Floor joists are horizontal load-bearing structures that span between walls or between a beam and a wall. They provide primary support to the floor systems. There are several types of floor joists available, each with its own merits. These include traditional lumber joists, engineered joists, and open web trusses.
This article discusses various types of floor joists to make an informed decision when choosing the appropriate type of floor joists.
3 Types of Floor Joists: Most Used
Three kinds of floor joists are most popular in the USA:
- Lumber Joists
- Engineered Joists
- Open Web Trusses
|Criteria||Traditional Lumber Joists||Engineered Joists||Open Web Trusses|
|Structural Configuration||Horizontal solid rectangular block||A horizontal beam-like structure in rectangular or I-shapes||Triangular configurations of beam-like components|
|Assembly||Direct installation on-site||Direct installation on-site||Need to be assembled before being delivered to the site for installation|
|Load Bearing Capacity||Low load-bearing capacity||High load-bearing capacity||Very high load-bearing strength|
|Frequency||The highest number of traditional joists are required||A relatively high number of floor-engineered joist panels are required||A small number of floor trusses are required|
|Holes||Holes are drilled||Holes are drilled||Already present|
|Span||Least span lengths||Smaller than trusses but higher than traditional joists||Possible to construct large spans of a room|
|Cost||Cheapest||Cheaper than trusses||Floor and roof trusses are very costly|
|Alterations||Easy to alter and manage||Easy to alter even after installation||Hard to alter truss systems after installation|
2x10 Lumber Floor Joists
2x10 wood joists are the traditional standard floor joists that have been widely used in residential construction for a long time.
These floor joists are horizontal, solid wood blocks used to support floors and are made of various wood types such as Spruce, fir, and Pine.
Due to the finishing process, the actual size of 2 x 10 is 1 1/2”x 9 1/4”.
These joists offer sufficient strength for a relatively low cost.
Additionally, they are easy to install, handle and replace.
However, these joists can only span up to 16’, a relatively smaller span length than engineered joists and open web trusses.
Engineered Floor Joists
Engineered floor joists have been increasingly replacing traditional lumber joists for some time now.
Compared to traditional 2x10s, they dissipate floor loads onto beams but more efficiently.
Engineered joists are typically available as I-shaped joists and are lighter than traditional lumber.
They consist of two flanges and a web and provide resistance against shear and bending forces.
Additionally, they are more durable and lightweight.
Typically engineered I-joists span up to 48’ but spans as long as 60’ are also possible.
Their depth ranges between 9 ½” to 16”, whereas the widths range from 2 ½” to 3 ½”.
Open Web Trusses
In contrast to engineered I joists, open web trusses offer greater strength, feasibility, and flexibility in design.
Open web floor trusses are also capable of spanning greater lengths than other joists and can meet complex design requirements.
They also have openings in their design that allow the passage of plumbing and electrical systems.
However, they are more expensive than traditional floor joists and are more common in large-scale projects than in residential construction.
A composite floor deck can also be used to strengthen a floor system without adding extra weight.
How to Strengthen Floor Joists?
Floor joists tend to degrade over time and lose their strength, resulting in sagging and uneven surfaces.
There are many ways to strengthen floor joists to avoid such problems.
One way is to provide beam-column supports at the mid-spans of the joist panels used under the floors.
This is an effective method for improving joist performance, but it reduces the free space in a room.
Another technique is to use sistering joist panels to secure already present joists, which are installed on both sides of a joist.
Metal wrapping is also a popular method for increasing joist strength and transferring the loads from the center to the ends of a joist.
Steel can also be directly used to reinforce the joist panels, increasing their strength and durability.
How Much Do Floor Joists Cost?
Normally, a traditional 2x10 joist costs about $30 for a 16’ span, whereas an engineered 2x10 joist costs around $40 for a span of 16’.
Floor trusses, on the other hand, cost around $4.40 per foot.
The cost of floor joists changes with the design requirements, specifically their lengths and sizes.
A floor joist's cost also depends largely on the material from which it is constructed.
Wooden floor joists are relatively cheaper than steel floor joists.
Frequently Asked Questions (FAQ)
What is the Common Spacing Provided Between Floor Joists?
According to the International Residential Code(IRC), the typical spacing between floor joists is 12”, 16”,19.2”, and 24”.
For most residential constructions, a spacing of 16" is used.
Can you Drill Holes in Engineered Floor Joists?
You can drill engineered floor joists to provide passage for plumbing ducts and electrical wiring.
However, the hole size should not exceed one-third of the joist depth.
How to Find the Location of Floor Joists?
Stud finders are an effective tool to find the location of floor joists.
Alternatively, gentle tapping with a hammer can indicate the presence of joists by their sound differences.