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Engineered Floor Joists: Complete Guide



V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com


Engineered I-Joists.

Engineered floor joists are made of wood strands bonded with adhesive. They are stronger and lightweight than traditional joists and can span up to 60 feet. However, they are more expensive than traditional joists. One of the most common types is I-joists.

A single batch of engineered joists is generally enough for constructing an entire house.

Variation in Engineered Joists.
Variation in Engineered Joists.

What are the Types of Engineered Floor Joists?

Typically, there are two types of engineered floor joists that are frequently used in floor and roof systems:

  1. Wooden I-Joists, with dimensional lumber top and bottom flanges and an oriented strand board (OSB) web.
  2. Open Web Trusses consist of wooden webs held by metal plates.
PropertyEngineered I-JoistEngineered Truss
ShapeHorizontal I-shaped membersTruss-shaped members
PreferenceSmall-scale projects Large-scale projects
OpeningsHoles need to be drilledHave existing openings
SpansRelatively shorter spans Longer spans
CostCheaper More expensive
Engineered I-Joist vs. Engineered Truss

Wooden I-Joists

Just like an I-beam, an I-joist consists of two flanges at the top and bottom and a web in between.

This configuration effectively resists the loadings on the joist.

I-joists have major applications in residential construction. Their shape is excellent for resisting shear forces and bending moments.

Moreover, compared to 2×10 lumber, I-joists can carry more loads.

The flexible nature of these joists also allows their length to be adjusted easily.

Additionally, I-joists cost less than other alternatives.

While they cannot achieve the same spans as open web trusses, they are easier to work with.

In contrast, traditional lumber joist span limits are lower when compared to I-joists.

Running electrical wiring and plumbing ducts through I-joists is also a hassle due to the presence of the OSB web.

Engineered I-Joist.
Engineered I-Joist.

TJI joists, a recently introduced type of engineered joists, are now available in the market.

They closely resemble the geometry of I-joists while offering a lighter-weight alternative.

Open Web Trusses

Open web trusses are a superior version of engineered joists and can span longer than I-joists.

They have openings in their webs, allowing passage for wires and ducts.

However, open web trusses, when compared to I-joists, are more expensive.

Replacing a truss during construction can also cause project delays because trusses are custom-made for a specific project.

Furthermore, open web trusses require a rim board or band joist at the end for proper load transfer and stability.

Their length can be trimmed but only under an engineer’s supervision.

Overall, engineered trusses are ideal for large-scale projects with big budgets.

Engineered Trusses With Openings.
Engineered Truss With Openings.

You may also enjoy reading:

Floor Trusses vs. Floor Joists: Explained

What are the Dimensions of Engineered Wood Joists?

Engineered joists are typically available in lengths of up to 48’. However, lengths of up to 60’ are also available.

The depths of an I-joist range between 9 ½” to 16”, whereas the width ranges from 2 ½” to 3 ½”.

Their web can be made thicker, and the lengths can be cut according to the requirements of a house.

There are codes and span tables available to check the dimensions of various types of engineered wood products.

Basic Joist Configuration.
Basic Joist Configuration.

Why are Engineered I-Joists Becoming More Popular?

I-joists are becoming quite popular in residential construction.

They offer several practical benefits compared to traditional sawn lumber joists because of their large spans.

For example, a 2×6 can span around 12′ without support which is much lower than the 60′ offered by engineered joists.

Additionally, you will only require half the number of engineered I-joists to meet the construction requirements as compared to traditional joists.

Furthermore, engineered joists make the installation process a lot quicker.

Whereas, in the case of traditional joists, column supports need to be set up in the middle of a room to support additional joist members.

I-joists are also much better at reducing floor bouncing or sagging compared to lumber joists.

How are Engineered Joists Installed?

The installation process of manufactured joists is quite simple.

Place them on the block wall for primary support on both sides.

If they rest on the framing, nail their flanges into the wood.

Engineered joists with long spans typically require no mid-span support unless reinforcement is necessary.

The long spans of engineered joists do not need to be supported in the middle unless strengthening is needed.

Installed Engineered I-Joists.
Installed Engineered I-Joists.

Can I Drill Holes into Engineered I-Joists?

Engineered wood joists have certain limitations when drilling holes in them.

It is important to avoid drilling holes in the flanges of an I-joist.

The International Residential Code (IRC) recommends limiting the size of the holes to one-third the depth of the I-joist, and they should not be located within the middle third of the span.

Additionally, the IRC suggests that any holes should not be located closer than 2 inches from the top or bottom of the I-joist.

It is also crucial to follow the manufacturer’s guidelines when drilling these joists.

Holes in Engineering I joist.
Holes in Engineering I joist.

How Do You Strengthen Engineered Joists?

There are multiple ways to strengthen joists used in wooden floor systems.

One method is to provide beam-column support at the mid-span of the joist panels supporting a floor.

Though effective, this method can decrease the space within the room.

Another common method is to sister the joist panels with more joists on either or both sides. This provides extra strength to the joist systems.

Nailing is used to sister the joists to each other.

Joist blocking and bridging are other techniques used to strengthen engineered joists and reduce floor vibrations.

Metal wrapping can also support the wood joist panels. The wrapping transfers the loads from the center to the ends of the joists.

Additionally, steel can be used to reinforce and increase the durability of joists.

Plywood sheathing can also be used to reduce the bounce and increase the strength of wood joists.

Sistering of Engineered Joist.
Sistering of Engineered Joist.

How Much Do Engineered Floor Joists Cost?

The cost of engineered floor joists depends on the size, type, and manufacturer.

On average, they cost around $4 to $8 per linear foot.

Additional costs are necessary for installation and other accessories like fasteners and hangers.

It is best to obtain quotes from different suppliers to ensure you are getting the best price for your specific needs.

Frequently Asked Questions

Are Engineered Joists Sustainable?

The use of renewable materials, efficient manufacturing processes, and energy-saving capabilities make them a viable option for sustainable construction.

However, a more sustainable option than engineered joists would be steel joists, as they can be fully recycled.

When Should You Replace Floor Joists?

In case of severe water damage, insect or termite infestations, or excessive wobbling, it is advisable to replace floor joists.

Otherwise, it is not advisable to replace joists but rather strengthen them using different available techniques.

Should Floor Joists Align with Wall Studs?

Although not always necessary, it is recommended to align floor joists with wall studs.

Doing so can allow for efficient installation of utilities and enhance the structural integrity of your home.

V Susan
Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com