There’s no question that brick and concrete are two of the most indestructible building materials on the planet. Combine these two time-tested building elements together, and you get another high-performing building material: concrete masonry units, or CMUs.
Let’s cover what CMUs are and what you need to know when choosing a concrete masonry unit insulation for your project.
Understanding Concrete Masonry Units (CMU)
Concrete Masonry Units (CMU) are large blocks of concrete used to construct foundations, basement walls, and even full height walls. Modular concrete units come in a variety of sizes, shapes, patterns, densities, colors, and textures.
Standard cinder blocks have a size of just less than 16” long by 8” tall and 8” wide. The modular CMUs can be stacked with mortar and other components to comprise the exposed exterior finish surface or hidden behind a cavity wall with a premium cladding secured to the structural CMU backup wall.
Typically, CMUs are only one component of many that make up a complete wall section. Another important component in wall systems is insulation. Concrete masonry unit insulation is desired (and often required) for occupied spaces where thermal comfort and energy efficiency are necessary. Let’s move on to address the reasoning behind why CMU block insulation is required.
Why Insulate CMU?
Concrete has some inherent insulating value, but concrete blocks only provide a thermal insulation value of around R-2 (empty cores, 8” deep) per wythe. Since walls often require insulation values in excess of R-20, concrete building blocks generally require additional insulation in order to achieve optimal thermal performance in occupied structures.
CMU block insulation is needed in order to:
Comply with energy codes
Provide thermal comfort
Reduce heating and cooling costs
For walls constructed out of concrete masonry units, builders can choose CMU wall insulation for either side of the wall, interior or exterior. The type of insulation you choose will depend on which side you want to insulate. Now, let’s cover the types of CMU wall insulation.
CMU Insulation Types
Concrete masonry unit insulation comes in many shapes, forms, and materials. Here are some common materials used to insulate a CMU block wall:
Core Fill Insulation
The voids inside concrete masonry units can be filled with various insulation materials in order to enhance the wall system’s R-value without adding width to the wall. The materials used for filling CMU block voids include the following:
Perlite
Vermiculite
Polyurethane Foam-in-Place
Grout
Filling the core of the CMU blocks only provides a slightly higher energy performance. For example, an empty core standard 8” CMU block (density of 135 pcf) has an R-value of 1.99, while a vermiculite-filled core CMU of the same size is upgraded to an R-value of 3.75. While the insulated block nearly doubles the R-value of its uninsulated counterpart, it still pales in comparison to the standard R-value requirements for wall systems.
CMU Insulation Inserts
Polystyrene inserts are designed to fit into the empty cores of standard-sized CMU blocks. This type of CMU insulation can be pre-installed at the factory during manufacturing or installed on-site by the contractor. Similar to loose granular fills, CMU insulation inserts add only a negligible difference to the insulating power inside your CMU block walls.
Spray Foam Insulation
Foam-in-place insulation is one way to add a measurable increase in thermal insulation to your CMU walls. Adding foam-in-place polyurethane insulation can increase your concrete wall’s R-value by 3.7. This type of insulation, however, can be costly for both material and installation.
Rigid Insulation
The best way to adequately insulate concrete masonry units is to design a wall system that includes a separate layer of continuous insulation. This can be achieved through cavity insulation, interior insulation, or exterior insulation.
Common insulation materials used in conjunction with CMU walls include the following:
Polyiso
EPS (Expanded polystyrene)
XPS (Extruded polystyrene)
Mineral Wool Boards
Board insulations allow designers to meet code requirements easily by adding as much insulation as needed simply by increasing the thickness of the boards. For example, to achieve R-20 with an empty core 8” CMU block wall, you could install 3-½” thick polyiso board insulation to meet the requirement.
The Best Choice: Polyiso CMU Wall Insulation
If you’re looking to achieve more insulating value with a thinner profile, polyiso is the best choice for insulating concrete masonry units. Polyiso boasts an impressive R-value of R-6 per inch which allows builders to achieve more with less.
Polyiso is also the natural choice for continuous insulation, which reduces heat loss and energy costs. This versatile insulation can be installed on the exterior face of the wall, interior side, or even inside the wall cavity. It can also be faced with different materials to enhance certain properties. For example, to achieve an air and vapor barrier, polyiso can be foil-faced and installed with sealed joints.
Rmax Polyiso for CMU
If you’re ready to insulate your CMU walls, take a step up with premium building materials that will level up your entire building envelope’s energy efficiency. Rmax offers a wide range of products, including our foil-faced versions Thermasheath® and ECOMAXci® FR Air Barrier. Our team can help you pick the right type for your job.