We have been working with a number of clients to undertake Greenhouse Gas Inventories (GHG) of proposed developments in order to reduce the embodied carbon of the materials. Using the bill of quantities to determine amounts, the GHG assessment focused on key materials that make up the sub and super-structure a new development.
Using the bill of quantities to determine amounts, the GHG assessment focuses on key materials – high cost items which make up the sub- and super-structure or cladding of a new development. Generally this means that elements such as concrete, steel, rebar, aluminium and glass are included in the inventory.
Figure 1 Typical breakdown of construction embodied carbon in a new office building
During a GHG Inventory, the focus should be on how to reduce the embodied carbon by working with the design team and the client to consider qualitative aspects such as durability of materials and design for demolition / reuse / recycling. Together the team should:
• Examine the type of materials, their efficient use and their expected life;
• Minimise wastage on site and design for deconstruction.
Quantitative assessments of individual materials should identify the range of embodied carbon within a material (due to embedded inconsistences in the available data or lack of appropriate data we would generally advise express the amount of embodied carbon in a material as a range, rather than absolute value). Following the inventory the team can identify and target the most appropriate opportunities for embodied carbon reduction through the specification of lower carbon versions. Such reductions provide clear benefits, often at little or no capital cost. For instance in relation to concrete, the structural team could aim to ensure that: cement replacement is specified; admixtures are incorporated; and to avoid over-specification of strength of concrete. Cement replacement is widely used in standard concrete mixes because it is cheaper – the reduced embodied carbon is a free bonus!
Unfortunately, due to inconsistent methodologies, the background data related to embodied carbon can often include a wide range of uncertainty (sometimes quoted by as much as +/- 30%). Furthermore, it may only be available for generic materials rather than products from specific suppliers.
There are however, a number of ways to improve the findings of an Inventory. Firstly, it is important that key fit out materials are not overlooked when compiling an inventory. A typical building will be refurbished once every 10 – 15 years so the embodied carbon of fit out materials, while appearing minor at first glance, soon add up over the lifetime of the building. Sharing resources and available data among design teams will also help encourage a stepped improvement in the methodology. Furthermore, we would always advise that the client or sustainability coordinator challenge the supply chain to provide independently verified, Environmental Product Declarations for concrete, reinforcement and formwork and steel.
Current London Plan Policy (#5.25) aims to avoid the use of high embodied energy materials. There is likely to be increased focus on this in the future that may even involve set targets similar to those that existing for operational carbon. It is therefore a sensible approach to include embodied carbon assessments as part of the sustainability statement of a proposed development. This will help establish the targets at an early stage and focus the efforts on a collaborative approach to reducing the embodied carbon of a development.