Potential for natural ventilation – mechanically ventilated and mixed mode assets

Scope of KBCN

This KBCN clarifies the associated compliance note for this credit.

  • NC 2011 & 2013 – No CN, but the principle of this KBCN can be applied.
  • NC 2014 v5.0 – CN 3.1
  • INC 2016 v2.0 and INC V6 – CN 3.11
  • RFO 2014 v2.0 – CN 7
  • RFO 2015 v1.4 – CN 5.2


Mechanically ventilated and mixed mode assets can potentially achieve the ‘potential for natural ventilation’ credit by:

  1. Meeting the relevant criteria for room depth and glazing area OR, where this is not possible:
  2. Show through modelling that the building has the potential to be ventilated entirely via a natural ventilation strategy.

For 2. the second paragraph of the CN allows flexibility in demonstrating adaptability to an entirely natural ventilation strategy.

An asset can allow for mechanical ventilation for ≤ 5% of its annual operating hours to boost ventilation rates, and (for this credit) can still be considered to be a fully naturally ventilated strategy.

≤ 5% mechanical ventilation requirement

The focus of this credit is to demonstrate future adaptability to introduce fresh air into the asset for occupant comfort, so this requirement relates only to the time that mechanical systems are used to drive air through the asset. The use of active heating / cooling is not considered in this calculation.

Natural Ventilation Heat Recovery Units (NVHR) systems can also be used, provided it meets this ≤ 5% requirement.

≤ 5% is a weighted average over all of the asset’s occupied spaces. The basis for the weighting will be determined by the modelling software used.

Scope and time scale of modelling

The modelling covers all occupied spaces. Where relevant, exclusions are allowed – see related KBCNs for details.

The modelling period is one year, during the asset’s operating hours.

The modelling must be based on a plausible scenario that is realistic. This means that:

  • Potential changes can be practically and reasonably achieved by future occupants.
    For example, the adaptation strategy must not require new or modified openings in the building envelope or include significant or disruptive changes to the internal layout.
  • The changes do not compromise the intended function or operation of the asset.
  • For speculative assets, a realistic notional layout can be used. See KBCN0408.
  • The modelling assumption does not need to factor in climate change.
    The aim of the credit is prove the validity of a future naturally ventilated scenario – if and when this is carried out is outside the scope of the certification.
22-Oct-2022 Content from KBCN1126 merged to this KBCN.