Whole-Wall R-Value: A Best Practice for Evaluating a Structure’s Potential Energy-Efficiency
Bautex insulated concrete block (ICB) mass walls provide continuous insulation and prevent thermal bridging. These attributes create a high and accurate whole-wall R-value, which ensures an energy efficient and comfortable home or building.
Which R-Value Estimation is Most Accurate?
Contractors and architects must consider many factors when building and designing a high-performing, energy-efficient commercial building or home, including the R-value (or, resistance value). The R-value represents a material’s or system’s resistance to heat flow by convection, conduction, and radiation.
Several methods estimate the R-value; unfortunately, each may give completely different results. The question is, which method is most accurate. Four common ways to report the R-values include the R-value of insulation, and the whole-wall, clear-wall, and center-of-cavity R-values.
R-Value of the Insulation
The R-value of insulation is the product’s resistance to heat flow through a given thickness of a material. The International Energy Conservation Code (IECC) mandates the installed R-values of insulation required to achieve best practices to insulate homes and buildings according to their climate zones. However, there are several problems with the R-value of insulation.
The R-value of the insulation neglects the insulation value of the other layers of the wall assembly, like the shealthy, drywall cladding, and air barriers. Furthermore, the R-value of insulation ignores thermal bridging.
During the 1990s, a report by the Oak Ridge National Laboratory (ORNL) Buildings Technology Center (BTC), evaluated the accuracies of R-values by studying the impact of all the individual elements of the building envelope on the R-value.
The study came up with three new ways to estimate R-values, besides the R-value of insulation: whole wall system R-value, clear-wall R-value, and center-of-cavity R-value.
The whole wall system is the R-value for the whole opaque system including all additional structural components (such as double studs), and enclosure interface details, including wall /roof, wall/wall (corners), and wall/floor connections. Whole wall R-value also considers the impact of thermal bridging based on the amount of framing in the wall compared to the amount of insulation as well as the effectiveness of the sealing of the enclosure at lowering air infiltration. Calculating the whole wall R-value is with an area-weighted average R-value for clear wall and wall interface details.
Clear-wall R-value includes the exterior wall area that contains only insulation and necessary framing products for a clear section. It is a section with no corners, windows, doors, or connections with foundation and roofs. The clear-wall R-value ignores thermal bridging associated with corners, windows, doors, or connections with foundation and roofs.
Center-of-cavity R-value estimates the R-value at the spot in the wall containing the most insulation. So, there is 0 percent framing factor and no accounting for any of the thermal short circuits through the framing. The center-of-cavity R-value does not take into account thermal bridging. The center-of-cavity R-values are often significantly higher than clear-wall R-values.
The Benefits of the Whole Wall R-Value
The whole wall R-value is the most precise measurement of a wall’s thermal resistance over clear-wall, center-of-cavity R-values, or R-value of insulation. The whole wall R-value takes into account the whole opaque wall system; therefore, it is often considerably lower than the clear-wall, center-of-cavity, or insulation R-values. In fact, the whole wall R-value on the same wall can be as much as 40 percent less than the clear-wall value.
Insulated concrete form (ICF) wall whole-frame R-values were 4 percent less than clear wall R-values. From a whole-wall perspective, an ICF wall performs up to the advertised R-values because thermal bridging is absent.
Standard 2 X 4 wood-frame R-values was 7.6 percent less than clear-wall R-value.
Steel frame C-stud whole-frame R-value was 23.3 percent less than clear-wall R-value.
Results of this study conclude that mass walls, like ICF walls, with continuous insulation and without thermal bridging, can produce an insulation value for the entire wall system closer to the manufacturers claimed R-value than either wood- or steel-framed wall systems.
Bautex Wall Assembly Provides High Whole-Wall R-Values
Construction with a mass wall, like the Bautex ICB, outperforms framed buildings with comparable stated R-values because ICB walls provide continuous layers of insulation with no thermal bridges. These are both attributes that produce reliable and accurate high whole-wall R-values.
The Bautex Block is a high thermal mass material that creates a tight building envelope for a high-performing energy-efficient home or building. The R-value of Bautex Blocks per inch is 1.84. The Blocks provide a high-level of continuous insulation with a whole wall R-value of 14 that resists the flow of heat by convection, conduction, and radiation.
Furthermore, the Bautex Wall System meets the thermal performance dictated by the International Residential Code (IRC) and International Building Codes (IBC) and provides an R-value that exceeds the ASHRAE 90.1 requirements for climate zones one through six. However, a building or home built with Bautex Block and a brick veneer achieves a whole-wall R-18 system; exceeding the ASHRAE 90.1 recommendations for zone seven.
The whole-wall method of estimating the R-value of a wall system provides a true measurement of a wall’s resistance to heat flow. Therefore, selecting products or systems that report whole-wall R-values, like Bautex wall system, will provide a more reliable estimate of a home or building potential energy-efficiency than products that report R-values based on other methods.