BC EWP | I-Joist 101

What Are I-Joists?

I-joists are structural engineered wood products used for framing floors and roofs. The consistency allows for solid performance and smooth ceilings.

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Like all joists, I-joists are typically used to transfer loads to beams, walls, and the foundation. Unlike traditional dimension lumber, which can twist, split, and bow, I-joists offer better consistency and strength while weighing less and being easier to handle. These attributes make I-joists popular with builders of single-family homes, as well as light commercial and multi-family structures.

What Are the Benefits of I-Joists?

I-joists have become a construction industry standard largely because they offer reliable strength, consistency, and engineered performance that can provide a better value than dimension lumber. But that&#;s just the start of their benefits.

More Strength: Thanks to their unique construction, some I-joists, including Boise Cascade® I-Joists, are 20 percent stronger than comparably sized dimension lumber.

Longer Lengths: I-joists can be used to create long spans with less blocking to install faster. Something that dimension lumber simply can&#;t match.

Easier Handling: Dimensional lumber can be heavy and difficult to handle, but I-joists are lightweight, helping to reduce labor hours and labor costs.

Adaptable on the Jobsite: Most I-joists come with pre-stamped knockouts for wires, and allow for larger holes to be cut out of the web for mechanicals and can have very little change in performance. This makes running HVAC, electrical, and plumbing much faster and simpler.

Faster Installation: I-joists can be quickly trimmed in the field and offer a wider nailing surface for speedy installation.

Always Consistent: I-joists are engineered and manufactured for reliability &#; you&#;ll receive the same carefully made, consistently performing, and professionally inspected product time after time.

Sustainably Made: A typical I-joist uses only about half the wood of dimension lumber. The raw materials used in the manufacture of BCI and AJS I-joists are sourced from sustainable and responsibly managed forests. Boise Cascade strives to maximize the use and minimize the waste of each log procured. Bark and material residuals are used for carbon-neutral biomass fuel to generate over 70% of the energy needed to manufacture our products, keeping our emissions and reliance on fossil fuels low.

What Is an I-Joist Used For?

I-joists are a go-to product for residential and multi-family construction projects because they&#;re available in common sizes for today&#;s construction projects. They can also reduce common mistakes and hassles to make: framing simpler, floors flatter, and homes perform to meet customer expectations.

The strength and stability of I-joists make them a popular choice for engineered floors and roof framing. I-joists come in longer spans than dimensional lumber but without the potential defects and imperfections that eat up time and labor at the job site. With less shrinking, twisting, and bowing, the result is simpler floor and roof layouts that perform over time. Their consistency and performance, along with proper design, helps reduce vibrations, which means less bounce, fewer squeaks, and solid, quiet floors.

How Are I-Joists Made?

I-joists consist of OSB web between two flanges, which are typically constructed of dimensional lumber or laminated veneer lumber (LVL) and joined by a durable structural adhesive. BCI® Joists use Versa-Lam® LVL for strength and durability while AJS joists have flanges made of machine stress-rated lumber.

A finished I-joist looks like the letter I, lending the product its name.

What Are Common I-Joists Sizes?

I-Joists are manufactured in a wide range of depths ranging from 9 ½&#;-24&#; and can be special ordered in lengths as long as 60 feet.

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BCI Joists are available in standard depths up to 20&#; and AJS joists are available in depths up to 24&#;. The extra depths make an ideal solution for multifamily applications.

How Far Do I-Joists Span?

The answer to this question depends on many factors unique to your project. Download the BCI or AJS I-joist Specifier&#;s guide to see I-joist span chart for your specific application or learn more about the Boise Cascade software suite.

If you are starting a new construction project, you may be wondering what the best option for your floor system will be: floor trusses, I-joists, or dimensional lumber floor joists. Each type has its own strengths and limitations. Continue reading this buying guide for some guidance on what may work best for your project.

If you are starting a new construction project, you may be wondering what the best option for your floor system will be: floor trusses, I-joists, or dimensional lumber floor joists. Each type has its own strengths and limitations. Continue reading this buying guide for some guidance on what may work best for your project.

Floor trusses can span farther between bearing points than I-joists, allowing for larger open rooms. This also reduces the need and cost for extra bearing posts, beams, and footings.

Floor trusses have built-in openings, which can be used to install HVAC ductwork, plumbing lines, and electrical wiring.

Custom-built floor trusses allow building designers to add extra loading for in-floor heat, heavy tile floors, heavy kitchen islands, quartz countertops, and high-traffic areas. I-joists are limited when it comes to accommodating extra loading.

Floor trusses offer four different bearing conditions for a wider variety of uses: bottom chord bearing, bottom chord bearing trimmable ends, top chord bearing, and mid-block bearing are all available. The multiple bearing conditions make matching existing floor heights much easier when using floor trusses. I-joists offer only one bearing condition.

Why Choose Floor Trusses?

&#; Floor trusses can span farther between bearing points than I-joists, allowing for larger, more open rooms. This also reduces the need and cost for extra bearing posts, beams, and footings.

&#; Floor trusses have an open web pattern and can include built-in openings, which can be used to install HVAC ductwork, plumbing lines, and electrical wiring.

&#; Custom-built floor trusses allow building designers to add extra loading for in-floor heat, heavy tile floors, heavy kitchen islands, quartz countertops, and high-traffic areas. I-joists are limited when it comes to accommodating extra loading.

&#; Floor trusses offer four different bearing conditions for a wider variety of uses: bottom chord bearing, bottom chord bearing trimmable ends, top chord bearing, and mid-block bearing are all available. I-joists and dimensional lumber offer only one bottom chord bearing condition.

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Duct Chart

When it comes to installing plumbing, wiring, and ductwork, the setup of a truss (especially an open-web truss) makes it relatively simple to get the job done. In contrast, I-joists are subject to building code restrictions that make it much harder to run wiring, ductwork, and pipes through them. For example, there are some restrictions as to how big of a hole can be drilled or cut into an I-joist. This can limit the size and placement of the ductwork and pipes.

Ductwork is usually installed under I-joists, requiring dropped ceilings or boxed soffits if the basement is to be finished. This in turn requires 9-foot-high basement walls to allow for an 8-foot finished ceiling. Using floor trusses allows you to utilize 8-foot basement walls, as the ductwork is installed within the openings of the floor truss. Additionally, having the mechanicals and ductwork hidden within the web openings of the floor truss allows for the easy installation of drywall to the bottom chord of the floor truss to finish off a ceiling.

Click to view full chart

When it comes to installing plumbing, wiring, and ductwork, the setup of a truss (especially an open-web truss) makes it relatively simple to get the job done. In contrast, I-joists are subject to building code restrictions that make it much harder to run wiring, ductwork, and pipes through them. For example, there are some restrictions as to how big of a hole can be drilled or cut into an I-joist. This can limit the size and placement of the ductwork and pipes.Ductwork is usually installed under I-joists, requiring dropped ceilings or boxed soffits if the basement is to be finished. This in turn requires 9-foot-high basement walls to allow for an 8-foot finished ceiling. Using floor trusses allows you to utilize 8-foot basement walls, as the ductwork is installed within the openings of the floor truss. Additionally, having the mechanicals and ductwork hidden within the web openings of the floor truss allows for the easy installation of drywall to the bottom chord of the floor truss to finish off a ceiling.

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For more information, please visit Common I-Joist Applications.