ICF and CMU Walls
Insulating Concrete Forms and Concrete Masonry Units
In construction there are two options when building concrete walls: ICF (insulating concrete forms) and CMU (concrete masonry units). For years, CMU’s have had a large advantage in construction, in part because builders knew about the long-term reliability of CMU’s, and when building structures, sticking with a proven commodity makes sense. Now more information is available for the long-term viability of and reliability of ICF construction.
What Is ICF?
ICF construction is when insulated hollow foam blocks are stacked in the shape of exterior and load bearing walls, then the forms have rebar added to them, then the forms are filled with concrete. The more obvious advantages of ICF walls is that construction is easier, there is a high thermal resistance, there is a thermal mass, and the construction is airtight. These benefits of ICF construction allow for relatively low heating and cooling costs.
Uses of ICF Walls
ICF walls are useful as exterior walls and as load bearing walls. Each of these uses is advantageous for the strength and airtight composition of an ICF wall and quality of construction.
What Are CMU Walls Used For?
CMU walls are used for many of the same uses that ICF walls are used for, and they can also be used for walls that are not load bearing. Precast CMU textured walls are made from stable and reliable materials that can withstand a great deal of weight and pressure and building with these concrete blocks makes for a reliable and safely built structure.
Another advantage of using CMU is when construction is in an area that does not allow for staging areas needed to pour concrete into forms for ICF walls. This can be especially useful when looking at infill projects in which unused, or not as conveniently accessed building sites are to be used. Often, getting large machines into these sites is challenging and this can make construction using anything other than CMU walls problematic.
There are options when insulating CMU walls. One option is to glue rigid foam panels, usually ¾ of an inch thick, directly to the face of walls. The advisable method of adding foam panels is to use panels that have a foil face to help serve as a barrier to air and moisture. Flashing tape might then be added to joints to help block air. Another option is to fill the hollow parts of the block with foam insulation.
Foam insulation is added from the inside of the project where it will be covered with drywall or other building compounds. The void in the blocks is filled with a non-toxic liquid, a foaming agent, and air. Another more cost effective, though not as efficient method, is to add a two by four framed wall to the inside of the CMU wall. This addition is not as energy efficient or airtight, but it can reduce wind.
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