Floor Framing

Following are the code requirements and instructions related to floor framing:

• Double joists are required under parallel bearing walls.

• If pipes penetrate floors where double joists are required, the joists must be separated and have full-depth, solid blocks at least every 4′ along their length.

• Bearing for joists must be Ш" minimum on wood or steel, and 3" minimum on concrete or masonry.

• Where joists lap, there must be a minimum lap of 3" or a wood or metal splice of equal strength.

• The ends of joists must be kept from turning by using Ш" full-depth solid blocking or by attaching them to a header, band, rim joist, or adjoining stud.

• Full-depth, solid blocking is required at intermediate supports in IRC seismic design categories D1, D2, and E. (See seismic maps in Chapter 9.)

• Bridging at 8′ O. C. is required only when joists are larger than 2 x 12, and both edges are not held in line, as with plywood floor sheathing and drywall sheathing, or if thicker than

2” nominal.

The “Floor Joists—Anchor or Ledger" illustration below shows how joists framing into girders must be supported by framing anchors or a 2 x 2 or larger ledger.

Engineered wood products, such as I-joists, can be notched according to the manufacturer’s specifications. (See Chapter 8 for more on engineered wood products.)

The “Framing Floor Openings" illustration shows the following code requirements and instructions
related to framing around openings in floors.

• If the header joists are more than 4′, the header joists and trimmer joists should be doubled.

• If the distance from the bearing point of a trimmer joist to the header joist is more than 3′, the trimmer joists should be doubled.

• If the header joist is greater than 6′, hangers must be used.

• If the tail joists are more than 12′, use framing anchors or a 2 x 2 ledger.

The “Seismic Floor Opening Framing" illustration shows what to do if you are building in IRC seismic design categories B, C, D, or E and the opening is greater than 4′ perpendicular to the joists. In such cases, you must provide blocking beyond the headers, and metal ties must be used to connect the headers with the blocks.

Floor Joists—Anchor or Ledger

Joist framed into girder must be supported by framing anchors or 2 x 2 or bigger ledger

Floor Joists—Drilling & Notching Requirements

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Trimmer joist

If header joist is more than 4′, double header joist and double trimmer joist.

Seismic Floor Opening Framing with an Opening Greater than 4′ Perpendicular to the Joists

or

Metal tie 16 ga. x iy2" x (opening width + 4′-0") (1 each side) use 24-16d common nails.

Sheathing to go on top of joists

From the IBC Code; this information is not listed in the IRC.

Framers, builders, architects, engineers, and building inspectors alike have contributed to the system of building codes we use today. You should be aware of the codes that apply to the part of the country you are working in, as well as the important features of those codes. This chapter will discuss what you should know about building code requirements.

Introduction to Building Codes

The Evolution of Building Codes

Although carpentry is one of the oldest professions, framing as we know it today didn’t start until 1832 when a man named George Snow wanted to build a warehouse in Chicago. It was difficult to obtain enough large timbers to build the structure using the traditional post and beam method. Being creative (as all good builders and lead framers must be), he cut up the small timbers he had growing on his property into pieces similar to 2 x 4s. He placed them in a repetitive manner, thus creating the first 2 x 4 style walls.

Since then, architects, engineers, builders, building inspectors, and framers have all contributed to the system we use today. Along the way, builders constructed buildings in the way they saw fit. Although this “every man for himself" approach to building gave us structures to live and work in, it did not guarantee that such buildings would last a lifetime, be safe to live and work in, or stand up against earthquakes and hurricanes.

It wasn’t until 1915 that a group of building officials decided they needed a standard. That year, the Building Officials & Code Administrators International (BOCA) was established to bring some uniformity to the systems being used.

The IBC

Two other building code agencies appeared not long after: the International Conference of Building Officials (ICBO), and the Southern Building Code Congress International (SBCCI). All three organizations worked to meet the particular needs of their regions of the country.

In the year 2000, these agencies combined their codes to create one common code that would cover the entire country. This code is divided into two books: the International Residential Code (IRC), which covers all one – and two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories in height, and the International Building Code (IBC), which covers all buildings. Separating the code in this way makes it easier to find the information you need. If you are building only houses, duplexes, or townhouses, you would go straight to the IRC.

There are two ways to comply with the code. The prescriptive method, most commonly used, gives specific requirements (such as how many inches on center to space the framing lumber) to build walls that are acceptable. The performance method tells us how a person can determine the strength of a wall using properly stamped, graded lumber, and if that strength meets the minimum code requirements.

Because the prescriptive system is most commonly used, it is the one we’ll cover here. It applies to conventional construction otherwise known as platform or balloon framing, which has been developed over the years on job sites, and has been tested and standardized. Prescriptive code requires no “engineering" design by a registered professional, as long as the project is built in compliance with the International Residential Code (IRC) or International Building Code (IBC).

(Note that with a performance-rated system, you will have a set of plans that you must follow to the letter. These plans come with structural components that must be used exclusively with the plans. Performance-rated codes require design by a registered professional who must specify in accordance with the IRC or IBC.)

A Framer’s Code Responsibility

Although it may seem that the codes are written for lawyers instead of framers, framers must be sure that their work complies to code. Note that some areas of the country may not be covered by a statewide, town, city, or county code. (Counties have historically been the jurisdictions controlling code establishment and enforcement.) Note, too, that code-writing organizations are not government agencies, so codes are not enforceable until or unless a government jurisdiction accepts the codes and makes them part of local law.

Code Revisions & Time Delays

Code Revisions

Revisions are important to keep in mind when working with codes. Codes are normally updated annually, and revised versions are published every three years. Typically, the revisions are not major, but it is important to know which code you must comply with. On some jobs the plans will indicate which codes apply. This information can usually be found on the cover page or with the general specifications in the plans. If the applicable code is not shown on the plans, ask the builder, owner, or whoever acquired the building permit about the code.

Time Delays

Another thing to keep in mind is the time that may elapse between when the code-writing organizations publish a revised code and when that code edition becomes the ruling code on the job you are framing. There are delays between when the code agencies certify the new codes and when the local government agencies review and approve them. There can also be delays between the date the permit is issued and the date the job is framed. It is not unusual to be working on plans that are three or four years or more behind the current building code. Although you have to comply with the code that is specified on the plans or that was used when the building permit was approved, you should also understand the current code because, in general, additions to the codes are improvements, or ways that contribute to making a building stronger. After every major earthquake or hurricane, codes have been adjusted and upgraded. By using the latest code, you can feel confident that you are framing with the latest construction knowledge.

Latest Code Used in This Book

This book uses the 2009 edition of the IBC and IRC to explain the major features of codes related to framing. These include structural requirements and life safety issues, and the spreading of fire. Although the code books may seem big and intimidating when you first see them, the number of pages that deal with framing are relatively few.

The following IBC & IRC Framing Index table is a handy list of all the framing sections of either code you might need. It was compiled based on the 2009 code books. In the IRC, the framing information can be found primarily in 4 of the total 43 chapters. In the IBC, 3 of the total 35 chapters deal with framing. The IRC framing chapters are 3, 5, 6, and 8. The IBC chapters containing framing information are 10, 12, and 23.

Important Code Features

What follows are key features of the code, and illustrations presented in a framer-friendly way. If you do a lot of framing, it’s a good idea to have a copy of the code book available for reference.

The three major categories used in the IBC are:

• Use and occupancy classification

• Fire-resistance-rated construction classification

• Seismic design categories

In the IBC, the seismic design categories are based on their seismic use group. The categories are A, B, C, D, Da, E, and F. Although they are similar to the categories in the IRC, there are some differences.