Floor/Ceiling Joist & Rafter module
Free Floor Joist, Ceiling Joist and Rafter Span Calculator — 2024 IBC Tables and Trus Joist TJI
Prescriptive span tables for floor joists, ceiling joists, and rafters per 2024 IBC Chapter 23 (Tables 2308.8 and 2308.11), plus Trus Joist® TJI® engineered I-joist spans. Allowable spans by species, grade, size, spacing, and loading, with the ceiling-height rafter adjustment and optional Simpson Strong-Tie hanger selection.
Free to use with no sign-up: the calculator runs in full in the browser with no account, no trial and no feature limits, and the full detailed calculation is shown on screen, step by step, with the code sections and tables it draws on, so it can be checked by hand. A free account keeps one project in the cloud; unlimited cloud projects and printing the report to PDF are Pro features.
What the calculator includes
- Floor joists, ceiling joists and rafters read straight from the 2024 IBC prescriptive tables — 2308.8.2.1(1) and (2), 2308.11.1(1) and (2), 2308.11.2(1) to (6) — digitized cell by cell for Douglas Fir-Larch, Hem-Fir, Southern Pine and Spruce-Pine-Fir in four grades at 12, 16, 19.2 and 24 in.
- The table's own load cases as choices: 30 or 40 psf floor live load at 10 or 20 psf dead, attic with or without storage, 20 psf roof live load or 30 and 50 psf ground snow, ceiling attached or not, and the rafter-tie question with the Table 2308.11.2(7) ceiling-height adjustment.
- A pass or fail per the table it read, with the table's maximum span beside the entered span, the Note a and Note b cells treated conservatively, and the footnotes that applied: 2 in end bearing, spans over 26 ft, lumber availability over 20 ft.
- Trus Joist TJI floor, roof and ceiling joists from the TJ-4000 specifier's guide and technical bulletins TB-805 and TB-824: depth and series, L/480 or L/360, snow and non-snow roof load columns, slope ranges, web-stiffener and creep notes, bearing lengths.
- Optional Simpson Strong-Tie joist hanger selection on the sawn-lumber paths: the reaction from the table load and spacing goes to the Hanger Selector with its load-duration class, and the chosen hanger's allowable is checked.
- The IBC section, the matching IRC table and the Weyerhaeuser documents are quoted from the book icon beside each choice, and no span is interpolated: every axis is one of the tabulated values.
In every StructSuite module
- The code clause behind a value is quoted verbatim beside it from a blue book icon — NDS 2024, SDPWS 2021, AISC 360-22, ACI 318-25, ASCE 7-22 and the 2024 IBC, FEMA P-750 and the I-joist manufacturer's technical bulletins — so the standard does not have to be opened to check it.
- A missing input stops the calculation rather than being filled in silently, and judgment choices start unselected.
- Where a limit applies it is checked as you type: beam RB and column ℓe/d, steel Lc/r, rebar ratios and spacing, fy and f′c.
- Every module prints into one calculation report (Pro) with a cover sheet, a table of contents with measured page numbers and a verification link a plan checker opens without an account.
StructSuite is an independent product and is not affiliated with, sponsored by or endorsed by Simpson Strong-Tie Company Inc. or any other manufacturer named here. Simpson Strong-Tie®, DTT, HDUE, SABR, Trus Joist®, TJI®, BCI®, LPI, Microllam®, Parallam®, TimberStrand® and Versa-Lam® are trademarks of their respective owners, used only to identify supported products and design-value sources.
See the method in a printed report
The sample calculation report (PDF) is a complete StructSuite report printed from the sample project — open it without an account.
Frequently asked questions
Is this an engineered design or a span table lookup?
A span table lookup. It reads the prescriptive spans of 2024 IBC Tables 2308.8 and 2308.11 for floor joists, ceiling joists and rafters by species, grade, size, spacing and loading, plus Trus Joist TJI I-joist spans. For an engineered member check per NDS 2024, use the beam calculator.
Does the result go into the calculation report?
Yes. Each module's result becomes a section of the project's calculation report, in the same order as the dashboard. Printing the report to PDF is a Pro feature; the calculation itself is free on screen.
Which tables does it read?
Floor joists from 2024 IBC Tables 2308.8.2.1(1) and (2), ceiling joists from Tables 2308.11.1(1) and (2), and rafters from Tables 2308.11.2(1) to (6) with the Table 2308.11.2(7) ceiling-height adjustment when the rafter ties are raised, each digitized cell by cell for Douglas Fir-Larch, Hem-Fir, Southern Pine and Spruce-Pine-Fir in four grades at 12, 16, 19.2 and 24 in spacing. Trus Joist TJI floor and roof spans come from the TJ-4000 specifier's guide and ceiling spans from technical bulletins TB-805 and TB-824. No span is interpolated: every axis is one of the tabulated values.
Is the floor/ceiling joist & rafter calculator free?
Yes. Free to use with no sign-up: the calculator runs in full in the browser with no account, no trial and no feature limits, and the full detailed calculation is shown on screen, step by step, with the code sections and tables it draws on, so it can be checked by hand. A free account keeps one project in the cloud; unlimited cloud projects and printing the report to PDF are Pro features.