What is a floor joist?
A floor joist is a horizontal structural component that spans an open space between beams that transmit the load to vertical structural components.
These joists, a component of the floor system, support the weight of the walls, furnishings, appliances, and even humans inside a room.
Because they support the dead loads of the flooring and furniture as well as the impact and vibrations of humans walking, the floor joists are crucial to the subfloor.
The typical floor joist spacing is 16 inches apart in the centre; however, this can change based on local building regulations and the construction specifications, as shown in the blueprint.
The joist should be made of high-quality wood to ensure a sturdy, long-lasting, level, and even flooring.
The following factors impact floor joist load capacities,
- Grade of timber or lumber.
- Wood Species
- Span Length
- Spacing between joists
- loads on the floor.
- Boards Width and thickness
Floor Joist Size And Spacing
Floor joists come in a variety of sizes and types. The most frequently used sizes are 2×6, 2×8, 2×10, and 2×12.
Floor joist spacing is typically kept between 12′′ and 24′′ apart from the centre, but this varies depending on joist size, timber size, building codes, and design requirements.
The table below shows the standard floor joist spacing for various sizes.
|Span in Feet||Standard Size||Spacing in inches|
|6,7 and 8||2×4||16|
Floor joists are normally 16 inches apart (measured from the centres of the joists). In this manner, as shown in the picture below, we can install an 8-foot (or 96-inch) long flooring spanning seven joists:
Although we can place our joists closer or farther apart than 16 inches, the following alternative on-centre spacings are common:
|Spacing In Inches||Number of joists beneath an 8-foot-long subfloor|
The distance between two supporting structures is known as a joist span. To assure accuracy, structural engineers typically calculate the spans.
Generally, greater joists are employed in larger structures. Floor joist spans, however, depend on factors including the type of floor joist, the type of dimensional lumber used to make them, and building codes.
It is essential to know that there are no standard joist sizes. While determining the proper joist size and span, different factors must be considered.
Joist Size Calculation
The depth required for a floor joist can be calculated using a simple formula: half the span plus two.
If a room’s floor were 16 feet long, for instance, divide that amount in half (eight) and then add two. As a result, the joist depth must be 10 inches.
Types of Floor Joists
Following are the floor joist types that are most frequently used.
- I Shaped or TJI joist:
- Solid Lumber
- Open Web Floor Trusses
An I-Shaped floor joist is a type of engineering wood joist. It’s also known as a TJI Joist because it resembles the capital letter I.
Various parts of the I are built using different materials. Wood or laminated veneer is typically used for tops and bottoms. Oriented strand boards (OSB) or plywood are frequently used as the centre support.
They have a longer span, are more environmentally friendly, and can carry heavier loads than solid wood.
Another side joist is not fire or water-resistant.
Advantages of I-Joists
- It Spans a greater distance than solid wood joists.
- These joists go up quickly.
Disadvantages of I-Joist
- During the fire, the I-joists failed quickly.
- These joists are costly.
Old-growth trees and strong wood are used to create solid lumber joists.
The price of solid lumber joists is determined by several factors, including board dimensions, wood grade, the wood’s quality, and wood life expectancy.
The Benefits of Solid Lumber Joists
- During a fire, it lasts a long time.
- It is less expensive than engineered wood.
The Drawbacks of Solid Lumber Joists
- It isn’t good for the environment.
- It’s intended for a shorter span.
Open Web Floor Trusses
If you’re looking for a joist with a variety of longer spans, depths, and load-carrying capacity, this open web floor truss type is for you.
Wood trusses have a low moisture capacity and shrink less than steel trusses.
The Advantages of Open Web Floor Truss
- These joists can support larger spans.
- These joists allow plumbing, electrical, and water supply lines to pass through without being cut.
The Cons of Open Web Floor Truss
- It is more expensive than I-joists.
- They are challenging to trim.
The following are common benefits of floor joists that are not dependent on the type of joist.
- They are horizontal components that act as a beam that helps to transmit loads to the ground.
- It helps to provide structural support.
- They bear the live, dead, and impact loads.
- They can support the weight of the entire new floor.
- Its installation is a cost-effective process.
The following are common floor joist disadvantages that are not dependent on the type of joist.
- They are not appropriate for large areas.
- They are not installed without the assistance of walls, columns, and beams.
- They are heavier than other types of trusses.
- They have design and modelling limitations.
The heavy lifting in a room is done by the floor joists, which hold up the floor and everything on it.
It’s crucial to select the ideal floor joists (material, size, etc.) for your particular requirements.
Despite the availability of span tables and joist calculators, a structural engineer should calculate the necessary joist specifications following the engineering of the building and local building codes.
What exactly is a floor joist?
It is a horizontal structural component that spans an open space between beams that transmit the load to vertical structural components.
What are the benefits of using floor joists?
They are horizontal members that function as beams to transmit loads to the ground.
It helps to provide structural support.
They bear the live, dead, and impact loads.
They can support the weight of the entire new floor.
Its installation is a cost-effective process.
What are the different types of floor joists?
The most common types of floor joists are as follows.
I shaped or TJI
Open Web Floor Trusses