Flues and Chimneys

The design and construction of flues and chimneys, for domestic buildings, during the post war period has produced great improvements in methods and materials which has increased their efficiency and safety in use. The requirements, with which they must comply, are set out in the Building Regulations (Part J) and Approved Document J.

Arising from these developments are integrated systems for flues and chimneys and are manufactured for solid fuel and gas appliances; these are supplied complete and ready for installation so have not been included.

Some terms, related to the traditional building of flues and chimneys, are now obsolete but have been included for reference to the methods used in the huge stock of our older buildings; where this occurs they has been indicated.

Number of terms found = 18. Displaying page 1 out of 1.

Back Gutter:

A flat lead gutter, about 125mm wide, formed between the back of the chimney and the slope of the roof covering to waterproof the junction and drain water away; a cover flashing is used to seal the joint between gutter and chimney.

Back-to-Back:

Term used to describe the construction of two fireplaces when the back wall of the recess is common to both. If within the same building the separating wall must not be less than 100mm thick but if Back-to-Back in adjoining buildings the wall must not be less than 200mm thick.

Chimney Breast:

Internal projection of brickwork built to contain a fireplace recess and flue at ground floor level but can continue to upper floors to contain additional fireplaces and flues. When a fireplace is required to be flush with an inner face of an external wall the the projection of the breast can be built externally to enclose flues.

Chimney Head:

Entire terminal of a chimney; the terminal is commenced with a series of corbels to form projections, which can be decorative, and is designed to throw water clear of the chimney. The head of the chimney is finished by bedding the chimney pots in a flaunching which weathers it and secures the pots.

Chimney Pot:

A terracotta funnel, of various shapes and sizes, designed to terminate a flue and improve the efficiency of its upward draught.

Chimney:

The brick structure enclosing a flue, or flues, which extends above roof level. A chimney stack may consist of a number of flues contained in one rectangular chimney or a number of individual shafts, one for each flue, which may be square or octagonal in section.

Constructional Hearth:

This concrete sub-hearth forms part of the structure of the building and supports the heating appliance. It must not be lower than the surface of any adjoining floor and its minimum dimensions must comply with the requirements of the Building Regulations.

Coring:

A craft process used when square section (9 inches x 9 inches) flues were formed in brickwork and lined internally by parging. The flue was kept clear, of mortar droppings, by means of a sack of straw drawn up the flue as work proceeded (now obsolete).

Fireback:

Unit, made of fireclay or refractory concrete, set in the recess of the chimney breast to form the back and side cheeks for an open fire. Although available as a one piece unit it is preferable that it is made up of at least two or more pieces; this reduces the tendency to cracking; makes it lighter to handle and easier to replace.

Flaunching:

The weathering on the head of a chimney that helps to secure the chimney pots; made from a 1:4 mix of O.P.C. and sharp sand.

Flue Liners:

Liners built to form a flue, in a chimney breast and chimney, which resists the products of combustion and minimise maintenance. Liners, for domestic flues, manufactured in fireclay or refractory concrete are 200mm in diameter with ends formed as a socket; available in a variety of lengths and bends. Gas flue block systems are designed so that they may be built flush to the surface in internal walls.

Front Apron:

A sheet lead weathering, in the front of a chimney, that lays over the roof covering and dressed up the chimney to seal the joint with the roof.

Gathering:

Inward corbelling above a fireplace recess to reduce the opening to the size required for the flue. Also used to describe the bringing together of a number of flues, within the roof space, to start the building of a multi flue chimney (now obsolete).

Jambs:

The piers (not less than 200mm thick) that support the chimney breast and form the sides of the fireplace recess. Jambs must extend down to the line of the main foundation.

Parging:

Application of a coat of lime mortar used to form a smooth internal lining to a brick flue; care needed where bends, or gathering over, occurred in a flue (now obsolete).

Stepped Flashing:

A strip of sheet lead cut to form steps up the sides of a chimney, parallel to the pitch of the roof, which are turned into and secured in the bed joints. This seals the sloping joint by covering the turn up of lead soakers placed between each slate or tile. As an alternative to soakers a secret lead gutter is sometimes used.

Throat:

The sloping reduction, in width, immediately above a fireback to form the start of a flue. This may be done by gathering over in brickwork or, more efficiently, by use of a pre-formed throat unit fitted on top of the fireback.

Withes:

Dividing walls that separate flues in a chimney breast and chimney; these short walls must have a minimum thickness of 100mm and be properly bonded into the outer walling.