framed and other

A mass wall is defined as a wall with total heat capacity greater than (1) 7 Btu/ft2·°F or (2) 5 Btu/ft2·°F, provided that the wall has a material unit weight not greater than 120 lb/ft³. (Heat capacity is defined as the product of the specific heat in Btu/lb -F, the thickness in ft, and the density in lb/ ft³.) Opaque spandrel panels are considered opaque wall and not fenestration. Standard 90.1-2019 defines fenestration as an assembly in the building envelope which allows light to pass. Hence an opaque spandrel wall is considered an experior wall and not fenestration.

Units

List: Mass Walls, Metal Building Walls, Steel Framing Walls, and Wood Framing and Other Walls

Input Restrictions

As designed

Baseline Building

All walls in the baseline building are modeled as “steel framed”

Applicability

All walls, required input

Definition

Wall geometry defines the position, orientation, azimuth, and tilt of the wall surface. The geometry of roofs should match the construction documents or as-built drawings as accurately as possible. Curved surfaces such as a dome or semi-circular wall may be approximated by a series of constructions. The details of how the coordinate system is implemented may vary between simulation engines. The data structure for surfaces is described in Section 3.11.3 of this manual.

Units

Data structure: surface

Input Restrictions

As designed

Baseline Building

Wall geometry in the baseline building is identical to the proposed design

Applicability

All opaque exterior surfaces exposed to ambient conditions

Definition

The solar reflectance of a material

Units

Unitless fraction between 0 and 1

Input Restrictions

For walls and other non-roof surfaces, the default reflectance is 0.3. The default values may be overridden only when the lower reflectance can be documented by manufacturers’ literature or tests.

Baseline Building

Same as proposed

Applicability

All opaque exterior surfaces exposed to ambient conditions; this is prescribed for exterior walls at 0.9

Definition

The thermal emittance of a material. For roofing materials, the 3-year-aged emittance value from CRRC testing should be used if available.

Units

Unitless fraction between 0 and 1

Input Restrictions

For walls and other non-roof surfaces: The value is prescribed to be 0.9. The default values may be overridden only in cases when the lower emittance can be documented by manufacturers’ literature or tests.

Baseline Building

Same as proposed

Applicability

All walls that use the layers method

Definition

A specification containing a series of layers that result in a construction assembly for the proposed design. The first layer in the series represents the outside (or exterior) layer and the last layer represents the inside (or interior) layer. See the building descriptors above for wall construction type.

Several software tools add the interior and exterior air films automatically to an envelope assembly. The interior and exterior air films should not be included in the construction in such cases.

Units

List: layers

Input Restrictions

As designed, with the construction assembly defined by a series of layers. Each layer specified, must consist of materials as described in Section 3.5.2.

Baseline Building

The baseline building wall type is steel framed where the insulation is installed within the cavity of the steel stud framing. The baseline building wall construction shall be modeled as layers. The U-factor required for baseline wall construction is defined in Table 23. The layer by layer construction corresponding to each U-factor shall be modeled as shown in Table 24. For existing buildings, the baseline walls shall follow the same rules as new buildings.