Assess a wall assembly

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2 Select a construction type.

New Construction

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Retrofit

Changes to an existing structure.

Your Wall Assembly

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Predicted Wall Assembly Performance

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Help reading the chart

The results are shown on a radar chart, also known as a web chart, spider chart, polar chart, or star chart. In this type of chart, individual points represent a variable or dimension of a single item, as opposed to representing the item itself within one dimension, which is more common. Each variable has its own axis on the chart, shown as a line drawn from the center to an edge (or corner) of the chart. A single item is shown as a series of single points plotted on each of the axes, i.e., a single item has a number of points equal to the number of axes. Points closer to the center of the chart indicate a lower value, while points closer to the edge indicate a higher value. Multiple items can also be plotted on a radar chart, to easily compare the values of multiple variables for each item.

The points plotted on the chart represent a wall assembly's durability and energy efficiency by corresponding to one of three different performance parameters: thermal, mold and moisture. Each parameter has an axis, and a point is plotted along that axis to indicate the performance of the given wall assembly within that parameter. Thermal performance is plotted along the top axis, mold performance is plotted along the bottom left axis, and moisture performance is plotted along the bottom right axis. Points plotted close to the center of the chart indicate poor performance, while points closer to the edge of the chart indicate better performance.

Points that belong to the same wall are connected by lines of the same color, ultimately forming a triangle that represents the overall efficiency of the wall assembly.

To learn more about these performance parameters, explore the section titled "Explain the parameters," which is shown at the bottom of this page.

Color is a variable in two dimensions of the chart: the background and the plotted points. Each point plotted on the chart has a color that represents what wall assembly it belongs to, either neon green or cyan, as shown in the legend at the bottom of the chart. Points that represent the same wall assembly are connected by lines of the same color.

The background color of the chart is divided into three separate regions - a red region, a blue-gray region, and a green region. When a point is plotted on the chart, the background color of the region the point resides in indicates whether the wall assembly's performance is failing, risky, or passing for the parameter represented by the point (thermal, mold, or moisture, i.e., the axis the point is on). The background colors correspond to wall performance as follows:

Passing value

Risky value

Failing value

The chart is shaped like a triangle to better emphasize that there are three parameters (thermal, mold and moisture) that are used to evaluate wall assembly performance. Each wall assembly is also represented by a triangle, formed by connecting the three points that represent its performance across the three parameters. However, the shape of the triangle may look very different from the shape of the chart itself.

If the wall assembly has relatively equal performance across all three parameters, the triangle formed by its three points will look like an equilateral triangle (similar to the area of the chart). It may be much smaller than the total chart area, shown below on the left, or it might take up almost all the chart's area, shown below on the right. If the former, the wall does not perform very well within any parameter. If the latter, the wall performs well across all parameters.

Note that the wall plot triangle is small but relatively equilateral — The areas highlighted in yellow illustrate two fairly equilateral triangles of different sizes, representing a wall with poor performance across all parameters (left) and a wall with good performance across all parameters (right).

Note that the wall plot triangle is large and relatively equilateral. — The areas highlighted in yellow illustrate two fairly equilateral triangles of different sizes, representing a wall with poor performance across all parameters (left) and a wall with good performance across all parameters (right).

If the triangle is not equilateral, the wall has an uneven performance; it performs well within some parameters, but not within all of them. An example is shown below. Again, the amount of chart space that each corner of the plotted triangle takes up helps indicate the wall's performance. If one region of the chart is almost completely covered, the wall performs well within the parameter indicated by the axis that runs through that chart region. If a region of the chart is completely uncovered, the wall performs very poorly within the parameter indicated by the axis that runs through the uncovered chart region.

Note that the wall plot triangle is very obviously scalene. — The area highlighted in yellow is very obviously scalene and represents a wall with uneven performance.

There are four ways to interact with the chart:

Action: Function
Click on a legend item: Toggle (show/hide) the plot of the selected item
Click on a plot point or area: Toggle (show/hide) point labels that reflect the region (pass, risky, fail) each point is plotted in.
Click the document icon: Will show a data view, which displays the raw performance values of each wall assembly.
Click the download icon: Download an image (.png) of the current state of the chart

Explain the parameters

The plotted thermal performance represents the predicted R-value of the wall assembly, which is calculated using the ASHRAE parallel path method. The result is determined by comparison to the required R-value, which is derived from the 2018 International Energy Conservation Code (IECC) using the prescriptive path option.

In this analysis, "pass" indicates an R-value above the requirement, while "fail" indicates anything below the requirement.

Note that the IECC R-value requirements are for new construction and not for retrofitting existing walls. When evaluating retrofit performance, use the result to gauge the extent of energy efficiency improvement, not the exact performance of the retrofitted wall.

The plotted mold performance is the inverse of the wall's estimated mold index. The mold index is determined via the material type, temperature, relative humidity, and duration of the building envelope component and is calculated in accordance with ASHRAE Standard 160, “Criteria for Moisture-Control Design Analysis in Buildings.”

In this analysis, “pass” indicates a minimal potential for mold growth within the proposed wall assembly and represents a mold index less than one. A “risky” assessment indicates a mold index between 1 and 3, while a “fail” rating denotes a mold index above three.

The plotted moisture performance indicates the wall assembly's predicted sheathing moisture content. The sheathing moisture content is equivalent to the maximum predicted percent moisture by mass of the wall assembly, which indicates how much moisture may be absorbed by the wall. It is calculated when the sheathing is wood-based or organic, because performance may be compromised if the sheathing is maintained at high levels of relative humidity for extended periods of time.

In this analysis, “pass” indicates the maximum exterior sheathing moisture content within the proposed wall assembly is between 0 and 16 mass percent. A “risky” assessment indicates that the maximum exterior sheathing moisture content within the proposed wall assembly is between 16 and 20 mass percent, while a “fail” rating denotes an exterior sheathing moisture content in excess of 20 mass percent. These ratings correspond to research and real-world observations of sheathing moisture content: a moisture content greater than 16% has been shown to support the growth of mold & mildew, while moisture content above 20% has been shown to cause wood rot and structural damage.

In general, the BSA uses the most commonly encountered wall components as defaults for the new/existing wall form. This is intended as a convenience for users performing retrofit analyses, who are likely to have some or all of these components in their wall assembly, so the number of options they will need to manually set is reduced. These defaults may not reflect your particular wall assembly, but they serve as a best-guess for what an existing wall today would be composed of.

Note that these values are not suggestions for new construction. For new construction, it is suggested that the user pick some kind of component wherever the default values indicate 'None'.

Wall Component	Default Value	Explanation
Exterior Cladding	Vinyl/Metal Siding	Most commonly used siding.
Air Space	None	Most modern buildings and houses are not built with an air space.
Continuous Insulation	None	Most modern buildings and houses do not include exterior insulation.
Continuous Insulation Thickness	None	If the continuous insulation is specified as 'None', the thickness must be none.
Water Resistive Barrier	Housewrap/Building Paper (>= 10 perm)	Building paper is commonly used in modern constructions.
Exterior Sheathing	Plywood/OSB /Fiberboard/Wood Plank	Plywood is often used as the exterior sheathing in modern constructions.
Wall Structure	2 x 4 16 inch. o.c. Wood Frame	2 x 4's are the most common frame materials in modern constructions.
Cavity Insulation	None	Most early modern buildings and houses (1940s - 1990s) have no cavity insulation.
Interior Vapor Retarder	None	Most modern buildings do not use an interior vapor retarder.
Interior Finish	Drywall/Latex Paint	Drywall with latex paint is the most commonly used interior finish in modern constructions.

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