Comprehensive Study Notes: Building Materials and Materiality

Timber as a Building Material: Properties, History, and Applications

• Historical Development of Timber Construction:
  • Pre-Industrial Timber Framing: Traditional half-timbered construction (Fachwerkbau) was the dominant regional building method across Germany, shaped by local climatic conditions, regional wood species, and craftsmanship.
  • Example: Rathaus Kirchheim unter Teck (built in 1724). Just 15 years after the municipal administration moved in, half-timbering was considered outdated and was completely plastered over; the historical framework was re-exposed in the 20th century.

• Resource Overexploitation (Around 1800): Approximately 90% of the population depended on agriculture. Forests served as raw material sources for firewood, mining timber, and charcoal production, and were heavily cleared for agricultural land. Overexploitation left Germany almost entirely deforested by 1800.
• Emergence of Sustainability (Nachhaltigkeit): Hanns Carl von Carlowitz published Sylvicultura oeconomica oder hauswirtliche Nachricht und naturmäßige Anweisung zur wilden Baumzucht in 1713, defining sustainability as continuous, consistent, and lasting utilization (kontinuierliche beständige und nachhaltende Nutzung).
• Industrialization & Urbanization: Industrialization broke the tight coupling between population growth and deforestation. Newer materials (steel, concrete, masonry) displaced timber as the dominant structural material in urban centers. During the Gründerzeit (ca. 1871–1914), timber was limited primarily to urban roof trusses (Dachstühle) and floor beam anchors (Balkenanker connecting wooden floor joists to exterior brick walls).

• Modern Prefabrication & Ideology: Konrad Wachsmann designed the Albert Einstein Country House in Caputh (1930) using early timber prefabrication systems. During the National Socialist era (1933–1945), timber construction was promoted as a "German tradition" and an ideological counter-design to Modernism (Neues Bauen), exemplified by the Kochenhofsiedlung in Stuttgart (1933).

• Post-War Rebuilding: Timber was increasingly perceived as rural and backward; post-war reconstruction turned heavily toward concrete and masonry.

• Contemporary Timber Renaissance: Growing ecological awareness re-established timber as a modern, high-tech material. Milestones include the Eisbärhaus in Kirchheim Teck (Bankwitz Architekten, 2009, based on the Vorarlberger Ökoleitfaden), robotic fabrication, modular prefabrication, and serial vertical extensions (Aufstockung). The BUGA Timber Pavilion in Heilbronn (2019, ICD + ITKE University of Stuttgart) represents advanced digital design and robotic assembly.

• Market Share Statistics: The percentage of residential buildings constructed in timber nationwide in Germany rose from 8% in 1991 to 17.8% in 2018, 18.7% in 2019, 20.4% in 2020, 21.2% in 2021, 21.3% in 2022, and 22% in 2023. In Baden-Württemberg (BW), the timber residential construction share reached 35.2%.

  • Structure and Anatomical Properties of Wood:

• Anatomy of a Tree Cross-Section (Querschnitt / Hirnschnitt):

  • Pith (Markröhre): The central core of the trunk.
  • Heartwood (Kernholz): The inner, dead structural core, often darker and impregnated with natural extractives for biological durability.
  • Sapwood (Splintholz): The outer, living wood layer responsible for water and nutrient transport.
  • Annual Rings (Jahrringe): Composed of light-colored Earlywood (Frühholz, rapid growth, large cells, lower density) and dark-colored Latewood (Spätholz, slow growth, thick-walled cells, high density).
  • Cambium (Kambium): The microscopic cell-dividing layer producing wood cells inward and bark cells outward.
  • Bark (Rinde): Composed of Phloem (Bast, inner living bark transporting sugars) and Outer Bark (Borke, protective dead outer layer).

• Cutting Planes:

  • Cross-Section (Querschnitt / Hirnschnitt): Perpendicular to the longitudinal axis.
  • Tangential Cut (Tangentialschnitt / Fladerschnitt): Parallel to the longitudinal axis and tangential to the annual rings.
  • Radial Cut (Radialschnitt / Spiegelschnitt): Parallel to the longitudinal axis through the pith.

• Anisotropy and Physical Mechanics:

  • Definition: Anisotropy refers to directional dependence of mechanical properties. Wood is composed of oriented cellulose fibers.
  • Load Capacity: Parallel/longitudinal to the fiber direction, timber can absorb approximately 10 times more force than perpendicular/transverse to the fiber direction.

• Wood Moisture and Hygrothermal Behavior:

  • Equilibrium Moisture Content (Ausgleichsfeuchte / Feuchtegleichgewicht): Wood continuously absorbs or releases moisture until it reaches equilibrium with ambient relative humidity and temperature. Standard equilibrium ranges include:
  • Enclosed heated spaces: $9 \pm 3\%$
  • Enclosed unheated spaces: $12 \pm 3\%$
  • Covered open structures: $15 \pm 3\%$
  • Fully weather-exposed structures: $18 \pm 6\%$
  • Swelling (Quellen) and Shrinking (Schwinden): Moisture change below the fiber saturation point induces dimensional changes. Shrinkage varies significantly across fiber directions (greatest tangentially, moderate radially, negligible longitudinally), causing distinct distortion shapes (Schwindformen) depending on cut geometry (Herzbrett, Mittelbrett, Seitenbrett, Kantholz).

• Softwood vs. Hardwood Classification:

  • Softwood (Nadelholz): Fast-growing, lighter, uniform cell structure, easy to work. Examples: Spruce (Fichte), Fir (Tanne), Larch (Lärche), Douglas Fir (Douglasie).
  • Hardwood (Laubholz): Slower-growing, higher density, harder, superior mechanical strength, often more complex to machine. Examples: Beech (Buche), Oak (Eiche), Ash (Esche), Black Locust (Robinie).

• Comparative Performance Overview:

  • Softwoods: Density e.g. Spruce $470\,kg/m^3$. Long, straight fibers. Ideal for structural framing, roof trusses, glulam, light wood framing. Advantages: affordable, lightweight, easy to process. Disadvantages: lower wear resistance, softer surface, susceptible to pests/fungi.
  • Hardwoods: Density e.g. Beech $720\,kg/m^3$. Short, entwined fibers. Ideal for flooring, furniture, stairs, heavy structural framing. Advantages: high hardness, superior compressive/bending strength, durable. Disadvantages: costly, heavy, prone to drying cracks (e.g. Beech).

• Trunk Utilization Zones: Crown (firewood), Industrial Wood (paper, particleboards), Top Log / Zopfstück (timbers, ties, pallets), Middle Log / Mittelstamm (beams, boards, posts), Butt Log / Erdstamm (premium joinery, glulam, veneer), Stump / Wurzelstock (decorative veneers).

  • Comprehensive Tree Species Overview:

• Spruce (Fichte, Softwood): 25% share of German forests. Harvest age $60\text{--}80\,\text{years}$. Lightweight, yellow-white, resinous. Used for roof structures, spars, interior framing.

• Pine (Kiefer, Softwood): 22% share. Harvest age $80\text{--}120\,\text{years}$. Yellow-reddish, resinous, durable. Used for doors, windows, flooring, log homes.

• Beech (Buche, Hardwood): 15% share. Harvest age $100\text{--}150\,\text{years}$. Light reddish, dense, neutral odor, sensitive to moisture. Used for stairs, furniture, parquet, interior fit-outs.

• Oak (Eiche, Hardwood): 10% share. Harvest age $150\text{--}200\,\text{years}$. Dark brown, acid odor, highly durable outdoors. Used for parquet, timber framing, bridges, hydraulic engineering.

• Larch (Lärche, Softwood): 2% share. Harvest age $80\text{--}120\,\text{years}$. Red-brown, resinous, intense forest smell. Used for facades, decking, outdoor structures.

• Douglas Fir (Douglasie, Softwood): 2% share. Harvest age $60\text{--}90\,\text{years}$. Reddish, citrus aroma, weather-resistant. Used for cladding, carports, fencing.

• Fir (Tanne, Softwood): 2% share. Harvest age $100\text{--}140\,\text{years}$. Light color, resin-free, neutral scent. Used for roof trusses, framing, windows.

• Black Locust (Robinie, Hardwood): Low share. Harvest age $30\text{--}50\,\text{years}$. Extremely hard, yellow-olive, invasive. Used for playground equipment, bridges, outdoor furniture.

• Ash (Esche, Hardwood): Low share. Harvest age $80\text{--}100\,\text{years}$. Tough, flexible, light yellow. Used for sports equipment, parquet, bentwood elements.

• Alder (Erle, Hardwood): Low share. Harvest age $50\text{--}70\,\text{years}$. Reddish-brown, moisture-resistant under water. Used for boat building, furniture.

• Birch (Birke, Hardwood): Low share. Harvest age $50\text{--}80\,\text{years}$. Light yellow, soft hardwood. Used for plywood, furniture, wall linings.

• Walnut (Walnuss, Hardwood): Low share. Harvest age $100\text{--}150\,\text{years}$. Noble dark brown, heavy. Used for luxury interior fittings, parquet.

  • Fire Performance and Weathering:

• Fire Resistance: Non-combustibility of a material does not equal fire resistance of an assembly. Bare steel (non-combustible) loses structural capacity within 30 minutes in a fire. Glued laminated timber burns on the exterior forming an insulating char layer (Verkohlungsschicht), retaining core structural capacity for over 90 minutes.

• Burn Rates:

  • Softwood and Beech glulam ($\text{density} \ge 290\,kg/m^3$): One-dimensional rate $\beta_0 = 0.65\,mm/min$, nominal rate $\beta_n = 0.7\,mm/min$.
  • Softwood solid timber ($\text{density} \ge 290\,kg/m^3$): $\beta_n = 0.8\,mm/min$.
  • Hardwood solid timber or glulam ($\text{density} \ge 450\,kg/m^3$): $\beta_0 = 0.50\,mm/min$, $\beta_n = 0.55\,mm/min$.

• Weathering and Discoloration: Exterior wood grays due to UV radiation and rain leaching (Auswaschung). Example: Kapelle Sogn Benedetg in Sumvitg (Peter Zumthor, 1988), where unpainted shingles turn silvery-gray over time.

• Forest Ecology and Sustainable Management:
  • Forest Services: Carbon storage, oxygen production, water/air filtration, soil protection, biodiversity, climate regulation, recreation.
  • Carbon Sequestration: German forests store $58\text{ million tonnes of } CO_2 \text{ per year}$, while harvested wood products retain an additional $3\text{ million tonnes of } CO_2 \text{ per year}$. 100% of German forests are legally sustainably managed, with 75% certified under strict independent standards (e.g. PEFC).
  • Forest Transformation (Waldumbau): Monoculture spruce forests are acutely vulnerable to climate change, droughts, storms, and bark beetle (Borkenkäfer) infestations. Sustainable forestry mandates transforming monocultures into diverse, permanent mixed forests (Dauerwald e.g. Bärenthoren model).
  • Lifespan Disparity: Tree growth cycles ($60\text{--}200\,\text{years}$) must be balanced against average building lifespans: Residential ($80\,\text{years}$), Office/Commercial ($60\,\text{years}$), Retail/Hotels/Clinics ($40\,\text{years}$), Temporary leisure facilities ($30\,\text{years}$).

Mineral-Bound Building Materials: Limes, Gypsums, and Cements

• Definition and Core Characteristics:

  • Mineral Materials: Inorganic, mostly geological raw materials characterized by high compressive strength, durability, and hardening via physical or chemical processes. Includes concrete, mortar, plasters, screeds, gypsum elements, and sand-lime bricks (Kalksandstein).
  • Distinction from Ceramics: Ceramic materials gain mechanical strength through firing and sintering (Brennen und Sintern). Mineral-bound materials bind aggregates together using a chemical binder that hardens via hydration or carbonatization.

• Historical Timeline of Mineral Binders:

  • Prehistoric & Ancient: Çatalhöyük (~9000 BC) early earth/lime plasters; Khafre Pyramid (2550 BC); 1st Century BC Roman hydraulic lime ("water mortar").
  • Roman Innovations: Opus signinum (lime mortar with crushed terra-cotta for waterproofing, linings, decorative screeds) and Opus caementitium (cast masonry or "Roman concrete", used in vaulting and aqueducts like the Eifel Aqueduct ~80 AD and Segovia Aqueduct ~98 AD).
  • 18th Century Science: John Smeaton (1756) analyzed hydraulic limes for Eddystone Lighthouse; James Parker patented "Parker Cement" (1796); Louis-Joseph Vicat published scientific studies on civil mortars and hydraulic limes.
  • Industrial Era: Joseph Aspdin and industrial pioneers developed Portland cement (1820s); Schifferdecker & Söhne (1883); Alsen cement factory in Itzehoe (1895). Sand-lime brick (Kalksandstein) production began around 1880. Modern gypsum plasterboards (Rigips, Gipsunion AG) emerged around 1910.

• Chemical Binding Principles and Hardening Cycles:

  • Non-Hydraulic Binders (Luftbindemittel): Require atmospheric carbon dioxide and air exposure to harden; not permanently water-resistant once cured (suitable mainly for interior applications). Examples: Air lime (Luftkalk), Gypsum (Gips), Anhydrite, Magnesia.

  • Air Lime Cycle (Kalkkreislauf):

  1. Burning (Kalkbrennen): Limestone is heated to approximately $900\,^\circ C$:        $CaCO_3 \rightarrow CaO + CO_2$
  2. Slaking (Kalklöschen): Quicklime reacts exothermically with water to produce calcium hydroxide:        $CaO + H_2O \rightarrow Ca(OH)_2$
  3. Carbonatization (Carbonatisierung): Applied slaked lime absorbs atmospheric carbon dioxide to re-form calcium carbonate:        $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$
  • Gypsum Cycle (Gipskreislauf):
  1. Calcining/Burning (Calcinieren): Natural gypsum dehydrates upon heating:        $CaSO_4 \cdot 2H_2O \rightarrow CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
  2. Rehydration (Anmachen mit Wasser): Hemihydrate recrystallizes with added water:        $CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$

• Hydraulic Binders (Hydraulische Bindemittel): Hardening occurs via hydration (chemical reaction with water); cured products harden under water and remain permanently water-resistant with high compressive strength. Examples: Hydraulic limes, Portland cement, masonry binders.

• Cement Hydration Cycle:

  1. Burning: Limestone and clay are sintered at $1450\,^\circ C$ into cement clinker, releasing process $CO_2$:        $CaCO_3 + \text{clay minerals} \rightarrow \text{Clinker} + CO_2$
  2. Hydration: Clinker ground with gypsum reacts with water to form Calcium-Silicate-Hydrate (C-S-H) phases and Portlandite:        $\text{Cement Minerals} + H_2O \rightarrow C\text{-}S\text{-}H \text{ phases} + Ca(OH)_2$

• Water-Binder Ratio (Wasser-Bindemittel-Wert): Stoichiometric water requirement for calcium sulfate hemihydrate is $0.19$. Practical job-site ratios range from $0.6\text{--}0.8$. Excess unreacted water evaporates post-hardening, leaving microscopic capillary pores that directly reduce ultimate mechanical strength.

  • Application Forms and Engineering Specifications:

• Masonry Mortar (Mauermörtel): Composed of binder, water, sand, and functional additives. Provides joint load transfer, stress compensation, airtightness, and acoustic sealing.

  • Normal Mortar (NM): Standard bed joint thickness $\approx 12\,mm$.
  • Lightweight Mortar (LM): Contains porous aggregates (perlite, pumice, expanded clay) for enhanced thermal insulation.
  • Thin-Bed Mortar (TM): Joint thickness $1\text{--}3\,mm$ for high-precision block masonry, reducing thermal bridging.

• Plasters (Putze): Applied in multi-coat systems: Vorspritz (adhesion spatter dash), Unterputz (basecoat leveling layer), and Oberputz (finish finish coat). Types include Gypsum plaster (smooth interior), Lime plaster (breathable, mold-inhibiting high pH), Lime-Cement plaster (durable, exterior), Cement plaster (high strength, wet rooms, plinths), and Renovation plaster (Sanierputz, high porosity for storing crystallizing salts in damp masonry).

• Screeds (Estriche): Provide level subfloors and load distribution.

  • Cement Screed (CT): Moisture-resistant, robust, used in basements, industrial floors, outdoor decks.
  • Calcium Sulfate Screed (CA / Anhydrite): Very low shrinkage, high thermal conductivity (ideal for underfloor heating), smooth, but moisture-sensitive.
  • Dry Screed (Trockenestrich): Prefabricated board elements, fast installation, zero construction moisture, lower maximum load capacity.
  • Terrazzo: Decorative polished screed consisting of a cementitious matrix with graded natural stone aggregates.
  • Construction Configurations: Bonded screed (Verbundestrich), Screed on unbonded/separation layer (auf Trennlage), Floating screed (Schwimmender Estrich over acoustic/thermal insulation layer).

• Sand-Lime Bricks (Kalksandstein): Manufactured from lime, quartz sand, and water, hardened under pressurized steam in autoclaves at $160\text{--}220\,^\circ C$. High density, precise dimensions, superior acoustic mass and fire protection (e.g. Kinderhaus Entlisberg, Bernath & Widmer with Gianluca De Pedrini, 2013, featuring slurry-washed sand-lime masonry).

  • Environmental Impact and Circularity:

• Cement Decarbonization: Cement manufacturing accounts for $\approx 8\%$ of total global $CO_2$ emissions. Breakdown: $\approx 1/3$ comes from thermal fuel combustion (energy), while $\approx 2/3$ stems directly from raw material calcination ($CaCO_3 \rightarrow CaO + CO_2$).

• Gypsum Recycling & Coal Phase-Out: Germany produces $240\text{ million } m^2$ of plasterboard annually, generating $10\%$ installation waste ($24\text{ million } m^2$ directly as waste). Flue-Gas Desulfurization gypsum (REA-Gips) from coal-fired power stations will disappear with the national coal phase-out, mandating closed-loop plasterboard recycling or increased natural gypsum quarrying.

Ceramic Materials in Architecture: Structural Ceramics, Tiles, and Systems

• Systematics and Material Classification of Baukeramik:
  • Classification Principles: Ceramics are categorized by grain size (coarse vs. fine), body density/water absorption (porous vs. dense/sintered), firing color (white/light vs. non-white), and product type.

• Coarse Ceramics (Grobkeramik):
  • Porous Body (Irdengut / Tongut, Water Absorption $> 10\%$):
    • Non-white burning: Masonry bricks (Mauerziegel including vertically perforated Hochlochziegel), floor tiles, roofing tiles (Dachziegel), clay pipes (Tonrohre), cable conduits.
    • White/light burning: Refractory items (Schamotte-, Sillimanit-, Dinassteine).
  • Dense Body (Sinterzeug / Tonzeug, Water Absorption $< 3\%$):
    • Non-white burning: Brick clinker (Klinker), brick slips (Riemchen), split tiles (Spaltplatten), floor clinker, vitrified stoneware pipes.

• Fine Ceramics (Feinkeramik):

  • Porous Body (Irdengut / Tongut):

    • Non-white burning: Pottery, flower pots, fayence, terracotta.
    • White/light burning: Glazed earthenware tiles (Steingutfliesen), wall tiles.

  • Dense Body (Sinterzeug / Tonzeug):

    • Non-white burning: Floor stoneware tiles (Steinzeugfliesen), fine terracotta.
    • White burning: Technical porcelain, sanitaryware (washbasins, sinks, lab counters), glass ceramics, oxide ceramics.

  • Earthenware (Steingut - STG) vs. Stoneware (Steinzeug - STZ) Tiles:

• Earthenware Tiles (Steingutfliesen, STG): Fired below sintering limit ($950\text{--}1150\,^\circ C$). Coarse-pored body with water absorption $> 10\%$ (Norm Group BIII). Low mechanical density; not frost-resistant. Requires a functional surface glaze. Soft and easy to cut. Exclusively used for interior wall coverings.

• Stoneware Tiles (Steinzeugfliesen, STZ): Fired above sintering limit ($> 1200\,^\circ C$) creating a dense vitrified matrix. Fine-pored with water absorption $< 3\%$ (porcelain stoneware / Feinsteinzeug $< 0.5\%$). High density, exceptional compressive and bending strength, frost-resistant, high wear resistance. Available glazed or unglazed/through-colored. Difficult to cut. Used for heavy-duty interior/exterior floors, facades, and public areas.

• Historical Evolution of Architectural Ceramics:
  • Mesopotamia (4th Millennium BC): Early facade protection using colored fired clay cones (Stiftmosaik / Tonkegel) embedded in rammed earth walls.
  • Ancient Egypt (3rd Millennium BC): Decorative glazed wall tiles in the Step Pyramid of Djoser.

• Babylon (604–562 BC): Relief-molded glazed brick facades, e.g. Ishtar Gate.

• Roman Antiquity: Hypocaust radiant underfloor heating using ceramic flue tiles (Tubuli).

• Middle Ages & Renaissance: Lead-glazed floor tiles in churches (13th C); tin-glazed earthenware (Fayence / Majolica) introduced via Islamic trade networks (15th C).

• Baroque (17th C): Delft Blue (Delfter Blau) tile industry in Holland.

• Industrial Era (19th C): Invention of dry pressing by Richard Prosser (1840) and Herbert Minton; mass production of vitrified tiles by Villeroy & Boch (1846). Architectural terracotta (Bauterrakotta) became vital for fireproof curtain facades after the Great Chicago Fire (1871).

• Postmodern & Contemporary: Rear-ventilated rainscreen ceramic facades (VHF) developed in response to the 1973 oil crisis, utilizing modular Design for Disassembly (DfD).

  • Industrial Shaping Processes (Formgebungsprozesse):

• Dry Pressing (Trockenpressen): Granular clay powder ($3\text{--}7\%$ water content) is compressed under high pressure in steel dies. High dimensional accuracy; ideal for standard wall/floor STG and STZ tiles.

• Extrusion (Strangpressen / Extrudieren): Plastic clay mass ($18\text{--}25\%$ water content) is vacuum de-aired and extruded through a shaped die (Extrusionsmatrize), then cut to length by wire. Used for split tiles (Spaltplatten), facade panels, bricks, and terracotta tubes.
• Wet Pressing (Feuchtpressen): Plastic clay ($14\text{--}22\%$ water content) is pressed between two-part molds under low pressure. Produces complex 3D profiles such as interlocking roof tiles (Falzdachziegel).
• Slip Casting (Schlickergiessen): Liquid clay slurry (Schlicker, $40\text{--}45\%$ water content) is poured into porous plaster molds. The plaster absorbs water, depositing a solidified ceramic shell inside the mold before excess slip is drained. Used for complex hollow sanitaryware (WCs, sinks).

• Installation Systems, Patterns, and Special Forms:
  • Installation Systems: Mortar-bonded thin-bed adhesive layers ($2\text{--}30\,mm$) vs. Dry-laid/Mechanically mounted systems (access floors, clipped rear-ventilated rainscreen facade panels).

• Tile Bond Patterns (Verlegeverbände): Grid (Schachbrett), Running bond (Halbverband / Drittelverband), Herringbone (Fischgrät / Schwalbenschwanz), Block pattern (Blockparkett), Diagonal.
• Special Architectural Ceramic Formats: Fayence, Zellige (chiseled Moroccan glazed tiles), Mettlacher Fliesen, Bauterrakotta, Raku tiles, Spaltplatten, Mosaics ($< 100\,mm$), stove tiles (Ofenkacheln), acoustic ceramic panels, paving clinker (Pflasterziegel).

• Re-Use, Thermodynamic Performance, and Innovations:
  • Facade Re-Use Projects: MVRDV Hagen Island (Den Haag, 2002) using full unglazed clay tiles; Loeliger Strub LysP8 (Basel, 2025) re-using reclaimed roof tiles as demountable facade cladding.

• Thermodynamic Evaporative Facades: BIOSKIN system at Sony R&D Office (Tokyo, 2011, Nikken Sekkei) uses water-carrying porous ceramic extrusions ($10\%$ porosity) for evaporative microclimate cooling, lowering ambient air temperatures by $2\,^\circ C$ and facade surface temperatures by $5\text{--}9\,^\circ C$. HSLU Research GreenBrick (2022–2026) integrates internal water circulation with plant growth channels for vertical urban greening and microclimate cooling.
• Robotic Mosaic Assembly: Automated computer-driven layout systems, e.g. Artaic / Eric Sealine Learning to Fly (2011), placing $200{,}000$ porcelain mosaic tiles across $130\,m^2$

Non-Ferrous Metals: Metallurgy, Applications, and Circular Design

• Classification of Architectural Metals:

  • Ferrous Metals (Eisenmetalle): Iron content $> 50\%$ (e.g. structural steel, cast iron, stainless steel).
  • Non-Ferrous Metals (Nichteisenmetalle): Iron content $< 50\%$ (e.g. Copper, Tin, Lead, Zinc, Aluminium).

• Historical Epochs of Non-Ferrous Metallurgy:

  • Copper Age (Kupferzeit / Chalcolithic, ca. 5000–3300 BC): Smelting of native copper; iconic finds include the copper axe carried by "Ötzi" the Iceman (ca. 3300 BC) and the See Riedmatt axe head near Zurich.
  • Bronze Age (Bronzezeit, from ca. 3300 BC): Alloy of copper and tin ($\approx 90\%$ Cu / $10\%$ Sn). Key artifacts: Nebra Sky Disk (Himmelsscheibe von Nebra, ca. 1600 BC) and weaponry from the Tollense Valley battlefield.

• Roman Era / Age of Brass (from ca. 1400–1000 BC): Widespread production of brass (Copper + Zinc alloy) for helmets and coins; silver coinage (Denar); gold treasures (e.g. Panagyurishte gold treasure).

• Modern Industrial Age: Development of lightweight structural metals, particularly industrial electrolysis of Aluminium (20th C, e.g. 1947 Airstream trailers).

  • Detailed Metallurgy of Key Non-Ferrous Metals:

• Copper (Kupfer, Cu):

  • Extracted from copper ores (e.g. Bingham Canyon Mine, USA).
  • High electrical and thermal conductivity; exceptional ductility.
  • Used for electrical wiring, plumbing pipes, underfloor heating loops, roof coverings, and rainwater drainage systems.
  • Natural Patina Formation: Bright metallic red $\rightarrow$ dark brown oxide $\rightarrow$ protective green/turquoise patina (composed of copper carbonates, sulfates, and basic carbonates). Example: Bremen Town Hall roof patina restoration (2016). Architectural examples: Notre-Dame de Paris, Stephansdom Vienna, Fire Station Chamonix (Studio Gardoni, 2016), Writers Studio Aarhus (Sleth, 2021).
  • Contact Corrosion Warning: Direct contact between copper and less noble metals (e.g. zinc, steel) in the presence of an electrolyte (rainwater) causes rapid galvanic corrosion of the less noble metal. Rainwater runoff from copper surfaces must never flow onto downstream zinc or steel roofing elements.

• Tin (Zinn, Sn):
  • Extracted from Cassiterite ore (Zinnerz).
  • Soft, low melting point ($231.9\,^\circ C$).
  • Used primarily as soldering alloy (Lötzinn with flux) for joining sheet metal roofs/pipes, and as the molten metal bath bed in the industrial manufacturing of flat Float Glass (Floatglasverfahren).
• Lead (Blei, Pb):
  • Extracted from ores: Galena (Bleiglanz, $PbS$), Cerussite ($PbCO_3$), Vanadinite, Crocoite, Wulfenite, Pyromorphite.

* Very soft, highly dense, toxic, highly malleable.
* Used for structural cames in stained glass windows (*Bleiglasfenster*) reinforced with internal steel bars, and for self-adhesive flexible flashing around roof penetrations, chimneys, and skylights (*Bleiverkleidung*).

• Zinc (Zink, Zn):
  • Extracted from Sphalerite / Zincblende ($ZnS$) and Zincite (e.g. Rosh Pinah mine, Namibia).

* Processed into rolled sheet coils; shaped manually using folding pliers (*Falzzange*).
* Commonly alloyed with titanium and copper to form Titanium Zinc (*Titanzink* e.g. Rheinzink) for enhanced creep resistance and durability. Example: *House on the Cliff* in Salobreña, Spain (GilBartolome Architects, 2015).

• Aluminium (Aluminium, Al):
  • Extracted from Bauxite ore via open-pit surface mining (e.g. Guinea).
  • Refined to alumina and converted to metallic aluminium via the energy-intensive Hall-Héroult smelting electrolysis.
  • Extruded into complex structural profiles (stranggepresst) or rolled into coils/sheets (e.g. Kalzip standing-seam roof/facade systems). Examples: Frey House I in Palm Springs (Albert Frey, 1947–1953).

• Ecology, Life Cycle Analysis, and Circular Architecture:
  • **Global Warming Potential ($GWP$
  • Circular Economy (Kreislaufwirtschaft) & Butterfly Diagram (Ellen MacArthur Foundation):
  • Biosphere (biological nutrients) vs. Technosphere (technical materials).
  • Priority technosphere strategies: Maintain/Prolong $\rightarrow$ Reuse/Redistribute $\rightarrow$ Refurbish/Remanufacture $\rightarrow$ Recycle.

• Re-Use Case Study: Kopfbauhalle 118 in Winterthur (baubüro in situ, 2022) incorporated reclaimed structural steel sections without remelting, alongside re-used corrugated sheet cladding.
• Design for Disassembly (DfD) Case Study: Student House at TU Braunschweig (Gustav Düsing & Max Hacke, Mies van der Rohe Award 2024 winner) utilizes a completely demountable bolted steel frame structure, featuring steel staircases designed as structural stiffening cores.

Earthen Construction and Earth Building Materials

• History and Vernacular Traditions of Earth Building:
  • Ancient & Vernacular Beginnings: Ancient Egyptian sun-dried mudbrick production (recorded in relief diagrams); Aït-Ben-Haddou in Morocco (11th Century earth citadel); Great Mosque of Agadez in Niger (16th Century, its $27\text{-meter}$ earthen minaret is the tallest mudbrick structure south of the Sahara); Shibam in Wadi Hadhramaut, Yemen (known as the "Manhattan of the Desert", featuring 16th-century earth tower houses rising up to 10 stories).
  • Pioneers of Modern Earth Architecture: Hassan Fathy advocated traditional earthen construction in Egypt, designing New Gourna in Luxor (1946–1952), New Baris Village (1963), and the Dar Al-Islam Mosque in Abiquiú, New Mexico, USA (1982).

• European Vernacular: Half-timbered earth infill (Lehmausfachung), e.g. Esslingen Old Town Hall (Altes Rathaus, built ca. 1420).

• Contemporary Earth Architecture: Solar-heated earth home in Santa Fe (1978); Haus Rauch in Schlins (Martin Rauch & Roger Boltshauser); Alnatura Headquarters in Darmstadt (HaasCookZemmrich).

  • Material Composition and Physics of Earth (Lehm):

• Constituents: Earth/Loam is a natural mixture of Clay (Ton, fine binder $< 0.002\,mm$), Silt (Schluff, $0.002\text{--}0.06\,mm$), Sand ($0.06\text{--}2.0\,mm$), and Gravel (Kies, $> 2.0\,mm$).

• Binding Force (Bindekraft) Classification:
  • Very lean (sehr mager): $50\text{--}80\,g/cm^2$
  • Lean (mager): $80\text{--}110\,g/cm^2$
  • Medium fat (fast fett): $110\text{--}200\,g/cm^2$
  • Fat (fett): $200\text{--}280\,g/cm^2$
  • Very fat (sehr fett): $280\text{--}360\,g/cm^2$
  • Pure Clay (Ton): $> 360\,g/cm^2$
• Binding Force Testing: Evaluated using the Ball Drop Test (Kugelfallprobe), where moist earth spheres are dried and dropped from table height to evaluate impact cohesion, alongside tensile rupture length testing.
• Geological Origin Types: Mountain/Slope Loam (Berglehm / Gehängelehm), Glacial Till (Geschiebelehm), Alluvial/River Loam (Schwemmlehm / Auenlehm).

• Hardening Mechanism: Earth hardens exclusively through physical drying (evaporation of water). It undergoes no chemical reaction or irreversible hydraulic setting. It remains 100% physically reversible: adding water transforms dried clay back into a plastic moldable slurry.

• Shrinkage Mitigation: Pure fat clay shrinks drastically upon drying, forming deep tension cracks. Sand, gravel, straw, hemp, or sawdust aggregates are added to control drying shrinkage.

  • Earth Construction Techniques by Consistency Class:

• Dry Class / Unfired Earth Blocks (Lehmsteine / Mud Bricks):

  • Governed by DIN 18945 (LR 4.1.3). Produced as strike-molded (formgeschlagen, f), hand-formed, or machine-pressed blocks (Grünlinge / CEB). Used for non-loadbearing interior partition walls, infills, and vaulting/domes (e.g. Gernot Minke's low-cost earth block light dome).

• 3D Printing and Extrusion:
  • Extruded earth strands (Lehmstrangverfahren) and robotic 3D printing of earth walls, e.g. TECLA House in Massa Lombarda, Italy (Mario Cucinella Architects with WASP, 2021).
• Earth-Moist Class / Rammed Earth (Stampflehm / Pisé):
  • Governed by DIN 18945 (LR 4.1.4 & LR 4.3.2). Earth-moist mixture is poured into rigid formwork in lifts ($15\text{--}20\,cm$) and mechanically compacted. Formwork can be stripped immediately. Rammed earth surfaces can be ground, polished, or embedded with hydronic heating pipes (Bauteilaktivierung).
  • Notable Rammed Earth Projects: Ezbet Abu Qarn (Cairo); Ringheiligtum Pömmelte Information Center; Gugler Printing House in Pielach (Ablinger, Vedral & Partner, 1998–1999); Ricola Herb Center in Laufen (Herzog & de Meuron with Martin Rauch, 2012 — largest prefabricated rammed earth building in Europe); Chapel of Reconciliation in Berlin (Kapelle der Versöhnung, Reitermann + Sassenroth, 1999); Kiln Tower for the Cham Brickworks Museum (Studio Roger Boltshauser); Weleda Logistics Center in Schwäbisch Gmünd (Michelgroup Architekten with ZRS Berlin).

• Wet / Doughy Class / Cob & Straw-Loam (Wellerlehmbau):
  • Wet mixture of earth and long straw piled in lifts ($60\text{--}90\,cm$ high) using pitchforks without formwork, then trimmed square with flat spades (e.g. residential home in Canton Solothurn by spaceshop Architekten).

• Soupy / Liquid Class / Mortars, Plasters, and Panels:

  • Earthen mortar (Lehmmörtel), Light earth (Leichtlehm mixed with wood chips/straw for insulation), Earthen wet plasters (Lehmputzmörtel), and prefabricated earthen drywalls (Lehmbauplatten).

• Earthen Floors (Lehmfußboden):

  • Layered rammed earth placed over gravel beds, compacted, and sealed with multiple coats of penetrating linseed oil (Leinöl / Fußboden-Hartöl).

• Timber-Earth Composite Floors (Holz-Lehmdecke / Earth-Tim):

  • Prefabricated floor systems combining mass timber joists with heavy acoustic earth infill elements (e.g. rematter.earth).

  • Ecological Performance and Structural Detailing Rules:

• **Global Warming Potential ($GWP$

  • Rammed earth wall (Stampflehmwand): $9\,kg CO_2\,eq/m^3$
  • Earth block masonry (Lehmbaustein): $94\,kg CO_2\,eq/m^3$
  • Earth drywall board (Lehmbauplatte): $0.05\,kg CO_2\,eq/m^3$
  • Interior earth plaster (Lehmputz): $93\,kg CO_2\,eq/m^3$
  • (Compared to Transport Concrete C25/30 at $229\,kg CO_2\,eq/m^3$ and Facing Brick at $533\,kg CO_2\,eq/m^3$).

• Indoor Environmental Quality: Earth plasters passively regulate indoor air humidity, absorbing excess moisture during high humidity and releasing it during dry periods (Feuchtepufferung).

• Erosion Control and Water Protection (Lehmbau-Regeln):

  • Earth is highly sensitive to liquid water, driving rain, and standing splash water (Spritzwasser).
  • Mandatory Protective Measures:
    • Elevated Base/Plinth (Sockelbildung): Constructing a splash-proof base using natural stone, brick, or concrete rising at least $30\text{--}50\,cm$ above ground level.
    • Generous Roof Overhangs (Konstruktiver Schutz): Protecting walls from direct rain exposure.
    • Erosion Breaks (Erosionsbremsen): Embedding horizontal rows of durable fired clay tiles or stones at regular vertical intervals within exposed rammed earth facades (e.g. Haus Rauch, Ricola Herb Center) to interrupt cascading rainwater runoff and prevent vertical erosion channels.