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.