Wis. Admin. Code Department of Safety and Professional Services SPS 321.18

Current through November 25, 2024

Section SPS 321.18 - Foundations

(1) GENERAL.

(a)Design. Foundation walls shall be designed and constructed to support the vertical loads of the dwelling, lateral soil pressure, and other loads without exceeding the allowable stresses of the materials of which the foundations are constructed.

(b)Lateral support at base. Lateral support such as floor slabs or framing shall be provided at the base of foundation walls.

(c)Lateral support at top. Lateral support shall be provided at the top of the foundation walls by one of the following:

2. Structural analysis. A system designed through structural analysis.

3. Anchor bolts.

a. Structural steel anchor bolts, at least 1/2 inch in diameter, embedded at least 7 inches into the concrete or grouted masonry with a maximum spacing of 72 inches and located within 18 inches of wall corners.

b. A properly sized nut and washer shall be tightened on each bolt to the plate or sill.

c. When vertical-reinforcing steel is provided in masonry construction, as required under sub. (3), the location requirements under subd. 3.a. shall be modified as necessary so anchor bolts are placed in the same core as the reinforcement without exceeding the limits of subd. 3. a.

d. Alternate foundation anchorage, designed and spaced in accordance with structural analysis and as required to provide equivalent anchorage to the requirements of subd. 3. a., is allowable.

4. Other mechanical fasteners.

a. Mechanical fasteners used in accordance with the manufacturer's testing and listing.

b. When vertical-reinforcing steel is provided in masonry construction, as required under sub. (3), the location requirements under subd. 4. a. shall be modified as necessary so the fasteners are placed in the same core as the reinforcement without exceeding the limits of subd. 4. a.

(d)Floor framing.

1. Floor framing shall be fastened to the sill plate by one of the following methods:

a. Mechanical fasteners used in accordance with the manufacturer's testing and listing.

b. In accordance with structural analysis.

c. In accordance with the fastener table printed in ch. SPS 325 Appendix A.

Note: Per s. SPS 321.22(1), sill plates are not required on foundation walls of poured concrete or on masonry walls with mortar- or grout-filled cores or on masonry walls with a solid block top course.

a. Where the floor framing is parallel to the foundation wall, solid blocking or bridging shall be installed in at least the first adjacent joist space at a spacing of no more than 32 inches on center.

b. Blocking and bridging shall be the same depth as the joist.

c. Fastening of the blocking or bridging shall be in accordance with structural analysis or the fastener schedule in Table 321.02-2.

Note: The floor-framing elements required in this section are intended to provide lateral support to the top of the foundation wall. See s. SPS 321.22(9) for further requirements relating to floor framing, including for bridging of floor framing to provide restraint against rotation or lateral displacement of the floor framing.

(e)Soil lateral load. Unless designed through structural analysis, soil lateral loads shall be determined from Table 321.18-A.

Table 321.18-A

SOIL LATERAL LOAD

Description of Backfill Material^e	Unified Soil Classification	Design Lateral Soil Load^a PSF per Foot of Depth
Well graded, clean gravels; gravel-sand mixes	GW	30^c
Poorly graded clean gravels; gravel-sand mixes	GP	30^c
Silty gravels, poorly graded gravel-sand mixes	GM	40^c
Clayey gravels, poorly graded gravel-and-clay mixes	GC	45^c
Well-graded, clean sands; gravelly sand mixes	SW	30^c
Poorly graded clean sands; sand-gravel mixes	SP	30^c
Silty sands, poorly graded sand-silt mixes	SM	45^c
Sand-silt clay mix with plastic fines	SM-SC	45^d
Clayey sands, poorly graded sand-clay mixes	SC	60^d
Inorganic silts and clayey silts	ML	45^d
Mixture of inorganic silt and clay	ML-CL	60^d
Inorganic clays of low to medium plasticity	CL	60^d
Organic silts and silt clays, low plasticity	OL	^b
Inorganic clayey silts, elastic silts	MH	60^d
Inorganic clays of high plasticity	CH	^b
Organic clays and silty clays	OH	^b

^aDesign lateral soil loads are given for moist conditions for the specified soils at their optimum densities. Actual field conditions shall govern. Submerged or saturated soil pressures shall include the weight of the buoyant soil plus the hydrostatic loads.

^bUnsuitable as backfill material.

^cFor relatively rigid walls, as when braced by floors, the design lateral soil load shall be increased for sand and gravel type soils to 60 psf per foot of depth. Basement walls extending not more than 8 feet below grade and supporting flexible floor systems are not considered relatively rigid walls.

^dFor relatively rigid walls, as when braced by floors, the design lateral load shall be increased for silt and clay type soils to 100 psf per foot of depth. Basement walls extending not more than 8 feet below grade and supporting flexible floor systems are not considered relatively rigid walls.

^eSoil classes are in accordance with the Unified Soil Classification System, ASTM D2487, and design lateral loads are for moist soil conditions without hydrostatic pressure.

(2) CONCRETE FOUNDATION WALLS.

(a)General structural requirements. Except as provided in par. (b), unless designed through structural analysis, the minimum thickness of concrete foundation walls shall be determined from Table 321.18-B, but in no case shall the thickness of the foundation wall be less than the thickness of the wall it supports.

(b)Equalized loading. A 6-inch nominal wall thickness may be used provided the fill on one side of the wall is within 12 inches vertically of the fill on the other side of the wall.

Note: See s. SPS 321.15(1) (c) for trench footing requirements.

Table 321.18-B

CONCRETE WALL THICKNESSES

Type of Concrete	Nominal Thickness (inches)	Maximum Height of Unbalanced Fill¹ for Material of Wall Being Supported (Wood frame - feet)
3000 psi	8	8
Unreinforced concrete	10	9
	12²	10
	14	11.5

¹Unbalanced fill is the difference in elevation between the outside grade and the basement floor.

²The maximum height of unbalanced fill for a 12-inch thick plain concrete wall may be increased to 12 feet provided the wall is constructed of concrete with a minimum compressive value of 6,000 psi at 28 days.

(3) MASONRY FOUNDATION WALLS.

(a)Dampproofing.

1. Except as allowed under subd. 3., masonry block foundation walls shall be coated with a layer of minimum 3/8-inch thick type M or S portland cement mortar parging on the exterior of the wall from footing to finished grade.

2. Masonry foundation walls shall be damp-proofed by applying to the exterior surface of the portland cement parging from footing to finished grade, a continuous coating of one of the following:

a. A bituminous coating applied in accordance with the manufacturer's instructions.

b. Acrylic-modified cement applied at a minimum rate of 3 pounds per square yard.

c. A layer of minimum 1/8-inch thick structural surface bonding material labeled as complying with ASTM C887.

Note: The ASTM C887 standard is entitled, "Standard Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar."

d. A waterproofing treatment applied in accordance with the manufacturer's instructions.

a. Parging of masonry block foundation walls is not required where a dampproofing material is sufficiently flexible to be listed or designed for direct application to masonry block.

b. Parging of masonry block foundation walls is not required where a layer of minimum 1/4-inch thick structural surface bonding material labeled as complying with ASTM C887 is used for dampproofing.

(b)Structural requirements. Unless designed through structural analysis, the masonry foundation walls shall be constructed in accordance with ACI 530.1 and the following requirements:

1. The minimum thickness of unreinforced masonry foundation walls shall be determined by Table 321.18-C, but in no case shall the thickness be less than the thickness of the wall it supports.

2. Reinforced masonry walls shall be reinforced in accordance with the requirements of Tables 321.18 -D, 321.18-E or 321.18-F. Vertical reinforcement shall be provided on each side of any opening and at intervals indicated in the appropriate table.

Table 321.18-C

PLAIN MASONRY FOUNDATION WALLS^d

Maximum Wall Height (ft-in)	Depth of unbalanced backfill height (ft)	Minimum nominal wall thickness (inches)
		Soil classes and lateral soil load^a (psf per foot below exterior grade
		GW, GP, SW and SP soils 30	GM, GC, SM, SM-SC and ML soils 45	SC, MH, ML-CL and inorganic CL soils 60
7-8	4 (or less)	8	8	8

	6	10	12	10 (solid^b)
	7	12	10 (solid^b)	12 (solid^b)
8-4	4 (or less)	8	8	8
	5	8	10	12
	6	10	12	12 (solid^b)
	7	12	12 (solid^b)	Note c
	8	10 (solid^b)	12 (solid^b)	Note c
9-1	4 (or less)	8	8	8
	5	8	10	12
	6	12	12	12 (solid^b)
	7	12 (solid^b)	12 (solid^b)	Note c
	8	12 (solid^b)	Note c	Note c
	9	Note c	Note c	Note c

^a For design lateral soils, see s. SPS 321.18(1) (e). Soil classes are in accordance with the Unified Soil Classification System and design lateral soil loads are for moist soil conditions without hydrostatic pressure.

^b Solid grouted hollow units.

^c An analysis in compliance with ACI 530 or reinforcement in accordance with Table 321.18-D, 321.18-E or 321.18-F is required.

^d Mortar shall be Type M or S and masonry shall be laid in running bond.

Table 321.18-D^b,c,d

8, 10 OR 12 IN. REINFORCED MASONRY FOUNDATION WALLS WHERE d >= 5 in.^e

Maximum Wall Height (ft-in)	Height of unbalanced backfill (ft)	Vertical reinforcement
		Soil classes and lateral soil load^a (psf per foot below exterior grade)
		GW, GP, SW and SP soils 30	GM, GC, SM, SM-SC and ML soils 45	SC, MH, ML-CL and inorganic CL soils 60
7-8	4 (or less)	#4 at 48" o.c.	#4 at 48" o.c.	#4 at 48" o.c.
	5	#4 at 48" o.c.	#4 at 48" o.c.	#4 at 40" o.c.
	6	#4 at 48" o.c.	#5 at 48" o.c.	#5 at 40" o.c.
	7	#4 at 40" o.c.	#5 at 40" o.c.	#6 at 48" o.c.
8-4	4 (or less)	#4 at 48" o.c.	#4 at 48" o.c.	#4 at 48" o.c.
	5	#4 at 48" o.c.	#4 at 48" o.c.	#4 at 40" o.c.
	6	#4 at 48" o.c.	#5 at 48" o.c.	#5 at 40" o.c.
	7	#5 at 48" o.c.	#6 at 48" o.c.	#6 at 40" o.c.
	8	#5 at 40" o.c.	#6 at 40" o.c.	#7 at 40" o.c.
9-1	4 (or less)	#4 at 48" o.c.	#4 at 48" o.c.	#4 at 48" o.c.
	5	#4 at 48" o.c.	#4 at 48" o.c.	#5 at 48" o.c.
	6	#4 at 48" o.c.	#5 at 48" o.c.	#6 at 48" o.c.
	7	#5 at 48" o.c.	#6 at 48" o.c.	#7 at 48" o.c.
	8	#5 at 40" o.c.	#7 at 48" o.c.	#8 at 48" o.c.
	9	#6 at 40" o.c.	#8 at 48" o.c.	#8 at 32" o.c.

^a For design lateral soil loads, see s. SPS 321.18(1) (e). Soil classes are in accordance with the Unified Soil Classification System and design lateral soil loads are for moist soil conditions without hydrostatic pressure.

^b Provisions for this table are based on construction requirements specified in s. SPS 321.18(3) (b).

^c For alternative reinforcement, see s. SPS 321.18(3) (b).

^d Mortar shall be Type M or S and masonry shall be laid in running bond.

^e The specified location of the reinforcement shall equal or exceed the effective depth distance, d, measured from the face of the soil side of the wall to the center of vertical reinforcement.

Table 321.18-E^b,c,d

10 OR 12 IN. REINFORCED MASONRY FOUNDATION WALLS WHERE d >= 6.75 in.^e

Maximum Wall Height (ft-in)	Height of unbalanced backfill (ft)	Vertical reinforcement
		Soil classes and lateral soil load^a (psf per foot below exterior grade)
		GW, GP, SW and SP soils 30	GM, GC, SM, SM-SC and ML soils 45	SC, MH, ML-CL and inorganic CL soils 60
7-8	4 (or less)	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 56" o.c.
	5	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 56" o.c.
	6	#4 at 56" o.c.	#4 at 48" o.c.	#4 at 40" o.c.
	7	#4 at 56" o.c.	#5 at 56" o.c.	#5 at 40" o.c.
8-4	4 (or less)	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 56" o.c.
	5	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 48" o.c.
	6	#4 at 56" o.c.	#4 at 48" o.c.	#5 at 56" o.c.
	7	#4 at 48" o.c.	#4 at 32" o.c.	#6 at 56" o.c.
	8	#5 at 56" o.c.	#5 at 40" o.c.	#7 at 56" o.c.
9-1	4 (or less)	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 56" o.c.
	5	#4 at 56" o.c.	#4 at 56" o.c.	#4 at 48" o.c.
	6	#4 at 56" o.c.	#4 at 40" o.c.	#4 at 32" o.c.
	7	#4 at 40" o.c.	#5 at 48" o.c.	#6 at 48" o.c.
	8	#4 at 32" o.c.	#6 at 48" o.c.	#4 at 16" o.c.
	9	#5 at 40" o.c.	#6 at 40" o.c.	#7 at 40" o.c.

^b Provisions for this table are based on construction requirements specified in s. SPS 321.18(3) (b).

^c For alternative reinforcement, see s. SPS 321.18(3) (b).

^d Mortar shall be Type M or S and masonry shall be laid in running bond.

^e The specified location of the reinforcement shall equal or exceed the effective depth distance, d, measured from the face of the soil side of the wall to the center of vertical reinforcement.

Table 321.18-F^b,c,d

12 IN. REINFORCED MASONRY FOUNDATION WALLS WHERE d >= 8.75 in.^e

Maximum Wall Height (ft-in)	Height of unbalanced backfill (ft)	Vertical reinforcement
		Soil classes and lateral soil load^a (psf per foot below exterior grade)
		GW, GP, SW and SP soils 30	GM, GC, SM, SM-SC and ML soils 45	SC, MH, ML-CL and inorganic CL soils 60
7-8	4 (or less)	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 72" o.c.
	5	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 72" o.c.
	6	#4 at 72" o.c.	#4 at 64" o.c.	#4 at 48" o.c.
	7	#4 at 72" o.c.	#4 at 48" o.c.	#5 at 56" o.c.
8-4	4 (or less)	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 72" o.c.
	5	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 72" o.c.
	6	#4 at 72" o.c.	#4 at 56" o.c.	#5 at 72" o.c.
	7	#4 at 64" o.c.	#5 at 64" o.c.	#4 at 32" o.c.
	8	#4 at 48" o.c.	#4 at 32" o.c.	#5 at 40" o.c.
9-1	4 (or less)	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 72" o.c.
	5	#4 at 72" o.c.	#4 at 72" o.c.	#4 at 64" o.c.
	6	#4 at 72" o.c.	#4 at 56" o.c.	#5 at 64" o.c.
	7	#4 at 56" o.c.	#4 at 40" o.c.	#6 at 64" o.c.
	8	#4 at 40" o.c.	#6 at 64" o.c.	#6 at 48" o.c.
	9	#5 at 56" o.c.	#7 at 72" o.c.	#6 at 40" o.c.

^aFor design lateral soil loads, see s. SPS 321.18(1) (e). Soil classes are in accordance with the Unified Soil Classification System and design lateral soil loads are for moist soil conditions without hydrostatic pressure.

^b Provisions for this table are based on construction requirements specified in s. SPS 321.18(3) (b).

^c For alternative reinforcement, see s. SPS 321.18(3) (b).

^d Mortar shall be Type M or S and masonry shall be laid in running bond.

^e The specified location of the reinforcement shall equal or exceed the effective depth distance, d, measured from the face of the soil side of the wall to the center of vertical reinforcement.

3. Vertical reinforcement shall have a minimum yield strength of 60,000 psi.

4. Solid-grouted hollow units or cores containing vertical reinforcement shall be filled with masonry grout that complies with ASTM C 476.

5. In lieu of the reinforcement provisions of Tables 321.18 -D, 321.18-E and 321.18-F, alternative reinforcing bar size and spacing having an equivalent cross-sectional area or reinforcement per linear foot of wall is permitted, provided the spacing of the reinforcement does not exceed 72 inches and reinforcing bar size does not exceed No. 11.

6. The depth below grade, wall height and reinforcement spacing may exceed the maximum values indicated in Tables 321.18 -D, 321.18-E and 321.18-F only if the design is based on structural analysis.

(4) WOOD FOUNDATIONS. Wood foundations shall be designed and constructed in accordance with the wood-foundation standard adopted in Table 320.24-6m.

Wis. Admin. Code Department of Safety and Professional Services SPS 321.18

Cr. Register, November, 1979, No. 287, eff. 6-1-80; am. (3) (intro), Register, February, 1985, No. 350, eff. 3-1-85; cr. (2) (c) to (e), r. and recr. Tables C and D, r. (3) (a) 2., renum. (3) (a) 1. to be (a), Register, January, 1989, No. 397, eff. 2-1-89; am. (intro.), (2) (b), (3) (b) and Table 21.18-D, cr. Table 21.18, r. (2) (c), renum. (2) (d) and (e) to be (2) (c) and (d), Register, March, 1992, No. 435, eff. 4-1-92; renum. (1) to (3) to be (2) to (4), and am. (3) (b), (4) (intro.) and (b), Table 21.18-A, r. (intro.) and Table 21.18, cr. (1), (3) (e), Register, November, 1995, No. 479, eff. 12-1-95; am (2), Register, January, 1999, No. 517, eff. 2-1-99; r. and recr. (1) (b), (3), Tables 21.18 -C and D, am. (2) (a), r. Table 21.18-B, renum. Table 21.18-A to be Table 21.18-B and cr. (1) (c), (d), Tables 21.18 -A, E and F, Register March 2001 No. 543, eff. 4-1-01; CR 02-077: r. (1) (c) 1., renum. (1) (d) to be (1) (e), cr. (1) (d), am. (4) (intro.), (b) and Tables 21.18 -A, C and F Register May 2003 No. 569, eff. 8-1-03; CR 08-043: am. (1) (d) 2. b. and Tables 21.18 -C to F, cr. (2) (a) (title) and (b) (title), r. and recr. (3) (a) and (4) Register March 2009 No. 639, eff. 4-1-09; correction in (1) (e), (2) (a), (3) (b) 1., 2., 5., 6., (4), Table 321.18-C to -F made under s. 13.92(4) (b) 7, Stats., Register December 2011 No. 672.

Amended by, CR 15-041: am. (1) (c) 3. a., cr. (1) (c) 3. d., am. (1) (d) 2. c., (4) Register December 2015 No. 720, eff. 1-1-16; CR 15-043: am. (1) (d) 1. c. Register December 2015 No. 720, eff. 1-1-16; correction under s. 13.92(4) (b) 7.Register December 2015 No. 720, eff.1/1/2016

The department will accept Permanent Wood Foundations Design and Construction Guide published by the Southern Forest Products Association through the Southern Pine Council, as complying with this standard. The Design and Construction Guide requires a 3.5 inch thick floor slab if a poured concrete floor slab is used.