material-selection

name	material-selection
description	Architectural material properties, durability, sustainability, specification, detailing, life-cycle assessment, and material palettes for building design
user-invocable	true

Material Selection

Comprehensive knowledge base for architectural material selection covering structural performance, durability, thermal and acoustic properties, fire resistance, embodied carbon, cost, and aesthetic quality. Invoke this skill when addressing questions about material specification, material comparison, life-cycle assessment, embodied carbon targets, material detailing, finish selection, or material-appropriate design strategies.

---

Section 1: Material Selection Methodology

1.1 Eight-Criteria Evaluation Framework

Every architectural material decision should be evaluated against eight performance criteria. Weight each criterion according to project priorities (structural warehouse vs. cultural institution vs. social housing).

Criterion 1: Structural Performance

• Compressive strength (MPa)
• Tensile strength (MPa)
• Elastic modulus (GPa)
• Yield strength and ductility
• Fatigue resistance for dynamic loads
• Span-to-depth ratio capability
• Connection and jointing methods

Criterion 2: Durability and Weathering

• Design life expectation (25, 50, 60, 100+ years)
• Resistance to moisture, freeze-thaw, UV, pollution, biological attack
• Maintenance frequency and cost
• Patina and aging character (graceful vs. degrading)
• EN 206 exposure classes (concrete); EN 350 durability classes (timber)
• Corrosion resistance (metals); efflorescence (masonry)

Criterion 3: Thermal Properties

• Thermal conductivity (λ, W/mK)
• Specific heat capacity (c, J/kgK)
• Thermal mass (decrement delay, admittance)
• Contribution to U-value calculation
• Thermal bridging potential (ψ-values at junctions)

Criterion 4: Acoustic Properties

• Sound absorption coefficient (α) and NRC
• Sound reduction index (Rw, dB)
• Impact sound insulation (Ln,w)
• Flanking transmission paths
• Resonant frequency (for panel absorbers)

Criterion 5: Fire Performance

• Euroclass rating (A1 to F) / ASTM E84 (Class A, B, C)
• Fire resistance period (REI 30 to REI 240)
• Reaction to fire (ignitability, flame spread, smoke production)
• Charring rate (timber: 0.65 mm/min softwood, 0.50 mm/min hardwood)
• Concrete cover requirements for fire rating
• Intumescent and board-based fire protection for steel

Criterion 6: Embodied Carbon and Sustainability

• Embodied carbon (kgCO2e per kg, per m², or per m³)
• LCA stages A1-A5, B1-B7, C1-C4, D
• Recyclability and recycled content
• Renewable/non-renewable resource base
• Transportation distance (local vs. imported)
• Circular economy potential (Design for Disassembly)

Criterion 7: Cost

• Material cost (per m², per m³, per linear meter)
• Installation labor cost
• Maintenance and replacement costs over design life
• Whole-life cost (initial + maintenance + replacement + end-of-life)
• Supply chain reliability and lead times

Criterion 8: Aesthetic Quality

• Color, texture, pattern, translucency
• Surface finish options
• Ageing character and patina
• Scale and module relationships
• Tectonic expression (honesty of material)
• Contextual appropriateness (regional materials, cultural associations)

1.2 Decision Matrix Template

Scoring: 1 (poor) to 5 (excellent) per criterion. Apply weighting multipliers (1.0-3.0) based on project priorities.

Criterion	Weight	Option A (Score)	A Weighted	Option B (Score)	B Weighted	Option C (Score)	C Weighted
Structural	1.5
Durability	2.0
Thermal	1.5
Acoustic	1.0
Fire	2.0
Embodied Carbon	2.5
Cost	2.0
Aesthetic	1.5
TOTAL	14.0		Σ		Σ		Σ

Interpretation: Highest weighted total = preferred option. Sensitivity analysis: vary weights ±0.5 to test robustness. If options score within 5%, treat as equivalent and decide on qualitative factors.

---

Section 2: Concrete

2.1 Types

In-Situ (Cast-in-Place):

• Poured into formwork on site; cures in position
• Maximum flexibility in form and geometry
• Grades: C20/25 (foundations), C30/37 (structural frames), C40/50 (high-rise columns), C50/60 (prestressed)
• Minimum 28-day strength; continued strength gain over months

Precast:

• Factory-produced elements (beams, columns, panels, stairs, floors)
• Superior quality control; consistent finish; rapid erection
• Hollow-core slabs: 150-500 mm deep, spans 6-16 m
• Sandwich panels: structural + insulation + facing leaf in single unit

Glass-Fibre Reinforced Concrete (GRC/GFRC):

• Thin (10-25 mm) concrete panels with alkali-resistant glass fibres
• Lightweight: 15-20 kg/m² (vs. 100+ kg/m² for solid precast)
• Cladding and facade applications; complex curved forms
• Flexural strength: 20-30 MPa (vs. 3-5 MPa for plain concrete)

Ultra-High Performance Concrete (UHPC):

• Compressive strength: 120-200 MPa (vs. 30-50 MPa standard)
• Steel fibre reinforced; no conventional rebar needed for thin sections
• Density: 2,400-2,600 kg/m³
• Enables extremely thin elements (25-75 mm structural walls, 15-30 mm panels)
• Self-healing micro-cracks; exceptional durability
• Cost: 5-10× standard concrete
• Exemplars: MUCEM Marseille (Ricciotti), Ductal bridges

Self-Compacting Concrete (SCC):

• Flows under its own weight; no vibration needed
• Superior finish quality; fills complex formwork without voids
• Used for architectural exposed concrete with demanding finish requirements

2.2 Finishes

Finish	Method	Texture	Typical Cost Premium
Board-marked	Sawn timber formwork; grain transfers	Rough, directional	+10-20%
Steel-formed	Steel or resin-coated plywood formwork	Smooth, uniform	Baseline
Polished	Diamond grinding after curing	Mirror-like, exposes aggregate	+30-50%
Acid-etched	Acid wash removes surface cement paste	Exposed fine aggregate	+15-25%
Sandblasted	Abrasive blasting	Exposed coarse aggregate	+20-30%
Bush-hammered	Mechanical hammering	Rough, stone-like	+25-40%
Pigmented	Integral oxide pigments	Colored throughout	+15-30%
White concrete	White Portland cement + white aggregate	Bright white	+40-60%
Fabric-formed	Flexible textile formwork	Organic, draped	+20-50%

2.3 Key Properties

• Density: 2,300-2,400 kg/m³ (normal weight); 1,400-1,800 kg/m³ (lightweight)
• Thermal conductivity: 1.0-1.8 W/mK (normal); 0.5-0.8 (lightweight)
• Specific heat capacity: 840-1,000 J/kgK
• Thermal admittance: 5.0-6.0 W/m²K (excellent thermal mass)
• Embodied carbon: 150-200 kgCO2e/m³ (standard OPC concrete); 80-120 kgCO2e/m³ (low-carbon with GGBS/PFA replacement)
• Fire rating: inherently non-combustible (Euroclass A1). Concrete cover for fire resistance: 25 mm (REI 60), 35 mm (REI 90), 40 mm (REI 120), 55 mm (REI 240)

2.4 Architects of Concrete

• Tadao Ando: Smooth board-marked finish with precise tie-hole patterns (600 mm grid); Church of the Light, Naoshima museums
• Peter Zumthor: Textured, layered concrete (Therme Vals — local quartzite aggregate; Bruder Klaus Chapel — charred timber interior formwork)
• Louis Kahn: Monumental concrete with expressed structure (Salk Institute, National Assembly Dhaka — concrete + marble aggregate)
• Oscar Niemeyer: Sculptural white concrete (Brasilia Cathedral — hyperboloid shell; Niteroi Museum)
• Le Corbusier: Beton brut (Unite d'Habitation, Chandigarh — board-marked exposed concrete)
• Zaha Hadid: UHPC and GRC for fluid geometries (Heydar Aliyev Center — GRC panels)
• Grafton Architects: Raw exposed concrete as civic material (UTEC Lima, Bocconi University)

---

Section 3: Steel

3.1 Structural Steel Grades

Grade (EN)	Yield Strength (MPa)	Tensile Strength (MPa)	Primary Use
S235	235	360-510	Light structures, secondary steelwork
S275	275	410-560	General building frames
S355	355	470-630	Most common structural grade; beams, columns
S460	460	540-720	High-rise, long-span, heavily loaded

ASTM Equivalents: A36 (≈S235), A992 (≈S345-S355), A572 Gr 50 (≈S345)

3.2 Stainless Steel

• 304 (18/8): 18% chromium, 8% nickel. General purpose. Interior and mild exterior use. Yield 210 MPa.
• 316 (18/10/3): Added molybdenum for enhanced corrosion resistance. Marine and polluted environments. Yield 220 MPa. Cost: +30-40% over 304.
• Duplex 2205: High strength (yield 450 MPa) + corrosion resistance. Structural applications. Cost: +50-70% over 304.

3.3 Weathering Steel (Corten A/B)

• Forms stable oxide patina (rust layer) that protects underlying steel
• Eliminates need for painting; self-healing if scratched
• Patina formation: 2-5 years for full development; color progression from orange to deep brown
• Critical: Must not be used where run-off stains adjacent materials (limestone, concrete). Requires detailing to manage staining. Not suitable for marine environments (chloride prevents stable patina).
• Exemplars: Angel of the North (Gormley), Barclays Center Brooklyn (SHoP), CaixaForum Madrid (Herzog & de Meuron)

3.4 Finishes

• Painted: Shop-applied primer + topcoat. Recoat every 15-25 years. Most common.
• Galvanized (hot-dip): Zinc coating 45-85 µm; 40-60 year life in mild environments. Matte silver-grey appearance.
• Powder-coated: Thermoset polymer; color range unlimited; 20-30 year life exterior. Polyester (standard) or PVDF (premium, 30+ years).
• Brushed/Polished: For stainless steel; various grades (No.4 brushed, No.8 mirror).
• Patinated: Applied patina (chemical acceleration of natural oxidation); controlled finish for bronze, copper, steel.

3.5 Key Properties

• Density: 7,850 kg/m³
• Thermal conductivity: 50 W/mK (carbon steel); 16 W/mK (stainless 304) — significant thermal bridging risk
• Elastic modulus: 200-210 GPa
• Embodied carbon: 1.55 kgCO2e/kg (primary/virgin, world average); 0.47 kgCO2e/kg (EAF recycled, 100% scrap). Steel is ~90% recyclable.
• Fire: Loses 50% strength at ~550°C; unprotected steel reaches this in 15-20 minutes in standard fire

3.6 Fire Protection Methods

Method	Achievable Rating	Thickness	Cost ($/m² protected)
Intumescent paint	REI 30-120	0.5-5.0 mm DFT	$30-120
Sprayed mineral fibre	REI 60-240	15-50 mm	$15-40
Board encasement (calcium silicate)	REI 60-240	15-50 mm	$40-80
Concrete encasement	REI 120-240	25-50 mm	$25-50
Water-filled hollow sections	REI 120+	N/A (hollow section)	$50-100 (system)

3.7 Connection Types

• Bolted: Site-assembled; adjustable; demountable (DfD-friendly). High-strength friction-grip (HSFG) bolts M16-M30.
• Welded: Strongest; continuous load path; shop-welded preferred (controlled conditions). Site welding possible but requires NDT.
• Pin joints: True pins (single bolt) allow rotation; used at truss nodes and portal bases.
• Moment connections: Resist rotation; bolted end-plate or welded. Create rigid frames for lateral stability.

3.8 Architects of Steel

• Mies van der Rohe: Expressed steel frame (Farnsworth House, Crown Hall, Seagram Building — bronze-anodized I-beams)
• Norman Foster: High-tech exposed steelwork (HSBC HQ Hong Kong, Millennium Bridge, 30 St Mary Axe diagrid)
• Renzo Piano: Lightweight steel + cable structures (Centre Pompidou with Rogers, Menil Collection)
• Santiago Calatrava: Sculptural steel ribs and masts (City of Arts and Sciences, Milwaukee Art Museum)
• Peter Rice (Ove Arup): Cast steel nodes and tensile structures (Lloyd's of London, Kansai Airport)

---

Section 4: Timber

4.1 Softwood Species

Species	Density (kg/m³)	Strength Class	Durability (EN 350)	Primary Use
European Spruce (Picea abies)	380-450	C16-C24	4 (poor)	Structural framing, CLT
Scots Pine (Pinus sylvestris)	440-530	C18-C27	3-4	Joinery, structural
Douglas Fir (Pseudotsuga menziesii)	480-560	C24-C30	3 (moderate)	Heavy structural, glulam
Western Red Cedar (Thuja plicata)	330-380	C14-C16	2 (durable)	External cladding, shingles
Larch (Larix decidua)	470-560	C24-C27	3 (moderate)	External cladding, decking
Sitka Spruce (Picea sitchensis)	380-440	C16-C20	4 (poor)	Structural framing

4.2 Hardwood Species

Species	Density (kg/m³)	Durability (EN 350)	Hardness (Janka, N)	Primary Use
European Oak (Quercus robur)	600-720	2 (durable)	5,600	Structural, flooring, joinery
Iroko (Milicia excelsa)	550-680	1-2 (very durable)	5,100	External joinery, cladding
Teak (Tectona grandis)	580-680	1 (very durable)	4,700	Marine, premium external
Accoya (modified Radiata Pine)	510	1 (very durable)	4,000	External, ground contact
American White Ash (Fraxinus americana)	600-680	4 (poor)	5,900	Internal flooring, furniture
American Black Walnut	560-640	3 (moderate)	4,500	Premium joinery, paneling
European Beech	660-740	5 (non-durable)	6,400	Internal flooring, furniture

4.3 Engineered Timber

Glulam (Glued Laminated Timber):

• Laminations: 25-45 mm thick; glued with MUF or PRF adhesive
• Grades: GL24h to GL32h (24-32 MPa bending strength)
• Spans: 6-40 m (beams), up to 100+ m (arches)
• Depth: typically span/15 to span/20 for beams
• Cross-section: 100-600 mm wide, 200-2,400 mm deep
• Can be curved (minimum radius ≈ 175× lamination thickness)

Cross-Laminated Timber (CLT):

• Orthogonal layers (3, 5, or 7 ply); typically spruce
• Panel sizes: up to 3.5 m × 16 m × 500 mm
• Walls: 100-300 mm thick; floors: 140-350 mm thick
• Spans: 4-8 m (floors), 3-4 m (walls for 6+ storey buildings)
• Compressive strength perpendicular: 2.5-3.0 MPa
• Airtightness: inherently airtight at panel body; joints sealed with tape/gaskets

Laminated Veneer Lumber (LVL):

• 3 mm rotary-peeled veneers; all grain parallel (unlike plywood)
• Higher strength than sawn timber of same species: bending 40-65 MPa
• Available as beams, studs, and rim boards
• Consistent, defect-free

Plywood:

• Cross-laminated veneers; balanced layup
• Structural grades: 12-25 mm for sheathing; 18-30 mm for flooring
• Marine plywood: WBP (weather and boil proof) adhesive; tropical hardwood species
• Birch plywood: premium face quality for joinery and furniture

4.4 Key Properties (Generic Softwood)

• Density: 350-550 kg/m³ (kiln-dried at 12% MC)
• Thermal conductivity: 0.13 W/mK (perpendicular to grain) — natural insulator
• Specific heat capacity: 1,600 J/kgK
• Embodied carbon: -1.0 to -1.6 kgCO2e/kg (carbon-negative — sequesters more CO2 during growth than emitted in processing)
• Embodied carbon (CLT panel): approximately -500 to -700 kgCO2e/m³ including sequestration
• Fire performance: Euroclass D (combustible) but predictable charring rate allows fire engineering
• Charring rate: 0.65 mm/min (softwood), 0.50 mm/min (hardwood), 0.70 mm/min (glulam)
• Fire-engineered CLT: 90-120 minute resistance achievable with oversized sections (add 40-60 mm sacrificial charring layer per exposed face)

4.5 Durability and Preservation

EN 350 Durability Classes:

1. Very durable (> 25 years ground contact): teak, iroko, accoya
2. Durable (15-25 years): oak, sweet chestnut, western red cedar
3. Moderately durable (10-15 years): Douglas fir, larch, Scots pine (heartwood)
4. Slightly durable (5-10 years): spruce, pine (sapwood), hem-fir
5. Not durable (< 5 years): beech, ash, birch (untreated external)

Preservation Methods:

• CCA (Copper-Chrome-Arsenic): UC4 ground contact; restricted in EU for non-industrial use
• Copper-based (ACQ, MCQ): residential-approved alternatives to CCA
• Thermal modification: heat treatment (180-230°C) improves durability to Class 1-2; darkens color; reduces strength 10-20%
• Acetylation (Accoya): chemical modification; Class 1 durability; 50+ year warranty above ground; dimensionally stable
• Oil/wax finishes: maintenance coats every 1-3 years for external; UV protection
• Fire retardant treatment: pressure-impregnated salts achieve Euroclass B (limited combustibility)

4.6 Architects of Timber

• Kengo Kuma: Timber as weaving/stacking element (Yusuhara Wooden Bridge Museum, V&A Dundee timber screen concept, Prostho Museum GC — interlocking timber grid)
• Shigeru Ban: Structural innovation (Centre Pompidou-Metz — glulam gridshell; Tamedia Office — interlocking timber frame no metal connectors; Paper Bridge)
• Peter Zumthor: Timber as sensory material (Steilneset Memorial — timber-framed cocoon; Swiss Pavilion Hanover 2000 — stacked timber beams)
• Hermann Kaufmann: Mass timber pioneer (Illwerke Zentrum Montafon — 8 storey CLT/glulam hybrid; LifeCycle Tower)
• Heatherwick Studio: Engineered timber at scale (Maggie's Leeds — timber lattice)

---

Section 5: Masonry

5.1 Brick

Types:

• Clay brick (fired): Most common; firing temperature 900-1,150°C determines color (buff to deep red to blue-black). Compressive strength 10-150 MPa.
• Calcium silicate (sand-lime): Autoclaved; consistent dimensional accuracy; limited color (white, grey, pastel). Strength 15-50 MPa.
• Concrete brick: Portland cement + aggregate; wide color range with pigments. Strength 7-40 MPa.
• Engineering brick: High-strength (≥ 70 MPa Class A, ≥ 50 MPa Class B) and low water absorption (< 4.5% A, < 7% B). Blue-black color. DPC, retaining walls, below ground.

Standard Sizes:

• UK standard: 215 × 102.5 × 65 mm (coordinating: 225 × 112.5 × 75 mm with 10 mm joints)
• US modular: 194 × 92 × 57 mm (7⅝ × 3⅝ × 2¼ in)
• US standard: 203 × 92 × 57 mm
• Metric modular: 190 × 90 × 57 mm (200 × 100 × 67 mm with joints)
• Roman: 295 × 90 × 40 mm (elongated, thin profile)
• Continental long format: 490 × 90 × 40-52 mm

Bond Patterns:

• Stretcher (running): All stretchers; half-bond offset. Single-leaf walls, cavity wall outer leaf. Most common.
• Flemish: Alternating headers and stretchers in each course. Full-thickness wall; decorative.
• English: Alternating courses of headers and stretchers. Strong cross-bonding; full-thickness wall.
• Stack bond: No offset; vertical joints aligned. Purely decorative (requires reinforcement or veneer application). Modernist aesthetic.
• Herringbone: Bricks at 45° in alternating directions. Decorative infill panels; paviors.
• Monk bond: Two stretchers + one header per course. Variant of Flemish.
• Header bond: All headers; full-thickness wall. Curved walls (radial bonding).

5.2 Stone

Stone Type	Density (kg/m³)	Compressive (MPa)	Porosity	Durability	Embodied Carbon (kgCO2e/kg)
Limestone (Portland)	2,000-2,500	20-60	5-20%	Moderate-Good	0.09
Sandstone (Yorkstone)	2,000-2,400	20-70	5-25%	Variable	0.06
Granite	2,600-2,800	100-250	0.5-2%	Excellent	0.70
Marble (Carrara)	2,600-2,800	50-150	0.5-3%	Good (interior)	0.12
Slate	2,600-2,800	100-200	0.1-1%	Excellent	0.03-0.05
Basalt	2,800-3,000	150-300	0.5-2%	Excellent	0.60
Travertine	2,200-2,500	30-80	5-15%	Moderate	0.12

5.3 Concrete Block

• Dense block: 2,000-2,200 kg/m³; compressive 7-35 MPa; thermal conductivity 1.0-1.5 W/mK. Structural walls, foundations.
• Lightweight aggregate block: 600-1,400 kg/m³; λ = 0.15-0.50 W/mK. Better insulation, reduced structural capacity.
• Aircrete (AAC — Autoclaved Aerated Concrete): 400-800 kg/m³; λ = 0.10-0.20 W/mK; compressive 2-7 MPa. Non-loadbearing and low-rise loadbearing. Excellent thermal performance. Easy to cut and shape.

5.4 Mortar and Joints

Mortar Designations (BS EN 998-2):

• M2 (1:2:9 cement:lime:sand): weak; heritage and soft brick
• M4 (1:1:6): medium; general brickwork above DPC
• M6 (1:½:4.5): medium-strong; external walls, moderate exposure
• M12 (1:¼:3): strong; engineering brick, retaining walls, below DPC

Joint Profiles:

• Flush: weathering neutral; clean modern appearance
• Bucket handle (concave): good weathering; most common
• Weathered (struck): sloped to shed water; traditional
• Recessed: shadow line aesthetic; poor weathering (not for exposed positions)
• Raked: deep recess for dramatic shadow; worst weathering performance

Embodied Carbon:

• Clay brick: 0.22 kgCO2e/kg (typical); 0.14 (low-carbon production)
• Limestone ashlar: 0.09 kgCO2e/kg
• Concrete block: 0.08-0.12 kgCO2e/kg
• AAC block: 0.28-0.34 kgCO2e/m² (per block face area)

---

Section 6: Glass

6.1 Glass Types

Float Glass: Basic annealed glass. Breaks into large sharp shards. Not safety glass. VLT 87% (clear 6 mm).

Toughened (Tempered): Heat-treated to 4-5× strength of annealed. Breaks into small granules. Safety glass for doors, balustrades, overhead. Cannot be cut after toughening.

Laminated: Two or more glass plies bonded with PVB or SentryGlas interlayer. Holds together when broken. Safety glass; security; acoustic; UV filtering. Structural glazing interlayer (SentryGlas) enables longer spans.

Insulating Glass Unit (IGU): Two or three panes separated by spacer bars and sealed cavity (air, argon, krypton). U-values: double air 2.8, double argon 1.1-1.3, triple argon 0.5-0.7 W/m²K.

Tinted Glass: Body-colored (grey, bronze, green, blue). Reduces VLT and SHGC. Absorbs solar energy (heats up).

Low-E Coated: Metallic oxide coating reflects long-wave infrared radiation. Soft coat (sputtered, pyrolytic) on surface 2 or 3 of IGU. Reduces U-value by 30-50%.

Solar Control: Selective coating that admits visible light while rejecting solar infrared. VLT:SHGC ratio (selectivity) ≥ 1.5 is good; ≥ 2.0 is excellent.

Fire-Rated: Wired glass (30 min integrity, no insulation); intumescent gel-filled (30-120 min integrity + insulation); borosilicate (integrity only).

Patterned/Textured: Rolled pattern on one surface. Obscured vision with light transmission. Reeded, fluted, hammered, stippled.

Printed/Fritted: Ceramic frit screen-printed and fused to glass surface. Solar shading, bird safety, decoration. Frit coverage 20-60%.

Etched/Sandblasted: Acid or abrasive surface treatment for translucency/privacy. VLT reduction 5-15%.

Dichroic: Vacuum-deposited metallic layers create color-shifting effects. Transmitted and reflected colors are complementary.

6.2 Structural Glass

• Glass fins: Vertical glass blades supporting glazed facades. Toughened + laminated. Depth 150-500 mm; spans 4-12 m.
• Glass beams: Laminated glass beams for roof support. Typically triple-laminated toughened. Spans 3-8 m.
• Glass floors: Laminated toughened panels; minimum 3-ply for redundancy. Anti-slip surface treatment. Design load: 5 kN/m² typical.
• Glass columns: Rare; bundled glass tube columns (Apple Stores); solid glass blocks (Hermes, Tokyo by MVRDV).
• Point-fixed glazing: Stainless steel bolt fittings through drilled holes; spider brackets. Eliminates framing for maximum transparency.

6.3 Key Properties

• Density: 2,500 kg/m³
• Compressive strength: 800-1,000 MPa (rarely governing)
• Tensile strength: 30-70 MPa (annealed); 120-200 MPa (toughened). Glass fails in tension.
• Elastic modulus: 70 GPa
• Thermal conductivity: 1.0 W/mK
• Thermal expansion: 9 × 10⁻⁶ /°C
• Acoustic: single 6 mm pane Rw ≈ 31 dB; laminated 6.4 mm Rw ≈ 34 dB; IGU 4-16-4 Rw ≈ 29 dB (coincidence dip)

6.4 Architects of Glass

• Norman Foster: Structural glass innovation (30 St Mary Axe diagrid, Apple Park, Great Court British Museum — glass roof)
• Renzo Piano: Layered glass skins (Shard, Fondation Beyeler, California Academy of Sciences)
• SANAA (Sejima + Nishizawa): Minimal glass enclosures (New Museum, Rolex Learning Center, Glass Pavilion Toledo — curved glass walls)
• Jean Nouvel: Glass as cultural narrative (Institut du Monde Arabe, Fondation Cartier — transparent layers)
• Apple Stores (Foster + Partners / Bohlin Cywinski Jackson): All-glass structures; glass fins, glass beams, glass stairs

---

Section 7: Metals and Composites

7.1 Aluminum

• Density: 2,700 kg/m³ (1/3 of steel)
• Tensile strength: 70-310 MPa (alloy-dependent; 6063-T6: 205 MPa)
• Thermal conductivity: 160-200 W/mK (severe thermal bridging; require thermal breaks in window/curtain wall profiles)
• Embodied carbon: 8.2 kgCO2e/kg (primary); 0.5 kgCO2e/kg (recycled). ~75% of all aluminum ever produced still in use.
• Finishes: anodized (10-25 µm; natural silver, bronze, black; 30+ year life), powder-coated (60-80 µm polyester; any color; 20-30 year life), PVDF-coated (premium; 40+ year life)
• Applications: curtain wall mullions and transoms, window frames, cladding panels, standing seam roofing, solar shading louvers

7.2 Zinc

• Density: 7,130 kg/m³
• Self-healing patina: natural zinc develops grey carbonate patina over 5-10 years
• Pre-patinated options: pre-weathered grey, blue-grey, graphite, pigmented
• Thickness: 0.7-1.0 mm for roofing/cladding (standing seam, flat lock tiles, shingles)
• Embodied carbon: 3.1 kgCO2e/kg (primary); largely recyclable
• Minimum slope: 3° (standing seam); 25° (overlapping tiles)
• Lifespan: 80-100 years in moderate climates
• Applications: roofing, wall cladding, rainwater goods, flashings

7.3 Copper and Bronze

Copper:

• Density: 8,900 kg/m³
• Patina progression: bright copper → brown (months) → dark brown (1-3 years) → green verdigris (7-15 years, climate-dependent)
• Pre-patinated and tin-coated options available
• Thickness: 0.6-0.7 mm for roofing; 3-6 mm for sculpture/cladding
• Embodied carbon: 2.7 kgCO2e/kg (primary); 0.5 (recycled)
• Lifespan: 100-200+ years (historical precedent: church roofs 300+ years)
• Applications: roofing, cladding, flashings, rainwater goods, feature panels

Bronze:

• Copper-tin alloy (typically 90/10 or 85/15)
• Rich golden-brown patina; darker than copper
• Used for doors, handrails, window frames, sculptural elements
• Architects: Mies van der Rohe (Seagram Building — bronze I-beams), Carlo Scarpa (Brion Cemetery — bronze gates)

7.4 Titanium

• Density: 4,510 kg/m³ (57% of steel)
• Corrosion resistance: superior to stainless steel in all environments
• Embodied carbon: 14.1 kgCO2e/kg (highest of common metals)
• Cost: 10-20× structural steel per kg
• Surface: matte grey; can be anodized for iridescent color
• Exemplar: Guggenheim Bilbao (Frank Gehry, 1997) — 33,000 m² of 0.38 mm titanium panels; fish-scale cladding; changes color with light and weather

7.5 ETFE (Ethylene Tetrafluoroethylene)

• Density: 1,750 kg/m³ (1% of glass weight per m²)
• Light transmission: 90-95% (clear single layer); 40-60% (printed/fritted)
• Tensile strength: 40-50 MPa (as film, 50-300 µm thick)
• Self-cleaning: non-stick surface; no wash maintenance
• Pneumatic cushions: 2-5 layers inflated at 200-600 Pa; U-value 1.8-3.5 W/m²K
• Lifespan: 25-50 years (UV-resistant fluoropolymer)
• Exemplars: Eden Project (Grimshaw), Allianz Arena (H&dM), Beijing Aquatics Center (PTW), Khan Shatyr (Foster)

7.6 GRP/FRP (Glass/Fibre Reinforced Polymer)

• Density: 1,500-2,000 kg/m³
• Tensile strength: 100-400 MPa
• Thermal conductivity: 0.3 W/mK (thermally non-conductive; no thermal bridging)
• Corrosion-immune; no maintenance
• Moldable to any shape (curved panels, ornamental elements, replica heritage details)
• Applications: cladding panels, window surrounds, cornices, columns (replica stone/timber appearance)

7.7 Terracotta

• Clay-based; extruded or pressed; fired at 1,000-1,200°C
• Rainscreen cladding: extruded hollow sections; 20-40 mm thick; back-ventilated cavity
• Baguettes: horizontal or vertical tubular/blade elements for solar shading and facade articulation
• Glazed terracotta: vitreous surface coating; colors unlimited; self-cleaning
• Density: 1,800-2,100 kg/m³
• Fire: Euroclass A1 (non-combustible)
• Embodied carbon: 0.45 kgCO2e/kg
• Exemplars: Natural History Museum London (Waterhouse), Renzo Piano (Central St Giles London — colored terracotta), MVRDV (Markthal Rotterdam — printed terracotta arches)

7.8 Ceramic Tiles and Cladding

• Porcelain: absorption < 0.5%; frost-proof; 12-20 mm thick large format (up to 1.6 m × 3.2 m)
• Stoneware: absorption 0.5-3%; good durability; glazed or unglazed
• Earthenware: absorption > 3%; interior only; hand-decorated (zellige, azulejo)
• Fire: Euroclass A1
• Applications: facade cladding (ventilated rainscreen), floor/wall finishes, pool surrounds

---

Section 8: Life-Cycle Assessment (LCA)

8.1 Whole-Life Carbon

Total carbon = Embodied carbon (A1-A5, B1-B5, C1-C4) + Operational carbon (B6-B7)

As buildings become more energy-efficient, embodied carbon becomes the dominant component (50-80% of whole-life carbon for Passive House-standard buildings).

8.2 LCA Stages (EN 15978)

Product Stage (A1-A3):

• A1: Raw material extraction
• A2: Transport to manufacturer
• A3: Manufacturing
• This is the "cradle-to-gate" embodied carbon — most commonly reported

Construction Stage (A4-A5):

• A4: Transport to site
• A5: Construction/installation process (energy, waste, temporary works)

Use Stage (B1-B7):

• B1: Installed product use (e.g., carbonation of concrete)
• B2: Maintenance
• B3: Repair
• B4: Replacement (components with shorter life than building)
• B5: Refurbishment
• B6: Operational energy use
• B7: Operational water use

End-of-Life Stage (C1-C4):

• C1: Deconstruction/demolition
• C2: Transport to disposal/recycling
• C3: Waste processing
• C4: Disposal (landfill)

Beyond Life (Module D):

• Credits for reuse, recycling, energy recovery
• Reported separately (not added to A-C total)
• Steel recycling credit: -1.3 to -1.5 kgCO2e/kg
• Timber reuse/energy recovery credit: variable

8.3 Embodied Carbon Benchmarks

LETI (London Energy Transformation Initiative) Targets:

Building Type	2020 Target (kgCO2e/m² GIA)	2030 Target	Notes
Office	< 600	< 350	A1-A5 upfront carbon
Residential	< 500	< 300	A1-A5 upfront carbon
School	< 500	< 300	A1-A5 upfront carbon
Retail/Warehouse	< 550	< 350	A1-A5 upfront carbon

RIBA 2030 Climate Challenge:

• 2020: < 600 kgCO2e/m² (A1-A5)
• 2025: < 450 kgCO2e/m²
• 2030: < 300 kgCO2e/m²

IStructE Targets (structure only):

• Residential: < 300 kgCO2e/m² (typical); < 200 (best practice)
• Office: < 350 kgCO2e/m² (typical); < 250 (best practice)
• Best-in-class timber buildings: < 150 kgCO2e/m² (structure)

8.4 Material-Level Embodied Carbon

Material	Unit	Embodied Carbon (kgCO2e)	Notes
Concrete (C30/37, OPC)	per m³	180-240	30-50% GGBS replacement reduces to 100-150
Structural steel (primary)	per kg	1.55	World average; UK ~2.0
Structural steel (recycled, EAF)	per kg	0.47	Electric arc furnace, 100% scrap
Steel rebar	per kg	1.40	Often high recycled content
Softwood timber (sawn)	per kg	-1.0 to -1.6	Carbon sequestration exceeds processing
CLT panel	per m³	-500 to -700	Including biogenic carbon
Glulam	per m³	-450 to -600	Including biogenic carbon
Clay brick	per kg	0.22	Range 0.14-0.30 depending on kiln
Limestone (Portland)	per kg	0.09	Low processing energy
Aluminum (primary)	per kg	8.20	High energy; use recycled where possible
Aluminum (recycled)	per kg	0.50	94% reduction from primary
Float glass	per kg	0.86
Mineral wool insulation	per kg	1.20
PIR insulation	per kg	4.20	High due to blowing agents
XPS insulation	per kg	4.40	Highest of insulation types
Wood fibre insulation	per kg	-1.10	Carbon-negative
Plasterboard	per kg	0.12	Low carbon; recyclable
Copper	per kg	2.70	High recyclability offsets
Zinc	per kg	3.10
ETFE	per kg	6.50	Very low quantity used per m²

8.5 Material Passports and Circular Economy

Material Passport: Digital record of all materials and components in a building — type, quantity, location, quality, toxicity, recyclability. Enables future recovery and reuse.

Circular Economy Principles for Architecture:

1. Design for Longevity: durable materials, adaptable layouts
2. Design for Disassembly (DfD): bolted connections (not welded/glued), layered construction (facade independent of structure), accessible fixings
3. Design for Reuse: standard sizes, undamaged removal, material banks
4. Use Recycled Content: specify minimum recycled content in steel (90%+ achievable), aluminum (50%+), concrete aggregate (20-30% RCA)
5. Use Renewable Materials: timber, bamboo, hemp-lime, straw, earth
6. Eliminate Waste: modular coordination, prefabrication, digital cutting optimization

Exemplars of Circular Design:

• Triodos Bank HQ (RAU Architects, 2019, Driebergen) — timber structure fully demountable; bolted steel connections; every element logged in material passport (Madaster platform)
• Park 20|20 (William McDonough, Amsterdam) — cradle-to-cradle certified; demountable facades; material passports for all buildings