Rebar and grout frequency can significantly alter the thermal performance of a wall system. Omni Block (with the assistance of the Masonry Institute of Michigan) has developed an accurate short-cut to determine whether or not Omni Block will prescriptively meet the International Energy Conservation Code (IECC) per ASHRAE 90.1 (2013).

The tan fields contain value options in their drop-down menus. Select the options that meet the design criteria of your specific project including the climate zone per ASHRAE 90.1.

Step 1: Select either 8 or 12 in the top drop-down menu cell. 8 means Omni Block System 8 and 12 means Omni Block System 12.

Step 2: Select the expected concrete density. Lightweight concrete density starts at 85 pounds per cubic foot and ends at a heavyweight density of 135. The heavier the concrete the less the thermal performance.

Step 3: Enter the expected vertical rebar frequency. For this calculator the cell frequency matters, but the size of the rebar does not.

Step 4: Enter the project’s climate zone or region per ASHRAE 90.1.

The maximum allowable U-factor per ASHRAE 90.1 is automatically entered in the bottom cell.

As long as the resulting Corrected U-Factor field is green, Omni Block passes the International Energy Conservation Code prescriptively.

The tables below the provide the supporting R-Value and U-Factor corrections based upon the frequency dynamic of the vertical rebar and grout for the System 8 block. For example, if the vertical rebar frequency, as determined by the structural engineer of record, is to be every 40″ on center then the R-Value is 18.2 and the U-Factor is 0.0549 at a concrete density of 115 pcf.

The tables below provide R-Value and U-Factor corrections based upon the frequency dynamic of the vertical rebar and grout for the System 12 block. For example, if the vertical rebar frequency, as determined by the structural engineer of record, is to be every 40″ on center then the R-Value is 26.4 and the U-Factor is 0.0378 at a concrete density of 115 pcf.