Engineered Floor Joists: Complete Guide

Engineered Floor Joists: Complete Guide

Engineered Floor Joists: Complete Guide

Engineered floor joists are joists made from a combination of traditional wood and engineered wood, giving them advantages over traditional joists. The advantage of using engineered wood joists is that they can span up to 60’ in length. Traditional Lumber joists are increasingly being replaced by engineered wood joists.

They come as rectangular panels or trusses and are installed beneath floors and roofs for the purpose of providing support to these structures.

Engineered joists are light in weight and easy to install, although they cost a bit more than traditional joists.

They come in both solid rectangular and I shape. The more common and preferred variation is the I-beam engineered joist.

Engineered joists also come in the form of trusses that are widely used in large-scale projects.

They can be cut into the required sizes due to their large spans and light weights.

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

Variation in Engineered Joists.
Variation in Engineered Joists.

What Are Engineered Floor Joists?

Engineered floor joists are used to bear structural loads and are used as supports to floor and roof systems in residential construction.

They are made from a mix of engineered wood and traditional lumber wood to form a compound that is both, lighter and stronger.

Normally, the most common shape given to engineered joists is that of an I-beam. However, truss joists are also readily used in bigger projects.

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

This configuration is used to effectively resist the loadings on the joist.

Thus, it can be claimed that I-joists are the most practical shape to use in construction.

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, which consist of wooden webbing held by metal plates.

Wooden I-Joists

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

The flexible nature of these joists also allows their length to be adjusted easily. I-joists cost less than other alternatives.

They do not reach the spans possible with open web trusses but are easy to work with.

However, 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.

Holes can be drilled into I-joists but are restricted in dimensioning and spacing.

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. They offer certain advantages in large projects.

First, they can span longer than I-joists.

Open web trusses have openings in their webbing, allowing passage for wires and ducts.

The costs and time of projects using open web trusses can be reduced significantly because they do not need to be drilled, but have openings allowing passage for electrical and plumbing ducts.

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

If a truss is to be replaced during construction, it can lead to project delays as they are custom-made for a project.

Even open web joists 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.

Which is Better I-joist or Open Web Truss?

PropertyEngineered I-JoistEngineered Truss
ShapeHorizontal I-shaped members.Truss-shaped members.
PreferencePreferred in small-scale projects.Preferred in large-scale projects.
OpeningsHoles need to be drilled into I-joists.Trusses have existing Openings.
SpansI-joists have relatively shorter spans.Trusses have relatively longer spans.
CostI-joists are relatively cheaper.Trusses are relatively expensive.
Engineered I-Joist vs. Engineered Truss

I-joists are preferable in small-scale residential construction, whereas open web trusses are used in large-scale projects.

Wider rooms are possible with open trusses but normally are not required in an average house.

I-joists need to be drilled to allow passage for wires and ducts, while the configuration of trusses already has openings.

Open web trusses are also more expensive than joists and as such not used often in home construction.

Overall the choice depends on the requirements of the project.

What Are the Dimensions of Engineered Wood Joist Panels?

Engineered joists have long spans, due to being durable and lightweight.

They 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”.

The 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 2x6 can span around 12' without support which is much lower than the 60' offered by engineered joists.

For instance, you will only require half the number of engineered I-joists to meet your construction requirements as compared to traditional joists due to their long lengths.

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.

They are to be rested on the block wall for the main support on both sides.

If they rest on the framing, then their flanges are required to be nailed into the wood.

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

They are installed in one go and supported at the ends by the wall.

The process is easier in contrast to traditional dimensional lumber installation, where there is a need to set up support in the middle of the span.

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

Can Holes be Drilled into Engineered I-joists?

Engineered wood joists are quite restricted when it comes to drilling holes in them. The flanges of an I-joist are off-limits when it comes to drilling.

The web of I-joists is used for drilling holes but only according to standards.

According to the International Residential Code (IRC), section R502.8.2, the holes are to be drilled on the web at a distance of 1/8” from the flanges.

The diameter of the holes can be kept as big as 1.5”.

They must be spaced at a distance equal to twice the diameter from the center of the adjacent hole.

Holes of other shapes such as rectangular holes can also be drilled into the webs of -joists.

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

Can You Replace Engineered Joists?

It is not wise to replace an entire panel of joists. Removing a joist panel would mean removing the support of your floors.

Hence, unless temporary support is set up, it is not advisable to remove engineered floor joists.

Furthermore, it is not easy to unplug an installed panel.

For these reasons, strengthening the wood joists is preferable to replacing them.

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 of the room itself.

Another 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.

Sistering is a quite common approach used to strengthen joists.

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

Another way is to use metal wrapping that supports the wood joist panels. The wrapping transfers the loads from the center to the ends of the joists.

Steel can also be used to reinforce the panels directly. This increases the durability of the joists considerably.

Lastly, 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?

On average, an engineered joist costs around $40 for a span of 16’. The cost of an engineered joist varies with its length.

It is also dependent on the availability of the joist type.

For example, a 2x3 flange I-joist is more common and easily available compared to a 2x4 flange I-joist is rare and thus would cost more.

Are Engineered Joists Safe to Use?

The safety of the wooden panels of engineered joists is dependent on the load applied.

If the applied load is within the stress limits of the joist, then the joist will function safely.

It is also important to allow a proper path for load transfer. The joist ends should be rested on enough area at the end walls.

If the bearing area of the resting joists is less than 3", the panels will lose half of their resisting capacity.

Thus, It is recommended to at least provide a bearing area of 3” to allow efficient load transfer.

To ensure the safety of floor and roof systems, it is common practice to provide extra joist panels than required.

With time joists are bound to undergo degradation and lose their capacity to resist loads.

Although there are ways to strengthen floor joists that have already degraded, periodic maintenance is the best solution.

Engineered I-joists are at a disadvantage when it comes to fire safety.

This does not mean that they are more prone to catch fire, but rather that in case of a fire, engineered wood is likely to burn more easily and rapidly.

This is due to the webs of engineered I-beam joists being made from oriented strand board (OSB).

Are Engineered Joists Sustainable?

Engineered joists are manufactured using a mix of different local wood species. They require less material and are thus easy to manufacture.

The materials required are also easily available.

The fast production, low pricing, and speedy recovery of woods make engineered joists quite sustainable to be used for residential construction.

A more sustainable option than engineered joists would be steel joists as they can be fully recycled.

Why Are Engineered Joists Given The Shape of an I-beam?

I-beam shape is the preferred shape given to engineered wood joists due to its efficient load resisting capability.

An I joist is split between an upper and lower flange that resists bending or flexural stresses, and a web in-between, which resists shear forces.


Engineered joists, whether they are used as I beam, or trusses are excellent for supporting the roof and floor framing systems.

They are strong, durable, lightweight, and easy to handle.

I-joists offer spans of up to 60’ and their installation process is quite simple.

They are easy to produce, cost-effective, and available in many variations. Engineered Joists require less material and are thus sustainable.

Holes can be drilled into them allowing passage for wires and ducts.

Frequently Asked Questions

Are I-joists Stronger than 2x10 Timber Joists?

Engineered I-joists are stronger than traditional 2x10 dimensional lumber joists.

Compared to 2x10 lumber, I-joists can carry more loads and can span longer as well.

When Should You Replace Floor Joists?

Floor joists should be replaced in case of severe water damage, insect or termite actions, and excessive wobbling.

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

How do you Stiffen Engineered Floor Joists?

The best way to strengthen floor joists is to provide support underneath them. Beam-column support provided at the mid-span is the best way to do so.

This increases the capacity of the joist panels and hinders the wobbling effects of the joists.

About 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

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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

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