In a row of homes the party walls act as cross walls that brace the building against sideways loads from wind and earthquake, so a gale of 24 m/s pushing about 42 kN onto a 30 m long, 3 m high face is shared among seven walls, roughly 6 kN each, against a sliding resistance of tens of kilonewtons. The weak direction is along the row, where the long front and back walls are pierced by windows and doors and rely on solid piers, a bond beam and a roof tied to the walls.
Part of Multi-Family Housing Design
Structural bracing is the arrangement of walls, ties and roof that keeps a building from racking or collapsing under sideways forces.
Wind Pushes Sideways, And Walls At Right Angles Carry It
Gravity loads press straight down; wind and earthquake push sideways (Wind Loads). A building resists a sideways push mainly through walls parallel to the push, acting as shear walls. In a row of homes the party walls run front to back, so they brace the row against wind on its long faces. They do nothing against wind on the end face; there, the front and back walls must do the bracing.
Worked Example: A Six-Unit Row In A Gale
Inputs: six units of 5 m frontage (row length 30 m), face height 3 m; design wind 24 m/s and dynamic pressure q = ½ × ρ × V² = 360 Pa, from Wind Loads; net pressure coefficient 1.3 for combined push on the windward face and suction on the leeward (assumed from common textbook values, which you should confirm for your roof shape); seven party and end walls (n + 1), each 5 m × 3 m × 0.4 m thick of earth at 1,500-2,000 kg/m³; friction coefficient at the base 0.5 (assumed).
- Pressure = 360 × 1.3 = 468 Pa.
- Face area = 30 × 3 = 90 m². Force F = 468 × 90 = 42,120 N ≈ 42 kN. This is a force; the weight of 4,300 kg would be the same 42 kN.
- Equal share across seven walls: 42 ÷ 7 = 6.0 kN each (a simplification: end walls carry about half the share of an interior one).
- Weight of one cross wall = 5 × 3 × 0.4 = 6 m³ of earth; mass 9,000 to 12,000 kg; weight 9,000 × 9.81 = 88 kN to 12,000 × 9.81 = 118 kN.
- Sliding resistance = 0.5 × weight = 44 to 59 kN against 6 kN of demand, a ratio of about 7 to 10.
The cross walls have large reserve in this case. The danger is elsewhere.
- Wind on the end face: 468 Pa × (5 m × 3 m = 15 m²) = 7.0 kN, resisted by the front and back walls. If those are mostly openings, there is little wall to resist it, and the weakest point is the corner and the pier between a door and a window.
What Can Go Wrong
- Long free walls. A front wall 30 m long between cross walls 5 m apart is held at each cross wall, but between them it bends out of plane under suction; the roof and the bond beam hold its top (Bond Beam and Top Plate).
- Weak joints between units built at different times. Units added later meet the party wall at a cold joint. Interlock the courses (alternate toothing) and tie the joint with wire, as the earthbag guide does at corners with barbed wire extending at least 50 cm along each wall face (Earthbag Building).
- Openings in the cross wall for doors between units remove shear capacity, so keep them small and framed with lintels (Doors and Windows).
- Weight in an earthquake. A massive wall carries a lateral force in proportion to its weight, and earth has little strength in tension; tie the walls into one ring with a continuous bond beam. No numerical earthquake rule is given here, because the corpus has none.
- The roof as the tie. A continuous roof ties the walls into one box, but a combustible continuous roof carries fire across the party walls; fire-stop the roof void (Row Houses).
What You Need
- A wind speed estimate for the site (Wind Loads)
- A continuous bond beam or top plate on every wall
- Foundations on one level and one material for the whole row
Method
Step 1: Orient the party walls across the strongest wind direction, which is usually the prevailing one.
Step 2: Keep openings in the long faces to piers of solid wall between them; place doors and windows well away from corners.
Step 3: Bond every new unit into the previous one’s party wall.
Step 4: Tie the top of all walls with a bond beam and fasten the roof to it against uplift.
Common Mistakes
- Treating kN as kg — 42 kN is about 4,300 kg of weight, not 42,000.
- Bracing only one direction.
- Cutting a wide opening through a party wall for a shared room.
Safety
Racked or leaning walls can fall without warning
A wall that leans, shows a stepped diagonal crack or has moved at a joint is unsafe. Move people out of the building and the strip of ground next to it equal to the wall height, and do not prop it from the inside.
What’s Next
- Learn next: Apartment-Style (Stacked Units) — bracing when the walls are taller
- Combine with: Structural Advantages of Shared Walls — the overview