Carbon Analysis
Estimate the whole-life carbon of your design: embodied carbon from the massing and facades, operational energy from the site's climate, rated against LETI and RIBA targets.
What is Carbon Analysis
Carbon Analysis estimates the whole-life carbon of your design while you work on it: the carbon in its materials (embodied carbon) and the carbon from the energy it will use (operational carbon), over a study period of 60 years by default.
The analysis is built from your project rather than generic averages:
- Your geometry. Footprints, floors, wall areas by orientation, roofs and balconies are measured on the model.
- Your facades. Glazing is measured on the facade you designed in the facade view: windows, ribbon glazing, curtain walls and shopfronts.
- Your uses. Each floor’s use (residential, office, retail, commercial, mixed) sets its energy profile, fit-out and targets.
- Your site. The site’s weather file gives the temperatures, the sun on each facade and the solar yield of roof panels. The country of the nearest weather station sets the carbon of its electricity.
Results update live as you change the massing, the facades or the assumptions.
Carbon Analysis is an early-stage tool for comparing options: a timber frame against concrete, a better envelope, less glazing on the west, more PV. It does not replace a whole-life carbon assessment (WLCA) carried out on a detailed design.
Opening Carbon Analysis
- Open your project in the editor.
- In Design Studio (3D) or the 2D view, click the Carbon Analysis icon in the left rail.
The panel loads the site’s weather data the first time it opens. Until it arrives, or if no weather data is available for the location, the panel shows embodied carbon only.
Reading the results
Headline figures
| Figure | What it means |
|---|---|
| Upfront carbon | Embodied carbon up to completion (modules A1–A5), per m² of gross internal area (GIA). Shown with its LETI band, from A++ to G. |
| Whole-life carbon | Embodied and operational carbon over the study period, in tonnes CO2e and per m². |
| Energy use | Delivered energy per m² per year (EUI), compared with the LETI 2030 target for your use mix. |
| Operational | Carbon from energy use in the first year, in tCO2e per year. |
Embodied carbon
- LETI band scale. Where the design’s upfront carbon sits among the LETI bands. For mixed-use projects, the band limits are weighted by the floor area of each use.
- By element. Upfront carbon of each building element, in tonnes and kg/m²: substructure, frame and floors, roof, external walls, glazing, balconies, fit-out, building services, photovoltaics and external works.
- Life cycle stages:
- Upfront (A1–A5): materials, transport and construction.
- Replacements (B4): components replaced during the study period (see Replacement intervals).
- End of life (C1–C4): demolition, transport and disposal.
- Embodied, whole life (A–C), compared with the RIBA 2030 target.
Operational energy
- By end use. Space heating, cooling, hot water, lighting, equipment and appliances, fans and pumps, in kWh/m² per year.
- Heating and cooling needs. The energy the building needs to stay comfortable, before system efficiencies, with a month-by-month chart.
- Heat pump SCOP, when a heat pump is selected.
- PV generation, when roof photovoltaics are set.
- Where heat is lost. Heat loss split between walls, glazing, roof, ground floor, thermal bridges, ventilation and air leakage. Use it to see which improvement matters most.
- Facades by orientation. Opaque wall and glazing areas facing each compass direction.
Over the study period
A cumulative chart of carbon year by year:
- Embodied carbon steps up at completion, at each replacement and at end of life.
- Operational carbon builds up every year.
By building
When the site has several buildings, each one is listed with its floor area, storeys, upfront carbon, energy use and glazing ratio.
Design assumptions
Open Design assumptions in the panel to set the choices the model cannot read from the geometry. They are saved with the project and used by the report.
| Setting | Options | Default |
|---|---|---|
| Structure | Reinforced concrete, steel frame, mass timber (CLT / glulam), hybrid timber–concrete | Reinforced concrete |
| Facade system | Brick, render on insulation, precast concrete, timber cladding, metal cladding, curtain wall | Brick |
| Fabric standard | Building regulations, high performance, Passivhaus | Building regulations |
| Heating & hot water | Gas boiler, air-source heat pump, district heating, direct electric | Air-source heat pump |
| Cooling | Offices & shops only, none, all floors | Offices & shops only |
| Glazing ratio | 10–90 % (see below) | 30 % |
| Roof photovoltaics | 0–90 % of the roof footprint | 0 % |
| Study period | 10–120 years | 60 years |
| Grid carbon | Country average, or your own value in gCO2e/kWh | Country average |
| Grid decarbonises | Electricity carbon falls to a quarter of today’s by 2050 | Off |
Glazing ratio only applies to buildings with their facade turned off. Buildings with a designed facade use the glazing actually drawn. The panel shows the measured ratio under the slider.
Grid carbon defaults to the average for the country of the site’s weather station, and to the world average if the country is unknown. Type a value to use your own, for example a supplier’s tariff or a future scenario. Clear the field to go back to the country average.
Carbon in the project report
Add the Carbon section to a report from the Report panel. It is included in the Full report and Design presets. The section uses the same assumptions as the panel, and spans two pages.
First page:
- Headline figures.
- The LETI rating strip.
- Embodied carbon by element, with replacements.
- The whole-life breakdown.
- The cumulative carbon chart.
Second page:
- Delivered energy by end use, with PV.
- Monthly heating and cooling needs.
- The assumptions, including U-values, heat pump SCOP and the grid factor’s source.
- The heat loss breakdown.
- A table by building.
How it is calculated
Embodied carbon
Element quantities are measured on the model and multiplied by typical carbon factors for the chosen structure and facade system. The factors are cradle-to-gate (A1–A3) values in the range of the ICE database, the LETI Embodied Carbon Primer and RICS whole-life carbon guidance. The model adds:
| Stage | Allowance |
|---|---|
| Transport to site (A4) | +3 % of A1–A3 |
| Construction (A5) | +6 % of A1–A3 |
| Replacements (B4) | Each component’s A1–A5, once per replacement within the study period |
| End of life (C1–C4) | 5 % of A1–A3 (including replaced components) |
How each element is measured:
- Foundations: from the footprint, growing by 5 % per storey above the first.
- Underground levels: each level below ground adds a basement slab of 110 kgCO2e per m² of its area, and retaining walls of 140 kgCO2e per m² of wall (the building’s perimeter by the total depth). Both count in the substructure. Underground levels are not heated, so they don’t change the floor area, the energy use or the per-m² figures.
- Frame: from the floor area.
- Glazing: from the measured glazed area. It is double glazed, or triple glazed for Passivhaus.
- External walls: from the opaque wall area. Higher fabric standards add insulation carbon.
- Roofs: from the roof surface. Pitched roofs include their covering (tiles, slate or zinc, as set in the facade view).
- Balconies: from the area of the balcony slabs.
- External works: from parking surfaces and landscaping.
Biogenic carbon stored in timber is not deducted, as in LETI’s upfront carbon figures.
Replacement intervals
| Component | Replaced every |
|---|---|
| Building services | 20 years |
| Fit-out and finishes | 20 years (half replaced) |
| Photovoltaics | 25 years |
| Roof coverings and membranes | 30 years |
| Glazing | 35 years, or sooner if the facade system is replaced sooner |
| Facade: brick, precast concrete | 60 years |
| Facade: timber or metal cladding | 40 years |
| Facade: curtain wall | 35 years |
| Facade: render on insulation | 30 years |
Operational energy
Each building runs through a monthly heat balance following ISO 13790. For every month, the model weighs heat losses through the envelope and ventilation against internal gains and solar gains through the glazing. The thermal mass of the structure is taken into account. The model uses:
- Monthly temperatures from the site’s typical meteorological year (TMY) weather file.
- Sun on each facade. Hourly direct and diffuse radiation is projected onto walls facing 16 compass directions, using the sun’s position at the site. A south-facing window gains more than a north-facing one.
- Ventilation and air leakage from the use profiles and the fabric standard. Outside homes, ventilation always has at least 73 % heat recovery, the EU Ecodesign minimum for air handling units.
Heating and cooling needs then go through the chosen systems:
| System | Efficiency | Energy |
|---|---|---|
| Gas boiler | 90 % heating, 85 % hot water | Natural gas, 183 gCO2e/kWh |
| Air-source heat pump | SCOP from 2.2 to 3.5, lower in colder climates; hot water 0.5 lower | Electricity |
| District heating | 100 % | Heat network, 170 gCO2e/kWh |
| Direct electric | 100 % | Electricity |
| Cooling | SEER 3.5 | Electricity |
The heat pump’s SCOP starts at 3.2. It is lowered for sites whose 99.6 % heating design temperature is below 0 °C, and kept between 2.2 and 3.5.
Lighting, equipment, hot water and fans come from each floor’s use profile:
| Use | Heating / cooling setpoint | Lighting | Equipment | Hot water | Cooled by default |
|---|---|---|---|---|---|
| Residential | 20 °C / 26 °C | 8 kWh/m² | 25 kWh/m² | 25 kWh/m² | No |
| Office | 20 °C / 24 °C | 15 kWh/m² | 30 kWh/m² | 5 kWh/m² | Yes |
| Retail | 18 °C / 24 °C | 30 kWh/m² | 25 kWh/m² | 3 kWh/m² | Yes |
| Commercial | 19 °C / 24 °C | 20 kWh/m² | 25 kWh/m² | 4 kWh/m² | Yes |
| Mixed | 20 °C / 25 °C | 12 kWh/m² | 25 kWh/m² | 15 kWh/m² | No |
Values are per m² of floor area per year.
Roof photovoltaics generate from the site’s solar radiation, with 20 % module efficiency and a 0.8 performance ratio. Generation offsets the electricity used in the building. Surplus exported to the grid is not credited.
Fabric standards
| Building regulations | High performance | Passivhaus | |
|---|---|---|---|
| Walls (U, W/m²K) | 0.26 | 0.18 | 0.12 |
| Roof | 0.16 | 0.12 | 0.10 |
| Ground floor | 0.18 | 0.13 | 0.10 |
| Glazing | 1.4 | 1.1 | 0.8 |
| Glazing solar factor (g) | 0.50 | 0.45 | 0.50 |
| Air leakage (air changes per hour) | 0.30 | 0.15 | 0.05 |
| Heat recovery on ventilation | None in homes, 73 % elsewhere | 75 % | 88 % |
| Thermal bridges | +15 % | +10 % | +5 % |
Curtain walls and metal cladding have higher U-values than the fabric standard (x1.3 and x1.05 on opaque areas) to account for spandrels and fixings.
Operational carbon
Each year’s electricity, gas and district heat is multiplied by its carbon factor:
- Electricity: the country average (recent national generation averages, from Ember / IEA data), or your own value.
- Grid decarbonisation (when turned on): the electricity factor falls in a straight line to 25 % of today’s value in 2050, then stays there.
Benchmarks
| Benchmark | Residential | Office, retail, commercial |
|---|---|---|
| LETI 2030 energy use (EUI) | 35 kWh/m²·yr | 55 kWh/m²·yr |
| RIBA 2030 embodied carbon (A–C) | 625 kgCO2e/m² | 750 kgCO2e/m² |
| LETI upfront carbon bands | A++ ≤ 50 … G ≤ 1,200 kgCO2e/m² | A++ ≤ 100 … G ≤ 1,300 kgCO2e/m² |
Mixed-use projects use targets weighted by the floor area of each use. All intensities are per m² of gross internal area (GIA), taken as 95 % of the gross floor area, as in the Statistics panel. The LETI rating leaves external works out.
Limitations
- Factors are typical values. Use project-specific Environmental Product Declarations (EPDs) and a full WLCA for planning submissions or certification.
- Surrounding buildings don’t shade the facades in the energy balance.
- Cores and internal layouts are not modelled. Fit-out and services are estimated per m² of each use. Underground levels add only their structure (slab and retaining walls), with no fit-out, services or excavation.
- Occupancy follows standard use profiles and is averaged over the month.
- Climate data is from a typical year at the nearest weather station. It describes average conditions, not extreme or future climates.
Tips
- Compare options, not absolute numbers. Change one assumption at a time and watch the upfront band and the EUI.
- Check where heat is lost before upgrading the fabric. If glazing or ventilation dominate, wall insulation alone won’t move the EUI much.
- Look at glazing by orientation. Large west- and south-facing curtain walls drive cooling in offices. Punched windows usually cut both cooling and embodied carbon.
- On a low-carbon grid (France, Nordic countries), embodied carbon dominates the whole-life total, so structure and facade choices matter most. On a high-carbon grid, heating systems and PV make a larger difference.