Boilers in loft spaces

Gas Safe Register’s Technical Team review the requirements when boilers are installed in a loft space.

Most boilers are installed in the kitchen, hallway or inside a cupboard. However, some homeowners may wish to investigate whether the boiler can be installed out of sight in the loft or roof space, particularly if space is at a premium. When planning to install the boiler in a roof space, the following considerations should be taken into account:

Access and lighting
The homeowner should provide measures as a minimum for their own safety and so that gas engineers can work in a safe environment. There should be a permanent means of safe access to the appliance. For example, this could be a permanently fixed retractable ladder to enter and exit the loft, with a safety guard around the loft access, which should be secured to the building’s fabric. The strength and design of the ladder should be such as to maintain safety. There should also be adequate fixed lighting.

The flooring area from the loft access to the boiler should be sufficient to allow access for normal use, servicing and maintenance, and should be extended to under and around the boiler. Consideration shall be given to a guard in order to prevent contact between stored articles and the boiler, its flue and pipework.

If the floor is of combustible material and supports the boiler, a non-combustible insulating base at least 12mm thick should be directly under the boiler.

The chosen location in the loft/roof space must be able to support the boiler’s weight once filled with water.

Gas supply
The gas pipework may need to be resized to provide the new boiler with the correct gas supply.

If the roof space has vapour-permeable underlay without specific ventilation, such as soffit board vents, they shall be treated as unventilated voids for the purpose of gas pipework and appliance installations. Where it is necessary to install pipework in such locations, additional ventilation shall be applied, with at least two ventilators per space, each with a free area of at least 50cm². For LPG and LPG/air mixtures, this must be at low level: for natural gas, it will be at high level. Pipework must not be laid below or within roof space insulation material.

Loft/roof space installations shall be installed in accordance with the manufacturer’s installation instructions and current Building Regulations.

Installations running a chimney system (twin pipe or concentric system) from a room-sealed, fan-assisted boiler, horizontally through the tiles of an adjacent tiled roof, should not be attempted unless specifically permitted by the boiler manufacturer’s installation instructions, as this technique is prone to blockages from snow. Condensing boilers may cause damage to the roof tiles immediately below the chimney outlet due to the condensate bleaching the colour in concrete tiles.

Guidance on the size, height, type, support and route of the chimney and the position of termination, including the possible consequences of any plume, is given in BS 5440-2:2023*.

The loft/roof space may need to be insulated to protect the boiler against temperature changes as a loft is usually an unheated space. Extreme temperature changes can affect the boiler and its internal parts, causing potential damage.

* BS 5440-2:2023 Chimneys, flue pipes and ventilation for gas appliances of rated input not exceeding 70kW net (1st, 2nd and 3rd family gases) – Installation and maintenance of ventilation provision for gas appliances. Specification.

Specific guidance for boilers installed in a roof space is provided in BS 6798: 2014 Specification for selection, installation, inspection, commissioning, servicing and maintenance of gas-fired boilers of rated input not exceeding 70kW net.

This article was originally published in the January/February 2024 issue of Registered Gas Engineer.

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