# Stairs and Railings

## Stair Geometry

### Dimensional Requirements
| Component | Residential | Commercial |
|-----------|-------------|------------|
| Riser height (max) | 7-3/4" | 7" |
| Tread depth (min) | 10" | 11" |
| Headroom (min) | 6'-8" | 6'-8" |
| Width (min) | 36" | 44" (varies by occ load) |
| Landing depth | Width of stair | Width of stair |

### Riser/Tread Relationship
```
2R + T = 24" to 25" (comfort formula)
R × T = 70 to 75 (alternate formula)

Example:
R = 7", T = 11"
2(7) + 11 = 25" ✓
7 × 11 = 77 (slightly high, but OK)
```

### Calculating Risers
```
Number of risers = Total rise / Target riser height

Example:
- Floor-to-floor: 9'-0" (108")
- Target riser: 7"
- Risers: 108 / 7 = 15.4 → 15 or 16 risers
- With 15 risers: 108 / 15 = 7.2" ✓
- With 16 risers: 108 / 16 = 6.75" ✓
```

### Variation Tolerances
| Dimension | Max Variation |
|-----------|---------------|
| Riser to riser | 3/8" |
| Tread to tread | 3/8" |
| Within flight | 3/8" largest to smallest |

---

## Stair Width Requirements

### By Occupant Load
| Occupant Load | Min Width |
|---------------|-----------|
| < 50 | 36" |
| 50-100 | 44" |
| > 100 | 0.3" per occupant |
| Sprinklered | 0.2" per occupant |

### Minimum Widths by Use
| Building Type | Min Width |
|---------------|-----------|
| Residential (dwelling) | 36" |
| Residential (common) | 44" |
| Assembly | 44" (more by calculation) |
| Business | 44" |
| Educational | 44" |
| Healthcare | 44" (72" with gurneys) |

### Measuring Width
- Clear width between handrails
- Handrails may project 4-1/2" each side
- Width at/below handrail height

---

## Landings

### Landing Requirements
| Requirement | Dimension |
|-------------|-----------|
| Min depth | Width of stair |
| Max rise between | 12'-0" |
| Doors | May not reduce to < 1/2 width |
| Min width at door | 44" |

### Door Swing on Landing
- Door may swing over landing
- Cannot reduce width > 7" when fully open
- Cannot reduce landing depth > 1/2
- Maintain min 44" when open

### Winder Stairs
| Requirement | Dimension |
|-------------|-----------|
| Tread at walk line | 11" min |
| Walk line location | 12" from narrow end |
| Narrow end | 6" min |
| Allowed | Dwelling units only |

---

## Handrails

### Height Requirements
| Application | Height |
|-------------|--------|
| Stairs | 34"-38" |
| Ramps | 34"-38" |
| Guards (commercial) | 42" min |
| Guards (residential) | 36" min |
| Guards (I-3, assembly) | 42" min |

### Graspability
| Profile | Dimensions |
|---------|------------|
| Circular | 1-1/4" to 2" diameter |
| Non-circular | 4" to 6-1/4" perimeter |
| Non-circular | 2-1/4" max cross-section |

### Handrail Continuity
- Continuous full length of flight
- Extensions at top and bottom
- Top extension: 12" horizontal
- Bottom extension: Sloped + 12" horizontal
- Return to wall or post

### Handrail Extensions
```
At top: 12" horizontal (parallel to floor)
At bottom: Tread depth + 12" min (sloped + horizontal)

Exception: May omit at guards if continuous
```

---

## Guards (Guardrails)

### When Required
- Open-sided walking surfaces > 30" above grade
- Exceptions: stages, loading docks

### Height Requirements
| Location | Height |
|----------|--------|
| Commercial/public | 42" min |
| Residential (R-2, R-3) | 36" min |
| Assembly seating | 26" at seat rows |
| Roof access (maintenance) | 42" |

### Opening Limitations
| Location | Max Opening |
|----------|-------------|
| General | 4" sphere cannot pass |
| Below 34" | 4" sphere |
| 34"-42" | No requirement (adults) |
| Risers (closed) | 4" sphere |
| Between tread/riser | 4" sphere |

### Ladder Effect
| Requirement | Dimension |
|-------------|-----------|
| Horizontal rails | Max 4" apart if climbable |
| Intermediate rails | Space to prevent climbing |
| Mesh/infill | Recommended for child safety |

---

## Stair Types

### Enclosed Exit Stair
- Fire-rated enclosure (1-2 hr)
- Self-closing doors
- No penetrations except necessary
- Exterior or vestibule at exit

### Open Stair
- Allowed within stories (not exit)
- Atrium conditions may apply
- Sprinklers typically required
- May need smoke barrier

### Exterior Stair
- Open to exterior on one side
- Minimum opening requirements
- Protected from adjacent openings
- Drainage considered

### Spiral Stairs
| Requirement | Dimension |
|-------------|-----------|
| Clear width | 26" min |
| Tread at walk line (12") | 7-1/2" min |
| Riser height | Same limits as standard |
| Headroom | 6'-6" |
| Use | Limited occupancy |

---

## Stair Construction Types

### Steel Pan Stairs
- Steel stringers and pans
- Filled with concrete
- Common in commercial
- Allows field adjustment

### Precast Concrete
- Factory-made treads
- Steel or concrete stringers
- Fast installation
- Limited flexibility

### Cast-in-Place Concrete
- Formed and poured on-site
- Integral with structure
- Custom configurations
- Labor intensive

### Wood Stairs
- Residential typical
- Stringers: 2×12 min
- Treads: 1" nominal minimum
- Fire-rated construction varies

---

## Ramp Design

### Slope Requirements
| Application | Max Slope |
|-------------|-----------|
| Accessible route | 1:12 (8.33%) |
| Curb ramp | 1:12 (8.33%) |
| Existing buildings | 1:10 to 1:8 (with limits) |
| Non-accessible | 1:8 (12.5%) |

### Ramp Dimensions
| Requirement | Dimension |
|-------------|-----------|
| Min width | 36" clear |
| Max rise per run | 30" |
| Landing length | 60" min |
| Landing width | Width of ramp |

### Edge Protection
- Required when > 4" drop-off
- Curb, rail, or wall
- 4" min height

### Cross Slope
- Max 2% (1:50)
- Applies to all accessible routes

---

## Special Stairs

### Alternating Tread Devices
- Allowed for limited use
- Single occupant, infrequent
- 7" min tread depth
- 50 occupants max

### Ships Ladders
- Steeper than standard stairs
- Limited to specific uses
- Alternating tread possible
- Handrails required

### Ladders
| Use | Requirement |
|-----|-------------|
| Equipment access | 12" width, 14" spacing |
| Roof access | 18" width |
| Pit access | 18" width |
| Height > 20' | Cage or safety device |

---

## Stair Details

### Nosing Design
| Requirement | Dimension |
|-------------|-----------|
| Projection | 3/4" to 1-1/4" |
| Radius | 1/2" max |
| Bevel | 1/2" max, 60° min |
| Uniform | Entire flight |
| Solid risers | Required for egress stairs |

### Stair Finishes
| Finish | Coefficient of Friction |
|--------|------------------------|
| Rubber treads | 0.8-1.0 |
| Carpet | 0.6-0.8 |
| Vinyl | 0.5-0.6 |
| Concrete (broom) | 0.6-0.8 |
| Metal (checkered) | 0.6-0.7 |
| Polished stone | 0.4-0.5 (requires nosing) |

### Stringer Types
| Type | Description |
|------|-------------|
| Closed | Treads housed in stringer |
| Open | Treads on top of stringer |
| Cut | Notched for treads |
| Mono | Single central support |

---

## Fire and Egress

### Exit Enclosure Requirements
| Building Height | Rating |
|-----------------|--------|
| 4 stories or less | 1 hour |
| More than 4 stories | 2 hours |

### Pressurization
- Required for high-rise
- Required for underground
- Minimum 0.10" w.g. differential
- Maximum 0.35" w.g. at door

### Re-Entry
- Re-entry every 5 floors
- Signage required
- Locks with fail-safe
- Stair identification

### Signage
- Floor number at each landing
- Exit discharge floor
- Direction to exit
- Tactile and visual

---

## Drawing Checklist

### Stair Plans Show
- [ ] Run direction (up/down arrows)
- [ ] Number of risers
- [ ] Riser and tread dimensions
- [ ] Width
- [ ] Handrail locations
- [ ] Door swings
- [ ] Fire rating

### Stair Sections Show
- [ ] Floor-to-floor height
- [ ] Riser height
- [ ] Tread depth
- [ ] Headroom clearance
- [ ] Handrail height
- [ ] Nosing detail
- [ ] Landing conditions
