This summer, we welcomed the introduction of the Building Safety Bill to the House of Commons, allowing for residents to have a greater say in the management of their buildings and, ultimately, improving health and safety.
Specifically, the bill will govern ‘higher risk buildings’, defined as more than 18m in height, or at least seven storeys, and containing a minimum of two residential dwellings. The specific building safety risks in scope are currently defined as ‘spread of fire’ and ‘structural safety’, but the Secretary of State will have the power to include additions where merited.
While we expect it to take at least nine months to pass through, there’s much to be thinking about in terms of how building owners and residents begin to engage with contractors, and develop a deeper understanding of the equipment and systems in their building.
Shared flue system challenge
Multi-residential buildings have experienced rapid growth across the country in recent decades, particularly in towns and cities. By nature, shared flue systems are most likely to have been installed into high-rise buildings or similar building types (i.e. more than 18m or seven storeys).
Most of these properties will likely have a mixture of gas appliances, such as central heating boilers, gas fires, and multi-point water heaters. Each will be connected to shared flue systems – historically the most common perhaps being the ‘SE-duct’ and ‘U-duct’ systems found in older multi-storey dwellings in many UK cities. These systems allow several appliances on different storeys to receive their air supply from, and discharge their combustion products to, a common duct – usually built into the building during construction.
At the time of their construction, both flue systems required careful dimensioning to ensure the correct flue flow pattern and were designed on the basis of relatively high temperature flue gases, from the standard efficiency gas appliances in use at that time.
Over recent years, the HHIC has been working to eradicate occurrences of incorrect installations, as older boilers, or water heaters, connected to shared flues were being replaced. Problems would mainly occur either through incorrect appliance selection or through incorrect connection of the appliance to the shared flue system.
A key consideration is that modern condensing boilers have much lower flue gas temperatures, with less buoyancy and a much higher level of condensed water vapour.
The use of a condensing boiler, or a change to the appliance type/heat input, may create a poor flue flow effect within the shared duct. Subsequently, combustion products, including water vapour, may be taken into those appliances sharing the flue, along with the previously ‘clean’ combustion air supply. Poor combustion can result in raised levels of carbon monoxide in the flue gases and, in some instances, cause the boiler to shut down.
Additional problems can occur due to the increased levels of condensation within a shared flue duct. These older ducts, unlike more modern communal flue systems (CFS) specifically designed to accommodate condensing boilers, were not designed to cope with high levels of condensation from boiler flue gases, or with the mildly corrosive nature of the condensed water vapour.
As a consequence, degradation of the flue duct walls may occur, unless the duct has been specifically adapted by a competent person to accept the use of condensing appliances (e.g. by lining, use of building exhaust fans with interlock, installation of a shared system chimney, etc.).
Like any HVAC equipment, when specified, installed, and maintained correctly, these systems are perfectly safe. But if the shared/communal parts of building flue systems are not, then they could, theoretically at least, increase the risk of fire spread, as by nature they pass upwards through a structure. This, of course, overlaps with the scope of the Building Safety Bill on the spread of fire, and is why it is critical for those ducts to be subject to a robust inspection and maintenance programme.
Accountability and maintenance
Future resident engagement strategies under the new Building Safety Bill should help to promote to building owners, as well as individual residents and landlords, the importance of having these shared elements regularly serviced and maintained by appropriately registered gas engineers, in addition to their private gas appliances.
Shared flue ducts should have an annual inspection to ensure that their condition remains suitable, and it is a legal requirement under Gas Safety (Installation and Use) Regulations 1998 (with 2018 amendments) for a landlord to confirm that the common duct has been inspected and has a valid certificate. The customer and/or engineer should obtain a copy of this certificate from the managing agent, landlord, or owner before any new or replacement appliance is connected to a shared flue.
This certificate should also be checked on the annual service visit and at any maintenance visits. In the absence of a certificate, the requirement of annual flue inspection should be highlighted to the customer and documented on any paperwork and, where required, the Gas Industry Unsafe Situations Procedure should be followed.
A together approach
The Building Safety Bill will place regulatory obligations on the accountable person for the building, appointed building safety manager, and other named duty-holders.
We hope and expect that this will translate into ensuring that the common parts of shared flue systems are suitably maintained/inspected, therefore ensuring resident and building safety.
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