Staircase details and formula

Clear, practical staircase details and formulas you can use for building designs. These follow common architectural/engineering standards and are suitable for Sri Lankan building codes as well.

✅ 1. Key Staircase Terms

• Riser (R): vertical height of one step

• Tread (T): horizontal depth of the step (where you place your foot)

• Flight: a continuous series of steps

• Landing: flat resting platform between two flights

• Width: clear stair width between walls/handrails

• Headroom: vertical clearance above the stairs (usually 2.1 m minimum)

• Pitch: angle of the staircase

✅ 2. Ideal Stair Dimensions (Standards)

These can be used in institutional, office, and public buildings:

Element	Standard Value
Riser height	150–170 mm
Tread depth	260–300 mm
Stair width	1.2 m minimum (public), 0.9 m (residential)
Landing length	1.2 m or width of stair, whichever is greater
Maximum risers in a flight	12–14
Minimum headroom	2.1 m

✅ 3. Staircase Formulas (Most Important)

Formula 1: Blondel’s Rule (Comfort Formula)

👉 2R + T = 600–650 mm

This ensures comfortable and safe walking.

Example:
If R = 160 mm → T = 600 – 2(160) = 280 mm

Formula 2: Room Height to Calculate Number of Risers

👉 Number of Risers = Total Floor Height ÷ Riser Height

Example:
Floor-to-floor height = 3300 mm
Riser = 165 mm
→ 3300 / 165 = 20 risers

Formula 3: Number of Treads

👉 Number of Treads = Number of Risers – 1

So if you have 20 risers → 19 treads.

Formula 4: Staircase Slope (Angle)

👉 tan θ = R / T

Ideal slope = 30°–35°

Formula 5: Total Run (Horizontal Length)

👉 Total Run = Number of Treads × Tread Depth

Formula 6: Landing Length

👉 Landing = Stair width (min)

Typically 1200 mm for public buildings.

✅ 4. Example Calculation (Common Floor Height = 3.3 m)

Let’s design a comfortable staircase.

Step 1: Select Riser

Choose R = 165 mm

Step 2: Number of Risers

3300 / 165 = 20 risers

Step 3: Treads

T = 280 mm (fits Blondel: 2×165 + 280 = 610 mm)

Number of treads = 20 – 1 = 19 treads

Step 4: Total Run

= 19 × 280 = 5320 mm (≈ 5.3 m)

Step 5: Stair Width

= 1.2 m

Step 6: Landing

= 1.2 m (minimum)

✅ 5. Typical Staircase Section (Dimensions)

• Floor height: 3300 mm

• Riser: 165 mm

• Tread: 280 mm

• Flight 1: 10 risers, 9 treads

• Landing: 1200 mm

• Flight 2: 10 risers, 10 treads

• Headroom: 2100 mm minimum

✅ 6. Additional Structural Details

Stair Waist Thickness

• RCC waist slab: 150–200 mm

• Load combinations: as per BS 8110 / EC2

Concrete Strength

• C25/30 or above for institutional buildings

Reinforcement

• Main bars: 12 mm @ 150 mm c/c

• Distribution: 8 mm @ 200 mm c/c
  (Actual design must be checked by structural engineer.)

Finishes

• Nonslip tiles or cement screed

• Handrails: 900 mm height