Floor Trusses vs Floor Joists: Explained

Floor trusses are an assembly of top and bottom chords separated by diagonal braces, while floor joists are horizontal members that connect beams. Floor trusses have a higher load-bearing capacity and provide greater span lengths, reducing the need for additional support. However, they are more expensive than floor joists.

Floor Trusses vs Floor Joists - Differences Explained

Floor trusses and joists are two distinct ways of supporting the span of a floor.

Here are the differences between them:

Characteristic	Floor Trusses	Floor Joists
Definition	Floor trusses are an assembly of top and bottom chords separated by diagonal & vertical braces	Floor joists are horizontal structural components that frame an open space. They usually exist between beams to transfer floor load to vertical members.
Configuration	They are made using treated lumber in a controlled factory environment.	Joists are made using treated lumber on-site.
Load-bearing capacity	High load-bearing capacity.	low load-bearing capacity in comparison to floor trusses.
Need for Intermittent support	Do not require intermittent support.	Require intermittent support like beams and posts.
Response against Bouncing	Excellent at preventing floor bounce.	Since floor joists shrink when they dry, they have less resistance against bouncing.
Frequency	Floor trusses are less in number in any structure.	Most structures require floor joists in abundance.
Span	Large spans are possible	Short spans only
Cost	Expensive	Cheap

Floor trusses are manufactured using high-quality lumber to meet the design requirements. 

All the joints of a floor truss are fastened and secured by heavy gauge steel plates. 

Additionally, they transfer the floor loads to load-bearing walls or other structural supports. 

Floor joists also take the loads from the floors and transfer them to the beams or vertical members.  

They are parallel and equidistant from each other and laid perpendicular to load-bearing beams. 

Generally, the center-to-center spacing between two adjacent joists is 16”.

A subfloor sheet of plywood is laid on the top of floor joists and nailed to the joists to make a large floor area. 

However, the problem of bouncy floors is a common issue in the case of wooden floor joists.

This happens due to the shrinking and warping of wood joists, causing the floor to move against the driving nails.

In modern-day construction, engineered timbers like I-joists are used. These products have considerably lower shrinkage issues.

Because of their easy installation and low cost, various types of floor joists are used in residential buildings. 

It is also important to choose lumber of the right size and grade for your floor joist.

Opt for an I-joist instead of a traditional wooden joist if you go with a floor joist system.

The choice between the two types is dependent on your requirements and budget.

A composite floor deck is another approach to reinforce your floor system without adding extra weight to the structure.

You might be interested in this:

Joists vs Beams vs Girders: Differences Explained

Floor Trusses vs Floor Joists- Configuration

Floor trusses result from the assembly of one or more triangular units created by connecting straight members in a controlled factory environment.

These members connect through steel plates of suitable strength, and the point where they meet is referred to as a node.

The top and bottom chords in these trusses are generally 2.5 and 3.5 inches wide.

In contrast, joists are straight members that form a horizontal framework and require more material to offer equal strength to the truss.

Load-Bearing Capacity Difference

The geometry of the triangles in floor trusses results in less deformation when subjected to loads, resulting in a higher load-bearing capacity than floor joists.

However, floor joists can deform when they are subjected to heavy load over a long period. 

Moreover, floor trusses have self-support systems, while floor joists require intermittent supports like beams, columns, and posts. 

If there is a need to support lateral and vertical loads, then floor trusses are a better choice for your structure. 

In contrast, floor joists cannot support lateral loads, and you have to install blocking between floor joists to support lateral loads, which raises the overall budget of your construction.

Stability Difference

In terms of stability of the structure, floor trusses can create a more stable floor structure than floor joists. 

They easily absorb impact loads, offering adequate support to your building.

Also, the tendency of twisting is very low in floor truss systems. 

The nailing surfaces are also wide, which allows easy gluing and attachment of floor sheathing.

Moreover, since floor trusses are formed by 2x3 or 2x4 lumber, shrinkage due to drying of lumber is negligible, providing a non-bouncy floor. 

Conversely, floor joists, when not properly supported and fastened at their ends, can twist and become less stable.

For this reason, band joists are an essential component of a strong floor joist system.

Are Floor Trusses Stronger than Floor Joists?

The strength of trusses is dependent on the specifications and the structural requirements. 

If you want to support a large span, then floor trusses are stronger because they can span large lengths with a deflection of only a few inches.

Because they can span over a larger length, you also don't need to provide intermittent beams and walls. 

Additionally, for supporting the same load conditions, trusses require less material compared to floor joists, making them a lightweight option.

Also, the spacing between two consecutive trusses can be much more than the spacing between floor joists. 

If your floor joists are sagging, there are ways to strengthen the joists from below.

Sistering of the joists is a widely used technique to strengthen the joists.

Are Floor Trusses Cheaper than I-Joists?

A major difference between I joists and floor trusses is their cost.

I-joists are much cheaper than floor trusses. 

If your span requirement is shorter than the length of your I-joist, you can trim it and proceed with the framing.

However, this is not possible in the case of floor trusses.

The manufacturer designs and builds it according to your requirements. This means a floor truss system arrives after an elaborate process, increasing the construction time.

How Far Can You Span with Floor Trusses?

The span of a floor truss is highly dependent on the material of the truss and loading conditions. In general, a wooden floor truss can span over 30 feet or more. 

However, manufacturers can increase the length of the span with suitable designs and materials. 

There is no specific building code that limits the length of a floor truss. 

The only requirement of a floor truss is that it should be strong enough to handle the load imposed and result in a bounce-free floor.

Frequently Asked Questions (FAQ)

Can Floor Trusses be Used for the Roof?

Floor trusses are designed to absorb loads from flat surfaces and pose a challenge when dealing with inclined roofs.

You have to make special bearing arrangements at the end of floor trusses so that they can rest on vertical members properly.

Why do Floor Trusses Have a Built-in Camber?

Cambers are slight upward arches or curves created between two chords of floor trusses to address dead-load deflections.

Pay careful attention during installation to prevent improper fitting of the members.

Which Floor Trusses Work Best?

Open-web trusses are the best choice for most construction projects since they are flexible and allow for easy installation of utilities.

However, you also need to consider the project's requirements while selecting a truss type.