Cob Construction — FarmPal

A sculptural building method using hand-mixed earth, sand, straw, and water formed into monolithic walls without molds or forms. One of the oldest and most artistic natural building techniques, allowing curved walls, built-in furniture, and organic shapes.

History

Used in England for 800+ years. Thousands of cob buildings from the 1400s still stand in Devon, UK. Revived by Ianto Evans and the Cob Cottage Company in Oregon.

Cost/sq ft
$5-$25
Build Time
12-30 weeks
Crew Size
2-10 people
DIY Friendly
Yes ✓
Code Compliance
challenging
Thermal Mass
very-high
R-Value
R-1 per 4 inches (mass wall stores/releases heat slowly)
Lifespan
500+ years (proven in UK)

Best Climates

temperate
mediterranean
mild humid

Resistance Ratings (1-5)

tornado★★★★☆
hurricane★★★☆☆
earthquake★★★★☆
fire★★★★★
flood★★☆☆☆
mold★★★☆☆
termites★★★★★
bullets★★★★☆

Materials

Clay-rich subsoil
Sharp sand
Straw (long fiber)
Water
Stone for foundation
Lime plaster

Build Steps

  1. 1Build stone or gravel bag stem wall (min 18" above grade)
  2. 2Mix cob on a tarp: stomp clay, sand, straw with feet (the "cob dance")
  3. 3Form cob into loaves about the size of a bread loaf
  4. 4Build walls in 12-18" lifts per day (no more to prevent slumping)
  5. 5Let each lift dry slightly before adding next (1-3 days)
  6. 6Knit each new lift into the previous with thumbing technique
  7. 7Sculpt window and door openings embed frames as you build
  8. 8Create built-in shelves, niches, benches as you go
  9. 9Top walls with bond beam for roof attachment
  10. 10Apply 2-3 coats of lime or earthen plaster

✓ Pros

  • •Almost free materials
  • •Incredibly artistic/sculptural
  • •Fireproof
  • •Excellent thermal mass
  • •Non-toxic
  • •Fun to build with groups

✗ Cons

  • •Very slow building process
  • •Poor insulation in cold climates
  • •Vulnerable to driving rain without protection
  • •Hard to get permits

⚠️ Warnings

  • •Never build in freezing temperatures water in cob will expand
  • •Must have proper foundation to prevent rising damp
  • •Slow process patience is essential
  • •Building codes may require engineer stamp