PDC Natural Building & Shelter Design 2 — Questions and Answers
Question 1: Adobe construction is distinguished from cob primarily by which characteristic?
- Using synthetic polymer binders instead of clay
- Being poured in place like conventional concrete
- Using pre-formed, sun-dried earthen bricks laid in courses (Correct answer)
- Requiring kiln firing for adequate structural strength
Correct answer: Using pre-formed, sun-dried earthen bricks laid in courses
Adobe uses pre-formed, sun-dried mud bricks laid in courses with earthen mortar, distinguishing it from monolithic methods like cob where the wall is built as a single mass.
Question 2: What is the primary structural advantage of rammed earth construction over other earthen building techniques?
- It has very high insulation values comparable to rigid foam board
- It creates dense, load-bearing walls with high compressive strength (Correct answer)
- It requires no formwork or specialized equipment to construct
- It is the lightest of all natural building materials per square foot
Correct answer: It creates dense, load-bearing walls with high compressive strength
Rammed earth compresses moist soil in formwork layer by layer, creating extremely dense walls with high compressive strength well-suited for load-bearing applications.
Question 3: How do Compressed Earth Blocks (CEB) primarily differ from traditional sun-dried adobe bricks?
- They use fired clay rather than sun-dried materials
- They incorporate Portland cement as a stabilizer in all formulations
- They are mechanically pressed to achieve higher density and uniformity (Correct answer)
- They are only suitable for below-grade foundation construction
Correct answer: They are mechanically pressed to achieve higher density and uniformity
CEB are formed using a mechanical press that compresses moistened earth under high pressure, producing a more uniform, denser block than hand-formed and sun-dried adobe.
Question 4: A thermal chimney (solar chimney) in a natural building functions by using which physical principle?
- Burning biomass fuel to heat air and distribute it through the building via ducts
- Using solar panels to power a fan that circulates cool air from underground
- Using heated air's natural tendency to rise, drawing cooler replacement air in at lower openings (Correct answer)
- Reflecting sunlight off mirrored surfaces onto water to generate cooling steam
Correct answer: Using heated air's natural tendency to rise, drawing cooler replacement air in at lower openings
A solar chimney works through the stack effect — the sun heats air inside the chimney, causing it to rise and exit at the top, drawing cooler outdoor air into the building from lower openings.
Question 5: In natural building, a 'rain screen' wall assembly primarily protects against what problem?
- Ultraviolet radiation degrading natural clay plasters over time
- Water infiltration by creating a drainage and drying cavity behind the outer cladding (Correct answer)
- Wind loads exceeding the structural capacity of earthen wall systems
- Insect infiltration through hairline cracks in natural plaster finishes
Correct answer: Water infiltration by creating a drainage and drying cavity behind the outer cladding
A rain screen creates a ventilated cavity between the exterior cladding and the wall assembly, allowing any water that penetrates the outer layer to drain away and dry before reaching the structural wall.
Question 6: Cordwood (stackwall or log-end) construction primarily uses which building technique?
- Whole timber logs notched and stacked horizontally in a log cabin style
- Short, debarked log sections stacked perpendicular to the wall face within a mortar matrix (Correct answer)
- Split firewood bundled and tied with wire to serve as insulation panels
- Milled dimensional lumber alternated with earthen mortar in horizontal courses
Correct answer: Short, debarked log sections stacked perpendicular to the wall face within a mortar matrix
Cordwood construction stacks short, debarked log sections perpendicular to the wall plane set in mortar, creating a wall with the wood's end grain exposed on both interior and exterior faces.
Question 7: What is the primary moisture-related challenge builders must address in straw bale construction?
- Straw shrinks excessively when dry, leaving structural gaps throughout the wall
- Straw bales must be kept dry before and during construction to prevent mold and rot (Correct answer)
- Finished straw bale walls cannot accept any type of plaster or render coating
- Straw loses all insulative value when exposed to cold winter temperatures
Correct answer: Straw bales must be kept dry before and during construction to prevent mold and rot
Straw bales must maintain low moisture content (below approximately 20%) before and during construction to prevent mold, rot, and structural degradation within the enclosed wall assembly.
PDC Natural Building & Shelter Design 2
Adobe construction is distinguished from cob primarily by which characteristic?