How far can the beam under a two-span joist sit from the middle of the house?

What it found

Two-span sawn-lumber joists (SPF No. 2) with unequal spans, reusing the finite-element beam of house-continuous and the NDS checks of house-spans with pattern loading and per-span deflection. For a 2x10 floor joist at 16 in, moving the beam off-centre costs 0.4% of total clear width at a short/long span ratio of 0.9, 4.3% at 0.7 and 13.3% at 0.5, because the short span relieves the long one (the long span grows from 15 ft 3 in to 17 ft 7 in); a 2x8 ceiling joist, which deflection governs, loses 5.1% at 0.9 and 24.1% at 0.5. A 28 ft wide house tolerates a beam 3.5 ft off the middle. Stylised. Not validated against published span tables, two spans only, no vibration, and not a design anyone should build from without a licensed review. The short span's end lifts off its support whenever live load is on the long span only (−103 lb per joist at a 10 ft short span, −271 lb at 6 ft; 2x10 floor).

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.