PROJECT TITLE Project No; 24
Chimney Breast CORE
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Construction of Chimney Breasts
The construction of chimney breasts and stacks is controlled by part L of the current Building Regulations.
It is vital that the highest standard of workmanship and the correct interpretation of Building Regulations is maintained throughout the construction of chimney breasts and stacks. Failure to do so can have devastating results.
The regulations are mainly concerned with preventing the spread of fire and the discharge of dangerous gasses given off by burning fuel, ensuring they are safely transported to the atmosphere without endangering health.
The following are definitions taken from the current Building Regulations:
CHIMNEY: Any part of the structure of a building forming any part of a flue other than a flue pipe.
FLUE A passage for conveying the discharge of an appliance to the external air.
CONSTRUCTIONAL A hearth forming part of the structure of a
SUPERIMPOSED A hearth not forming part of the structure of
HEARTH: a building
Construction of Chimney Breasts
Open fires have to be enclosed within a brick recess. The position that the fire is located within the building will dictate the style and thickness of the brick surrounding that recess.
Fireplace on External cavity wall
This can be achieved in two ways:
This method increases the area of the room placing the fire appliance on a flat wall.
Fireplace on Internal Wall
Constructional Details of Fire
The base of the fire opening must have a constructional hearth that projects beyond the face of the opening and extends beyond the opening width.
The opening must be bridged with an adequate lintel or throat unit.
Provision must be made at the top of the opening to reduce itís overall width to allow for the flue liners to be positioned.
Woodwork must not be built into any wall nearer than 200mm from the inside of the opening.
Every fire must have itís own individual flue.
Throat Units and Flue
The fire opening is a minimum of 522 mm wide. It has to be reduced at the top of the fire opening to receive a 225 mm flue liner.
This can be carried out in two ways:
1. A Traditional lintel is used to bridge the opening and the brickwork is corbelled in to close the opening.
The underside of corbels can be shaped to ensure smooth passage of gasses when appliance is fitted.
2. The lintel can be replaced by a precast refractory concrete throat unit which provides access for forming throating when an appliance is fitted and supports the flue liners.
This is the most effective method as it reduces the opening and provides excellent support for the flue liners.
Chimneys built before the 1960s were rarely lined. They were rendered internally with lime mortar. This operation was called parging. When modern day fuels were introduced there was a large increase in the sulphur content discharged into the flue.
The sulphur dioxide, when mixed with condensation in the flue, would seep into the mortar joints. This created an acid known as sulphuric acid. This would crystallise and expand causing the chimney stack to lean.
Regulations were changed to make the lining of chimneys compulsory.
This is achieved by building in a non Ė combustible flue liner manufactured from clay or terra cotta.
Liners are manufactured circular or square in section and contain a rebated or socketed joint to assist in providing an adequate seal.
CIRCULAR SOCKET LINERS
SQUARE REBATED LINERS
Construction of Flues
In the past it was considered good practice for several bends to be placed throughout the full height of a flue.
Building research findings proved this to be false as the bends caused greater friction, slowing the gasses down.
Modern practice is to break the line of the flue once using purpose made liner bends.
The angle of the flue should not be less than 30 degrees from the vertical.
Flue liners should be positioned and jointed ahead of the surrounding brickwork.
The space should be filled with a weak mortar mix or insulating concrete.
Insulating concrete is a mix of vermiculite granules mixed with cement. This allows for expansion of the liner, so reducing the risk of damage to the structural brickwork surrounding the flue.