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TJI Joists Explained: Pros and Cons of Using it

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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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TJI Joists

A TJI joist is a type of engineered wood joist commonly used in residential construction. 

Made from a combination of compressed wood strands, adhesive, and wax, TJI joists are popular among builders and engineers because they can cover long distances without sagging or warping. TJI joists also offer several size options, making them ideal for construction projects. 

What are TJI Joists?

TJI Joists
TJI Joists

The brand Weyerhaeuser designed TJI joists or Trus Joist I-Joists as a new type of engineered joist.

Due to their superior physical characteristics, contractors prefer utilizing TJI joists in flooring and roofing systems. 

Their geometry is similar to that of an I-joist, with a web-oriented vertically between two horizontal flange elements. 

However, these joists are considerably lighter than I-joists, enabling them to span longer distances without intermediate or end support. 

Since they are a form of engineered wood, TJI joists are more expensive than traditional sawn lumber or dimensional lumber.

Still, their added material and physical properties justify their higher cost.

Why Choose TJI Joists?

While it is true that TJI joists are more expensive, they are superior in almost every other way when compared to regular dimensional lumber. 

You should choose TJI joists for the following reasons:

Strength

TJI joists comprise a complex and unique combination of compressed wooden strands. 

Unlike traditional lumber, which comprises a single species of wood, TJI joists utilize strands of varying wood species, giving them more strength and flexibility. 

This allows them to span greater distances than a conventional I-joist without sagging or warping. 

Their strengths make them an ideal option for creating open floor plans or designs with fewer load-bearing walls.

Stability

Along with greater strength, TJI joists possess higher stability than conventional timber.

Since they utilize engineered wood, TJI joists are less prone to varying weather conditions.

This means that these joists do not expand, contract, or twist over time as much as traditional lumber when subjected to changes in temperatures and humidity levels. 

Design Flexibility

Weyerhaeuser produces TJI joists in a wide range of sizes and depths.

This affords architects and designers flexibility in their building design and allows them to use minimal interior load-bearing walls. 

Moreover, the added flexibility provided by TJI joists results in a more open and spacious living area, making efficient use of space.

Ease of Installation

Due to their lightweight and more significant span coverages, the TJI joist’s installation process is more straightforward, uncomplicated, and faster. 

They come with pre-cut knockouts to facilitate easy installation, which helps reduce installation time and labor costs. 

TJI joists with pre-cut knockouts also help to install the plumbing and electrical lines quickly.

Sustainability

The manufacturing process of TJI joists entails sourcing wooden strands from sustainable forests. 

Using wooden strands not only results in greater strength of the element but also produces less waste and during manufacturing. 

Uniformity

Since TJI joists are engineered wood products, they are uniform in size and quality than traditional timber. 

The uniformity not only assures engineers of its load-bearing capabilities but also improves the overall efficiency of the framing system.

Energy Efficient

TJI joists, with additional insulation coatings, can help reduce the energy costs incurred for heating your residence. 

Thermally insulated TJI joists retain heat better than conventional timber; this makes them more energy-efficient and environmentally friendly.

Cost Effective

While the procurement costs of TJI joists are higher than conventional timber, TJI joists prove to be more cost-effective in the long run. 

TJI joists have a greater life span and are stronger; hence, you can afford to have greater spacing in your design. 

Additionally, they do not require frequent maintenance if damaged, can be easily repaired, and do not need additional materials to maintain their load-bearing efficiency.

Apart from the listed advantages above, TJI joists provide better acoustic insulation and are more fire-resistant. 

Installation of TJI Joists

Installation of TJI Joists
Installation of TJI Joists

Before installing the TJI joists, ensure that you follow the below guidelines; failure to do so can result in serious injuries. 

Safety Guidelines

  • Ensure all blocking, hangers, rim boards, and rim joists form a stable connection at TJI joist’s end supports.
  • Install a durable deck or sheathing material and securely fasten it to the first four feet of the joists at the end of the bay or adjacent to a braced end wall.
  • To ensure safety and structural stability, nail 1×4 bracing to a braced end wall or a sheathed area and each joist.
  • Before placing additional loads on the system, ensure the sheathing is fully attached to each TJI joist.
  • Brace the top and bottom flanges of the ends of cantilevers to ensure safety and stability.
  • The flanges should maintain a straight alignment within 1/2 inch of their accurate alignment.

Installation Guidelines

The actual installation guidelines for TJI Joists are as follows: 

  • Decide on the appropriate layout and spacing of the TJI joists, considering the structure’s span and load requirements.
  • To install the TJI joists, place them on the rim joists and attach them using hangers or mechanical fasteners.
  • Provide extra support and minimize deflection by installing blocking between the TJI joists at mid-span and load-bearing walls.
  • Install bridging or strapping between the TJI joists to distribute loads and prevent twisting.
  • After installing the TJI joists, ensure they are level and make any necessary adjustments. 
  • Follow the manufacturer’s instructions to install the subflooring and other finish materials.

TJI Joists: Size and Span

One of the main advantages of using TJI joists is that they are available in different sizes.

Weyerhaeuser provides TJI joists having depths of 9½”, 11 7⁄8″, 14″, 16″, 18″, 20″, 22″, and 24″ and flange widths of 1¾”, 21⁄16″, 25⁄16″, and 3½”. 

TJI joists have a maximum span that varies based on joist size, spacing, load capacity, end use, and building code requirements. 

The following table shows a TJI joist’s spanning capabilities when used as a floor joist.

40 PSF Live load/15 PSF Dead LoadDirectly Applied CeilingDirectly Applied CeilingDirectly Applied CeilingDirectly Applied Ceiling
TJI 210Simple or Continuous SpanSimple or Continuous SpanContinuous Span Continuous Span
Joist Depth12″ O.C.16″ O.C.12″ O.C.16″ O.C.
9 1/2″16′-1″15′-3″16′-10″15′-11″
11 1/2″18′-1″17′-1″19′-2″17′-10″
14″20′-2″18′-9″21′-3″19′-10″
16″21′-11″20′-5″23′-2″21′-7″
Floor Span Table

For a detailed breakdown of the spanning capabilities of a TJI joist under varying spacing and end-use conditions, please refer to the product brochure provided by Weyerhaeuser

How Much Weight Can TJI Joist Support?

TJI joists can usually sustain considerable weight, partly due to the wooden fibers’ basic internal structure and geometry.

The manufacturer claims a TJI joist can hold up to 55 pounds per square foot loading. 

Moreover, a TJI joist can sustain a maximum bottom flange load of 500 pounds for every 5 feet, which is 250 pounds on either side. 

Consult a structural engineer to determine the exact loading conditions and capabilities of your TJI joist.

Cost of TJI Joists

The cost of a TJI Joist is contingent on the joist’s span, the span’s length, and the quantity needed for a particular project.

Additionally, the joist’s depth is also a significant contributor to the total cost of the TJI Joist. 

A TJI joist spanning 20 feet usually costs around $100 – $175, depending on the depth of the joist.

Joists spanning 24 feet generally have a cost range of $130 – $200. 

The cost of a joist spanning 26 feet and 30 feet typically ranges from $150 – $220 and $165 – $250, respectively.

A joist with higher spanning capabilities, somewhere near 36 feet, will cost you around $200- $300. 

Procuring a TJI joist with a maximum span of 60 feet is a rarity.

If you can procure one, it will set you back $350 – $500.

Knockout Holes in TJI Joists

Knockout Holes in TJI Joist
Knockout Holes in TJI Joist

TJI joists can include knockout holes that allow pipes, ducts, or utilities to pass through them. 

The size, location, and number of knockout holes may vary depending on the joist’s specific design and intended use. 

To maintain the structural integrity of the joist, it is crucial to consult the manufacturer’s specifications and building codes to ensure that any knockout holes are appropriately located and sized. 

It is best to reinforce any knockout holes to prevent the joist from weakening or failing under load.

Here are the drilling guidelines for TJI joists.

T20 Joist DepthHole Shape2″3″4″6 1/2″8 7/8″
9 1/2″Round1′-0″1′-6″2′-6″5′-6″
9 1/2″Square/Rectangular 1′-0″2′-0″2′-6″5′-0″
11 1/2″Round1′-0″1′-6″2′-0″3′-0″6′-0″
11 1/2″Square/Rectangular 1′-0″1′-6″2′-0″5′-0″6′-6″
14″Round1′-0″1′-0″1′-0″2′-0″3′-6″
14″Square/Rectangular 1′-0″1′-0″2′-0″4′-0″6′-6″
16″Round1′-0″1′-0″1′-0″1′-0″2′-6″
16″Square/Rectangular 1′-0″1′-0″1′-0″3′-0″6′-6″
The minimum distance between the edge of the hole and the nearest end support
T20 Joist DepthHole Shape2″3″4″6 1/2″8 7/8″
9 1/2″Round2′-0″2′-6″3′-6″8′-0″
91/2″Square/Rectangular 2′-0″3′-0″4′-0″7′-6″
11 1/2″Round1′-0″1′-0″2′-0″4′-6″9′-0″
11 1/2″Square/Rectangular 1′-0″2′-0″3′-0″8′-0″10′-0″
14″Round1′-0″1′-0″1′-0″2′-6″5′-6″
14″Square/Rectangular 1′-0″1′-0″2′-0″6′-0″10′-0″
16″Round1′-0″1′-0″1′-0″1′-6″4′-0″
16″Square/Rectangular 1′-0″1′-0″1′-0″5′-0″10′-6″
The minimum distance between the edge of the hole and the nearest intermediate or cantilever support

Do TJI Joists and I-Joists Differ from One Another?

I-Joist
I-Joist
PropertyTJI JoistsI-Joists
Depth Range9 1/2″ to 24″9 1/2″ to 16″
Span RangeUp to 48 feetUp to 32 feet
Standard Lengths20, 22, and 24 feet8, 9, 10, and 12 feet
CostExpensiveLess Expensive than TJI joists
TJI vs I-Joists

Yes, TJI joists and I Joists are different.

TJI joists are joists manufactured by Weyerhaeuser and are excellent load-bearing elements. 

Weyerhaeuser uses laminated veneer lumber (LVL) for the flanges and an OSB (oriented strand board) for creating TJI joists. 

On the other hand, several manufacturers produce I-Joists. 

A combination of sawn lumber or LVL for the top and bottom flanges and an OSB or plywood web makes up an I-joist. 

A main difference between TJI joists and I-joists is that TJI joists have a broader flange than I-joists. 

This can provide more surface area for attaching subflooring or drywall. 

Additionally, TJI joists are available in deeper sizes, which enables longer cantilevers and greater spans.

Overall, both TJI joists and I-joists are similar in geometry and function, but the differences in their materials, manufacturing processes, and costs separate them. 

Frequently Asked Questions(FAQ)

Is it Possible to Drill Through TJI Joists?

Yes, it is feasible to drill through TJI joists, but be very careful and adhere to the manufacturer’s specifications. 

TJI joists have specific hole sizes, locations, and spacing requirements to preserve their structural strength.

It’s essential to avoid drilling through the center of the joist or in the top and bottom flanges, as it can considerably weaken the Joist. 

Is Bridging Necessary for TJI Joists?

Bridging is essential for distributing loads, preventing the joists from twisting, and minimizing deflection. 

The specific requirements for the spacing and installation of bridging may differ based on the manufacturer’s specifications and building codes. 

How can TJI Joists be Cut?

You can cut TJI joists using a handsaw or a power saw with a fine-tooth blade. 

While cutting TJI joists, wearing the appropriate safety gear, like eye and ear protection, is essential.

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