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R404.2 Wood Foundation Walls

Residential Code 2018 of Kansas > 4 Foundations > R404 Foundation and Retaining Walls > R404.2 Wood Foundation Walls

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Wood foundation walls shall be constructed in accordance with the provisions of Sections R404.2.1 through R404.2.6 and with the details shown in Figures R403.1(2) and R403.1(3).

R404.2.1 Identification

Load-bearing lumber shall be identified by the grade mark of a lumber grading or inspection agency that has been approved by an accreditation body that complies with DOC PS 20. In lieu of a grade mark, a certificate of inspection issued by a lumber grading or inspection agency meeting the requirements of this section shall be accepted. Wood structural panels shall conform to DOC PS 1 or DOC PS 2 and shall be identified by a grade mark or certificate of inspection issued by an approved agency.

R404.2.2 Stud Size

The studs used in foundation walls shall be 2-inch by 6-inch (51 mm by 152 mm) members. Where spaced 16 inches (406 mm) on center, a wood species with an F_b value of not less than 1,250 pounds per square inch (8619 kPa) as listed in ANSI AWC NDS shall be used. Where spaced 12 inches (305 mm) on center, an F_b of not less than 875 psi (6033 kPa) shall be required.

R404.2.3 Height of Backfill

For wood foundations that are not designed and installed in accordance with AWC PWF, the height of backfill against a foundation wall shall not exceed 4 feet (1219 mm). Where the height of fill is more than 12 inches (305 mm) above the interior grade of a crawl space or floor of a basement, the thickness of the plywood sheathing shall meet the requirements of Table R404.2.3.

TABLE R404.2.3

PLYWOOD GRADE AND THICKNESS FOR WOOD FOUNDATION CONSTRUCTION (30 pcf equivalent-fluid weight soil pressure)

HEIGHT OF FILL (inches)	STUD SPACING (inches)	FACE GRAIN ACROSS STUDS			FACE GRAIN PARALLEL TO STUDS
		Grade^a	Minimum thickness (inches)	Span rating	Grade^a	Minimum thickness (inches)^{b, c}	Span rating
24	12	B	¹⁵/₃₂	32/16	A	¹⁵/₃₂	32/16
					B	¹⁵/₃₂^c	32/16
	16	B	¹⁵/₃₂	32/16	A	¹⁵/₃₂^c	32/16
					B	¹⁹/₃₂^c (4, 5 ply)	40/20
36	12	B	¹⁵/₃₂	32/16	A	¹⁵/₃₂	32/16
					B	¹⁵/₃₂^c (4, 5 ply)	32/16
					B	¹⁹/₃₂ (4, 5 ply)	40/20
	16	B	¹⁵/₃₂^c	32/16	A	¹⁹/₃₂	40/20
					B	²³/₃₂	48/24
48	12	B	¹⁵/₃₂	32/16	A	¹⁵/₃₂^c	32/16
					B	¹⁹/₃₂^c (4, 5 ply)	40/20
	16	B	¹⁹/₃₂	40/20	A	¹⁹/₃₂^c	40/20
					A	²³/₃₂	48/24

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per cubic foot = 0.1572 kN/m³.

Plywood shall be of the following minimum grades in accordance with DOC PS 1 or DOC PS 2:
1. DOC PS 1 Plywood grades marked:
  1. 1.1. Structural I C-D (Exposure 1).
  2. 1.2. C-D (Exposure 1).
2. DOC PS 2 Plywood grades marked:
  1. 2.1. Structural I Sheathing (Exposure 1).
  2. 2.2. Sheathing (Exposure 1).
3. Where a major portion of the wall is exposed above ground and a better appearance is desired, the following plywood grades marked exterior are suitable:
  1. 3.1. Structural I A-C, Structural I B-C or Structural I C-C (Plugged) in accordance with DOC PS 1.
  2. 3.2. A-C Group 1, B-C Group 1, C-C (Plugged) Group 1 or MDO Group 1 in accordance with DOC PS 1.
  3. 3.3. Single Floor in accordance with DOC PS 1 or DOC PS 2.
Minimum thickness ¹⁵/₃₂ inch, except crawl space sheathing shall have not less than ³/₈ inch for face grain across studs 16 inches on center and maximum 2-foot depth of unequal fill.
For this fill height, thickness and grade combination, panels that are continuous over less than three spans (across less than three stud spacings) require blocking 16 inches above the bottom plate. Offset adjacent blocks and fasten through studs with two 16d corrosion-resistant nails at each end.

R404.2.4 Backfilling

Wood foundation walls shall not be backfilled until the basement floor and first floor have been constructed or the walls have been braced. For crawl space construction, backfill or bracing shall be installed on the interior of the walls prior to placing backfill on the exterior.