Content of the LETI Declaration


The LETI declaration seeks to reward the efforts applicants make towards energy efficiency, low carbon heat and low carbon electricity. It does not set additional requirements but simply provides information which can better inform the client, the local authority and all stakeholders. Using it leads to a focus on outcomes, to deliver better buildings.

The LETI declaration contains specific questions that act as pointers and prompts for predicted energy consumption and carbon emissions, carbon content of heat, low carbon electricity, energy bills, data disclosure, lifecycle carbon and air quality. The declaration is not a rating tool, and there is no score. It is purely a set of pointers to move towards zero emissions new buildings.

A separate declaration for air-conditioned offices has also been developed, that additionally includes questions around solar gain, free cooling, lighting and HVAC controls. It also specifies Design for Performance guidance including enhanced modelling, contractual arrangements for performance verification and disclosure and early operation commitments.

The LETI declaration asks if the following issues have been considered:

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1.      Designing for outcomes - Estimate of future energy use and carbon emissions


Predicted energy consumption: Predicting a building's energy consumption (in kWh/m2) is a key LETI  recommendation in order to help making buildings more energy efficient, lower carbon and less expensive to run. LETI encourages more sophisticated and accurate energy modelling - beyond the Part L compliance models. This is to reduce the performance gap between part L design predictions and as-built energy performance. Examples include PHPP and TM54.

LETI believes that a fundamental step in the path to achieving operational zero carbon emissions is a shift from the Part L carbon metric to an absolute kWh metric -  to allow the full range of stakeholders involved in the design, operation and delivery of our buildings to understand, and therefore fully contribute to, reducing energy consumption. This is in line with similar international standards and global best practice such as: Toronto’s Zero Emissions Buildings Framework, Vancouver’s Zero Emissions Building Strategy, the Canadian Green Building Council’s Zero Carbon Building Standard and the Passivhaus standard.

7.      LETI Air Conditioned Office declaration

The LETI Air-conditioned office Declaration provides pointers specifically for large multi-tenanted office developments, broadly using principles from the BBP-backed Design for Performance initiative.

Energy demand reduction: Including information on solar gain control, infiltration at entrances, lighting controls, demand-led ventilation control, free cooling and night purge.

Responsibilities for whole building HVAC: Ensuring that the landlord has control or at least central visibility of all systems and that the landlord's MEP engineers have effective oversight of tenant fit-outs.

Contractual arrangements for performance verification and disclosure including confirmation of the base building performance target in contractual documentation.  

Independent Design Review of design and simulation studies by an approved expert in design of HVAC services, tuning of buildings, energy auditing and modelling.

Enhanced modelling scenarios: off-axis modelling, monthly energy budgets for monitoring & verification, detailed HVAC systems modelling, modelling studies to inform a preliminary ‘Description of Operations’ (DesOps).

Early operation commitments: Monthly monitoring reports comparing sub-metered data with simulated predictions and at least 4 BMS tuning exercises during the course of the defects liability period.

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Predicted carbon emissions: To assist in predicting carbon emissions and reaching zero carbon by 2030 the LETI Declaration requires CO2 emissions to be disclosed using three different factors. These include using current Part L factors (although it is now widely accepted that these are out-of-date), current CO2 emission factors as defined by the Department for Business, Energy and Industrial Strategy (BEIS), and a projection for 2030 as per the National Grid's slow progression scenario. This will assist in understanding how close the building is to reaching zero carbon by 2030. The Declaration also asks if the development will achieve net zero carbon operation on-site during operation.

2.      Energy efficiency

Fabric first: An efficient building fabric drastically reduces energy consumption and decreases capital and maintenance expenditures on active building services. The risk of ‘locked-in’ inefficiency in the building fabric is more acute than that of building services – getting it right first time is important as a ‘fix it later’ approach is challenging. The declaration provides the opportunity to commit to a fabric first standard such as Passivhaus, AECB silver, Low energy (PHI), BREEAM, Interim FEEs, Full FEES, HQM.

3.      Low carbon heat generation for space heating and hot water

Carbon content of heat: The method by which heating and hot water is generated has a significant impact on carbon emissions associated with a development.  It is recommended that the carbon emissions associated with heating and hot water are calculated, using relevant carbon factors (present and future) and presented to the design team, so that consequences of decisions can be fully understood.

A Zero Carbon Transition Plan: LETI advocates the elimination of fossil fuel use. Where this is not possible, LETI encourages developments that use fossil fuels to produce a Zero Carbon Transition Plan. This should show how heat systems/networks will deliver fossil fuel free heat by 2030 with no negative impact on air quality. LETI suggest that this plan is updated every five years.

Low temperature networks: An extra low grade heat network delivers heat at a temperature of around 50 degrees (sometimes known as 4th generation district heating). This means a greater use of secondary heat sources and that the hot water for the heat network can be generated by heat pumps (now or as a switch to heat pumps in the future), and the delivery losses are reduced compared to a network where heat is distributed at higher temperatures. The LETI declaration enables the discussion of supply and return temperatures within the design team by asking for them to be disclosed.

4.      Low carbon electricity

Electricity Generation:  Generating electricity without using fossil fuel is important in the delivery of net zero carbon buildings. The most common renewable proposed and installed is photovoltaics (PV). The LETI declaration asks for the amount of PV to be disclosed as a proportion of building footprint area, this is used to understand if PV generation has been optimised.

Demand management and peak load reduction: As the electricity grid decarbonises, using electricity to generate heating and domestic hot water (typically through heat pumps), becomes a cost effective, energy efficient and low carbon solution, and it appears likely that more heating and domestic hot water will be delivered by electricity over time. However, electric solutions (for heating and cooling) will put continued and growing pressure on the electricity grid, exacerbated further by the additional expansion requirements to meet the demand from the increase in electric vehicles. The LETI declaration asks if heating or cooling systems have technology enabled to reduce their demand at peak times and if they include energy storage (thermal or battery storage) in order to smooth peak demand and energy loads on the National Grid.

5.      Commitments

The LETI declaration gives the opportunity to commit to the following:

Energy affordability: It is important that the cost of heat is considered as part of the energy strategy. Where the price of heat and associated service charges are estimated, the impacts of future energy bills and fuel poverty are more likely to be taken into account. To encourage energy affordability the LETI declaration asks if the price of heat to the end user will be estimated during design.

Construction quality: Where changes are made at detailed design and the construction stage ( eg. U-values, air tightness), LETI encourages these to be recognised and reported as part of post occupancy data collection. This assists in determining the performance gap.


Knowledge sharing: Disclosure of building energy use is a central component underpinning progress in reducing carbon emissions and running costs. The LETI declaration asks if the energy data will be disclosed for 5 years. This is in support of the Draft London Plan (Dec 2017) - Policy SI 2 Minimising Green House Emissions, and the London Environment Strategy 2018 Proposal 6.1.4.b to encourage the design of effective methods to ensure the energy and carbon performance of new developments meet their agreed designed standards.

6.      Lifecycle Carbon and Air Quality

Lifecycle carbon: Carbon lifecycle assessments can identify significant scope to reduce carbon impacts, through design, reuse, recycling, sourcing, disposal and substitution of materials with lower carbon or more durable alternatives. Ultimately the aim is to start the behavioural change around embodied carbon within the construction industry. There are various lifecycle carbon and embodied carbon assessments available; the LETI declaration will start to track which type of assessments are most used.

 Air Quality: Much of London experiences poor air quality; it is important that new developments do not aggravate the issue. The LETI declaration records if the development will have a negative, neutral or positive impact on air quality.  

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