News Article

ICF vs CMU: Understanding Your Options

Con­crete mason­ry units (CMU) and insu­lat­ed con­crete forms (ICF) are two choic­es for wall sys­tems in both com­mer­cial and res­i­den­tial con­struc­tion. The goals of CMU and ICF wall sys­tems are to cre­ate durable struc­tures that are resis­tant to fire, rot, mold, and mois­ture. Both also strive for excel­lent indoor envi­ron­men­tal qual­i­ty (IEQ). There is one sig­nif­i­cant dif­fer­ence between ICF and CMU con­struc­tion. Insu­lat­ed con­crete forms, like the Bau­tex Wall Sys­tems, are quick­er and eas­i­er to build than CMU; there­fore, ICF saves mon­ey, reduces labor, and low­ers con­struc­tion risks over CMU wall sys­tems.

Insulation Requirements for CMU and ICF

Since 1999, the ASHRAE 90.1 (the U.S. ener­gy stan­dard) has ref­er­enced pre­scrip­tive R‑value rec­om­men­da­tions for con­tin­u­ous insu­la­tion, for all com­mer­cial and res­i­den­tial sin­gle or multi‐​family struc­tures greater than three sto­ries in height above grade. The quan­ti­ty of insu­la­tion required (as indi­cat­ed by the R‑value) by the stan­dard depends upon the cli­mate zone, the wall type, and whether the struc­ture is res­i­den­tial or non-res­i­den­tial. Wall types include wood, steel framed, met­al build­ing, and mass walls.

Both CMU and ICF are mass walls. Mass walls pro­vide ener­gy effi­cien­cy through mass rather than insu­la­tive val­ues. The mass allows the wall sys­tem to store ener­gy dur­ing the day and release it through­out the night, which makes mass walls a good choice in hot and humid cli­mates where the tem­per­a­ture varies sig­nif­i­cant­ly through­out the day. The R‑value require­ments for mass walls range from 5.7 to 25 depend­ing on the cli­mate zone and whether the struc­ture is res­i­den­tial or non-res­i­den­tial.

Concrete Masonry Units (CMU)

The inven­tion of the con­crete block occurred in 1830. How­ev­er, in the Unit­ed States, it was not wide­ly used until the first half of the 20th cen­tu­ry. Three events led to the increase in CMU con­struc­tion: the 1904 St. Louis Louisiana Pur­chase Expo­si­tion (St.Louis World’s Fair) that pro­mot­ed con­crete blocks, the for­ma­tion of a domes­tic Port­land cement indus­try, and the devel­op­ment of con­crete block machin­ery. The basic design of CMU has not changed in decades. CMU are con­crete blocks made from Port­land cement, aggre­gates like quartz and stone, and water. The blocks come in an assort­ment of shapes and are sol­id or hol­low, with two or three voids or cores.

R-Values of CMU

Con­crete block walls have very low R‑values rang­ing from 2 to 3, and insu­lat­ed CMU have R‑values rang­ing from 4 to 14, depend­ing on the blocks thick­ness and den­si­ty. Insu­lat­ed CMU is not wide­ly used in the U.S. which, in many cas­es, requires CMU walls to be insu­lat­ed with addi­tion­al mate­ri­als and sys­tems.

Advantages of CMU

CMU are durable and resis­tant to mois­ture, fire, rot, and mold. CMU are also pest-resis­tant and a good sound-proof­ing mate­r­i­al. Insu­lat­ed CMU pro­vide an R‑value com­pli­ant with zones 1 – 5, accord­ing to the ASHRAE 90.1, which reduces ener­gy use and is good for the envi­ron­ment.

Disadvantages of CMU

Unfor­tu­nate­ly, the design of the CMU has not kept up with the rise in demands on wall sys­tems. For the past 50 years, builders and archi­tects have strived to improve on the ener­gy-effi­cien­cy, dura­bil­i­ty, and fire and wind resilience of wall sys­tems. Mod­ern wall sys­tems must also pro­vide occu­pants with a high lev­el of indoor envi­ron­men­tal qual­i­ty.

Instead of improv­ing the design of CMUs, design­ers and builders have added new com­po­nents, extra lay­ers, and addi­tion­al steps to CMU con­struc­tion. These steps have com­pli­cat­ed the process and result­ed in more mon­ey and time spent and increased oppor­tu­ni­ties for errors dur­ing the build­ing of a CMU wall sys­tem.

CMU appear­ance is anoth­er dis­ad­van­tage. CMU have an indus­tri­al look unless a fac­ing, like stuc­co, is applied over it.

Insulated Concrete Forms (ICF)

Insu­lat­ed con­crete forms were first devel­oped in Bel­gium in 1937 by Swiss nation­als August Schnell and Alsex Bosshard. The pro­posed pur­pose of these ICFs was to cre­ate a fast, cost-effec­tive, and sol­id con­struc­tion method using most­ly unskilled labor. How­ev­er, reg­is­tra­tion of the first mod­ern patent appli­ca­tion for ICF didn’t occur until the late 1960s.

Today, ICF are cast-in-place con­crete walls, insert­ed between two lay­ers of insu­la­tion. Insu­lat­ed con­crete form walls are made by dry-stack­ing expand­ed poly­styrene foam pan­els or inter­lock­ing hol­low extrud­ed poly­styrene foam, to a wall’s length. The forms are braced and rein­forced. Indus­try pro­fes­sion­als then pour con­crete into the hol­low form pan­els.

R-Values of ICF

R‑values for ICF con­struc­tion vary with the type of ICF and thick­ness of the foam. An exam­ple of an ICF prod­uct is the Bau­tex Wall Assem­bly. Bau­tex Blocks are made from 90 per­cent foam plas­tic insu­la­tion encap­su­lat­ed in a cement matrix. Bau­tex Blocks achieve an R‑value of R‑14. The Bau­tex Wall Sys­tem exceeds by three times the 2018 Inter­na­tion­al Res­i­den­tial Code (IRC) insu­la­tion require­ments of mass walls in cli­mate zones 1 and 2.

There are sev­er­al ben­e­fits to insu­lat­ed con­crete form wall sys­tems.

  • ICFs are disaster‑, fire‑, and pest-resis­tant.
  • ICFs are also noise-reduc­ing, healthy, easy to main­tain, and ener­gy-effi­cient.
  • ICF struc­tures are aes­thet­i­cal­ly pleas­ing and pro­vide design flex­i­bil­i­ty, such as com­plex archi­tec­tur­al con­tours and curves.
  • Impor­tant­ly, ICFs are easy and quick to install.

ICF vs. CMU

ICF and CMU wall sys­tems both strive to cre­ate ener­gy-effi­cient, durable, storm and fire resilient wall sys­tems. The wall sys­tems must also cre­ate a healthy and com­fort­able envi­ron­ment for the occu­pants of the build­ing or home. Where the two meth­ods part ways are the ease and effi­cien­cy of the build­ing process. Insu­lat­ed con­crete foam takes half the time to con­struct over con­crete mason­ry unit walls. For exam­ple:

  • A con­crete mason­ry wall needs an appli­ca­tion of insu­la­tion. Apply­ing insu­la­tion over the con­crete mason­ry wall involves a sec­ond trade to the job site. The sec­ond trade adds one more day of cost­ly labor to the wall con­struc­tion project.
  • A con­crete mason­ry wall often needs instal­la­tion of an air and mois­ture bar­ri­er, fur­ther adding anoth­er trade and more labor to the wall con­struc­tion project.
  • The light­weight nature of ICF speeds con­struc­tion time over CMU.

Build­ing a wall sys­tem with ICF sim­pli­fies con­struc­tion, short­ens the sched­ule, reduces cost and lessens con­struc­tion prob­lems over CMU con­struc­tion.