low energy and solar solutions

Part L2A

Part L2A is assessed on five criterion:

Criterion 1: Achieving an acceptable Building CO2 emission rate

This involves the calculation of a predicted carbon dioxide emission rate from the building and compares this with a building with identical geometry and functions but with nominal specifications similar to minimum standards. A naturally ventilated building will need to emit 23% less, an air conditioned building 28% less than a building built to nominal specifications.

Emissions represent only those from providing the main building services (heating: space and water, cooling, ventilation and lighting).

Criterion 2: Limits on Design Flexibility

PartL2A describes minimum requirements for the following elements/systems

  • external fabric: individual and area weighted U values.

  • Heating (and cooling if appropriate) plant efficiencies and controls

  • Pipework and ductwork insulation

  • lighting efficiencies

  • light switching

  • metering

Criterion 3: Limiting the effects of solar gains in summer

Evidence is required that naturally ventilated perimeter spaces will not experience excessive gains from the combined effects of solar gains from sunlight, heat emitted from fixed lighting, occupants and equipment. Assessment is made based on

  • detailed glazing specification, shading provided by the building, adjacent buildings and fixed shading devices

  • fixed values (CIBSE TM37) for occupancy and lighting based on space function

  • weather data for the region (CIBSE Guide A)

Criterion 4: quality of construction and commissioning

A building air permeability test constructed once the building is constructed, complete with any services which penetrate the envelope. Building Services will need to be commissioned and any ductwork will require pressure testing. Data from these tests is required in order to complete Criterion 1.

Criterion 5: Providing Information

This requires building log books for building owners/users to help them to run the buildings services in the intended manner. Part of the advice on this requirement is that the data used in the calculations for Criterion 1 is passed onto the owners. CIBSE Low Carbon Consultants logo

Main Links



Part L2A



Part L2A links



2nd Tier Docs


l-e-s-s home