Chapter 6: Net Zero Carbon Buildings (the LETI approach)
The Low Energy Transformation Initiative (LETI) was established in 2017 to support the transition of London's built environment to net zero carbon, providing guidance that can be applied to the rest of the UK. LETI is a network of over 1,000 built environment professionals who are working together on the path to a zero carbon future. LETI believe that to meet our climate change targets all new buildings must operate at net zero carbon by 2030 and all buildings must operate at net zero carbon by 2050. In order to achieve this, LETI believes that by 2025, all new buildings must be designed to deliver net zero carbon.
The Council encourages all new buildings to be built to net zero carbon standards as defined by LETI and should seek to achieve LETI's Key Performance Indicators (KPIs). LETI's three core principles and KPIs are outlined below. Energy use targets are more transparent and robust than carbon reductions targets and are the best way to ensure zero carbon is delivered in practice. This policy approach to net zero carbon based on energy metrics has now been accepted by the Planning Inspectorate through the examinations into Cornwall and Bath and North East Somerset Local Plans. LETI's definition of net zero carbon means whole life carbon. Whole life carbon is formed of operational and embodied carbon.
Operational carbon is the emissions from the energy consumed by a building associated with heating, hot water, cooling, ventilation, and lighting systems as well as equipment such as fridges, washing machines, TVs, and cooking. For buildings, embodied carbon is the carbon emissions emitted from producing a building's materials, their transport and installation on site as well as their disposal at end of life.
For LETI, a net zero carbon building in operation means a building which does not burn fossil fuels, is 100% powered by renewable energy and achieves a level of energy performance in-use in line with our national climate change targets. There are 3 core principles:
Buildings should use energy efficiently. The lower the energy demand of the building, the easier it is to achieve net zero in use. Space heating demand expresses the amount of energy the building needs for heating and is impacted by site and orientation, window design, form, building fabric, materials and detailing, and ventilation.
Energy Use Intensity (EUI) expresses the total amount of energy a building uses and can be measured in-use through the energy meter) with kWh/m2.yr as a unit. It is impacted by the space heating demand, the choice of heating system, ventilation system, lighting, cooking, appliances, and equipment. LETI believe that EUI should replace carbon emission reductions as the primary metric used in policy, regulations, and design decisions.
Low carbon heating
All new buildings should be built with a low carbon heating system and must not connect to the gas network.
Renewable energy generation
In new buildings, annual renewable energy generation should be at least equal to the residual total energy use of the building (the EUI) (i.e. the regulated and unregulated energy use but excluding EV charging). If this is not possible on-site, it should be demonstrated that the equivalent of 120 kWh/m2 (footprint)/yr of renewable energy is generated across the development.
The diagram, below, produced by LETI and included in their Climate Emergency Design Guide, summarises the LETI approach to net zero carbon.
Calculations should be carried out using predictive energy modelling tools, such as Passivhaus Planning package (PHPP) or equivalent.
Post occupancy monitoring should be undertaken on a percentage of homes (e.g. 30%) and be spread across phases for a period of 5 years to demonstrate the energy performance standards and aid learning, innovation and skills development in the design and construction industry. The post occupancy evaluation should include qualitative (occupant satisfaction questionnaires) and quantitative data (energy monitoring to review against targets set).
Measuring and reporting of upfront embodied carbon emissions is encouraged on major development proposals using a recognized standard methodology such as RICS. Developments should be designed to reduce embodied carbon emissions and best practice targets should be aimed for. LETI sets out some KPI for upfront embodied carbon emissions (building life cycle stages A1-A5); this includes the following elements: substructure, superstructure, MEP, facade & internal finishes.
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