Stacking family units on several floors gives the smallest footprint per family but the heaviest structural and escape problems: three storeys of 0.4 m earth wall weigh about 44-59 kN per metre of wall before any floor load, so the foundation under a bearing wall carries about 73.5-88 kN per metre, which soft clay can bear only on a footing 1.5-3.7 m wide and sand on one under 1 m. Upper units also need two ways out that do not depend on one internal stair, which is why stacked housing suits only skilled builders, good ground and a mostly able-bodied population.
Part of Multi-Family Housing Design
Stacked housing places family units on top of each other in a multi-storey building reached by outside stairs or balconies, as in Roman insulae.
Height Multiplies Load, Fire Risk And Access Problems
The multi-family guide lists the strengths: the smallest footprint per family, warmth that rises from lower to upper units, and good defence because upper floors are hard to enter. It lists the weaknesses: complex structure because upper floors carry heavy loads, difficult access for elderly or disabled residents, dangerous fire escape from upper floors, and harder water delivery and waste handling at height.
The structure is where an error is hardest to correct, so the arithmetic follows.
Worked Example: Load On A Bearing Wall
Inputs, with sources:
- three storeys, each 2.5 m high (assumed), walls 0.4 m thick (the multi-family guide’s 40 cm earth wall);
- earth density 1,500-2,000 kg/m³ (the range used in Earth Load Calculations);
- floor span 4 m between bearing walls (assumed), so a party wall carries the half-span from each side, a tributary width of 4 m;
- floor dead load 1.0 kN/m² (assumed, timber floor with finish) and live load for residential rooms 40 lb/ft² = 40 × 0.0479 = 1.92 kN/m² (Live Loads);
- roof load 1.5 kN/m² (assumed);
- weight force = mass × 9.81 m/s².
- Wall volume per metre of length = 3 storeys × 2.5 m × 0.4 m × 1 m = 3.0 m³.
- Wall mass = 3.0 × 1,500 = 4,500 kg to 3.0 × 2,000 = 6,000 kg; weight = 4,500 × 9.81 ≈ 44 kN to 6,000 × 9.81 ≈ 59 kN per metre.
- Two upper floors: 2 × (1.0 + 1.92) × 4 m = 23.4 kN per metre.
- Roof: 1.5 × 4 m = 6 kN per metre.
- Total at the base = 44 + 23.4 + 6 ≈ 73.5 kN/m to 59 + 23.4 + 6 ≈ 88 kN/m.
The unit here is newtons: 73.5 kN is the weight of about 7,500 kg, not 73,500 kg.
- Footing width = load per metre ÷ bearing pressure. The foundation guide gives 500-1,000 lb/ft² for soft clay (23.9-47.9 kPa) and 2,000-4,000 lb/ft² for sand (95.8-191.5 kPa) (Foundation Design).
- Soft clay: 73.5 ÷ 47.9 ≈ 1.5 m up to 88 ÷ 23.9 ≈ 3.7 m.
- Sand: 73.5 ÷ 191.5 ≈ 0.4 m up to 88 ÷ 95.8 ≈ 0.9 m.
The same wall on a 0.6 m footing would press the soil at 73.5 ÷ 0.6 ≈ 123 kPa to 88 ÷ 0.6 ≈ 147 kPa, well above soft clay’s capacity. This is why heavy multi-storey earth walls demand good ground, why a lighter timber frame above the first floor is common, and why the stacked model is for skilled builders.
What You Need
- Sound ground and a foundation computed as above
- Outside stairs and balconies of non-combustible material or heavy timber, linking at least two stairs
- Water and waste routes that work above ground level
Method
Step 1: Test the ground before choosing the number of storeys (Foundation Design).
Step 2: Limit height to what the foundation and builders can do; keep upper walls lighter than lower ones.
Step 3: Provide two escape routes from every upper unit, such as a balcony joining two separate stairs, so one burning stair does not trap anyone.
Step 4: Put the units least able to climb on the ground floor (Accessibility and Aging in Place).
Common Mistakes
- One internal stair for all upper units.
- Reading kilonewtons as kilograms — 73.5 kN is the weight of about 7,500 kg, so calling it 73,500 kg overstates it 9.81 times.
- Putting the kitchen under a timber floor with no fire separation.
Safety
Falls, fire and collapse
A fire in a stacked building spreads upward and traps occupants above it. Keep stairs outside, non-combustible and in pairs, and fit guard rails to every balcony. A wall that cracks or leans under load is an emergency: evacuate, do not prop it from underneath.
What’s Next
- Learn next: Structural Bracing — lateral stability for tall walls
- Combine with: Courtyard Cluster — the low-rise alternative