Modeling Eaves in Ekotrope

What are eaves?

In general, an eave is the lower edge or border of a sloping roof that projects beyond the exterior wall of a building. It serves different purposes, such as water management, ventilation, and thermal regulation of the attic space.

When and how to model eaves in Ekotrope?

Ekotrope now supports modeling eaves on the roof. It is required to be modeled only when its presence affects the thermal resistance of the roof system. Typically, when the attic floor is insulated and the eave height is less than that of the insulation/framing height, eaves create areas of reduced insulation thickness at the perimeter of the attic floor. In such cases, it is recommended to model eaves as per the following guidelines:

1. Specify the ceiling framing height and eave height in inches. Measure the eave height from the bottom of the first stud layer (counting from the interior to exterior in the roof assembly). Do not include the sheathing or other layers that are between the stud layer and the interior conditioned space.
2. Specify the eave length in feet (not inches).
3. Specify roof slope in inches per ft. For roofs with more than one slope (e.g., Gambrel roof), use the slope measured at the eave edge.
4. We recommend using Ekotrope Version 5.0 or later for the accurate calculation when modeling roof components with eaves.

Here are a couple of examples to illustrate the eave assembly:

where,

• frameH = ceiling framing height (inches)

• eaveH = eave height (inches)

• slope = roof pitch (inches per ft)

* Image courtesy of ANSI/RESNET 301-2022

How will eaves affect the calculation?

Ekotrope RATER calculates the effective thermal resistance for roof/ceiling assemblies with eaves in accordance with ANSI/RESNET 301-2022 Section 4.2.2.2. Modeling eaves in ANSI/RESNET 301-2019 or earlier is not mandatory. There is a known bug in Ekotrope Versions prior to 5.0 in the calculation when the roof/ceiling is modeled with eaves. We recommend using Ekotrope Version 5.0 or later for accurate results. 

Generally, if the insulation thickness is less than the normal thickness for the area under eaves, the effective thermal resistance will be less than that of a roof/ceiling without eaves. Any reference home that specifies R-value (or U-factor) for ceiling insulation will remain unchanged in the presence of eaves.

If you have any questions, please feel free to contact support@ekotrope.com.