It Is A Legal Requirement
A building permit is required for building a deck if decks attached to dwellings and detached decks which serve an exit.
Patios do not require a permit.
ILHR 21.225 Decks.
Decks attached to dwellings and detached decks which serve an exit shall comply with the applicable
provisions of this chapter, including but not limited to:
(1) Excavation requirements of s. COMM 21.14;
(2) Footing requirements of s. COMM 21.15 (1) (f);
(3) Frost penetration requirements of s. COMM 21.16;
(4) Load requirements of s. COMM 21.02;
(5) Stair, handrail and guardrail requirements of s. COMM 21.04; and
(6) Decay protection requirements of s. COMM 21.10.
COMM 21.02 Loads and materials.
Every dwelling shall be designed and constructed in accordance with the requirements of this section.
(1) DESIGN LOAD. Every dwelling shall be designed and constructed to support the actual dead
load, live loads and wind loads acting upon it without exceeding the allowable stresses of the material.
MINIMUM LIVE LOADS FOR FLOORS (TABLE 21.02)
Component Live Load (pounds per sq. ft.)
Exterior balconies, decks, porches 40
for floor joist calculations, see App. 34–37 & App. 25 Table F-2 of the Wisconsin Administrative Code
for beam calculations, see COMM/ILHR 21.22 (TABLES A, B, and C) of the Wis. Adm. Code
If you need help in calculating joist and beam sizes, consult a lumber supplier.
COMM 21.04 Stairs and elevated areas.
Every exterior stair shall conform to the requirements of this section.
(1) STAIR DETAILS. (a) Width. Stairs shall measure at least 36 inches in width. Handrails and
associated trim may project no more than 4½ inches into the required width at each side of the stairs.
(b) Headroom. Stairs shall be provided with a minimum headroom clearance of 76 inches. The
clearance shall be measured vertically from a line parallel to the nosing of the treads to the ceiling or soffit
directly above that line.
(c) Treads and risers. 1. Except for spiral stairs and winders, risers may not exceed 8 inches in
height measured vertically from tread to tread. Treads shall be at least 9 inches wide measured horizontally
from nosing to nosing.
2. Within individual stairways, tread widths and riser heights may vary in uniformity by a maximum
of 3/16 inches. Variations in uniformity may not cause either dimension in subd. 1. to be exceeded.
RESIDENTIAL DECK CONSTRUCTION
(2) HANDRAILS AND GUARDRAILS. Handrails or guardrails shall be provided on all open sides
of stairs consisting of more than 3 risers and on all open sides of areas that are elevated more than 24 inches
above the floor or exterior grade. Handrails and guardrails shall be constructed to prevent the through
passage of a sphere with a diameter of 6 inches or larger. Handrails and guardrails shall be designed and
constructed to withstand a 200 pound load applied in any direction. Exterior handrails and guardrails shall
be constructed of metal, decay resistant or pressure-treated wood, or shall be protected from the weather.
(a) Handrails. Stairs of more than 3 risers shall be provided with at least one handrail for the full
length of the stairs.
1. Height. Handrails shall be located at least 30 inches, but no more than 38 inches above the nosing
of the treads. Measurements shall be taken from the hard structural surface beneath any finish material to
the top of the rail. Variations in uniformity are allowed only when a rail contacts a wall or newel post or where
a turnout or volute is provided at the bottom steps.
2. Clearance. The clearance between a handrail and the wall surface shall be at least 1½ inches.
. . .
4. Projection. Handrails and associated trim may project into the required width of stairs and
landings a maximum of 4½ inches on each side.
5. Size and configuration. Handrails shall be symmetrical about the vertical centerline to allow for
equal wraparound of the thumb and fingers.
a. Handrails with a round or truncated round cross sectional gripping surface shall have a maximum
whole diameter of 2 inches.
b. Handrails with a rectangular cross sectional gripping surface shall have a maximum perimeter
of 6¼ inches with a maximum cross sectional dimension of 2f inches.
c. Handrails with other cross sections shall have a maximum cross sectional dimension of the
gripping surface of 2f inches with a maximum linear gripping surface measurement of 6¼ inches and a
minimum linear gripping surface of 4 inches.
6. Continuity. Handrails shall be continuous for the entire length of the stairs except in any one of
the following cases:
a. A handrail may be discontinuous at an intermediate landing.
b. A handrail may have newel posts.
c. A handrail may terminate at an intermediate wall provided the lower end of the upper rail is
returned to the wall or provided with a flared end, the horizontal offset between the two rails is no more than
12 inches measured from the center of the rails, and both the upper and lower rails can be reached from the
same tread without taking a step.
(c) Guardrails. 1. Application. All openings between floors, and open sides of landings, platforms,
balconies or porches that are more than 24 inches above grade or a floor shall be protected with guardrails.
2. Height. Guardrails shall be located at least 36 inches above the floor. Measurement shall be
taken from the hard structural surface beneath any finished material to the top of the rail.
RESIDENTIAL DECK CONSTRUCTION
(3) LANDINGS. (a) Intermediate landings. A level intermediate landing shall be provided for any
stairs with a height of 12 feet or more. Intermediate landings shall be at least as wide as the stairs and shall
measure at least 3 feet in the direction of travel. For curved or semicircular landings, the radius of the landing
shall be at least equal to the width of the stairs.
(b) Landings at the top and base of stairs. A level landing shall be provided at the top and base of
every stairs. The landing shall be at least as wide as the stairs and shall measure at least 3 feet in the
direction of travel.
(c) Doors at landings. Except as provided in subds. 1. to 4., level landings shall be provided on each
side of any door located at the top or base of a stairs, regardless of the direction of swing.
. . .
3. A landing is not required between a sliding glass door and the top of an exterior stairway of 3 or
4. The exterior landing, platform or sidewalk at an exterior doorway shall be located a maximum of
8 inches below the interior floor elevation. The landing, platform or sidewalk shall have a length at least equal
to the width of the door.
COMM 21.10 Protection against decay and termites.
. . .
(3) IDENTIFICATION. (a) All pressure-treated wood and plywood shall be identified by a quality mark
or certificate of inspection of an approved inspection agency which maintains continued supervision, testing
and inspection over the quality of the product in accordance with the adopted standards of the American
Wood Preservers Association.
COMM 21.14 Excavations for footings and foundations.
. . .
(2) EXCAVATIONS FOR FOOTINGS. All footings shall be located on undisturbed or compacted soil,
free of organic material, unless the footings are reinforced to bridge poor soil conditions.
COMM 21.15 Footings.
(1) SIZE AND TYPE.
. . .
(f) Deck footings. Decks attached to dwellings and detached decks which serve an exit shall be
supported on a structural system designed to transmit and safely distribute the loads to the soil. Footings
shall be sized to not exceed the allowable material stresses. The bearing area shall be at least equal to the
area required to transfer the loads to the supporting soil without exceeding the bearing values of the soil.
(2) SOIL-BEARING CAPACITY. No footing or foundation shall be placed on soil with a bearing
capacity of less than 2,000 pounds per square foot unless the footing or foundation has been designed
through structural analysis. The soil-bearing values of common soils may be determined through soil
COMM 21.16 Frost penetration.
(1) GENERAL. Footings and foundations, including those for ramps and stoops, shall be placed
below the frost penetration level, but in no case less than 48 inches below grade measured adjacent to the
footing or foundation. Footings shall not be placed over frozen material.