Though floor trusses and floor joists both support the floor of a structure, there are some major differences that make them distinct.
The difference between floor trusses and floor joists is that 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 compared to floor joists.
Floor Trusses vs Floor Joists - Differences Explained
|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|
Floor Truss vs Floor Joist
Floor trusses and joists are two distinct ways of supporting the span of a floor.
Because of their easy installation, various types of floor joists are used in residential buildings.
There are some instances where floor trusses become necessary.
A good example is in commercial buildings.
The choice between the two types is dependent on your requirement and budget.
A composite floor deck is another approach to reinforce your floor system without adding extra weight to the structure.
Floor trusses vs Floor Joists- Configuration
Floor trusses are formed by the assembly of one or more than one triangular units. These triangular units are formed by connecting straight members in a controlled factory environment.
These members are connected through steel plates of proper strength and the meeting point of members is called nodes.
However, a joist is a horizontal diaphragm of a floor structure. It is long and heavy lumber that takes the load from the floor.
Often supported by beams, a huge number of joists are laid at a distance of only a few feet.
A truss offers equal strength to a solid beam or girder by efficiently using less material.
On the other hand, a joist requires more material to offer equal strength to the truss.
Load-bearing Capacity Difference
The load-bearing capacity of trusses is higher than floor joists.
The triangles in floor trusses deform much less when they are subject to load because of their geometry.
However, floor joists can deform when they are subjected to heavy load over a long period.
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 as well as vertical loads then floor trusses are a better choice for your structure.
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.
In terms of stability of the structure, floor trusses can create a more stable floor structure in comparison to floor joists.
Floor trusses provide a wide and stable bearing surface which leads to better stability. The tendency of twisting is very less in floor truss systems.
Since floor trusses are formed by 2x3 or 2x4 lumber, shrinkage due to drying of lumber is negligible, providing a stable and non-bouncy floor.
In the case of floor joists, the connections can loosen up because of the drying of lumber. This can result in more movement of the floor.
Floor trusses can easily absorb impact loads which can be critical in some contexts.
Floor trusses also provide deep-rooted structural support to your building.
If the ends of floor joists are not supported and fastened properly, then they are prone to twisting. This makes them relatively less stable.
For this reason, band joists are an essential component of a strong floor joist system.
If stability is a high priority, then floor trusses are a better choice.
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 millimeters.
Because they can span over a larger length, you do not need to provide intermittent beams and walls.
For supporting the same load conditions, trusses require less material compared to floor joists.
Also, the spacing between two consecutive trusses can be much more than the spacing between floor joists.
Because of less material consumption, trusses are lightweight.
In addition to all these things, they provide a wider nailing surface for proper nailing strength.
Floor trusses offer better strength and stability than floor joists in larger spans.
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.
In fact, Floor trusses are one of the most expensive floor support systems.
If your span requirement is shorter than the length of your I-joist, you can trim it and proceed with the framing.
This is not possible in the case of floor trusses.
You have to order your floor trusses according to your requirements.
The manufacturer designs it, and builds it according to your requirements. This means a floor truss system arrives after an elaborate process.
This can increase the time it takes to complete construction.
Though trusses require less material, their manufacturing cost is high because trusses are custom-made.
On the other hand, an I-joist is a mass-produced standardized product that costs much less.
How Far can you Span with Floor Trusses?
A 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 span with suitable design and material.
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.
What are the advantages of a Floor Truss system?
- Floor trusses facilitate a wide and stable bearing surface that makes them perfect for seamless working around them.
- Nailing surfaces are wide which allows easy gluing and proper attachment of floor sheathing.
- Minimum shrinkage, twisting and warping.
- Reduced need for intermittent beams, walls, and columns.
- Open spacing in floor trusses facilitates easy run of plumbing and electrical runs.
Are Floor trusses worth it?
Floor trusses require a higher initial investment compared to other floor support system. However, they generally pay for themselves in the long run.
The lack of any bounce on the floor is the biggest advantage.
What is a Floor Truss?
Floor trusses are designed and manufactured using high-quality lumber to meet your design requirements.
Trusses were first used in bridges to support long spans.
Because of their tremendous advantages and versatility, engineers also started using them in modern building designs.
Floor trusses have top and bottom chords that are separated with diagonal or vertical components. These components, by joining together, create a series of multiple interconnected triangles.
All the joints of a floor truss are fastened and secured by heavy gauge steel plates.
The top and bottom chords are generally 2.5 and 3.5 inches wide. These dimensions make gluing, nailing, and screwing processes easier.
The open webs of a floor truss eliminate the need for drilling or cutting and allow easy placements of plumbing pipelines, HVAC, electrical conduits, etc., and also encounter the bouncing of the floor.
Floor loads are also transferred by trusses to load-bearing walls or other structural supports.
What is a Floor Joist?
Floor joists span over a large open space, generally between load-bearing walls or intermittent beams.
They are the part of your floor assembly that carries the weight of everything inside your room e.g. furniture, walls, appliances, and even the weight of residents also.
Floor joists are horizontal members that take the loads from the floors and transfer them to the beams or vertical members.
Floor joists span throughout the floor area and provide support to the floor.
Floor joists are parallel and equidistant from each other and laid perpendicular to load-bearing beams.
A subfloor sheet of plywood is laid on the top of floor joists and nailed to joists to make a large floor area.
If you want to construct a house then floor joists are a popular and cheap option for your floor system.
Generally, the center-to-center spacing between two adjacent joists is 16”.
However, depending upon the exact structural requirements and local building code provisions, spacing between joists can be modified.
The dimensions and spacing of floor joists are highly sensitive to the distance between supports and the loading environment.
The problem of bouncy floors is a common issue in the case of wooden floor joists.
When wooden joists dry, they shrink and warp.
Because of this, the floor can move against the driving nails and causes a squeaky floor system.
In modern-day construction practice, engineered timbers like I-joists are used. These products have considerably lower shrinkage issues.
Because of the easier installation and low cost of floor joists, you will find them in most residential buildings.
It is very important to choose lumber of the right size and grade for your floor joist.
If you choose the wrong lumber, there is every possibility of your floor joist snapping.
Most licensed contractors can help you choose the right lumber for building the joist.
Unlike floor trusses, floor joists require supports either from beams or walls and they span perpendicular to the length of a room or beam.
Floor joists are found in abundance in most residential buildings.
If you are looking for a convenient, easy to install, and cost-effective solution for your floor, then joists are a good option.
Opt for an I-joist instead of a traditional wooden joist if you go with a floor joist system.
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Frequently Asked Questions (FAQ)
Can trusses span 40 feet?
Trusses can span 40 feet and are quite common in residential as well as commercial buildings.
As the span increases, the cost of the truss system also increases exponentially.
Since trusses can not be framed on-site and are usually framed off-site, it is framed in small parts for the sake of easy transportation and then connected by a suitable fastening method.
Can floor trusses be used for roof trusses?
Floor trusses are designed to absorb loads from flat surfaces. Since roofs are inclined in most cases, there can be a possibility of failure of floor trusses to absorb loads from the roof surface.
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 arch or curves that are intentionally created between two chords of floor trusses.
Cambers in floor trusses are usually intended to compensate or to hide dead-load deflections.
These cambers should be provided very carefully otherwise they can create an improper fitting of members.
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