Floor Joists: Types & Construction Details

A floor joist is a structural member in a building’s construction that supports the floor. They run perpendicular to the floor beams and provide the necessary strength and stability to the flooring system. Floor joists are typically made of wood, steel, or a combination of both, and are placed in a uniform spacing to create a grid-like structure.

The material used, spacing, and thickness of the joists depend on the load they need to support, the height of the floor, and the type of flooring system used. Floor joists are a crucial component of a building’s structure and play a critical role in determining the overall strength and stability of the floor.

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Types of Floor Joists

Here most commonly used types of floor joists are given below,

1. I Joist

I-Shaped floor joist is an engineering type wood joist, also it is known as a TJI Joist because they look like the capital letter I.

Different parts of the joist are made of different materials like Top and bottom parts of the joist are made with a laminated veneer or wood and the center part is made with an oriented strand board (OSB) or plywood.

Those have a long span and eco friendly in nature and carry higher loads than solid timber.

Another side joists cannot resist fire or water.

Advantages of I-Joists

This is having a longer span than solid wood joists.
These joists are easy to place.

Disadvantages of I-Joists

I-Joists are failing quickly during the fire accident.
These joists are costly.

2. Solid Lumber Joist

Solid Lumber Joists are made up of old-growth trees and solid timber.

The cost of solid lumber joists depends on the various factor,

Size of Boards.
Grade of Wood.
Quality of Wood.
Life Span of Wood.

Advantages of Solid lumber joists

It last longer.
It is less expensive as compared to engineer-type wood.

Disadvantages of Solid lumber Joists

It is not environmentally friendly.
It is designed for a Shorter Span.

3. Open-Web Floor Trusses Joist

If you are looking for a joist that offers a range of various longer spans, ranges of depth, and Load carrying capacity then go for this open web floor type.

Wood Trusses are a having a low moisture capacity and shrink less.

Advantages of Open web Floor Truss

These joists are suitable for a longer span.
These joists accommodate the passing plumbing, electrical, and water supply line without cutting.

Disadvantages of Open web Floor Truss

This is Costly as compared to I-Joists.
These joists are difficult to Trimmed.

4. Steel Joist

Steel joists are a type of structural element used in construction to support the floor or roof of a building. They are made from rolled steel shapes and are designed to be lightweight, strong, and durable.

Steel joists are commonly used in commercial, industrial, and high-rise construction, where their ability to span long distances and support heavy loads is a key advantage.

Floor Joist Spacing

Mostly, floor joist spacing is kept between 12″ to 24″ Inches apart from the center, but it depends on the size of the floor joist timber size, building codes, and requirements of the design.

The following table shows the standard floor joist spacing with different sizes.

	12″	16″	24″
2 x 6	10 – 10	9 – 10	8 – 7
2 x 8	13 – 1	12 – 4	11 – 3
2 x 10	15 – 3	14 – 4	13 – 6
2 x 12	17 – 2	16 – 2	15 – 3

Calculation of Joist Size

For example, if you had a floor in a room that spans 16 feet, you would divide the room span and get 8 feet, and then ass two means 10.

That means you need a depth of joist that will be 10 inches.

The Standard Size of floor joists is 2×8, 2×10, and 2×12.

Advantages of Floor Joist

The following advantages of Floor Joists are Common, which are not dependent upon the type of joist,

They are vertical members and work as a beam transferring a load to the ground.
The joists support the structure.
They are bearing the live load, Dead load, and impact load.
The Joists are sufficient to carry the weight of whole new floors.
The installation process of floor joists is affordable.

Disadvantages of Floor Joist

The following Disadvantages of Floor Joists are Common, which are not dependent upon the type of joist,

They are not suitable for large areas.
They are not placed without the support of walls, columns, and beams.
The Joists have more weight as compared to other trusses.
The joists have a limitation in design and model.

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Floor Joists: Types & Construction Details