1. Drafting 2 – Honors Architecture Ardrey Kell High School
Floor Framing
Drafting 2 – Honors Architecture
Ardrey Kell High School
Charlotte, NC
Teacher: John Glenn

2. Floor Joists
Floor joists are the framing members that create the support system of a framed floor over a crawl space, basement, or floor below in a residential structure.
There are three materials commonly used for floor joists:
Dimension Lumber
Floor Trusses
I-Joists

3. Top & Bottom chords made of laminated veneer wood.
I-Joists
Top & Bottom chords made of laminated veneer wood.
I-joists are manufactured wood products that provide exceptional strength and durability, as well as structural efficiency.
They are made with a laminated veneer top and bottom chords, and a web made of oriented strand board.
I-joists are able to span much greater distances than dimension lumber, cost less, and are easier to install. This makes them the first choice for use in residential construction for most homebuilders.
Web made of OSB

4. Holes cut in i-joists for HVAC ductwork
I-joists are engineered to allow them to have the webs cut which allows for ease of running utilities through the floor system.
Cuts must be of a certain size, and are only allowed in specific locations, so care must be taken to ensure they are installed correctly.
The spacing of i-joists is typically 12, 16, or 24 inches on center. The closer the i-joists are spaced, the stronger the floor system.
Holes cut in i-joists for HVAC ductwork

5. Floor Trusses with metal webs
Floor trusses are modular, engineered units that are built in a factory and shipped to where they will be used. They are designed specifically for each individual application.
Loads are transferred through the truss chords and webs. Metal plates are used to hold the individual pieces together.
Trusses are lightweight, strong, and provide ease of use when running utilities through the floor system.
Floor Trusses with metal webs
Wood Floor Trusses

6. Metal plates rub against joist hangers causing squeaks in the floor.
Floor Trusses
A drawback common to floor trusses is that they sometimes cause squeaks in the floor system.
Squeaks are typically a result of the metal plates that are used to hold the truss together, rubbing against joist hangers that hold the joist at a girder connection
Metal plates rub against joist hangers causing squeaks in the floor.

7. The dimension lumber shown is 2x8 Spruce
Floor joists made of dimension lumber are not as common as they once were. With the invention of I-joists, and floor trusses, the use of dimension lumber has been greatly reduced.
Dimension lumber is simply large pieces of wood cut and processed directly from a tree. Typical sizes of dimension lumber used for floor joists are: 2x8, 2x10, 2x12 and 2x16.
Dimension lumber is heavier, more expensive, and does not allow for as long of spans as engineered products.
The dimension lumber shown is 2x8 Spruce

8. Girders
Floor Joists are often needed to span long distances, and in many cases these distances are too great for the joists to span safely.
Often mid-span support is required. In these cases, girders are used to support the middle of the joists.
Joists may either sit on top of the girder, or may be hung from the side of a girder.
Girders are usually multi-ply, meaning there are numerous beams nailed, or bolted together to form a single strong beam.
Joist
Girder
Joist Hanger

9. Girder with joists above, and supported by CMU piers
Girders
When girders are drawn on a foundation plan, they are typically called out as the example below shows:
(3) 2x10 SYP Built-Up Girder
This indicates that the girder is made of three 2x10’s that are laminated together with nails and/or bolts. The 2x10’s are made from Southern Yellow Pine.
For extra heavy loads, LVL’s are used instead of 2x10’s, or other dimension lumber. LVL’s are engineered wood beams. LVL stands for laminated veneer lumber.
Girder with joists above, and supported by CMU piers
CMU Pier

10. Girders
The girder shown on the left below shows joists hanging from the girder. The picture on the right shows the joists sitting above the girder.

11. Bridging
Bridging is used to stiffen the floor system by spreading loads over multiple joists.
Bridging is created by using wood or metal pieces placed diagonally between the joists.
The pictures at left illustrate each type of bridging.
Wood Bridging
Metal Bridging

12. Blocking
Blocking serves the same purpose as bridging in that it spreads loads over multiple joists, thereby stiffening the floor.
Blocking also serves as a way to ensure that the joists stay in a vertical position when a load is applied to them.
See the illustration at right for an example of blocking.
Blocking

13. Tongue and Groove Connection
Floor Sheathing
Floor sheathing is the structural component of a building that forms the subfloor of a residential structure.
The subfloor is the surface that carpet, tile and other flooring materials are placed upon.
Most sheathing is T&G plywood or Oriented Strand Board (OSB). T&G plywood has a tongue and groove cut into the edges so that they form an interlocking panel that can be laid flat upon the floor joists. The sheathing is held down by glue and nails or screws.
Tongue and Groove Connection

14. Floor Sheathing
The picture on the right illustrates the installation of floor sheathing on the floor joists.
Floor sheathing is generally 5/8” or 3/4” thick

15. End of Presentation