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.

Whole Wall System R-Value, Clear-Wall R-Value, and Center-of-Cavity R-Value

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.

A report by Chris­t­ian and Jan Kos­ny 1999 com­pared clear-wall and whole-wall R-val­ues of forty dif­fer­ent wall sys­tems. In every case, the clear-wall R-val­ue was high­er than the whole-wall R-val­ue. For exam­ple,

  • 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.