May 31, 2016

What Does “R-Value” Really Mean?

R-Value is just one variable in energy-efficiency

Thermal and real image of a windowWhen it comes to energy efficiency, the industry buzz of “R-Value” (thermal resistance or ability to prevent heat transfer) continues to cause confusion – and false assumptions. R-values are often used synonymously with building energy efficiency performance. In reality, R-value is only a partial predictor of a building’s energy efficiency, at best.

R-value is a starting point for comparing insulation systems, but remains only one factor. Design, materials and construction science will play a huge role in energy efficiency.

A structure’s optimal energy efficiency is achieved when important variables work in harmony: architecture and building system design, materials and construction method. Relying on just one is like removing two legs from a three-legged stool. Imperfections in the installation of insulating materials – including air gaps and improper compression of the insulation – can dramatically reduce the performance of a wall system. Other factors, such as thermal mass and air infiltration through the wall envelope can also make a significant impact on energy performance – positively or negatively.

According to the American Society of Heating, Refrigeration and Air Conditioning (ASHRAE) 90.1 standard*, the “effective” R-value of a wood-framed building with studs on 16-inch centers, using conventional R-13 cavity insulation (i.e., the actual thermal resistance provided by the insulation in a given assembly), is only R-9. For a wall assembly using light gauge metal framing and the same R-13 cavity insulation, the effective R-value is only R-6 – more than a 57 percent reduction in insulating performance.

This happens because thermal bridging occurs through the structural framing members and uninsulated design features of the walls, which reduces the overall effectiveness of the wall insulation.

While using more insulation may appear to increase energy efficiency, there is a point of diminishing return when adding insulation to a wall system no longer improves energy performance. This was demonstrated in a National Concrete Masonry Association (NCMA) study** completed in 2013 that showed for every building, there is an optimal amount of insulation that can be installed in a wall system.

Adding insulation beyond that optimal amount no longer produces any savings in energy consumption. They summarized that money for excess insulation would be put to better use by improving other components of the building envelope and mechanical systems.

The Bautex Wall System provides any building with an R-14 continuously insulated wall system. This meets and exceeds 2015 ICC/IBC building codes, which are effective in Texas on Sept. 1, 2016. Bautex enables architects and contractors to be confident that the building will surpass the energy efficiency demands of even the most stringent building codes. And building owners will realize years of substantial, reliable savings from reduced energy costs.

Download Understanding R-value, Mass Walls, Continuous Insulation and Air Tightness