IECC Table C402.1.3 - Unclear requirements regarding slab on grade insulation (under slab horizontal)

[peri_5xg]

I am trying to figure out the distance I need to extend the insulation under slab for a slab on grade application. The attached image from Upcodes is saying that Table C402.1.3 indicates that the table should tell me the distance (circled in red). When looking at the table, I don't see anything. All I see is the vertical requirement (Example: " Slab-on-grade < unheated slabs < Climate Zone 6 < R-10 for 24" below"). Am I missing something here?

 

[RLGA]

I don't understand your confusion. The table states XX" below--below meaning below the slab (i.e., not on top of the slab).

If it is installed vertically, it is XX" from the top to below the slab (or the top of the footing, whichever is shortest) as described in Section 402.2.4.1, or horizontally XX" from the face of the stem wall below the slab.

 

[steveray]

C402.2.4.1 Insulation Installation​

Where installed, the perimeter insulation shall be placed on the outside of the foundation or on the inside of the foundation wall. The perimeter insulation shall extend downward from the top of the slab for the minimum distance shown in the table or to the top of the footing, whichever is less, or downward to not less than the bottom of the slab and then horizontally to the interior or exterior for the total distance shown in the table. Insulation extending away from the building shall be protected by pavement or by not less than 10 inches (254 mm) of soil.

We see the TOS missed a lot....

 

[peri_5xg]

I don't understand your confusion. The table states XX" below--below meaning below the slab (i.e., not on top of the slab).

If it is installed vertically, it is XX" from the top to below the slab (or the top of the footing, whichever is shortest) as described in Section 402.2.4.1, or horizontally XX" from the face of the stem wall below the slab.

I understand the XX being the vertical distance. That's clear to me. I am asking about the horizontal distance of the insulation below the floor slab. the wording is unclear to me in section C402.2.4.1. "Total distance" means what? why use the word "total" as it it implies the addition of two or more things. So for example, I am looking at Table C42.1.3. Climate Zone 6 requirements for and unheated slab and it is saying I need R-10 for 24'" below. so if the stem wall is 30", I only have to go 24" if the stem wall is 10", I extend the CI to the top of the footing. my question, does this 24" the min distance to extend horizontally under the floor slab as well? that's the question that is unclear on this chart.

 

[peri_5xg]

C402.2.4.1 Insulation Installation​

Where installed, the perimeter insulation shall be placed on the outside of the foundation or on the inside of the foundation wall. The perimeter insulation shall extend downward from the top of the slab for the minimum distance shown in the table or to the top of the footing, whichever is less, or downward to not less than the bottom of the slab and then horizontally to the interior or exterior for the total distance shown in the table. Insulation extending away from the building shall be protected by pavement or by not less than 10 inches (254 mm) of soil.

We see the TOS missed a lot....

This paragraph is unclear. Maybe it's the wording. Please let me know if my interpretation is correct. I am looking at Table C42.1.3. Climate Zone 6 requirements for and unheated slab and it is saying I need R-10 for 24'" below. So if the stem wall is 30", I only have to go down 24" wit the CI, but if the stem wall is 10", (shorter distance that 12" I only have to extend down to the top of the footing. my question, does this 24" the min distance to extend horizontally under the floor slab as well? that's the question that is unclear on this chart.

 

[steveray]

This paragraph is unclear. Maybe it's the wording. Please let me know if my interpretation is correct. I am looking at Table C42.1.3. Climate Zone 6 requirements for and unheated slab and it is saying I need R-10 for 24'" below. So if the stem wall is 30", I only have to go down 24" wit the CI, but if the stem wall is 10", (shorter distance that 12" I only have to extend down to the top of the footing. my question, does this 24" the min distance to extend horizontally under the floor slab as well? that's the question that is unclear on this chart.

The down plus the horizontal have to equal the chart

 

[RLGA]

The down plus the horizontal have to equal the chart

According to Section 402.2.4.1, the horizontal portion must be equal to the distance in Table 402.1.3--the vertical portion along the edge of the slab is not included in that distance. Thus, if it is a 6-inch slab and Table 402.1.3 requires 24 inches, then there will be 30 inches of insulation.

However, if vertical insulation is only used, then only 24 inches of insulation is required which includes the portion along the edge of the slab.

 

[wwhitney]

According to Section 402.2.4.1, the horizontal portion must be equal to the distance in Table 402.1.3--the vertical portion along the edge of the slab is not included in that distance.

The language that steveray posted does not agree with the above, you get credit for the vertical portion along the edge of the slab, as implied by the word "total" indicating a summation:

C402.2.4.1 . . . or downward to not less than the bottom of the slab and then horizontally to the interior or exterior for the total distance shown in the table.

Cheers, Wayne

 

[steveray]

The language that steveray posted does not agree with the above, you get credit for the vertical portion along the edge of the slab, as implied by the word "total" indicating a summation:



Cheers, Wayne

For reference I was using 2021 IECC as modified by CT, but I don't believe we changed that...Cut and paste off of upcodes....

 

[Penguin87]

I don't understand your confusion. The table states XX" below--below meaning below the slab (i.e., not on top of the slab).

If it is installed vertically, it is XX" from the top to below the slab (or the top of the footing, whichever is shortest) as described in Section 402.2.4.1, or horizontally XX" from the face of the stem wall below the slab.

^ This

Which is supported in ASHRAE, for which IECC is mostly based off of

(See section A6.1 in ASHRAE 90.1-20XX