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