Excerpts from Everybodys Building Code

PREFACE

Building codes are adopted by governments to
preserve your family’s physical and fiscal health and
safety. If you are someone who likes to do-it-yourself,
a homeowner acting as your own contractor, a
contractor, a home inspector, a real estate agent, or
anyone else who wants to protect themselves, their
family, and their customers by using the International
Residential Code® (IRC) 2009, then this is your
building code book. This book makes the IRC more
accessible and easier to understand so you can use
the IRC without becoming a code expert.

This book does not replace the IRC. It contains
selected IRC provisions and omits others. While
every effort has been made to accurately present the
IRC with easy to understand language, pictures, and
diagrams, this book is not the IRC. In a dispute, the
wording in the IRC, as interpreted by the local building
official, is the final authority on what IRC provisions
mean.

This book does not replace “how to do it” books. If, for example, you wish to replace a water
heater, learn the steps for doing so in a “how to do it” book. Use this book to learn if your work
complies with IRC 2009 provisions. You should review the IRC provisions in this book before
you do the work to avoid changing completed work that does not comply with the IRC.

If you need a more detailed and professional understanding of the IRC, I urge you to acquire
the IRC Commentary. This large two-volume work contains all IRC provisions accompanied by
lengthy explanations and illustrations. It is a valuable resource and is well worth the cost.

Finding all relevant IRC provisions is often a challenge. This book gives you two options for
finding the provisions you need. You may use the extensive index at the back of this book to
find code provisions relating to a word such as switch, stud, or shingle. You may also use the
Table of Contents to find code provisions relating to a topic such as receptacle installation. Be
careful when using the Table of Contents because code provisions about a topic may appear in
more than one place. Looking for similar topics in related areas is often a good idea to be
certain you have found all relevant code provisions.

The Table of Contents is almost a book in itself. It lists every IRC provision discussed in this
book, along with additional explanation and discussion material. Once you are familiar with
the material in the Table of Contents, you will know if the IRC addresses a topic and, if so,
where to find it. By using both options, you should find the IRC provisions that will help you
safeguard those who rely on you to keep their home safe.

CHAPTER 2 DEFINITIONS

Air intake opening (gravity) A gravity air intake opening is any opening that allows air to flow
into the home through natural means. Operable windows and doors are the most common
examples. Less common examples include combustion air openings, makeup and ventilation
air openings, and soffit vent openings.

Air intake opening (mechanical) A mechanical air intake opening is one that draws air into the
home using a fan, blower, or other powered means. A common example is an outside air intake
duct connected to the return boot of a forced-air HVAC system. These ducts are being installed
in some new homes to mix outdoor air with the return air to increase air changes per hour in
the home and to improve indoor air quality.

Attic, habitable A habitable attic is a habitable space located directly under the roof. Habitable
attics have no exterior walls. Interior walls, if any, are knee walls between the rafters above and
the floor below. An example of a habitable attic is an attic area that is accessible by permanent
stairs. A habitable attic is not considered a story so it does not add to the number of stories
above grade and it does not place additional load requirements on the supporting framing. A
habitable attic is designed as a sleeping area for determining floor joist spans. A habitable attic
must have the minimum floor space (70 square feet) and minimum ceiling height as required
in Sections R304 and R305.

Span The span is the unsupported distance between framing members. Example: the span of
a 120 inches long floor joist with 1 ½ inches bearing on each end support is 117 inches.
Example: the span of a sheet of subfloor between joists spaced 16 inches on center is 14 ½
inches. See also Roof span.

Stud, jack A jack stud is a vertical support member in a wall that runs between the bottom of a
header and the wall bottom plate and helps support the header.

Stud, king A king stud is a vertical support member in a wall that runs beside a header
between the wall top and bottom plates and helps support the header.

Surcharge A surcharge on a retaining wall is a vertical load in addition to the retained earth.
The load is usually additional earth above the top of the retaining wall, but the load could be
imposed by a nearby structure such as a swimming pool or a building.

Swale A swale is a ditch or depression intended to drain storm water runoff from a residential
lot to the street or other storm water collection area.

CHAPTER 15 KITCHEN AND CLOTHES DRYER EXHAUST SYSTEMS

CLOTHES DRYER EXHAUST SYSTEMS (M1502 AND G2439)

Installation Requirements
1. Construct, install, and terminate clothes dryer exhaust ducts according to the clothes dryer
manufacturer's installation instructions. If the clothes dryer manufacturer is not known during
construction, use the IRC requirements. The clothes dryer manufacturer is rarely known during
construction, so the manufacturer's installation instruction exception rarely applies.
2. Do not connect clothes dryer exhaust ducts to any other system such as bathroom exhaust
fan ducts, plumbing vents, and fuel-burning equipment vents and flues.
3. Do not install clothes dryer exhaust ducts in or through any fireblocking, draft stopping, or
fire-resistance rated assembly unless the duct is constructed and installed to maintain the
code required fireblocking or draft stopping.
4. Do not run clothes dryer exhaust ducts into or through other ducts or plenums. Example:
do not run a clothes dryer exhaust duct into or through an HVAC supply or return duct or
into or through a combustion air duct.
5. Install the clothes dryer exhaust duct during construction if space for clothes dryer is
provided.

Duct Construction
1. Use a 4 inch diameter smooth wall metal clothes dryer exhaust duct, unless the clothes
dryer manufacturer's instructions allow another size.
2. Install duct joints so that the inside part of the joint fits into the outside part of the joint in
the direction of the air flow.
3. Do not use screws or other fasteners that penetrate the duct and could trap lint. Pop rivets
(1/4 inch) are usually considered acceptable fasteners.
4. Support the duct at least every 4 feet. Joints and elbows are vulnerable areas for separation.
5. Protect the duct with at least 16 gage shield plates if the duct is within 1 1/4 inches from the
edge of a framing member. Extend the shield plate at least 2 inches above sole plates and
below top plates. Protect the duct with shield plates at any other location where it is likely to be
penetrated by fasteners.

Duct Length
1. Do not exceed 25 feet developed length between the beginning of the clothes dryer exhaust
duct and the duct termination, unless the clothes dryer manufacturer's installation instructions
allow a longer length. Developed length means the straight line length of the duct, reduced by
bends in the duct.
2. Reduce developed duct length by 2 1/2 feet for every 45 degree bend and by 5 feet for every
90 degree bend. You may use the manufacturer provided developed length for smooth radius
bends. You may use the IRC table for smooth radius bend developed length if the
manufacturer's instruction are not available.
3. Do not include the transition duct in the dryer duct developed length.
4. Locate a permanent label within 6 feet of the clothes dryer exhaust duct connection that
shows the exhaust duct's developed length. This requirement applies only when the duct is
concealed.
5. Note that IRC Section G2439.5.5.1 specifies a developed clothes dryer duct length of not
more than 35 feet. Verify with the local building official which length applies in your area.

Duct Termination
1. Terminate clothes dryer exhaust ducts outside the building. Outside the building does not
include attics and crawl spaces.
2. Locate the clothes dryer exhaust duct termination at least 3 feet from any opening to the
building, unless the clothes dryer manufacturer's installation instructions specify another
location. The clothes dryer manufacturer is rarely known during construction, so the
manufacturer's installation instruction exception rarely applies.
3. Provide a backdraft damper at the duct termination or at another approved location.
4. Do not install a screen at the exhaust duct termination. A screen will trap lint.

Transition Duct
1. The transition duct is the duct (usually flexible duct) between the dryer and the start of the
smooth wall dryer exhaust duct.
2. Limit the transition duct length to 8 feet.
3. Use only one piece of listed and labeled transition duct. Do not splice together two or more
lengths of transition duct material.
4. Do not run the transition duct through walls or in concealed spaces.