Hearths: A Guide to the Building Regulations
A hearth provides the site for the open fire or stove to sit and protects any combustible materials underneath or around the fire or stove from the heat or from any burning fuel that may fall from the fire or stove. A hearth must extend a minimum of 300mm (12 inches) in front of the fire or stove and 150 mm (6 inches) to the side of the fire or stove (see diagram 4). Under some circumstances the minimum depth of a hearth plate is 12mm (see below). The regulations also require the hearth to be set at a different level than the surrounding floor space to clearly define and mark the safe area. This can easily be done as the hearth can be set at a higher level than the surrounding floor level.
Diagram 1. Constructional Hearth Suitable for Solid Fuel Appliances Including Open Fires
If a stove has been tested and shown not to raise the upper surface of the hearth to a temperature in excess of 100C the stove can be placed upon a non combustible hearth or stove plate with a minimal thickness of 12mm. Recommended materials include , marble, stone, granite, slate and tiled hearths or glass and resin floor plates. If a stove is untested or raises the surface area of the hearth in excess of 100C or in the case of an open fire and if the hearth sits on a bed of combustible materials such as floorboards etc then the hearth needs to at least 250mm (9. 8 inches) in thickness. Alternatively, the hearth may be 125mm (5 inches) thick if there is a 50mm (2 inches) air gap between the combustible material and non combustible hearth (see diagram 6).
Diagram 2. Cross Section of Hearth for Open Fires and Appliances Raising Hearth Surface Temperature in Excess of 100C
If the hearth is to be sited on a non-combustible floor such as a precast concrete slab the total depth of the hearth and floor must be a minimum of 250mm (9.8 inches) or 125mm if there is a 50mm air gap beneath it.
Please note for free standing appliances, that is a stove that is not fitted to an existing fireplace or chimney the minimum hearth size should measure 840mm by 840mm (33.07 inches). Again there must be a clearance of 150mm from the sides and rear of the stove to the edges of the hearth and in theory 225mm from the front of the stove to the hearth if the stove is designed to be run with the doors closed. In practice all stoves can be used with the doors open so it is recommended that the hearth extends from the front of the stove by a minimum of 300mm. For large stoves this means that the hearth will need to be in excess of 840mm by 840mm.
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