A plain masonry foundation wall is being checked using 2021 IRC Table R404.1.1(1). An interior concrete slab-on-grade is provided and contacts the wall’s interior surface. Under footnote c, which unbalanced-backfill-height measurement is permitted?
- ATop of wall to exterior finished grade
- BExterior finished grade to the bottom of the footing
- Exterior finished grade to the top of the interior concrete slab
- DTop of wall to the top of the slab
Where to look it up
https://core-docs.s3.amazonaws.com/documents/asset/uploaded_file/3836/Lennox/3042182/2021_International_Residential_Code.pdf
Why C is correct
Footnote c normally measures the difference from exterior finished ground to the lower of the supporting footing’s top or interior finished ground. It permits measurement to the interior concrete slab’s top when a slab-on-grade is provided in contact with the foundation wall’s interior surface. The question explicitly supplies that contact condition. This definition does not establish all lateral-support or backfill-construction requirements, nor does simply finishing any slab automatically authorize reducing a wall design. See Table R404.1.1(1), printed p.4-23. Source: https://core-docs.s3.amazonaws.com/documents/asset/uploaded_file/3836/Lennox/3042182/2021_International_Residential_Code.pdf