Comcheck and R-values for Exterior Walls

[Meadowbend99]

Did comcheck recently change the structure for inputting exterior wall r-values? I typically put in size of area, but it did not come up. I'm using 2015 IECC and we're in 2a. I should be okay to use R-13 insulation for an alteration to an existing structure with exposed walls for an office space. It will not pass with R-13, only R-20.

 

[RLGA]

It’s probably looking for continuous insulation (R-3.8 minimum) on the exterior side of the wall.

You have to keep in mind there are three methods for compliance with the IECC:

1. The R-value method per C402.1.3;
2. The U-factor, C-factor, and F-factor method per C402.1.4; and,
3. Component performance alternative per C402.1.5.

If the insulating products in your wall assembly provide the minimum required R-values per Table C402.1.3 for the type of assembly listed (R-value method) then there is no need to use ComCheck—just show your wall assembly and the specified minimum R-value required. For wood-framed walls, you need either R-13 in the stud cavities plus R-3.8 continuous insulation on the outside, or R-20 within the stud cavities.

ComCheck (I admit I’ve never really used it on a project) is most beneficial when determining compliance using the component performance alternative, which determines the balance between varying performance levels of all building envelope assemblies; thus, by using high-performing assemblies (those that exceed minimum prescriptive performance) you can offset the use of lower-performing assemblies that do not meet the minimum prescriptive requirements.