Building Science

What Does “R-Value” Really Mean?

R‑Value is just one variable in energy-efficiency

When 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