Lesson 02: Upfront Carbon — The Product and Construction Stages (Modules A1–A5)

Learning objectives

By the end of this lesson, you will be able to:

  • Formulate and compute the mathematical equations governing Upfront Embodied Carbon (Modules A1–A5) per BS EN 15978 and RICS standards.
  • Interpret Type III Environmental Product Declarations (EPDs) conforming to BS EN 15804+A2:2019, specifically distinguishing between $\text{GWP-fossil}$ and $\text{GWP-biogenic}$.
  • Calculate freight emissions in Module A4 using mass-distance logistics modeling, payload capacities, and transport mode emission factors.
  • Model the compounding effect of site material wastage rates in Module A5 on raw material extraction (A1–A3) and transport (A4).
  • Quantify on-site installation energy, site accommodation emissions, and construction waste disposal.

Key concepts

1. The Composition of Upfront Carbon

Upfront Carbon encompasses all greenhouse gas emissions released from the initial extraction of raw earth materials up to the practical completion of the building asset [S04, S06]. It comprises two primary life cycle stages:

  1. The Product Stage (Modules A1–A3): Cradle-to-factory-gate production of building components.
  2. The Construction Process Stage (Modules A4–A5): Transportation to the jobsite and physical assembly on-site.

Upfront carbon is mathematically formulated as:

$$\text{EC}_{\text{upfront}} = \text{EC}_{A1-A3} + \text{EC}_{A4} + \text{EC}_{A5}$$

2. Module A1–A3: Product Stage and EPD Mechanics

The product stage captures the industrial processing chain [S01, S02]:

  • A1 (Raw Material Supply): Extraction of ores, quarrying limestone and aggregates, forestry, and fossil feedstocks.
  • A2 (Transport to Manufacturer): Freight transporting extracted raw ingredients to smelting mills, cement kilns, or fabrication plants.
  • A3 (Manufacturing): High-temperature processing, chemical synthesis, machining, and final component fabrication.

Primary Material Emission Mechanisms

  • Cement & Concrete: In ordinary Portland cement (CEM I), approximately 60% of emissions stem from chemical calcination ($\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$) occurring at $1450^\circ\text{C}$, with the remaining 40% from fossil fuel combustion to fire the kiln [S05, S07]. Replacing CEM I with Supplementary Cementitious Materials (SCMs) such as Ground Granulated Blast-furnace Slag (GGBS) or Pulverized Fuel Ash (PFA) dramatically reduces A1–A3 emissions.
  • Structural Steel: Primary steelmaking via the Blast Furnace-Basic Oxygen Furnace (BF-BOF) route typically yields $2.0 \text{ to } 2.5\text{ kgCO}_2\text{e}/\text{kg}$ of steel [S07]. Secondary steelmaking via the Electric Arc Furnace (EAF) route utilizing 90%+ scrap metal yields $0.4 \text{ to } 0.8\text{ kgCO}_2\text{e}/\text{kg}$ [S05, S07].
  • Timber: Trees sequester atmospheric carbon dioxide via photosynthesis ($6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$). Under EN 15804+A2 [S02], this biogenic carbon storage is reported as a negative emission ($-1$) in Module A1–A3, but must be paired with fossil emissions from harvesting, drying kilns, resin production, and fabrication.

Reading Modern EPDs (BS EN 15804+A2:2019)

Under the A2 amendment of EN 15804 [S02], EPDs no longer provide a single Global Warming Potential ($\text{GWP}$) number. They mandate four distinct sub-indicators:

  • $\text{GWP-fossil}$: GHG emissions from fossil fuels and industrial calcination.
  • $\text{GWP-biogenic}$: Carbon removals into biomass (negative) and physical releases (positive).
  • $\text{GWP-luluc}$: Emissions from land use and land use change.
  • $\text{GWP-total}$: The arithmetic sum of fossil, biogenic, and luluc impacts.

[!CAUTION] Biogenic Carbon Masking: When assessing building frames, never use $\text{GWP-total}$ of timber to claim that a building has “zero upfront carbon” if the wood will release that stored carbon at end of life. The RICS Whole Life Carbon Standard [S04] and IStructE [S05] mandate that fossil emissions and biogenic carbon storage must be reported transparently and tracked through end-of-life modules C3/C4.

3. Module A4: Transport to Construction Site

Module A4 covers freight from the manufacturer’s gate to the construction site [S01, S04]. Transportation carbon depends on three variables:

  1. The mass of material transported ($M_i$ in tonnes).
  2. The one-way distance travelled ($d_i$ in kilometers).
  3. The mode-specific emission factor ($\text{EF}_{\text{trans}, m}$ in $\text{kgCO}_2\text{e}/(\text{t}\cdot\text{km})$), accounting for vehicle capacity utilization and empty return trips.
$$\text{EC}_{A4} = \sum_i M_i \times d_i \times \text{EF}_{\text{trans}, m}$$

Standard Default Transport Scenarios (RICS 2023 & IStructE 2022)

When supplier-specific factory locations are unknown during early design stages, the RICS standard [S04] and IStructE guidance [S05] provide empirical default scenarios:

Material OriginDefault ModeOne-Way Distance ($d$)Emission Factor ($\text{EF}_{\text{trans}}$) [S04, S05]
Locally sourced (Ready-mix concrete, aggregates)Rigid HGV (>17t)50 km$0.134\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$
Nationally sourced (Precast concrete, bricks, rebar)Articulated HGV (>33t)300 km$0.088\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$
European imports (Structural steel sections, CLT)Articulated HGV + Ferry1,500 km road + 200 km seaRoad: $0.088$; Sea: $0.016\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$
Global imports (Stone cladding, specialized glass)Container Ship10,000 km sea$0.012\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$

4. Module A5: Construction Installation and Site Wastage

Module A5 accounts for all activities required to install components on site [S01, S04]. It is divided into two distinct sub-components:

  • Module A5.site (Site activities): Direct fuel burned by site plant (excavators, mobile piling rigs, tower cranes, mobile elevating work platforms), electricity consumed by site cabins and tools, and temporary works (scaffolding, formwork timber).
  • Module A5.waste (Material wastage): The embodied carbon of surplus materials ordered, delivered, and discarded due to cutting off-cuts, handling damage, and over-ordering.

The Compounding Mathematical Effect of Material Wastage

When a structural drawing calls for a net installed quantity of material $M_{\text{installed}}$, the contractor must purchase an inflated gross quantity $M_{\text{purchased}}$ to cover the site wastage rate $W_i$ (expressed as a decimal, e.g., $5\% = 0.05$) [S05]:

$$M_{\text{purchased}, i} = M_{\text{installed}, i} \times (1 + W_i)$$

Because that surplus material had to be manufactured ($A1–A3$) and delivered to site ($A4$), site wastage increases the upstream A1–A4 footprint:

$$\text{EC}_{A1-A3, \text{gross}} = \sum_i M_{\text{installed}, i} \times (1 + W_i) \times \text{EF}_{A1-A3, i}$$

$$\text{EC}_{A4, \text{gross}} = \sum_i M_{\text{installed}, i} \times (1 + W_i) \times d_i \times \text{EF}_{\text{trans}, i}$$

The disposal of that wasted material on-site is then booked directly into Module A5 [S04, S05]:

$$\text{EC}_{A5.\text{waste}} = \sum_i \left( M_{\text{installed}, i} \times W_i \right) \times \left( d_{\text{waste}} \times \text{EF}_{\text{trans}} + \text{EF}_{\text{waste-treatment}} \right)$$

Typical Benchmark Wastage Rates (IStructE 2022 & RICS 2023) [S04, S05]

  • In-situ cast concrete: $3\% \text{ to } 5\%$
  • Fabricated structural steel: $1\% \text{ to } 2\%$
  • Reinforcing steel (rebar cut and bent on site): $5\% \text{ (or } 1\% \text{ if factory pre-cut)}$
  • Facing brickwork / concrete blocks: $5\% \text{ to } 10\%$
  • Plasterboard / internal linings: $10\% \text{ to } 15\%$

Worked example

Problem Statement

Calculate the total Upfront Embodied Carbon (Modules A1–A5) for the construction of a reinforced concrete structural bay in a commercial building.

The structural schedule specifies:

  1. Concrete: $120\text{ m}^3$ of in-situ grade C30/37 concrete.
    • Density: $2{,}400\text{ kg}/\text{m}^3$.
    • A1–A3 Emission Factor: $0.115\text{ kgCO}_2\text{e}/\text{kg}$ (low-carbon concrete with 50% GGBS substitution) [S07].
    • Wastage rate ($W_{\text{conc}}$): $5\%$ ($0.05$).
    • Delivery: Local batching plant, $25\text{ km}$ via ready-mix transit mixer ($\text{EF}_{\text{trans}} = 0.160\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$) [S05].
  2. Reinforcing Steel (Rebar): $14.4\text{ tonnes}$ ($14{,}400\text{ kg}$) of high-yield deformed steel rebar.
    • A1–A3 Emission Factor: $0.780\text{ kgCO}_2\text{e}/\text{kg}$ (EAF UK/EU recycled steel) [S05, S07].
    • Wastage rate ($W_{\text{rebar}}$): $3\%$ ($0.03$).
    • Delivery: National fabricator, $150\text{ km}$ via articulated HGV ($\text{EF}_{\text{trans}} = 0.088\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$) [S04].
  3. On-Site Installation (A5.site):
    • Tower crane, vibrators, and site power allocate $1{,}250\text{ kgCO}_2\text{e}$ of fuel and grid electricity for this bay.
  4. Site Waste Processing (A5.waste):
    • Disposal transport and recycling treatment for construction waste equals $18.5\text{ kgCO}_2\text{e}/\text{tonne}$ of wasted material [S04].

Step-by-Step Solution

Step 1: Material Quantities and Masses

  • Concrete Mass:

    $$M_{\text{installed, conc}} = 120\text{ m}^3 \times 2{,}400\text{ kg}/\text{m}^3 = 288{,}000\text{ kg} = 288.0\text{ tonnes}$$

    $$M_{\text{purchased, conc}} = 288.0\text{ t} \times (1 + 0.05) = 302.4\text{ tonnes} = 302{,}400\text{ kg}$$

  • Rebar Mass:

    $$M_{\text{installed, rebar}} = 14.4\text{ tonnes} = 14{,}400\text{ kg}$$

    $$M_{\text{purchased, rebar}} = 14.4\text{ t} \times (1 + 0.03) = 14.832\text{ tonnes} = 14{,}832\text{ kg}$$

Step 2: Module A1–A3 (Product Stage with Wastage Allowance)

  • Concrete A1–A3:

    $$\text{EC}_{A1-A3, \text{conc}} = 302{,}400\text{ kg} \times 0.115\text{ kgCO}_2\text{e}/\text{kg} = 34{,}776.0\text{ kgCO}_2\text{e}$$

  • Rebar A1–A3:

    $$\text{EC}_{A1-A3, \text{rebar}} = 14{,}832\text{ kg} \times 0.780\text{ kgCO}_2\text{e}/\text{kg} = 11{,}568.96\text{ kgCO}_2\text{e}$$

  • Total Module A1–A3:

    $$\text{EC}_{A1-A3} = 34{,}776.0 + 11{,}568.96 = 46{,}344.96\text{ kgCO}_2\text{e} \approx 46.34\text{ tCO}_2\text{e}$$

Step 3: Module A4 (Transport to Site)

  • Concrete Freight:

    $$\text{EC}_{A4, \text{conc}} = 302.4\text{ tonnes} \times 25\text{ km} \times 0.160\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km}) = 1{,}209.6\text{ kgCO}_2\text{e}$$

  • Rebar Freight:

    $$\text{EC}_{A4, \text{rebar}} = 14.832\text{ tonnes} \times 150\text{ km} \times 0.088\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km}) = 195.78\text{ kgCO}_2\text{e}$$

  • Total Module A4:

    $$\text{EC}_{A4} = 1{,}209.6 + 195.78 = 1{,}405.38\text{ kgCO}_2\text{e} \approx 1.41\text{ tCO}_2\text{e}$$

Step 4: Module A5 (Site Installation & Site Waste Disposal)

  • Direct Site Installation Energy (A5.site):

    $$\text{EC}_{A5.\text{site}} = 1{,}250.0\text{ kgCO}_2\text{e}$$

  • Site Waste Generated:

    $$M_{\text{waste, conc}} = 302.4 - 288.0 = 14.4\text{ tonnes}$$

    $$M_{\text{waste, rebar}} = 14.832 - 14.4 = 0.432\text{ tonnes}$$

    $$\text{Total Wasted Material} = 14.4 + 0.432 = 14.832\text{ tonnes}$$

  • Waste Disposal & Processing Emissions (A5.waste):

    $$\text{EC}_{A5.\text{waste}} = 14.832\text{ tonnes} \times 18.5\text{ kgCO}_2\text{e}/\text{tonne} = 274.39\text{ kgCO}_2\text{e}$$

  • Total Module A5:

    $$\text{EC}_{A5} = 1{,}250.0 + 274.39 = 1{,}524.39\text{ kgCO}_2\text{e} \approx 1.52\text{ tCO}_2\text{e}$$

Step 5: Total Upfront Embodied Carbon (A1–A5)

$$\text{EC}_{\text{upfront}} = \text{EC}_{A1-A3} + \text{EC}_{A4} + \text{EC}_{A5}$$

$$\text{EC}_{\text{upfront}} = 46{,}344.96 + 1{,}405.38 + 1{,}524.39 = 49{,}274.73\text{ kgCO}_2\text{e} \approx 49.27\text{ tCO}_2\text{e}$$

Summary Breakdown:

  • Product Stage ($A1–A3$): $46{,}345\text{ kgCO}_2\text{e}$ ($94.0\%$)
  • Transport ($A4$): $1{,}405\text{ kgCO}_2\text{e}$ ($2.9\%$)
  • Site Works & Waste ($A5$): $1{,}524\text{ kgCO}_2\text{e}$ ($3.1\%$)

Notice that Product Stage (A1–A3) dominates upfront carbon by over 90%, highlighting why low-carbon material specifications (e.g. SCM replacement in concrete, recycled steel) are the primary levers for upfront decarbonization [S05, S06].

Visual explanation

The diagram below tracks how raw materials are extracted, transported, and compounded by on-site wastage during physical erection.

Upfront Carbon Industrial Supply Chain & Site Wastage (A1–A5)

Dual-stream flow tracking raw material extraction through logistics and on-site wastage compounding to Practical Completion.

Dual-Stream Process
Stream 1 Concrete Supply Chain (A1–A4)
A1
Quarrying & SCM Feedstocks

Limestone, aggregates, GGBS/PFA

↓
A2–A3
Clinker Calcination Kiln

High-heat chemical decarbonation

↓
A3
Batching & Blending

CEM I vs CEM III SCM mix design

↓
A4
Transit Mixers (50 km)

Time-constrained drum haulage

Stream 2 Reinforcing Steel Chain (A1–A4)
A1
Scrap Metal / Iron Sourcing

EAF scrap yard collection

↓
A2–A3
EAF Scrap Smelting

Electrified high-recycle metallurgy

↓
A3
Rolling Mill & Fabrication

Billet rolling & scheduled bending

↓
A4
Articulated HGVs (200 km)

Regional freight with empty return

Gate 3 Construction Site Convergence & Handover (A5)
A5 Waste
Compounded Site Wastage

Off-cuts, pump line washout & skips

A5 Plant
Site Erection & Plant

Tower cranes, pump trucks & diesel

Day 1 Handover
Practical Completion

Total locked-in Upfront Carbon (A1–A5)

Module Inspector
[A1] Quarrying & SCM Feedstocks

Limestone quarrying, clay extraction, and secondary cementitious sourcing (GGBS from blast furnace slag, PFA from pulverized fuel ash).

Formula Mass (t) × Quarrying Extraction EF
Standard EN 15804+A2 / MPA Generic
Benchmark Crushed aggregates ~0.008 kgCO2e/kg
View Standard Schematic (Mermaid Code)
flowchart TD subgraph A1_A3["Module A1–A3: Product Stage"] Agg["Aggregates & SCM Quarrying"] --> Kiln["Cement Calcination Kiln"] Kiln --> Batch["Concrete Batching Plant"] Iron["Scrap & Ore Sourcing"] --> Smelt["Steel Melting (EAF / BOF)"] Smelt --> Mill["Rebar Rolling Mill"] end subgraph Logistics["Module A4: Transport Logistics"] Batch --> Transit["Transit Mixers (50 km)"] Mill --> Artic["Articulated HGVs (200 km)"] end subgraph Site["Module A5: Construction Site"] Transit & Artic --> SiteGate["Site Delivery Gate"] SiteGate --> Storage["Material Handling & Storage"] Storage --> Wastage["On-site Wastage (3%–5%)"] Storage --> Installed["Permanently Installed Bay"] Wastage --> Disposal["Waste Skip & Recycling"] Plant["Cranes & Diesel Generators"] --> Erection["Bay Erection"] end Installed & Disposal & Erection --> Complete["Practical Completion (Total A1–A5)"] classDef mat fill:#fdfbf7,stroke:#de634d,stroke-width:2px; classDef trans fill:#fdfbf7,stroke:#e1a102,stroke-width:2px; classDef site fill:#fdfbf7,stroke:#3b827e,stroke-width:2px; classDef out fill:#fdfbf7,stroke:#6366f1,stroke-width:2px; class Agg,Kiln,Batch,Iron,Smelt,Mill mat; class Transit,Artic trans; class SiteGate,Storage,Wastage,Installed,Disposal,Plant,Erection site; class Complete out;

Reading the Diagram

  • Upstream extraction and manufacturing generate over 90% of the greenhouse gas burden before any truck leaves the depot.
  • Materials flowing into Module A4 are not merely the net designed volume; they must include the additional volume destined to become scrap on site.
  • On the jobsite (Module A5), materials split into permanently incorporated structural fabric versus wasted material routed to disposal skips.

Practice

Exercise 1: Compounding Effect of Wastage

A commercial building specifies $200\text{ tonnes}$ of structural steelwork.

  • Steel A1–A3 emission factor: $1.80\text{ kgCO}_2\text{e}/\text{kg}$.
  • Transport distance to site: $200\text{ km}$ at $0.088\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$.
  • Case 1: Prefabricated modular frames with a factory-controlled wastage rate of $1\%$.
  • Case 2: Site-cut beam sections with a wastage rate of $6\%$.

Calculate:

  1. The gross mass of steel purchased for Case 1 and Case 2.
  2. The combined A1–A4 carbon emissions for Case 1 and Case 2.
  3. How many tonnes of $\text{CO}_2\text{e}$ are saved simply by shifting cutting and detailing off-site to reduce wastage from $6\%$ to $1\%$?

Exercise 2: Evaluating Transport Penalties

An architect is comparing two cladding stone options:

  • Option A (Local Granite): Transported $80\text{ km}$ by rigid HGV ($\text{EF} = 0.134\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$). A1–A3 factor: $0.220\text{ kgCO}_2\text{e}/\text{kg}$.
  • Option B (Imported Marble): Transported $400\text{ km}$ by road ($\text{EF} = 0.088$) plus $4{,}000\text{ km}$ by container cargo ship ($\text{EF} = 0.012\text{ kgCO}_2\text{e}/(\text{t}\cdot\text{km})$). A1–A3 factor: $0.180\text{ kgCO}_2\text{e}/\text{kg}$.

Assuming $500\text{ tonnes}$ of stone are installed with a $4\%$ wastage rate:

  1. Compute the transport emissions (Module A4) for both options.
  2. Compute the combined A1–A4 upfront emissions for both options.
  3. Does Option B’s lower quarrying/cutting factor compensate for its shipping logistics?

Answers and hints

Exercise 1 Answers

  1. Purchased mass:
    • Case 1: $200\text{ t} \times 1.01 = 202.0\text{ tonnes}$.
    • Case 2: $200\text{ t} \times 1.06 = 212.0\text{ tonnes}$.
  2. A1–A4 emissions:
    • $\text{Unit A1–A4 Factor} = 1{,}800\text{ kgCO}_2\text{e}/\text{t} + (200\text{ km} \times 0.088) = 1{,}800 + 17.6 = 1{,}817.6\text{ kgCO}_2\text{e}/\text{t}$.
    • Case 1: $202.0\text{ t} \times 1{,}817.6\text{ kgCO}_2\text{e}/\text{t} = 367{,}155.2\text{ kgCO}_2\text{e} = 367.16\text{ tCO}_2\text{e}$.
    • Case 2: $212.0\text{ t} \times 1{,}817.6\text{ kgCO}_2\text{e}/\text{t} = 385{,}331.2\text{ kgCO}_2\text{e} = 385.33\text{ tCO}_2\text{e}$.
  3. Savings: $$385.33 - 367.16 = 18.17\text{ tCO}_2\text{e} \text{ saved}$$ Reducing wastage by just 5% saves over 18 tonnes of carbon purely through avoided upstream production!

Exercise 2 Answers

  1. Module A4:
    • Purchased mass: $500\text{ t} \times 1.04 = 520\text{ tonnes}$.
    • Option A (Local): $520\text{ t} \times 80\text{ km} \times 0.134 = 5{,}574.4\text{ kgCO}_2\text{e} \approx 5.57\text{ tCO}_2\text{e}$.
    • Option B (Import): $520\text{ t} \times [(400 \times 0.088) + (4{,}000 \times 0.012)] = 520 \times [35.2 + 48.0] = 520 \times 83.2 = 43{,}264.0\text{ kgCO}_2\text{e} \approx 43.26\text{ tCO}_2\text{e}$.
  2. Combined A1–A4:
    • Option A A1–A3: $520{,}000\text{ kg} \times 0.220 = 114{,}400\text{ kgCO}_2\text{e}$. $$\text{Total Option A} = 114{,}400 + 5{,}574.4 = 119{,}974.4\text{ kgCO}_2\text{e} \approx 120.0\text{ tCO}_2\text{e}$$
    • Option B A1–A3: $520{,}000\text{ kg} \times 0.180 = 93{,}600\text{ kgCO}_2\text{e}$. $$\text{Total Option B} = 93{,}600 + 43{,}264.0 = 136{,}864.0\text{ kgCO}_2\text{e} \approx 136.9\text{ tCO}_2\text{e}$$
  3. Conclusion: No. Option B’s shipping penalty ($43.26\text{ t}$) substantially outweighs its quarry manufacturing advantage ($20.8\text{ t}$ savings), making the local stone $16.9\text{ tCO}_2\text{e}$ lower in net upfront carbon.

Next steps

In this lesson, you mastered how raw material manufacture (A1–A3), transport logistics (A4), and site assembly and wastage (A5) dictate Upfront Carbon.

Continue to Lesson 03: The In-Use Stage (Modules B1–B5) and Operational Interplay, where we examine how component replacement cycles over a 60-year lifespan accumulate embodied carbon, and analyze the trade-off between operational carbon savings (B6) and embodied carbon investments.

Test the impact of transport distances and wastage rates in the Whole Life Embodied Carbon Simulator.

References