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

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

Summary: Select TJI roof joists for a residential roof using Weyerhaeuser TJ-4000 span tables for 9-1/2 in. through 16 in. depths: pick the Low slope column for…

Overview

Select TJI roof joists for a residential roof using Weyerhaeuser TJ-4000 span tables for 9-1/2 in. through 16 in. depths: pick the Low slope column for roof slopes 6:12 or less, scan for required span, and verify horizontal clear span.

Problem statement

A one-story residence has conventionally framed roof joists (I-joists) bearing on exterior bearing walls. The roof pitch is 4:12 (6:12 or less), so the TJ-4000 table uses the Low horizontal-deflection column for the selected design roof load. Roof dead plus roof live are represented by the non-snow ASD column Non-snow 125% — (roof live + dead) (20 + 15) psf per the guide. Joists are spaced 16 in. on center. The engineer will use 11-7/8 in. depth TJI 230 from the 9-1/2 in. through 16 in. roof chapter. The horizontal clear span between bearing walls (measured along the horizontal projection of the joist per TJ-4000) is 19 ft 0 in. Ceiling below is not driving this example; the focus is roof table selection.

How to use the 9-1/2 in.–16 in. roof table (TJ-4000): (1) Determine appropriate roof loads and load duration factor as required by the project and the guide. (2) If roof slope is 6:12 or less, use the Low column for the chosen design roof load; if slope is between 6:12 and 12:12, use the High column. (3) Scan down the column until you find a tabulated span that meets or exceeds your horizontal clear span. (4) Select the TJI joist series and on-center spacing that corresponds to that row.

General notes (TJ-4000): Tables assume minimum roof slope 1/4:12, uniform loads, the more restrictive of simple or continuous span, deflection criteria of L/180 for total load and L/240 for live load, and minimum bearing length of 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 continuous spans, the ratio of short span to long span should be 0.4 or greater to prevent uplift issues. For 2024 IBC, snow loads in ASD are adjusted per ASCE 7 combinations (TJ-4000 references 0.7S where applicable). A support beam or wall at the high end is required; a ridge board alone does not provide adequate support. For flat roofs or other loading conditions not shown, use the manufacturer’s software.

Workflow in StructSuite

Open the Floor Joist, Ceiling Joist & Rafter module. Select Roof Joist & Rafter. Under Rafter design basis, select TJI® Joist (roof). Under Depth and roof slope (TJ-4000), select 9-1/2 in. through 16 in. depths — Roof slope 6:12 or less. Under Rafter spacing (inches on center), select 16. Under Design Roof Load, select Non-snow 125% — (roof live + dead) (20 + 15) psf. Under Joist depth, select 11-7/8". Under TJI joist designation, select TJI 230. Under Horizontal clear span, enter 19 ft and 0 in. StructSuite compares the span to the TJ-4000 tabulated maximum horizontal clear span for that row and column and reports SATISFACTORY or NOT SATISFACTORY.

Design considerations (excerpt)

TJ-4000 roof tables are separate from IBC common-rafter tables: horizontal clear span, factored ASD roof load columns, and Low vs High columns for 9-1/2 in.–16 in. depths. Pick TJI® Joist (roof) so StructSuite uses the specifier guide data embedded in the app. If you leave RAFTER SPANS FOR COMMON LUMBER SPECIES, you are in IBC Chapter 23 prescriptive tables instead.

The chapter label fixes which printed TJ-4000 table you are emulating: narrow depths split Low (slopes ≤ 6:12) vs High (6:12 to 12:12). Spacing must match a table column (16, 19.2, or 24 in. o.c. in StructSuite). The Design Roof Load row must match your ASD combination from the project (non-snow vs snow…

Related terms

  • StructSuite
  • structural engineering
  • design example
  • framing
  • tji roof joist span 9 5 16 low slope

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