The defensive-architecture guide’s table of wall thickness needed to stop a rifle round names no cartridge, range or test, so none of it can be checked here, but a mass-per-area check shows where to be careful: its earth, stone, brick, concrete and sandbag entries all lie between 345 and 810 kg per m² of wall, while softwood logs at 125-175 kg and plastered straw bale at about 150 kg are 2 to 6 times lighter. Treat those two as cover from view and not as protection from rifle fire until they are tested, and put earth fill, not straw or wood, in any refuge wall.
Part of Defensive Architecture
Ballistic resistance by material is the comparison of how thick a wall of each common building material must be to stop a rifle round, and what that implies for which walls to trust.
A Thickness Without A Cartridge Is Half A Claim
The guide’s table lists the thickness to stop a rifle round: earthbag with earth fill 30-40 cm; rammed earth 35-45; stone 20-30 (it can shatter and send fragments); concrete or urbanite 15-25 if solid; solid brick 20-25; softwood log 25-35 if tight-fitted; plastered straw bale the full 45 cm width (“surprisingly good, dense straw absorbs energy”); and sandbags 40-45. It concludes that earthbag, straw bale and rammed earth walls at normal building thickness give meaningful protection. The fortification guide supports the idea for earth and sandbags and says mass stops projectiles (Fortification Materials).
What is missing is the cartridge, the range, whether the earth is dry or wet, and whether one hit or many. Penetration depends strongly on all of them, and armour-piercing or large-calibre rounds go through far more than a common rifle round. I cannot verify the table’s thicknesses against a test from the sources available here, so this article does not endorse any single figure.
Worked Example: A Consistency Check By Mass Per Area
The fortification guide’s principle is mass. A cheap check is to compute the mass of each wall per square metre of its face, thickness times density, and see whether the entries that are said to stop the same round have similar masses. The densities are assumed typical values (compacted earth 1,600 and rammed earth 1,800 kg/m³ within the earth guide’s 1,500-2,000 range; stone 2,500; concrete 2,300; brick 1,800; softwood 500; straw bale 100-130; plaster 1,700, in coats 3 cm thick on each side of the bale); they are not from this corpus except the earth range, and the plaster thickness is also assumed.
| Material | Thickness | Mass per m² of wall |
|---|---|---|
| Earthbag, earth fill | 30-40 cm | 0.30 × 1,600 = 480 to 0.40 × 1,600 = 640 kg |
| Rammed earth | 35-45 cm | 0.35 × 1,800 = 630 to 0.45 × 1,800 = 810 kg |
| Stone | 20-30 cm | 500 to 750 kg |
| Concrete | 15-25 cm | 345 to 575 kg |
| Brick | 20-25 cm | 360 to 450 kg |
| Sandbags | 40-45 cm | 640 to 720 kg |
| Softwood log | 25-35 cm | 0.25 × 500 = 125 to 0.35 × 500 = 175 kg |
| Plastered straw bale | 45 cm | bale alone 0.45 × 100 = 45 to 0.45 × 130 = 59 kg; with 3 cm of plaster each side 2 × 0.03 × 1,700 = 102 kg more, 147 to 161 kg |
- The first six rows lie between 345 and 810 kg per m², a spread of 810 ÷ 345 = 2.3 times.
- The last two rows differ. Softwood log at 125-175 kg is 345 ÷ 175 = 2 to 810 ÷ 125 = 6.5 times lighter than those rows.
- Plastered straw bale at about 150 kg is 345 ÷ 161 = 2.1 to 810 ÷ 147 = 5.5 times lighter.
Mass is not the only factor. A hard face over a soft core can behave differently from a uniform wall, and the table may rest on tests I cannot see. But a result that puts a wall four times lighter than an earth wall in the same category is a claim that needs its source, and the guide gives none. The table also lists denser rammed earth as needing a greater thickness than looser earthbag, the reverse of what density predicts; the difference is within the uncertainty.
What You Need
- Earth, gravel or sand for fill, and a way to tamp it
- Weatherproof plaster over earthbag or fill, to keep it from rotting
- A written statement of the threat and its cartridges, if known
- A test, if one can be done safely and legally, or an honest “unknown”
Method: Choose A Wall For A Refuge
Step 1: Name the threat tier (Threat Categories & Likely Scenarios).
Step 2: Use earth, gravel or sandbag fill for the refuge wall, at the thick end of the guide’s range, with stone and brick as secondary.
Step 3: Keep the fill dry and plastered, since bags rot and fill spreads.
Step 4: Avoid straw and softwood as the protective layer unless tested; use them as insulation or cover.
Step 5: Make openings small and shuttered, because the opening is the weak point.
Step 6: Check the roof and floor, which are walls too.
Common Mistakes
- Quoting a thickness without a round. There is no such figure.
- Trusting one hit. A wall that stops one round may fail on repeated hits at the same spot.
- Stone without a backing. It can shatter and throw fragments.
- Believing a hardened building makes the settlement safe. Walls do not fight; people do.
Safety
False assurance and fire
A shelter wall that is believed to be bulletproof and is not puts people at the wall when they should be elsewhere. A hardened refuge is also a fire risk if it has a thatch roof, a single barred door or a stove: a room holding a crowd must exit outward by pushing, with nothing to work first. Heavy walls fall hard; keep clear of a leaning wall by at least its height.
What’s Next
- Learn next: Reinforced Community Buildings — applying the walls to the hall and stores
- Combine with: Safe Rooms & Refuge Points — the room the wall protects