Here you can find a list of the most commonly used words and terms in the timber supply chain.

Carbon Terms

Biogenic Carbon

Carbon derived from biomass.

Carbon Dioxide (CO2)

Greenhouse gas generated by cellular respiration in organisms as well as the burning of fossil fuels. Excess CO2 is known to be the key cause of climate change on Earth.

Carbon Dioxide Equivalent (CO2e)

Unit for comparing the radiative forcing of a greenhouse gas to that of carbon dioxide.

Carbon Footprint

Sum of greenhouse gas (GHG) emissions and GHG removals in a product system, expressed as CO2 equivalents (CO2e) and based on a life cycle assessment using the single impact category of climate change. The carbon footprint of a house is equivalent to its Whole Life Carbon. The carbon footprint of a brick is equivalent to its Embodied Carbon.

Carbon Negative / Climate Positive

An activity that goes beyond achieving net zero carbon emissions to create a benefit by removing additional carbon dioxide from the atmosphere.

This would need to be demonstrated across the whole life of the product or asset, not just part of the lifecycle, in the form of an EPD for products or Whole Life Carbon Assessment for assets, along with evidence of carbon removal offsets (where applicable).

Carbon Neutral

A carbon neutral footprint (as defined by the Carbon Trust) is one where the sum of Scope 1 & 2 greenhouse gas emissions produced is offset by natural carbon sinks and/or carbon credits.

The Carbon Trust no longer verify Carbon Neutral claims, and instead encourage the move to Net-Zero Carbon.

Carbon Offset

Mechanism for compensating Embodied or Operational Carbon through the prevention of the release of, reduction in, or removal of an amount of greenhouse gas emissions in a process outside the product system under study.

Carbon Positive

How organizations sometimes describe Carbon Negative or Climate Positive. As it is confusing, we don’t recommend its use.

Carbon Removal

Activities that remove and durably store atmospheric CO2. Can be biological (e.g. reforestation) or technical (e.g. sequestering carbon deep underground).

Carbon Sequestration

The process of removing CO2 from the atmosphere and storing it in a stable long-term carbon reservoir (e.g. within the timber of a tree).

Embodied Carbon

GHG emissions associated with the material, construction, maintenance and demolition processes throughout the whole life cycle of an asset (Modules A1-A5, B1-B5, C1-C4).

Expand on Embodied Carbon, through our new Timber Knowledge Sheet 

Low Carbon

Products with a Cradle to Gate (Modules A1-A3) Carbon footprint lower than 100kgCO2e/m3, excluding any sequestered biogenic carbon within the product.

Net-Zero Carbon

Where a process’s scope 1, 2 and 3 greenhouse gas emissions are reduced to zero, or to a residual level that is consistent with reaching net-zero emissions at the global or sector level in eligible 1.5°C scenarios or sector pathways and neutralising any residual emissions in the form of carbon removal. See Net Zero Roadmap

Net-Zero Embodied Carbon

A ‘Net Zero Embodied Carbon’ product or asset is one where the sum of embodied GHG emissions (Modules A1-A5, B1-B5 & C1-C4) and offsets (in the form of carbon removal) equals zero.

Net-Zero Whole Life Carbon

A ‘Net Zero Whole Life Carbon’ product or asset is one where the sum of all asset related GHG emissions, both operational and embodied, (Modules A1-A5, B1-B7, C1-C4) and offsets (in the form of carbon removal) equals zero.

Operational Carbon

GHG emissions arising from all energy and water consumed by a product or asset in use, as projected or measured, over its life cycle (Modules B6-B7).

Stored Carbon

The total of all biogenic carbon stored within the asset at practical completion (normally obtained from data within the EPD).

Upfront Carbon

GHG emissions associated with product manufacture, transport and construction processes up to practical completion of an asset (Modules A1-A5). Any biogenic carbon must be excluded from the upfront assessment and stated separately as Stored Carbon.

Whole Life Carbon

Sum total of all asset related GHG emissions, both operational and embodied over the life cycle of an asset including its disposal. Whole Life Carbon = Operational Carbon + Embodied Carbon (Modules A1-A5, B1-B7, C1-C4). The potential benefit from future energy recovery, reuse, and recycling (Module D) is reported separately.

Zero Carbon

Causing or resulting in no release of carbon dioxide into the atmosphere, without the use of offsetting. This would need to be demonstrated in the form of an EPD for products or Whole Life Carbon Assessment for assets.

Sustainability Terms


Material of biological origin excluding material embedded in geological and/or fossilized formations.

Circular Economy

An economy that is restorative and regenerative by design, and which aims to keep products, components and materials at their highest utility and value at all times, distinguishing between technical and biological cycles.


Part of a construction containing a defined combination of construction products (e.g. ground floor, roof, external wall).

Element Unit Quantity (EUQ)

A unit of measurement that relates solely to the quantity of the element or sub-element itself (e.g. the area of the external walls, the area of windows and external doors and the number of internal doors).

Environmental Product Declaration (EPD)

An EPD provides environmental information about a product in a standardised format using an consistent methodology. For construction products in Europe, the European standard EN 15804 provides the format and methodology.

Global Warming

A gradual increase in the overall temperature of the earth’s atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, CFCs, and other pollutants.

Greenhouse Gas (GHG)

Gaseous constituent of the atmosphere, both natural and anthropogenic, that absorbs and emits radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth’s surface, the atmosphere, and clouds.

Gross Internal Area (GIA)

Gross internal area is the area of a building measured to the internal face of the perimeter walls at each floor level.

Life Cycle Assessment (LCA)

Compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle.

Radiative Forcing

An externally imposed perturbation in the radiative energy budget of the Earth’s climate system – causes global warming.

Renewable Resource

A natural resource which will replenish to replace the portion depleted by usage and consumption, either through natural reproduction or other recurring processes in a finite amount of time in a human time scale.

Timber Terms

Engineered Wood Products (EWP)

Wood as a material can be very versatile as it comes in all sorts of shapes and sizes. EWPs are made of wood in the form of sawn timber boards, veneers, particles or fibres held together with, in most cases, some type of adhesive.

To name a few of the most popular EWP’s that are available in the market:

  • Cross-laminated Timber (CLT)
  • Plywood
  • Laminated Veneer Lumber (LVL)
  • Glue Laminated Timber (Glulam)
  • Oriented Strand Board (OSB)
  • I-Beams

Eurocode 5 (EC5)

Eurocode 5 contains timber design principles and essential application rules to realise them. Application rules are presented as design formulae eliminating the need for the material-specific tables that were presented in the BS 5268 family of standards. It applies for civil engineering works from solid timber, sawn, planned or in pole form, glued laminated timber or wood-based structural products, (e.g. LVL) or wood-based panels jointed together with adhesives or mechanical fasteners and is divided into the following parts.


Hardwood timber comes from “Deciduous” trees, these ones are known due to the fact that they lose their leaves every year. Examples of hardwood trees are, Oak, Iroko, Sapele, Teak, among others.

Expand your knowledge on hardwood timber here

Mass Timber

Mass timber construction differs from light-frame wood construction as it employs EWPs, typically consisting of substantial wood panels, columns, or beams. These elements are often produced off-site for constructing load-bearing walls, floors, and roofs.

Mass timber is designed to possess robust strength characteristics similar to concrete and steel, yet it is significantly lighter in weight. Mass timber products are comprised of thick, compressed layers of wood, forming sturdy, load-bearing components that can be assembled into panelized sections.

Mass Timber Components

Mass timber is the name given to types of engineered timber that can be used as structural building materials. Mass timber components are made from small planks or layers of timber bonded together to increase their strength and form load-bearing components such as panels, beams and columns. Components are made in factories to precise specifications.

Mass timber components include CLT panels, LVL and glulam products suited to post and beam construction which can be combined to create a range of structural systems.

Moisture Movement

Refers to the dimensional changes that occur when dried timber is subjected to changes in atmospheric conditions. It is classed as small, medium or large and is not directly related to the shrinkage which occurs when green timber is dried to moisture contents suitable for internal use. For structural purposes, movement is not usually significant but species with small movement should be specified where stability in varying humidities is important eg decorative wood flooring.

Panellised Mass Timber

Panellised construction uses off-site prefabricated mass timber panels that are assembled on site. Categorised as an MMC Category 2 solution, this system utilises the two-way spanning capability of CLT panels to form a honeycomb structure that transfers vertical and lateral loads. In this system, mass timber panels are used for both floors and walls, with the walls bearing the structural load and enhancing airtightness. In low and mid-rise buildings, panels can be used for the core of a building, replacing concrete.

Responsible Purchasing Policy (RPP)

TDUK’s Responsible Purchasing Policy (RPP) was developed in 2003 as a risk management framework for continuously improving the awareness, understanding, and capacity of timber trade members to meet the requirements of the UK Timber Regulation (UKTR) and the Construction Products Regulation (CPR), as outlined in the TDUK Code of Conduct. At its core, the RPP equips members with tools, guidance, and an independent annual audit (RPP audit) to facilitate the ongoing enhancement of compliance with applicable legislation. This ensures a level playing field for all members and instills market reassurance and confidence for customers engaging with TDUK members.

All timber Operator members who place timber on the UK market are obligated to undergo an annual review and audit for their imports. The audit is conducted by the Soil Association UK.


Softwood timber comes from “Coniferous” also known as “evergreen” trees, these ones are known due to the fact that they do not lose their leaves. Examples of softwood trees are, Pine, Larch and Douglas Fir.

These terms in fact have no bearing on the actual “hardness” or “softness” of the material. Some hardwoods are so dense they will not even float, other are so soft and light they can be used as insulation.

Expand your knowledge on softwood timber here

Timber Moisture Content

The strength and the stiffness of timber are affected by its moisture content. Moisture content is generally expressed as:

Weight of water/weight of oven-dried wood x 100 = Moisture content

In simple terms, the lower the moisture content of a piece of timber, the stronger it is and, conversely, the higher its moisture content, the weaker it is.

More on moisture in CLT

Use Class

The minimum standards for the treatment of wood are set out in British Standard BS8417 (Preservation of Wood: Code of Practice). In this standard, the level of treatment is tailored to the application ‘Use Class’ of a wood product as defined in BS EN 335 (Durability of wood and wood-based products).

Find out more on Preservative treatment here

Use Class 2 (UC2)

Use class 2 is for end uses where wood is used indoors, above ground and within the building envelope, but with an occasional risk of wetting (from plumbing leaks for example).

More on UC2 here

Use Class 3 (UC3)

Use Class 3 is for end uses where wood is used outdoors NOT in contact with the ground.

More on UC3 Here

Use Class 4 (UC4)

Use Class 4 is for end uses where wood is in contact with or very close to the ground and frequently wet.

More on UC4 here and expand for specifying, buying and installing here

Volumetric Modular Construction

Volumetric timber construction is an effective means of construction due to the accuracy and quality that can be achieved using prefabricated timber components. Classified as a MMC Category 1 solution, timber volumetric systems use CLT or closed timber panels for walls and slabs to minimise junctions and defects, increasing quality and in-use performance.


BS EN 15804:2012+A1:2013

Sustainability of construction works. Environmental product declarations. Core rules for the product category of construction products.

BS EN 15804:2012+A2:2019

Sustainability of construction works. Environmental product declarations. Core rules for the product category of construction products.

BS EN 15978:2011

Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method.

BS EN 16485:2014

Round and sawn timber. Environmental Product Declarations. Product category rules for wood and wood-based products for use in construction.