TJI Roof Joist Design Example (TJ-4000): 9-1/2 in. through 16 in. Depths, Low Roof Slope Columns, and StructSuite

This note walks through roof joist selection using Weyerhaeuser TJI® joist roof span tables from TJ-4000 (Specifier’s Guide). It explains the Low vs High horizontal-deflection columns for 9-1/2 in. through 16 in. depths, design roof load column choices (non-snow and snow ASD combinations), joist spacing (16, 19.2, and 24 in. o.c. in StructSuite), depth and TJI series, horizontal clear span measured along the horizontal projection, deflection criteria, bearing notes, and how StructSuite supports the workflow in the Floor Joist, Ceiling Joist & Rafter module when you choose Roof Joist & Rafter and TJI® Joist (roof).

Official reference (same document as linked in StructSuite)

StructSuite links to the publisher’s document library entry for the guide:

Weyerhaeuser — TJ-4000 (Specifier’s Guide for TJI joists, USA)

Use that PDF as the authority for exact table text, footnotes, and product definitions. The discussion below is educational; always confirm details against the current TJ-4000 edition you are working under.

What StructSuite does for TJI roof joists

In the Floor Joist, Ceiling Joist & Rafter module, after you select Roof Joist & Rafter and TJI® Joist (roof), StructSuite lets you:

• Choose the TJ-4000 roof chapter for 9-1/2 in. through 16 in. depths, including Roof slope 6:12 or less (Low column set) vs Between 6:12 and 12:12 (High column set).
• Set Rafter spacing to a tabulated value (16, 19.2, or 24 in. on center).
• Pick a Design Roof Load line that matches the guide’s ASD factored combinations (non-snow 125% roof live+dead columns; snow 115% snow+dead columns, per the labels in the app and TJ-4000).
• Select Joist depth, TJI joist designation (series), and enter Horizontal clear span (ft and in.), then read SATISFACTORY / NOT SATISFACTORY against the tabulated maximum span for that row and column.
• Show deflection criteria (L/180 total load and L/240 live load per TJ-4000 roof tables), bearing length reminders where applicable, and creep or footnote (1) messaging when the digitized table cell carries those flags.

That mirrors a prescriptive table lookup for roof I-joists without replacing connection design, bracing, or load path documentation on the construction documents.

Roof slope and Low vs High columns (9-1/2 in. through 16 in.)

For the 9-1/2 in. through 16 in. roof chapter, TJ-4000 provides paired columns for each Design Roof Load combination: a Low horizontal-deflection column and a High horizontal-deflection column.

How to use the table (guide logic)

1. Determine appropriate roof loads and load duration factor for the project.
2. If roof slope is 6:12 or less, use the Low column for the selected design roof load. If slope is between 6:12 and 12:12, use the High column.
3. Scan down that column until the tabulated span meets or exceeds the horizontal clear span of the application.
4. Select the TJI joist and on-center spacing for that row.

In StructSuite, the radio under Depth and roof slope (TJ-4000) labeled 9-1/2 in. through 16 in. depths — Roof slope 6:12 or less selects the Low column set; Between 6:12 and 12:12 selects the High column set. Match that choice to the actual roof pitch on the plans.

Design roof load columns and joist spacing

Each Design Roof Load option in StructSuite corresponds to a specific column in the digitized TJ-4000 roof tables (non-snow and snow combinations as labeled). Changing the design roof load line moves you to a different column; allowable span in that cell is whatever the guide tabulates for that spacing, depth, series, and Low/High band.

Joist spacing

• Roof span tables in StructSuite use 16, 19.2, and 24 in. o.c. (there is no 12 in. o.c. column in the roof digitization).

If the project’s loads or spacing do not match a listed combination, do not assume an arbitrary nearby column is conservative; use Weyerhaeuser software or engineered design per the guide for cases outside the tables.

Depth, TJI series, and horizontal clear span

• Depth (9-1/2 in., 11-7/8 in., 14 in., 16 in., etc.) identifies the member in plans and picks the row family in the span tables.
• TJI series (110, 210, 230, 360, …) indicates stiffness / capacity tiers for a given depth; higher series generally allow longer spans for the same spacing and column, subject to the actual tables.
• Span in TJ-4000 roof tables is horizontal clear span measured along the horizontal projection of the rafter or roof joist, not along the slope. StructSuite follows the same convention in Horizontal clear span.

Footnote (1), creep, and special cell flags

When the governing table cell carries footnote (1) or creep-related flags, TJ-4000 is calling attention to additional manufacturer rules or long-term deflection considerations (including creep under sustained load). In StructSuite, when those flags apply, the result panel surfaces short notes so you know to read the full footnote text and publisher guidance in the current PDF—not just the span number.

Complete bearing, stiffeners, and connection design per the manufacturer and adopted code; the span table does not replace detailed drawings.

General notes (typical TJ-4000 roof chapter, 9-1/2 in. through 16 in.)

The following assumptions are typical of TJ-4000 roof span material for this depth chapter (confirm against your PDF edition):

Tables are based on

• Minimum roof slope 1/4 :12 (for this chapter).
• Uniform loads.
• The more restrictive of simple or continuous span (as stated in the guide).
• Deflection criteria of L/180 total load and L/240 live load (per guide).
• Minimum bearing length 1-3/4 in. at ends and 3-1/2 in. at intermediate bearings without web stiffeners for these depths, unless the guide requires otherwise for a specific product or condition.

Continuous spans

• For continuous spans, the ratio of short span to long span should be 0.4 or greater to help limit uplift concerns (per guide).

Snow and code

• For 2024 IBC, snow loads in ASD are adjusted per ASCE 7 load combinations; TJ-4000 references 0.7S where applicable in guide notes.

Ridge / high-end support

• A support beam or wall at the high end is required; ridge board applications do not provide adequate structural support by themselves in the guide’s framing assumptions.

Outside the tables

• For flat roofs or other loading conditions not shown, use Weyerhaeuser software or other approved design methods per the publisher.

Worked example (prescriptive table check)

Given (aligned to StructSuite labels and TJ-4000 roof chapter for narrow depths)

• Roof pitch 4:12 (≤ 6:12), so use the Low slope column set for the selected design roof load.
• Design Roof Load: Non-snow 125% — (roof live + dead) (20 + 15) psf.
• Spacing: 16 in. o.c.
• Depth: 11-7/8 in., TJI 230.
• Horizontal clear span (trial): 19 ft 0 in.

Steps in StructSuite

1. Open Floor Joist, Ceiling Joist & Rafter → Roof Joist & Rafter → TJI® Joist (roof).
2. Under Depth and roof slope (TJ-4000), select 9-1/2 in. through 16 in. depths — Roof slope 6:12 or less.
3. Set Rafter spacing to 16.
4. Select the Design Roof Load line above.
5. Set Joist depth to 11-7/8" and TJI joist designation to TJI 230.
6. Enter Horizontal clear span = 19 ft 0 in. and read SATISFACTORY or NOT SATISFACTORY.

Interpretation

• If NOT SATISFACTORY, increase series, depth, tighten spacing, shorten span, or add supports.
• Verify bearing lengths and any footnotes on the construction documents.

Interactive design example (read-only wizard): Open this example in StructSuite

TJI roof (engineered I-joist) vs. common lumber (IBC Chapter 23 rafter tables)

Use TJ-4000 for TJI roof joists; use IBC 2308 rafter tables when the project uses common lumber and the RAFTER SPANS FOR COMMON LUMBER SPECIES path in StructSuite.

References

1. Weyerhaeuser, TJ-4000 — Specifier’s Guide for TJI Joists (USA) — Weyerhaeuser document library (TJ-4000)
2. International Building Code (adopted edition for your jurisdiction) — wood roof framing in Chapter 23 when using prescriptive dimensional lumber; deflection and loads per Chapters 16 and project criteria.
3. ASCE 7 (adopted edition) — load combinations and snow for ASD where applicable.

StructSuite embeds the same TJ-4000 document in the TJI roof joist UI for convenience; engineering decisions remain the responsibility of the licensed professional of record.