Carbon Methodology

CarbonWARM is based on a lifecycle analysis including materials displacement, so it is NOT suitable for scope 3 reporting under the GHG protocol. If you need information for your scope 3 carbon inventory, see our guidance below.

The factors quoted above are from CarbonWARM2, a methodology published by the Waste Resources Action Programme (WRAP), a global environmental action NGO which aims to move society towards the principles of Circular Living. CarbonWARM is mentioned in the UK Government GHG Conversion Factors for Company Reporting published by DESNZ as a better alternative to those factors for the purposes of comparing waste management options (but not mandatory reporting). However, the methodology also has its own set of assumptions and limitations that should be considered when deriving figures. We’ve done our best to follow the guidance given, but our calculation is our own work and not yet independently verified.

This calculation only applies to reporting for collections on or after 01 January 2026. For earlier periods we will continue to use our previous calculation which included savings from collection efficiency, raw materials displacement, and partial landfill diversion, for a total of 498kgCO2e per tonne collected. Reports spanning both periods will use the old calculation for collections before 2026 and the new calculation for collections in 2026 and after. Since the methodology differs, carbon figures should not be directly compared between these periods. We can provide a like-for-like comparison on request.

These factors do not include landfill diversion. To calculate the benefit compared to landfill, an additional 921kg CO2e per tonne diverted must be added to these reduction figures (representing the methane that would be emitted by decomposition in landfill). If you want reporting including whole or partial landfill diversion credit please contact us. All of the wood we collect is either recycled or reused.

The base tonnages that the factors are applied to are estimated based on visual volume. The derived calculations may therefore not be as accurate as tonnages measured directly by weighbridge. 

We include the impact of wood waste sent for bulk recycling (reported as ‘recycled’ on our reports) in our carbon figures. This recycling is conducted externally, but is a significant part of the downstream impact of our collected wood. The wood recycled in this way is sold to end-markets not obliged to report outcomes, so we estimate recycling outcomes based on national averages provided by the Wood Recyclers Association (WRA). The split is currently around 72% biomass (65% large-scale biomass, 2% small-scale biomass, and 5% exports which are mostly used in European power stations) and 28% other uses such as particleboard, surfacing and animal bedding.

When making a carbon reduction estimate, an important consideration is the baseline being used for comparison. Our reported carbon benefit represents the impact of the reuse and recycling activity we enable in the context of the wider economy, by providing sources of materials and energy at a comparatively lower environmental cost than primary manufactured alternatives. It is therefore not a comparison to alternative waste management options, but alternative power and material production options.

Wood that is used or reused in long-term items such as construction or furniture can create climate benefit by acting as a carbon store. This benefit depends on complex factors like how long the wood is in use and the end-of-life outcome, which is why we haven’t included it, but it is a significant factor that whole-life systems like EN 15978 do account for, and is becoming increasingly important as the potential of construction to sequester carbon is realised.

The CarbonWARM methodology specifies that the factor for wood recycling assumes direct displacement of an equal quantity of virgin timber. In reality, recycled and reused wood can displace a range of carbon-intensive materials such as metal and plastic if it is cost-effective enough, for example, a wooden garden table could displace a plastic or metal one. This would likely result in a higher benefit.

WRAP has no specific factor for reused wood, and their recycling estimate is based on particleboard manufacture. Reusing wood is much more energy-efficient and keeps the wood in a more intact state, so our expectation is that reuse would save more carbon than recycling. We are working to find a compatible way of representing specific reuse benefits.

Wood classed as ‘low grade reuse’ on our reports is used for a range of purposes including woodwork practice, crafts, commercial firewood, heating our premises, and donation to the community, who similarly may use it for things like heating or DIY. To keep things simple we currently class all low-grade reuse with our other reuse, but there is an argument that at least some of this wood would be better classed in the ‘energy from waste’ category. We are open to feedback on the most suitable classification.