Wis. Admin. Code Department of Safety and Professional Services SPS 327.31

Current through September 30, 2024

Section SPS 327.31 - Wood frame floors

Unless designed through structural analysis, wood frame floors shall comply with the following requirements:

(1) FLOOR JOISTS.

(a) Floor joists shall comply with the structural requirements and live load determination under s. SPS 327.20.

(b) Where the joists of a floor system are parallel to, and located between bearing walls above and below, the joists shall be doubled.

(2) FLOOR TRUSSES. Metal plate connected wood floor trusses shall be designed in accordance with the Design Specifications for Metal Plate Connected Parallel Chord Wood Trusses and the National Design Specification for Wood Construction. Truss members shall not be cut, bored or notched.

(3) GIRDERS AND BEAMS.

(a) Wood girders and beams shall be fitted at the post or column. Adjoining ends shall be fastened to each other to transfer horizontal loads across the joint. Beams shall also be fastened to the posts with framing anchors, angle clips, or equivalent.

(b) Where intermediate beams are used, they shall rest on top of the girders; or shall be supported by ledgers or blocks fastened to the sides of the girders; or they may be supported by approved metal hangers into which the ends of the beams shall be fitted.

(c) Lateral restraint for all wood beams shall be provided at all columns using a saddle or other approved connection where the beam meets one of the following conditions:

1. The beam is not restrained at both ends.

2. The beam is more than 11 1/4 inches deep using actual measurement.

Note: A saddle supports the beam on the bottom and allows for the through-connection of fasteners into the side of the beam.

(4) BEARING AND END CONFIGURATION.

(a)Sawn lumber.

1. `Joists.' Wood joists made of sawn lumber shall meet the following bearing requirements:

a. Wood joists supported on wood or metal shall have a bearing surface of at least 1 1/2-inches measured from the end of the joist.

b. The tail end of a floor joist may not extend past the edge of a beam by more than the depth of the floor joist.

c. Wood floor joists with ends that intersect over a beam shall have the ends overlap at least 3 inches and be securely fastened together with at least two 12d common nails or the ends shall be butt-jointed or face-jointed and fastened with ties, straps, plates or solid blocking.

2. `Beams and girders.' Beams and girders made of sawn lumber shall have a bearing surface on their supports of at least 3 inches parallel to the beam or girder and be at least as wide as the beam or girder.

(b)Engineered wood products. Bearing surface for engineered wood products shall be in accordance with the manufacturer's instructions provided those instructions were developed through structural analysis or product testing and are applicable to the configuration.

(5) NOTCHING AND BORING. Notching and boring of beams or girders is prohibited unless determined through structural analysis.

(a)Notching of floor joists.

1. Notches located in the top or bottom of floor joists shall not have a depth exceeding 1/6 the depth of the joist, shall not have a length exceeding 1/3 the joist depth nor be located in the middle 1/3 of the span of the joist.

2. Where floor joists are notched on the ends, the notch shall not exceed 1/4 the depth of the joist. Notches over supports may extend the full bearing width of the support.

(b)Boring of floor joists.

1. `General.' A hole may not be bored in a floor joist within 2 inches of a notch or another hole. In no case shall the distance between adjacent holes be less than the diameter of the larger hole.

2. `Holes near the edge.' Holes bored in the top or bottom 2 inches of a joist shall follow the limitations for notching under par. (a).

3. `Other holes.' Holes bored in floor joists that are not within 2 inches of the top or bottom of the joist shall have their diameter limited to 1/3 the depth of the joist.

(c)Engineered wood products. Notching or boring of engineered wood products shall be done in accordance with the manufacturer's instructions provided those instructions were developed through structural analysis or product testing.

(6) OVERHANG OF FLOORS.

(a)General. Except as provided in pars. (b) and (c), a floor joist overhang shall be cantilevered beyond the outer edge of the supporting wall below it by no more than the actual depth of the joist or shall be designed through structural analysis in accordance with s. SPS 327.20(3).

(b)Joist overhangs parallel to the main floor framing system. Joist overhangs that are extensions of, and parallel to, the main floor framing system may extend beyond the depth of the joist without structural analysis provided they meet all of the following conditions:

1. The overhang is cantilevered no more than 2 feet beyond the outer edge of the supporting wall below it.

a. The overhang supports a uniform load limited to the weight of the bearing wall and the tributary roof area above it.

b. The tributary length of the roof area, excluding the eave overhang, is no more than 2 feet greater than the actual length of the joist directly below.

c. The eave overhang is no more than 2 feet.

Note: The tributary length is usually half the span of the joist or rafter.

3. The joist overhang does not support any concentrated loads. For the purposes of this subsection, a framed opening in the wall with a rough opening of 4 feet or less shall be considered uniform loading.

a. The cantilevered joist is doubled at the supporting wall.

b. The doubled joist length extends inward beyond the inner edge of the supporting wall by the same distance as the cantilever.

c. The added joist member is secured to the main joist.

(c)Joist overhangs perpendicular to the main floor framing system. Joist overhangs that are perpendicular to the main floor framing system, or lookout joists, may extend beyond the depth of the joist without structural analysis provided they meet all of the following conditions:

1. The joist overhang is cantilevered no more than 2 feet beyond the outer edge of the supporting wall below it.

a. A double floor joist is used to support the lookout joist.

b. The double floor joist is located a distance of at least 2 times the cantilever length inward from the outer edge of the supporting wall below.

c. The lookout joists are fastened to the double joist with metal hangers.

3. The joist overhang supports no more than either a non-bearing wall or a wall that supports only a roof which spans no more than the floor overhang cantilever length plus the eave overhang.

(d)Other joist overhangs. All overhangs longer than the depth of the supporting joist that do not meet all of the conditions under par. (b) or (c) shall be designed through structural analysis.

(7) FLOOR OPENINGS. Trimmers and headers shall be doubled when the span of the header exceeds 4 feet. Headers which span more than 6 feet shall have the ends supported by joist hangers or framing anchors, unless the ends are supported on a partition or beam. Joists more than 8 feet long that frame into headers shall be supported on metal framing anchors or on ledger strips of at least 2 inches b`y 2 inches nominal.

(8) FLOOR SHEATHING, BOARDS AND PLANKS.

(a)Plywood sheathing. Plywood sheathing used for floors shall be limited to the allowable loads and spans shown in Table 327.31-A.

(b)Combination subfloor-underlayment. Combination subfloor-underlayment shall be installed in accordance with Table 327.31-B.

(c)Floor boards. Where wood boards are used for floor sheathing, the boards shall comply with the minimum thicknesses shown in Table 327.31-C.

(d)Planks. Planks shall be tongue and groove or splined and at least 2 inches, nominal, in thickness. Planks shall terminate over beams unless the joints are end matched. The planks shall be laid so that no continuous line of joints will occur except at points of support. Planks shall be nailed to each beam.

(9) BRIDGING.

(a)Sawn lumber. Bridging shall be provided for sawn lumber framing at intervals not exceeding 8 feet where the nominal depth to thickness ratio is greater than 4 to 1.

Note: This 4:1 ratio means bridging is required for wood-framed floors having nominal 2X10 or deeper solid-sawn-lumber joists, to provide restraint against rotation or lateral displacement.

(b)Engineered products. Bridging shall be provided for engineered framing products in accordance with the manufacturer's recommendations.

(10) SILL PLATES. All of the following requirements apply to a sawn-lumber sill plate with uniform loading that is partially extended beyond the load-bearing surface of a foundation wall in order to put the exterior surface of an upper-lying wall flush with or beyond the exterior surface of insulation that is placed on the outside of the foundation wall:

(a) The center of any anchor bolt shall be set back from the side edge of the sill plate by a distance of at least 4 times the diameter of the bolt.

(b) The thickness of the concrete or mortar cover around any anchor bolt shall comply with ACI 318 section 7.7.

Note: Under ACI 318 section 7.7, the minimum cover for a 5/8-inch-diameter or smaller bolt is 1 1/2 inches.

(c) With wood floor joists that are parallel to the foundation wall, the sill plate may not extend beyond the load-bearing surface of the wall by more than one-half of the nominal thickness of the joist that bears on the sill plate.

(d) As used throughout this subchapter and in the standards that the subchapter incorporates by reference, the shorter side of the cross-sectional area of a wood member is the thickness of the member. The longer side of the cross-sectional area is the depth, when the longer side is vertical; and it is the width when the longer side is horizontal.

Table 327.31-A

ALLOWABLE SPANS FOR PLYWOOD FLOOR SHEATHING CONTINUOUS OVER TWO OR MORE SPANS AND FACE GRAIN PERPENDICULAR TO SUPPORTS¹

Span Rating²	Plywood Thickness	Maximum span³
32/16	15/32", 1/2", 5/8"	16"⁵
40/20	19/32", 5/8", 3/4", 7/8"	20"^4,5
48/24	23/32", 3/4", 7/8"	24"

¹ These values apply to C-D, C-C, and Structural I and II grades only. Spans shall be limited to values shown because of possible effect of concentrated loads.

² Span Rating appears on all panels in the construction grades listed in footnote 1.

³ Plywood edges shall have approved tongue and groove joints or shall be supported with blocking, unless 1/4 inch minimum thickness underlayment or 1 1/2 inches of approved cellular or lightweight concrete is installed or finished floor is 25/32-inch wood strip. Allowable uniform load based on deflection of 1/360 of span is 165 pounds per square foot.

⁴ For joists spaced 24 inches on center, plywood sheathing with Span Rating 40/20 or greater can be used for subfloors when supporting 1 1/2 inches lightweight concrete.

⁵ May be 24 inches if 25/32-inch wood strip flooring is installed at right angles to joists.

Table 327.31-B

MINIMUM THICKNESS FOR PLYWOOD COMBINATION SUBFLOOR-UNDERLAYMENT. PLYWOOD CONTINUOUS OVER TWO OR MORE SPANS AND FACE GRAIN PERPENDICULAR TO SUPPORTS^1,2

Plywood Grade	PlywoodSpeciesGroup	Maximum Support Spacing³
		16" o.c	20" o.c	24" o.c
		PanelThickness(inches)	PanelThickness(inches)	PanelThickness(inches)
Sanded exterior type	1	1/2	5/8	3/4
	2 & 3	5/8	3/4	7/8
	4	3/4	7/8	1
Underlayment C-C Plugged Sturd-I-Floor⁴	All Groups	APA Rated Sheathing and APA Rated Sturd-I-Floor shall be installed consistent with their rating.

¹ Spans shall be limited to values shown, based on possible effect of concentrated loads.

² Unsupported edges shall be tongue and groove or blocked except where 1/4 inch underlayment or 25/32-inch finish floor is used.

³ Underlayment, C-C Plugged, sanded exterior type: allowable uniform load based on deflection of L/360 span for spans 24 inches or less is 125 psf; and for spans 48 inches, 65 psf.

⁴ The department will accept subfloor underlayment panels such as Sturd-I-Floor which meet the requirements of APA manufacturing specifications for Sturd-I-Floor panels.

Table 327.31-C

MINIMUM THICKNESS OF FLOOR BOARDS

Minimum Net Thickness
Joist Spacing	Perpendicular to Joist	Diagonal to Joist
24"	11/16"	3/4"
16"	5/8"	5/8"

Wis. Admin. Code Department of Safety and Professional Services SPS 327.31

Adopted by, EmR1703: emerg. cr., eff. 2-6-17; CR 17-017: cr. Register March 2018 No. 747, eff. 4-1-18; (6) (d) (title) created under s. 13.92(4) (b) 1, Stats., Register March 2018 No. 747, eff. 4/1/2018

Under sub. (6), wood floor joists that are perpendicular to the foundation wall can extend beyond the foundation wall by a distance of up to the depth of the joist.