Building standards technical handbook 2020: domestic

The building standards technical handbooks provide guidance on achieving the standards set in the Building (Scotland) Regulations 2004. This handbook applies to a building warrant submitted on or after 1 March 2021 and to building work which does not require a warrant commenced from that date.

6.6 Mechanical ventilation and air conditioning

Mandatory Standard

Standard 6.6

Every building must be designed and constructed in such a way that:

  1. the form and fabric of the building minimises the use of mechanical ventilating or cooling systems for cooling purposes, and

  2. ventilating and cooling systems installed are energy efficient and are capable of being controlled to achieve optimum energy efficiency.


This standard does not apply to buildings which do not use fuel or power for ventilating or cooling the internal environment.

6.6.0 Introduction

It is not desirable that dwellings or buildings consisting of dwellings have air-conditioning systems or use mechanical ventilation systems for cooling purposes, as this leads to increased energy use and higher carbon dioxide emissions. In view of this, guidance is intended to promote designs that avoid the need for such systems in dwellings. However where such systems are installed, which should generally only be a consideration when working with existing buildings, a performance specification to limit energy use is set out.

With the drive to reduce carbon dioxide emissions and limit energy demand in buildings, the need arises to consider efficient use of mechanical systems, including ventilation. Accordingly, guidance is now offered on power consumption and controls of such systems and on the efficiency of systems that incorporate heat recovery.

Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).

6.6.1 Form and fabric of the building

Reduce overheating - in order to minimise any need for mechanical ventilation for cooling or air-conditioning due to high internal temperatures in hot weather the following issues should be considered with regard to the form and the fabric of the dwelling:

  1. proportion of translucent glazing taking into account the need for daylighting and artificial lighting (Section 3 Environment and Standard 6.5)

  2. orientation of translucently glazed areas

  3. solar shading or other solar control measures where areas of the external building fabric are susceptible to solar gain

  4. natural ventilation (including night cooling), and

  5. thermal mass.

Further information is available in the Energy Saving Trust publication CE129 - 'Reducing Overheating - A Designer's Guide' [].

Poor cross ventilation/high proportion of translucent glazing - where a dwelling has little or no cross ventilation (e.g. flats with all external windows/rooflights on one southerly elevation which is orientated between due east and due west) or a high proportion of translucent glazing:

  1. the dwelling should be designed to avoid high internal temperature (refer to advice above), and

  2. it should be shown by calculation that the ‘likelihood of high internal temperature in hot weather’ in the dwelling is ‘not significant, slight or medium’. The recommended method to assess this is Appendix P to SAP 2012. The intention is to avoid the situation where a dwelling occupier installs mechanical cooling or air-conditioning at a later date.

Cooling system - where a mechanical cooling system is to be considered for a dwelling:

  1. the dwelling should first be designed to avoid any need for a cooling system (refer to advice above), and

  2. then the ‘likelihood of high internal temperature in hot weather’ should be assessed using Appendix P of SAP 2012.

If the 'likelihood of high internal temperature' is 'not significant, slight or medium' an air-conditioning system should not be installed.

6.6.2 Efficiency of mechanical ventilation and air conditioning systems in new and existing buildings

Guidance on the efficiency of mechanical ventilation and air conditioning systems is given in the Domestic Building Services Compliance Guide for Scotland

The document replicates guidance published in support of building standards elsewhere in the UK and supports standardisation of the specification and expected performance of fixed building services throughout the UK. The guidance applies to new systems and replacement, in whole or in part, of existing systems. It also addresses improvement work to existing systems as a consequence of replacing components.

Clause 6.6.3 provides information on situations not addressed in that document.

6.6.3 Design and installation of Ductwork

The design and installation of ductwork design can have a significant effect on the effectiveness of a ventilation system. Further guidance on basic good practice in installation and commissioning of ventilation systems can be found in the BSD ‘Domestic Ventilation’ Guide, published on the Building Standards Division website.

Reference should be made to Section 3: Environment for the provision of ventilation to buildings.

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