What Is Floor Joists & 3 Types of Floor Joists

8 min readMar 14, 2023

What Is Floor Joists & 3 Types of Floor Joists

What Are Floor Joists?

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.

Floor Joists

For floor joists used high-quality timber which is help to give durability, evenness of floor, and strength.

This joist must be closely spaced and fixed in nature so that it sufficiently takes all loads like live load, dead load, impact load, and sagging of flooring, prevent bending, etc.

Floor Joist load capacities depend upon the following factors,

- Grade of timber or lumber.

- Species of Wood.

- Length of the joist span.

- The load was placed on the floor.

- Width of Timber Boards

- The thickness of Timber Boards.

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 610–109–108–72 x 813–1 12–411–32 x 1015–314–413–62 x 1217–216–2 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 2x8, 2x10, and 2x12.

Types of Floor Joists

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

- I Shaped Floor Joist

- Solid Lumber

- Open Web Floor Joist

1. I Joist

I-Shaped Floor 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 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

Open Web Floor Truss 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.

Some of the benefits of using steel joists include:

Strength: Steel is one of the strongest materials used in construction, and steel joists are designed to withstand heavy loads and resist bending and twisting.

Durability: Steel is highly resistant to corrosion, fire, and other environmental factors, making steel joists a long-lasting and low-maintenance option.

Cost-effectiveness: Steel joists are typically more affordable than other types of joists, such as solid-sawn lumber or engineered wood.

Versatility: Steel joists are available in a wide range of sizes and shapes, allowing for customization to suit specific construction needs.

Ease of installation: Steel joists are typically prefabricated, which makes them easy to transport and install on-site.

Factors to Consider When Choosing Floor Joists

Choosing the right type of floor joists is an important consideration for any construction project, as the joists will determine the structural integrity, stability, and safety of the building. When selecting floor joists, there are several key factors to consider:

Load Capacity: Floor joists must be able to support the weight of the floor and the people and objects that will be on it.

The load capacity of the joists will depend on factors such as their size, shape, and material, so it is important to choose joists that are suitable for the intended use.

Span: Floor joists must span the distance between supports, such as walls or beams. The span of the joists will impact the height of the floor and the amount of space available below it, so it is important to choose joists that are suitable for the intended span.

Dimensional Stability: Floor joists must maintain their shape and size over time, without warping or twisting. The dimensional stability of the joists will depend on factors such as their material and the environment in which they will be used, so it is important to choose joists that are suitable for the intended use.

Cost: Floor joists are an investment, and the cost of the joists will depend on factors such as their material, size, and shape.

It is important to choose joists that are within the budget for the project, while also considering factors such as their load capacity, span, and dimensional stability.

Availability: Floor joists must be readily available for the project, and it may be necessary to consider alternative options if the preferred type of joist is not readily available.

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.

Conclusion:

In conclusion, floor joists are a critical component of any construction project, and play a vital role in determining the structural integrity, stability, and safety of a building.

There are several types of floor joists available, including solid sawn lumber, engineered wood, steel, and concrete, each with its own unique benefits and limitations.

Choosing the right type of floor joists is an important consideration, and requires careful evaluation of factors such as load capacity, span, dimensional stability, cost, availability, and environmental considerations.

Whether you are building a residential or commercial structure, selecting the right type of floor joist will help ensure the long-term success of your project.

FAQs:

What is a Floor Joist?A Floor Joist is a timber beam that is perpendicular to the beam and parallel to the walls for providing a supportive framework for flooring.
This Floor Joist is play a very vital role in the subfloor structure, because they carry the dead load of the furniture, flooring load, vibration of people walking and impact load, etc.What are the advantages of Floor Joist?Floor Joists are vertical members and work as a beam that transfers a load to the ground.
The Floor joists support the structure.
Floor Joists are bearing the live load, Dead load, and impact load.
Floor Joists are sufficient to carry the weight of whole new floors.
The installation process of the floor joist is affordable.What materials are floor joists made of?Floor joists are typically made of wood, engineered wood, or steel.How much weight can a floor joist support?The weight a floor joist can support depends on several factors, including its size, material, and spacing. A 2x8-inch joist, for example, can typically support up to 5,000 pounds.What happens if floor joists are too weak?If floor joists are too weak, they may sag, deform, or even collapse, causing damage to the floor and the building.

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