Understanding the Language of Low Carbon and Offsite Construction

Offsite and low carbon are changing the way we talk about construction projects with a host of new terminology.

Here’s a quick run through of some of the most important terms and what they mean (and in some cases, don’t mean):

Net Zero

A ‘net zero carbon building’ could refer to the operational phase or the entire lifecycle – so it’s important to clarify exactly what people mean.

Operational net zero carbon means that all of the energy needs of the building come from renewable sources. In theory, if the whole of the UK’s energy supply was switched to renewables, the entire existing built environment would become operationally net zero. In practice, operational net zero also needs well insulated and highly energy-efficient buildings.

Embodied Carbon

True net zero carbon construction measures the carbon emissions generated to create, operate and decommission the building at the end of its life. So, we also have to understand the embodied carbon of construction materials and processes.

The term ‘embodied carbon’ is misleading. It sounds like there is carbon somehow incorporated into the material or structure. In fact, the opposite is true.

Carbon dioxide and other greenhouse gases are emitted when raw materials are extracted, processed and fabricated into construction materials. Further ‘embodied’ carbon is emitted during the construction process. ‘Embodied’ means that they are already a fact. Once you’ve made a ton of concrete there’s nothing you can do to reverse the 600 Kg or so of CO2 emitted in the process.

Sequestered and Biogenic Carbon

This type of carbon really is locked into materials such as structural timber. This is the CO2 extracted from the atmosphere by photosynthesis and stored in the cells of trees as they grow. There it remains until the wood decomposes or is burned. This ‘biogenic carbon’ is why structural timber has a net negative level of embodied carbon.

Low Carbon Construction

Net zero carbon has to consider how the energy needed to operate the building is generated. This could be outside the scope of the construction project. This is one reason why it’s common to talk about low or ‘lower’ carbon construction.

These terms are not precisely defined. Are they including embodied carbon? What is the ‘low’ carbon being compared with?

It’s impossible to make sense of this term without knowing the context or having specific data such as embodied carbon, U values and air permeability.

If you want to quantify the carbon impact of a proposed construction project, Innovaré’s carbon calculator tool will help.

Modern Methods of Construction (MMC)

This is another catch-all term that’s hard to define precisely. In general, it refers to construction methods that are digitally enabled (widespread use of BIM etc) and which use manufacturing-based approaches instead of traditional construction methods and trades. It can include innovations such as 3D printing.

MMC is often used interchangeably with offsite construction, although they are not quite the same.

Offsite Construction

This is possibly the most misunderstood term of all. Literally, this is construction that takes place away from the construction site. It could refer to a prefabricated staircase or an entire building structure made in a factory.

To try to get a more precise picture it’s usual to talk about pre-manufactured content. This specifies the percentage of the building that is fabricated offsite.

Of course, there are different types of offsite. There’s volumetric offsite that ships building units to the site as large boxes that are often fully fitted-out.

There’s also the panelised offsite method that uses Structural Insulated Panels (SIPs). These are large format, precision-made panels that combine structural and thermal properties. The panels are assembled onsite either to form the structure or as wrap or infill for steel, concrete or glulam.

The panelised offsite method offers almost unlimited options for designers and architects while also delivering low carbon construction – both operational and embodied.

If you want advice or information on MMC, offsite or low carbon construction (and access to proven solutions) contact (enquiries@innovaresystems.co.uk) for more information or take a look at our resource centre.