Reinforce the buildings the whole settlement depends on, the gathering hall, the food and water stores and the clinic, and leave houses ordinary. Thickening the walls of a hall with a 44 m perimeter and 3 m walls by 20 cm adds 26 m³ of wall and about 42 tonnes, so do it in the design, with a wider footing, a non-combustible roof, small shuttered windows and exits that open outward by pushing.
Part of Defensive Architecture
Reinforced community buildings are the shared buildings of a settlement, built or strengthened to a higher standard so that they stand and protect their contents and occupants when other buildings do not.
The Hall Is Already The Strongest Building, So Start There
The defensive-architecture guide names the community buildings and refuge points as the buildings to harden, and the safe-room section calls the gathering hall the settlement’s strongest building and the best place for a safe room. The hall guide asks for two exits (a clear opening of at least 120 cm for a stretcher), a floor of earth with stone or brick, and a metal roof, with thatch a fire risk in a building where fires burn regularly (Community Gathering Hall). The emergency-shelter guide adds that the hall, with the floor space it has, shelters only part of the settlement, so decide who goes where (Emergency Shelter Capability). The structural side of a large roof is covered separately (Large-Span Roof Structures).
Worked Example: The Price Of Thicker Walls
Inputs: a hall 10 m by 12 m, so a perimeter 2 × (10 + 12) = 44 m; walls 3 m high; extra thickness 20 cm; earthbag or rammed earth fill at 1,600 kg/m³ (assumed, inside the 1,500-2,000 range of the earth guide).
- Wall face area: 44 × 3 = 132 m².
- Extra volume: 132 × 0.20 = 26.4 m³, about 26 m³.
- Extra mass: 26.4 × 1,600 = 42,240 kg, about 42 tonnes; in force 42,240 × 9.81 = 414 kN.
- Extra line load: 0.20 × 3 × 1,600 × 9.81 = 9.4 kN per metre of wall. On soft clay at 24-48 kPa (Foundation Design) that needs a further 9.4 ÷ 48 = 0.20 to 9.4 ÷ 24 = 0.39 m of footing width.
- Openings: two exits of 1.2 m and four windows of 1 m × 0.6 m take about 2 × (1.2 × 2.0) + 4 × (1 × 0.6) = 4.8 + 2.4 = 7.2 m² out of the 132 m², or 5%, but they are where the wall is weakest.
So retrofitting is feasible but not cheap, and thickening is far easier when the building is designed thick than when it is added.
What You Need
- A list of the buildings to reinforce with a reason for each
- Footing width from the soil test and the wall load
- A non-combustible roof: metal, tile or earth
- Small, high windows with interior shutters
- Doors that open outward by pushing, at least two on different walls
Method: Reinforce Without Making A Trap
Step 1: Reinforce the hall first, then the water and food stores, then the clinic.
Step 2: Make the walls thick from the start where you can; where you cannot, add an outer shell of earthbag or rammed earth with a footing to match.
Step 3: Fit the roof with metal, tile or earth and screen all vents (Ember Protection).
Step 4: Keep windows small and high, with interior shutters of thick wood or metal lining that close and bar from inside.
Step 5: Make every exit from the main hall outward and push-open. Put the barring on the outside, for when the building is empty.
Step 6: Keep a small hardened room for non-combatants inside, with its own rules (Safe Rooms & Refuge Points).
Common Mistakes
- Hardening the walls and leaving a thatched roof. One burning ember undoes it.
- A single door. The hall holds a crowd and it will have a fire.
- A bar on the hall’s main door. A bar cannot be lifted against a crowd.
- Using the hall’s strength as a reason to crowd it. Capacity is set by floor space, water and toilets.
Safety
The hall is where a crowd presses on a door
On the exit of a hall or any room that can hold a crowd, a drop bar is a crush mechanism: a bar cannot be lifted against a press of bodies pushing the door shut, and in a fire that is the press you get. The one-movement test, that a child in the dark can open it, is necessary but not enough, since a bar passes it in a quiet room and fails it under a crowd. The exit opens outward, by pushing, with no bar, hook, latch or lock to work first. Secure the hall from outside when it is empty.
What’s Next
- Learn next: Safe Rooms & Refuge Points — the protected room inside
- Combine with: Fire-Resistant Building Materials — the roof and walls against fire