Plywood and OSB Sheathing Span Rating
Allowable spacing / live load / total load from APA span-rating tables; pass/fail against user-supplied design loads.
Example
You enter
- Panel thickness (in) 0.5
- Span rating 24/16
- Application roof
- Support spacing (in) 24
- Live load (psf) 30
- Dead load (psf) 8
You get
- Allowable spacing 24 in OC
- Allowable live 40
- Allowable total 50 psf
- Spacing pass Yes
- Live pass Yes
- Total pass Yes
- Pass Yes
- Application roof
Checked against published worked examples from: APA Engineered Wood Span Ratings (project bundled).
Details, formula, and sources
Formula or tableRoof: allowable spacing = APA E30 Table 33 max span for the rating (with or without edge support: clips, blocking or T&G); allowable live = the Table 33 value at the next tabulated spacing at or above the actual spacing; allowable total = live + 10 psf dead. Floor: allowable spacing and total load from the rating. Pass/fail = (support_spacing ≤ allowable_spacing) AND (live_load ≤ allowable_live) AND (live + dead ≤ allowable_total).
Source and editionAPA - The Engineered Wood Association published span-rating tables by name. Cited by APA name only; numeric tables shipped under APA's technical-bulletin reuse policy. IRC 2024 (International Residential Code). §R503 / §R803 references the APA tables (unchanged from 2021).
Free accessAPA technical bulletins free at apawood.org/publications.
What governsEstimate. AHJ and licensed structural engineer govern.
API field namespanel_thickness_in, span_rating, application, support_spacing_in, live_load_psf, dead_load_psf, allowable_spacing_in, allowable_live_psf, allowable_total_psf, spacing_pass, live_pass, total_pass, pass
- Span-rating table data/construction/apa-span-ratings.json keyed to rating × applicationAPA technical bulletins