Chicago Building Codes Department of Buildings
This section includes definitions of the most commonly used terms
and phrases associated with porches and decks. The definitions are
presented to provide a consistent understanding of those terms. A
consistent meaning of terms allows building owners and all of those
involved in the design and construction process to have the same
understanding and be able to readily communicate with one another.
BALUSTER – An element used as infill in guards on decks or stairs.
The infill occurs between the top rails and the decks or stair treads.
For porches, a commonly used baluster consists of 2×2 lumber
oriented vertically and spaced with a clear distance of less than 4
Balusters must be attached to the guardrail systems to prevent being
dislodged by impact or other lateral forces. The use of nails is not
sufficient to attach balusters. Balusters must be attached to supporting
wood members with screws sufficient to prevent being dislodged or
becoming loose over time.
BEAM – A horizontal member used to transfer or carry loads from one
structural element to another. Beams frame into other beams, columns
or building walls to support joists, landings or stair stringers.
Sometimes, beams are called “lookouts” or “girders”, depending upon
BEAM POCKET – An opening in a masonry building wall used to
support one end of a beam that runs perpendicular to the wall. Note
that beam pockets should not be located over door or window
BOLLARD – A device that is commonly used to protect portions of
buildings or other structures from damage by vehicles. A typical
bollard consists of 4 inch or larger steel pipe filled with concrete and
set in a concrete foundation.
BRICK VENEER – A non-load bearing masonry facing that provides a
weather barrier, but does not add to the structural integrity of the wall.
Brick veneer is attached to the structural wall to prevent the veneer
from being toppled by wind loads and in some cases to carry the load
of the brick. The structural wall can consist of concrete block, wood
frame, light gage metal frame or other systems.
BRIDGING – See Joist Bracing.
BUILDING PERMIT – A document issued by the City of Chicago that
gives a building owner legal permission to make an improvement to
their property. Obtaining a permit requires the submittal of an
CARRIAGE BOLT – A steel bolt with a round shaped head and
threaded shaft that, with a nut, is used to make a connection between
structural components. As the nut on the carriage bolt is tightened, a
square portion of the shaft directly under the head becomes embedded
in the wood preventing the bolt from turning. (See Materials Section
for further information.)
CELL – The hollow space inside of a concrete block which may or may
not be filled with grout and reinforcement steel.
COLUMN – A vertical member, continuous or in spliced sections, that
is used to support the levels of a porch, deck, landing or stairway. A
column transfers the load from the decks of the porch to the ground
below. Sometimes, columns are called “uprights” or “posts.”
COMMON BRICK – Can typically be found on the side and rear
elevations of older masonry buildings. Common brick is typically softer
and dimensionally less exact than face brick and was less expensive
than face brick.
CONCRETE – A manmade material that is cast into shapes and is
used extensively for foundations and other building structural
components. Concrete is also used extensively for driveways,
sidewalks and curbs. Concrete is primarily made up of Portland
cement and large and small aggregates such as crushed stone and
sand. The Portland cement chemically reacts with water to form a
paste that, when cured, binds the aggregates into a structural shape.
(See Materials Section for further information.)
CONCRETE BLOCK – Also known as “Concrete Masonry Unit” or
“CMU.” Concrete block is commonly available in nominal 2 inch to 12
inch thicknesses and in 4 inch and larger sizes is hollow. Concrete
block is frequently used as the structural portion of a wall, supporting
both gravity and wind loads.
DECK – A general term that refers to one level of framing of a porch.
The term may also refer to a single level platform constructed near
grade adjacent to single family residences. A deck may consist of
decking, joists and beams joined to create one structural platform.
DECKING – Refers to boards that form the walking surface of porches.
They are typically nailed or screwed to joists and/or beams. Wood
decking can consist of either tongue and groove or individually spaced
boards. Plywood is not an acceptable decking material for porches or
DEPARTMENT OF BUILDINGS (DOB) – The City of Chicago’s
Department of Buildings, which is a regulatory agency responsible for
issuing permits for construction and conducting inspections, is
dedicated to advancing public safety through vigorous enforcement,
community partnership and use of creative technical solutions thereby
making Chicago a safe place to live, work, and build.
DOWNSPOUT – A hollow metal tube or pipe that conducts the flow of
rainwater from the gutters to grade or other pipes.
FACE BRICK – Is a hard fired clay or shale that is used in masonry
wall construction. Unlike common brick, face brick is dimensionally
accurate, with carefully controlled colors and texture. Face brick is
used on exterior walls where a durable and architecturally significant
façade is desired.
FASTENER – A general term referring to dowel type connectors such
as bolts, nuts, screws, and nails. (See Materials Section for further
FLASHING – Typically a thin sheet of material that is formed into a
shape and is used to prevent water from infiltrating to the interior of a
building. Flashing can be fabricated from lead, copper, galvanized
steel, stainless steel, modified bitumen, or plastic. It is used to bridge
gaps between building surfaces such as walls and roofs. Flashing is
also installed in walls above windows, doors and ledger beams to
conduct water that has infiltrated the façade of a building back to the
exterior face of the building. (See Materials Section for further
FOOTING – The portion of the building or structure foundation that
bears directly on the soil. The foundation may also include walls or
piers that bear on the footing. The bottom of the footing must be a
minimum of 42 inches below grade. The footing (or pad) must also be
large enough to spread the load onto the supporting soil without
exceeding the allowable soil bearing pressure.
FRAME CONSTRUCTION – The creation of wall and floor structures
using dimension lumber that is nailed together. The most common
form of wood frame construction used today is platform framing. A
typical frame wall is constructed with 2×4 dimension lumber used as
studs, headers and sill plates.
PORCH DESIGN & CONSTRUCTION GUIDELINES 2
A GLOSSARY OF TERMS
GROUT – A concrete mix, with small aggregate, that is used to fill
voids in masonry walls such as cells in concrete block. The grout is
intended to enhance the structural integrity of the masonry wall.
GUARD – Guards are used to enclose the edges of porches, decks,
and stairs to minimize the possibility of users from falling from those
elevated structures to lower levels. Guards used at the edges of
porches or decks must be a minimum of 42 inches in height. Guards
may be commonly known as porch or deck guardrails. Guards can
also include handrails and stair guards. (See also Handrails and Stair
GUTTER – A trough located at the eave or low edge of a roof to collect
rain water. The rain water is then conducted to the ground through
downspouts. Gutters can be formed or extruded from metal or plastic.
HANDRAILS – A horizontal or sloping rail intended for grasping by the
hand for guidance or support.
HEX BOLT – A steel dowel type fastener with a hexagonal-shaped
head and threaded shaft that, with a nut, is used to make a connection
between structural components. (See Materials Section for further
HOT-DIP GALVANIZING – A process by which steel is made resistant
to corrosion (rusting) by being dipped in a liquid form of zinc. Hot dip
galvanizing provides a thicker coating of zinc than other plating
processes. A metal connector or fastener that is hot dipped galvanized
will be resistant to corrosion for a far longer time than a steel item that
is electroplated. (See Materials Section for further information.)
JOIST – A member that spans between beams or beams and walls.
Joists are uniformly spaced; typically at 16 inches on center. Joists
can bear on top of beams or frame into the sides of beams using joist
hangers. Where joists bear on top of beams, they must be adequately
attached to prevent lateral displacement.
JOIST BRACING – Also known as “Bridging”. The bracing or bridging
provides restraint against rotation of joists in long spans. Joist bracing
may consist of solid wood pieces, diagonal metal lacing, or diagonal
JOIST HANGER – A prefabricated metal connector used to join wood
joists to beams. Proprietary connectors are available from several
manufacturers. For the hanger to be fully effective, the connector must
be installed in compliance with the manufacturer’s instructions.
LAG BOLT OR LAG SCREW – A steel dowel type fastener that has
tapered threads at one end and a hex head at the other. Lag screws
are used to attach wood members together or metal connectors to
wood members. (See Materials Section for further information.)
LANDING – A horizontal surface of limited area that the user walks
upon to make the transition from one flight of stairs to another.
LATERAL BRACING – Is a system within the porch structure to
prevent lateral movement such as racking and possible collapse.
Many, if not most, porches rely on the buildings that they are attached
to for lateral stability. Therefore, the porch structures must be securely
attached to the main buildings through the ledger beams or other
means. However, even with attachment to the main building the
outstanding or free edge of the porch structure must be braced. This is
especially true of stair structures that are constructed at the edge of
the main porch platforms or decks. (See Drawing 1D for a plan of this
type of porch.)
The forces that can cause racking of a porch structure are wind loads,
vibration and impact from porch use and out of plumb framing.
Because these forces can occur or impinge on any porch structure,
every porch structure must be designed and constructed to include a
lateral bracing system. The lateral bracing system must be designed
to resist a lateral load equal to at least the wind load plus 2% of the
gravity dead and live loads. The minimum wind load is defined as 20
pounds per square foot (psf) in the Chicago Building Code.
Lateral bracing is therefore most commonly found on the face of the
porch structure that is parallel to the rear wall of the building. This is
also considered to be the free edge(s) of the porch platform(s). X, K or
inverted V bracing is commonly used for this purpose as are diagonal
braces at the corners of posts and beams. The X, K or inverted V
bracing carries the lateral load from the various levels of the porch to
As the building is typically considered adequate to provide some lateral
support, no bracing is usually considered necessary to prevent
movement perpendicular to the rear wall of the building. It is also
possible, with some porch configurations, to brace the porch structure
with diagonal bracing in the plane of the decks. If the porch decks are
designed to act as horizontal diaphragms, then it is possible for the
entire structure to be adequately braced using the stability of the
building. Bracing of decks can be accomplished by the use of
dimension lumber attached diagonally under the joists and beams.
Furthermore, decks can be turned into diaphragms by installing the
deck boards on a 45 degree angle.
Because of the multitude of porch configurations in the City of Chicago
and many possible bracing configurations, specific methods of lateral
bracing are not considered, in detail, in these Design Guidelines.
LEDGER BEAM – Not a beam in the conventional sense; it does not
span some distance carrying load. Rather, a ledger beam is rigidly
attached to a building facade and provides for a transfer of load from
the joists or other beams directly to the wall to which it is mounted.
Ledger beams provide support not only for gravity (vertical) loads but
also provide transfer of lateral loads for stability for the entire deck
structure. Wood or steel ledger beams are most commonly bolted to
brick, concrete block or wood frame walls. Ledger beams must not be
supported on brick veneers or building sheathing.
MASONRY CONSTRUCTION – Typically refers to wall construction
that consists of concrete block and/or brick and is the primary means
of structural support for the building. In this type of construction, the
masonry walls are said to be bearing walls.
MORTAR – A fundamental component of a masonry wall. Mortar is
not filler, rather it supports and bonds the concrete block, brick and/or
cut stone together. Mortar typically consists of Portland cement, lime
and sand. The proportions of these components vary depending upon
the type of wall and masonry materials used.
MULTIPLE WYTHE SOLID BRICK – Consists of multiple vertical
layers or wythes of brick that are bonded together into a solid wall.
NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION
– The NDS is published by the American Forest and Paper Association
and is the standard for the design of wood members used in porch
structures. The NDS provides the maximum stresses and forces that
wood members and wood connections can support or carry.
NOSING – An extension of a stair tread beyond the face of a riser. In
wood construction, stair treads commonly include nosings.
PIER – A short concrete column cast on top of a footing. In the context
of porch and deck construction, the pier supports a column or post. It
is a portion of the foundation that transfers the column load to the
footing and is almost entirely below grade.
PORCH DESIGN & CONSTRUCTION GUIDELINES 3
A GLOSSARY OF TERMS
PLYWOOD – A manufactured wood product that is comprised of
multiple wood veneers that are glued together under high pressure.
Plywood is available in 4 feet by 8 feet sheets, in a number of
thicknesses and made from many different species of wood.
PORCH – An open structure that is typically located at the rear of a
building that forms a part of the means of egress from the building.
Porches are typically of differing construction from the principal portion
of the building and are separated from the building by a fire rated wall.
Porches include decks, stairs and landings but not all of the deck areas
are necessarily a part of the means of egress path. A porch may or
may not include a roof.
PORCH (3D GRAPHIC) – Below is an illustration of a porch with the
various components annotated.
PRESSURE TREATED LUMBER (See “Wolmanized Lumber”) – Is
commonly known as treated lumber or “Wolmanized Lumber.” In
general, the treatment process involves filling the cells of the wood with
chemical compounds that are toxic to micro-organisms and insects and
significantly reduces the deterioration of the wood in-use. There are
several varieties of chemical treatment available, which are described
in more detail in the Materials Section. (See also Wolmanized Lumber)
REDI-MIX CONCRETE – Concrete that is purchased from a supplier
and delivered by truck to the construction site.
REINFORCEMENT – Consists of deformed steel bars that are
incorporated into structural concrete members such as slabs, beams,
columns and foundations. (See Materials Section for further
RIM JOIST – A component of a wood platform frame used for a floor or
flat roof. The rim joist forms the perimeter of the platform frame.
RISER – A component of a stair consisting of a board closing the gap
between the treads. The rise is the vertical dimension between each
tread. The rise between all of the treads in a flight of stairs must be
SHEATHING – A sheet type material that is applied over structural
framing. On wall framing, the sheathing is placed on the outside face
of the 2×4 studs to provide a back-up for siding, stucco or brick veneer.
The wall sheathing also provides lateral stability for the wood frame
building. On roof framing, sheathing is the structural surface upon
which the roofing is installed. Structural sheathing typically consists of
plywood or oriented strand board (OSB). Fire-rated sheathing includes
SIDING – The exterior finish material used on the outside of a building
of frame construction, generally consisting of wood, aluminum, or vinyl.
SOUTHERN YELLOW PINE – The most commonly used species of
wood for porch and deck construction in the Chicago area. It has good
structural properties and accepts pressure treatment well. (See
Materials Section for further information.)
SPLICE – The connection of two structural members to form a longer
and structurally continuous member.
STORY HEIGHT – The vertical dimension between finished floor levels
of a building.
STAIR GUARD – A component of a stair that is intended to minimize
the possibility of a fall from a stair to a lower level. Guards whose top
rail also serves as a handrail shall have a height of between 34 inches
and 38 inches.
STAIR STRINGER – Supports the stair treads and spans from floor to
floor or floor to intermediate level. Even though stair stringers are
sloped, they are beams.
STRUCTURAL GLUED LAMINATED SOFTWOOD TIMBER – is an
engineered wood product that is constructed of multiple layers of wood
to form a relatively large beams and columns. These beams and
columns are commonly known as Glulams and are frequently available
in widths of 3-1/2” to 5-7/16” and in depths of 9-1/2” to 18”. Because
Glulams are constructed of carefully selected glued wood their strength
is considerably higher than similar sized solid wood members. The
use of these members may be suitable for deck and porch construction
but are not specifically referenced in these Guidelines.
STUCCO – Also known as cement-plaster and is an exterior building
finish. It is made from Portland cement, sand and lime and is applied
in three coats on top of lath. The top or finish coat can be smooth or
STUD – A vertical structural member that is typically a wood 2×4 used
in frame construction.
TREAD – A horizontal component of a stair that the user steps upon to
ascend or descend from one level to another. The rise is the vertical
dimension between each tread. The width of all treads and height of
all risers must be dimensionally consistent and not vary within any
flight of stairs.
UNIT (Dwelling Unit) – Refers to a single apartment in a multi-family
WET SERVICE USE – is a condition where the porch structure is
exposed to rain or snow. Lumber is said to be used under wet service
conditions when the moisture content of the wood is above 19% for an
extended period of time.
Wet service is of importance because the allowable stresses and
capacity of wood members and their connections is reduced. In
addition, the metal connectors and fasteners are exposed to conditions
PORCH DESIGN & CONSTRUCTION GUIDELINES 4
A GLOSSARY OF TERMS
that will cause accelerated corrosion and must be protected using a
process such as Hot-Dip Galvanizing.
WOLMANIZED LUMBER (See Pressure-treated Lumber) – Is a
trade name and it is used generically to refer to preservative treated
lumber that is commonly used in porch and deck construction. (See
Pressure Treated Lumber and Materials Section for further
WYTHE – A single continuous vertical layer of brick in a wall. Solid
brick walls typically consist of multiple layers or wythes to form one
solid wall. For example, a 12 inch thick solid brick wall would be
constructed of three wythes of brick.