Satisfactory fire and carbon monoxide detection: tolerable standard guidance

Guidance relating to the Tolerable Standard on satisfactory fire detection and satisfactory carbon monoxide detection.

Chapter 17 Satisfactory Carbon Monoxide Detection

17.1. A house meets the Tolerable Standard if it complies with the relevant requirements in relation to satisfactory carbon monoxide (CO) alarms.


17.2. The Tolerable Standard is amended by the Housing (Scotland) Act 1987 (Tolerable Standard) (Extension of Criteria) Order 2019 and now includes this new element covering CO alarms. For the first time, assessors will consider the presence, type and condition of CO alarms in a house when deciding if the house meets the Tolerable Standard [see note 1]. These criteria, which already formed part of the Repairing Standard (as it applies to certain tenanted properties), now apply to all houses.

17.3. This chapter of the guidance aims to provide the information and advice needed to carry out an assessment of CO alarms in a house for the purposes of the Tolerable Standard. The methodology is based on the normal walk-through survey used for other elements of the Tolerable Standard, with the potential for support from a qualified specialist.


17.4. The Tolerable Standard was first defined in the Housing (Scotland) Act 1969 which was then repealed and replaced by the Housing (Scotland) Act 1987. The Housing (Scotland) Act 1987 (Tolerable Standard) (Extension of Criteria) Order 2019 added fire and CO detection equipment to the Tolerable Standard. This is in recognition of the danger posed to the occupants of a house by CO in concentrations hazardous to health, and the vital role early detection and warning in buildings can play in the protection and safety of the occupants. As noted above, the Tolerable Standard also forms part of the Repairing Standard, under section 13 of the Housing (Scotland) Act 2006, which landlords must comply with under section 14 of that Act.


17.5. The revised Tolerable Standard includes a criterion requiring that a house has 'satisfactory equipment installed for detecting, and for giving warning of, carbon monoxide present in a concentration that is hazardous to health'. This guidance defines what is 'satisfactory' by setting out the requirement for:

  • CO detectors to be fitted in all rooms [see note 2] where there is a fixed combustion appliance (excluding an appliance used solely for cooking [see note 3]) or a flue.

17.6. CO detector: A device that detects the presence of CO in a concentration that is hazardous to health, giving an audible, and in some cases visible, warning. CO detectors should comply with BS EN 50291 and be powered by a battery designed to operate for the working life of the detector. The detector should incorporate a warning device to alert the users when its working life is due to expire. Hard wired mains operated CO detectors complying with BS EN 50291 (Type A) with fixed wiring (not plug in types) may be used as an alternative, provided they are fitted with a sensor failure warning device. The detector should be regularly maintained and tested in accordance with the manufacturer's instructions.

17.7. Combustion appliance: a fixed appliance (such as boilers, fires (including open fires), heaters and stoves) designed and installed to operate on a carbon based fuel (i.e. oil, solid fuel or gas).

17.8. All CO detectors should be either:

  • ceiling mounted and at least 300 mm from any wall (unless otherwise indicated by the manufacturer) or
  • wall mounted and positioned at least 150 mm below the ceiling and higher than any door or window in the room (unless otherwise indicated by the manufacturer). [see note 4]

17.9. Combined smoke/CO detectors may be installed, providing they meet the appropriate requirements of BS EN 50291 with regard to CO detection/alarm activation and the requirements of BS EN 14604 with regard to smoke detection/alarm activation. [see note 5]

Making the assessment

17.10. In making an assessment, assessors should take account of the layout and design of the building, and any advice given by a competent person. Further information can be found in the Building Standards Domestic Technical Handbook.

17.11. Local authorities may use their statutory powers to require owners to carry out work on substandard housing. However, as is the case for other elements of the Tolerable Standard (e.g. serious structural problems through to other failures such as insufficient loft insulation), it is expected that any intervention is proportionate, rational and reasonable. Local authorities are to consider the cost of any intervention alongside the cost of assisting owners to bring their property up to the minimum standard for satisfactory carbon monoxide detection. As a general rule it is preferable that owners should carry out necessary works on a voluntary basis rather than as a result of enforcement action, with further information set out in Chapter 2 – local authority powers.

17.12 Recent cases in the sheriff court support the view that local authorities have to consider carefully which enforcement powers are appropriate to address a failure in meeting the Tolerable Standard and careful investigation must be carried out as to the cause of the failure as well as engagement with the owners.


The following notes have been added to clarify some technical points in Chapter 17 of this guidance:

1. The Tolerable Standard is a minimum standard, and does not preclude additional carbon monoxide detectors.

Additional standards may apply if work is carried out under a building warrant or where an electrician is installing mains-wired alarms.

2. This guidance applies to rooms, meaning parts of the house that are used for living accommodation. A house does not fail the Tolerable Standard if there is no carbon monoxide detector in a part of the house that is not used as, or has not been converted for use as, living accommodation, such as cellars, attics and garages. However, if a new carbon fuelled appliance is installed, or an existing appliance replaced, Scottish Building regulations must be complied with and may require the installation of a carbon monoxide detector (see Building Standards Technical Handbook: Domestic, section 3.20.20,

3. A carbon monoxide detector is not required for a gas cooker or hob.

4. Carbon monoxide detectors in the space containing the combustion appliance should be sited between 1m and 3m from the appliance. A carbon monoxide detector should not be placed in a cupboard or other small enclosed space. If this is where the appliance is, the detector should be located at the appropriate distance outwith that space. Additional guidance on the siting of carbon monoxide detectors, including enhanced coverage, can be found in BS EN 50292.

5. The Tolerable Standard does not require carbon monoxide detectors to be interlinked, or to be interlinked with fire alarms.

6. Under the Equality Act 2010, deaf people can expect the same level of protection from CO as specified in this guidance through provision of specialist deaf alerts. For homeowners these may be provided by Health and Social Care Partnerships. Specialist deaf alerts must be consistent with the level of protection required for those who are not deaf.

Landlords have a duty to make reasonable adjustments to properties for disabled people.

Where telecare is in use, effective CO alarms should be installed which are compatible with any telecare alarms, and connected to the telecare system, ensuring a single system approach.



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