Roof Insulation

Modified on Wed, 10 Feb, 2021 at 11:14 AM

Wall, Roof and Framed Floor Library Help

For details on modeling hollow-core concrete block walls, please read this article.

Name	Identifier for the Wall, Roof or Framed Floor
Description	Notes describing the Wall, Roof or Framed Floor
Has Radiant Barrier (Roof only)	Check this box if the roof assembly includes a properly installed radiant barrier. Note: when adding a radiant barrier with ducts in the attic, the Duct Location should be changed.

Assembly Calculator

Ekotrope includes a tool called the Assembly Calculator to help design and evaluate the insulative properties of walls, framed floors, and roofs. All three of these operate in roughly the same manner. When you are editing or creating a wall, framed floor, or roof component, there will be an example assembly already in place. To build the assembly you want, start with the example and modify it until it reflects the intended design. The Assembly Calculator calculates R/U Values using the Area Weighted Average R Value Methodology. (See: Krigger et al. Residential Energy, Cost Savings and Comfort for Existing Buildings. 5th Edition. 2009. Pg. 67.)

Air films are included automatically by Ekotrope, so do not add layers to the interior and exterior to represent air films.

Sections

The calculator itself is split into three sections.

Assembly Properties

On the top left there are Assembly Properties, these are automatically updating estimated cost per square foot and calculated R-Value of the assembly.

Layers

Below the Assembly Properties is a series of layers. Each of these layers represents either one type of continuous insulation or one set of studs with cavity insulation.

Layer Edit

To the right of the Assembly Properties and Layers sections is the Layer Edit section which allows you to view and edit the characteristics of individual layers.

Using the Calculator

Designing an assembly in the calculator involves adding and removing, rearranging and modifying layers until it accurately describes the intended assembly.

Layer Order

Layers are ordered from top to bottom as exterior to interior for walls and roofs, but as interior to exterior for floors. The order can be modified by clicking and holding on a layer, then dragging it to a new position and releasing the layer.

Adding and Removing Layers

A new layer can be added to either the exterior or interior by clicking the green + on the proper side.

A layer can be removed by clicking the red X to the right of the layer.

Editing a Layer

Click on a layer to select it and a green arrow will appear to indicate the layer you’ve chosen. Once selected, the Layer Edit section on the right side of the calculator will change to display the characteristics of that layer. Once displayed, you can modify the layer.

Continuous Layers

Continuous layers represent things like rigid insulation, siding, plywood, or wallboard. Any continuous layer has a material out of which it is composed. By default Ekotrope will provide reasonable values for costing and thermal resistivity of that material, but custom values can also be specified.

Note: Although you can add more materials to a single continuous layer, there is no practical difference between adding materials to a layer and adding extra layers, assuming properties are identical.

Material	The selected material changes Ekotrope’s defaults about costing and resistivity. It also changes the image of the layer.
Depth	The depth of this layer (inches).
Insulation Grade (for cavity insulation)	Insulation Grade as defined by RESNET Standards. Grade I: Perfectly installed Grade II: Some gaps and cracks Grade III: Major gaps and missing insulation For a more detailed definition of Insulation Grades please refer to RESNET HERS Standards Appendix A.
Per Inch / Total	Select which way you would like to input thermal resistivity, in R value Per Inch or Total R value.
R / Inch (if “Per Inch” is selected)	Resistivity of the insulating material in R value per inch.
R (if “Total” selected)	Total resistivity of the insulating material in R value.

Stud/Cavity Layers

Stud layers are like continuous layers, but have additional characteristics that must be provided. If a stud cavity contains multiple layers of insulation, use the green + below the material section to add additional materials within the cavity. This can be used to describe an assembly like the “Flash & Batt” technique.

Stud Type	Can be wood or steel. If steel is selected, the gauge (thickness) of the steel used in the stud must also be provided.
Depth	How deep the studs are in inches (e.g. 5.5 for a 2x6 stud).
Width	How wide the studs are in inches (e.g. 1.5 for a 2x6 stud).
Spacing	How widely are the studs spaced in inches (e.g. 16 for 16” O.C. construction)
Framing Fraction	Fraction of surface area comprised by framing members. This is calculated by Ekotrope, but can be overridden. Click the information icon for more detail. NOTE: This field is used to determine whether walls use advanced framing techniques, which is a mandatory ENERGY STAR requirement. Framing fraction must be equal to or less than 0.19 to meet ENERGY STAR requirements.
$ / s.f.	Additional cost per square foot of the assembly due to framing. This does not affect HERS Ratings.