GuidelineRecommended
Allowable deflection limits: L/360 floor live load, L/240 roof, L/180 ceiling
HUD RSDG §5.5Description
Member deflection under design loads shall not exceed: L/360 for floors under live load only; L/240 for roof or ceiling rafters with no plaster ceiling below; L/180 for roof rafters with plaster ceiling below; L/240 for exterior walls (drift). L is the member span.
Why this exists
Deflection limits keep finishes intact (drywall cracks at greater deflection), prevent springiness, and limit dynamic loads on connections. The L/360 limit is the most-cited residential floor stiffness target.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
floorLiveLimit | min | 360 | L/divisor | Floor live-load deflection divisor |
roofLimitWithPlaster | min | 180 | L/divisor | Roof rafter with plaster ceiling |
roofLimitNoPlaster | min | 240 | L/divisor | Roof rafter with no plaster ceiling |
Categories
Structure
Source
HUD (US Department of Housing and Urban Development)no manifest entry
Residential Structural Design Guide, Second Edition (2nd ed)
Section: Chapter 5, §5.5
Published 2000-01-01 · last verified 2026-05-10
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Continuous load path from roof to foundation · HUD RSDG §2.4
- Residential structural reliability targets 1-in-100 to 1-in-1000 annual probability of failure · HUD RSDG §2.5
- Residential floor live load: 40 psf minimum (30 psf sleeping rooms) · HUD RSDG §3.4
- Wind load design uses ASCE 7 basic wind speed for the locality · HUD RSDG §3.6
- Ground snow load for Virginia: 25 psf eastern, up to 40 psf western mountains · HUD RSDG §3.7
Last reviewed 2026-05-10.