Floor Joist Explained: What It Is and Why It Matters

Whenever a new structure has to be constructed, structural integrity and strength are two main factors that cannot be overlooked.

If so, it may result in severe consequences, like premature cracking, early damage, and, worse, complete collapse. Over the years, strict regulations and practices have been introduced in the construction industry for structural safety.

These help constructors ensure every component of a building can exhibit strength and stability in all circumstances. One such practice that has become an integral part of every project is building floor joist.

You can consider them to be a support framework that strengthens the entire floor from within. Placed between beams or planks, these distribute the pressure evenly.

By doing so, they ensure durability and an extended lifetime of the entire building. With this in mind, we have outlined the significance of a floor joist in every project, regardless of whether it’s a simple house or a colossal apartment.

Floor Joists: Moving Beyond Beams and Planks for Construction

Vertical structural components like beams and planks give the shape desired for the floors. However, they have a humongous amount of open space in between.

When the subfloors and top layers are constructed, they put a lot of pressure on them. Over time, the load applied exceeds their tolerance limit, causing cracks to develop. If left unattended, the floors can collapse.

To prevent this from happening, constructors use a special horizontal structure to fill up the open space between the beams and planks.

This is known as a floor joist, and it is positioned at an exact 90-degree angle with vertical structures. Wooden or steel beams are positioned parallel to one another. Equal spacing is maintained between every horizontal beam to ensure uniform load distribution.

Types of Floor Joists: Detailed Illustration

Solid Lumber Joists

• Solid hardwood is used to make planks of varying thicknesses and sizes.
• Span distance is dependent on numerous variables, including deflection, board size, spacing, and species.
• They are most resistant to fires and can offer greater safety.
• Solid hardwood planks are hard to acquire due to dependency on trees.
• Also, the span distance is very limited, which further restrains customization.

I-joists

• These look just like the English alphabet I. Each section comprises three parts, namely the top and bottom horizontal planks and a middle vertical plank.
• Laminated veneer or hardwood is mostly used for the top and bottom parts. On the other hand, the middle plank is usually made from Oriented Strand Board or plywood.
• I-joists can last longer than the solid lumber floor joist.
• They do not weigh much due to the use of plywood and laminated veneer. This makes maneuvering in tight spaces easy.
• Fire resistivity is not as much as compared to lumber planks.
• The upfront investment for building I-joists can increase the overall project budget.

Open-Web Floor Trusses

• Cantilevered wooden planks and beams are used to create the supportive floor joist structure.
• Since it has an open structure, no additional hole has to be made for accommodating pipes and electrical wires.
• Also, most floor trusses do not require accurate measurements for construction.
• Joints are highly durable and can last for a long time.
• The span distance is quite huge compared to other types of floor joists.
• The wooden planks have very specific lengths, which largely restrict trimming.

Significance of Floor Joists in Construction

Structural Support With Even Load Distribution

The entire horizontal structure created with a floor joist helps in even load distribution. It doesn’t allow the stress to accumulate at any single point.

As a result, the entire structure retains its integrity for years to come. The joists are made to offer perfect balance to two load types, namely:

• Dynamic weights due to the movement of furniture, people, and appliances.
• Static load from the subfloor, flooring materials, and other structural components.

The vertical beams and planks won’t have to bear the entire load all by themselves. Hence, the risks of sudden collapses can be reduced greatly by including a floor joist in between.

Framework for Flooring Materials

Floor joists provide a great framework for constructing the top layers easily. The planks are thick enough to support the following:

• Subfloors: The structural layer of any flooring that provides thickness and stability to the buildings. These can be of various types, like OSB, concrete, and even plywood. With joists underneath, their installation won’t be very difficult.
• Top flooring layer: Most joists are designed in a way to bear the weight of the topmost floor layer. It can be made from laminated planks, plywood boards, carpets, and several other components.

Apart from this, a floor joist also allows soundproofing and thermal insulation. The open spaces between the horizontal planks dampen the sound waves, thereby ensuring echoes or reverberations can’t be heard from other rooms.

With proper installation, it can also make the rooms thermally insulated, preventing any heat exchange.

Increased Floor Stability and Strength

The vertical beams or planks are usually placed at a great distance from one another. Owing to this open space between them, the floors are at greater risk of sagging, cracking, and collapsing.

This is where a floor joist comes into the picture! 

• Most joists are placed in a way so that the floor doesn’t feel unstable or bouncy under extreme loads.
• These help in maintaining proper floor leveling without any unevenness.
• They also prevent cracking, warping, and any other type of long-term structural damage in the floor.

Easier Mechanical and Electrical Installations

Thanks to a well-constructed floor joist, installing mechanical and electrical components is hassle-free. The open space between the planks is primarily used to create a route for:

• Plumbing pipes for drainage and water supply
• HVAC ductwork
• Electrical wires

Closure

Constructing a floor joist can improve the overall structural stability and safety of any building. It not only distributes the weight evenly but also prevents the floor from long-term damage.

However, every constructor needs to select the right joist type based on the desired span distance, overlaying floor layers, and the overall project budget. Only then its benefits can be harnessed completely.