Sadly, there are no formal guidance documents or best practice methods available for the purposes of making safe redundant and/or defunct flue systems either in a domestic or commercial environment currently available to the general public or in fact local building control professionals, this is far from either adequate or acceptable given known safety issues.

Redundant flues and chimneys require a complex thought process and expert evaluation approach to determine and identify potential fire risks and structural mishaps before sealing up has occurred and to plan and avoid the possibility of something undesirable, harmful, or negative from happening. Redundant flue systems within masonry chimneys therefore do represent a well-documented and recognised risk, the following guidance may help in deciding the best route of action to take prior to a blocking up or closing off activity occurring:-

1) A single redundant flue system left unchecked and closed off from visual inspection over a period of time overlooking potential structural integrity and safety issues when permanently sealing off may be considered poor housekeeping. Before doing so it would be prudent to seek expert advice and evaluation. 

2) This scenario is multiplied when there is more than one flue system within a single masonry chimney serving numerous fireplace openings with otherwise unknown compartment and/or Midfether defects clearly representative of safety and/or structural risk.

2) Existing defects can increase exponentially if they remain unseen, simply covering up a fireplace opening or capping off a chimney pot will not alleviate future issues from occurring hence why it is essential that yearly visual inspections take place.

3) Typical methods of blocking up or sealing a redundant flue system involve boarding up an existing fireplace opening, installing a louvered vent and attaching a cowl of some type to an existing chimney pot in theory may seem suitable but to an expert there is a more robust method.

4) Blocking up or sealing over an existing fireplace opening and then installing a cowl to a chimney pot may allow air flow, however by doing so will allow the passage of air (Oxygen) to feed a potential upper floor, loft or roof space fire, this scenario is multiplied many times in an HMO, public building or domestic mid terrace environment where fire resistant roofing material is unlikely to be present.

5) An inexpensive option would be to create a ‘Thermal Plug’ a combination of readily available and inexpensive inert fire resistant materials inserted the entire length of a flue system offering a more robust structural, thermally stable and safer environment compared with simple air ventilation or temporary balloon method, an extremely important consideration if intending to make a flue system redundant in either a multi occupancy, semi-detached or terraced building where a Party Wall scenario or age related defects may exist. 

6) Installation of a Thermal Plug can be if correctly carried out by a Controlled Services expert easily removed for intended future use or when a property is sold and new owners wish to reuse a redundant flue system.

NACE offer formal expert evaluation services and technically competent advice on this and other related Controlled Services matters, for further useful advice and guidance please call our technical help line 01223 774477 or email us at: technical@nacegroup.co.uk