some Georgian and Victorian terraces and count the pots on each stack. This will tell you how many flues and fireplaces the house originally had.
When we look inside a period house we see what we tend to think of as a fairly massive brick structure protruding from the wall. In most cases this is not, in fact, a solid brick structure, but a honeycomb of hollow flues.
The chimney breasts and flues in older properties were built in traditional brickwork and lime mortar and were built up as the walls of the house were raised. It was quite an art for the bricklayer to connect the right flues to the right fireplaces and make sure that they all avoided each other. For this reason flues in older properties rarely run in a completely vertical line from bottom to top; it is normally necessary for the flues to be off-set at some point to avoid fireplaces on the floors above.
Traditionally brick flues were almost always 225mm (9”) square internally. The main reasons for this were that it was a practical size for the efficient escape of flue gases and it was also the standard length of a brick. As I mentioned there is often a honeycomb of flues in the same chimney breast and the ‘wall’ separating two adjoining flues was generally 112mm (4 ½ “) or ½ a brick thick. The brickwork dividing two flues is also called the ‘withe’.
Traditional brickwork in lime mortar is not particularly airtight and in order to minimise any leakage of flue gases the flue was ‘parged’ or ‘pargetted’ internally as it was built. The pargetting would consist of a fairly rough coat of lime mortar. This deteriorates over the years and often becomes loose and cracked and can also be dislodged when the flues are swept. It is also not unknown for individual bricks in the ‘withe’ to become dislodged over the years with the result that gases from one flue could leak into the adjoining flue.
When surveyors carry out either Building or Homebuyer Surveys they will not be able to assess the internal condition of an old flue and their report will normally contain a warning that the flue could be damaged or defective. Defective flues can be repaired by inserting a pre-formed flue liner into the flue, although this can be a relatively expensive operation in a multi-storey house.
As open fires fell out of favour it became common to remove the original open fireplaces and brick up the openings. Although this seems a relatively straightforward cosmetic operation, it does pose a number of potential problems. The original open fireplaces provided an efficient form of ventilation. Even if the fire was not in use the flue would promote air movement with warm air tending to rise up the flue and escape through the chimney. This helped to reduce condensation in houses. It should also be remembered that the flue is open at the top. When coal fires were being used this was not a problem as the heat from flue gases would keep the chimneys dry. If the fireplaces are sealed up rainwater can still enter the top of the flue, but there is no longer sufficient air movement through the chimney and flue and dampness within the chimneys can be a problem.
When fireplaces are sealed up internally it is important to make sure that a suitable terminal is fitted to the top of the chimney pots. This should prevent rain entering the flue whilst still allowing ventilation. It is also necessary to provide ventilation to the flues within the building so that air can still enter the bottom of the flue and escape through the terminal on the chimney stack. When carrying out Homebuyer Reports or Building Surveys the surveyor will check that any redundant flues are fitted with suitable terminals at roof level and also make sure that the flues are ventilated inside the house.
As we said earlier, brick chimney breasts are quite bulky and can occupy a relatively large area in smaller houses. Not surprisingly, quite a few chimney breasts were removed when the open fires were no longer required in order to free up much needed floor space. This is not a problem, provided that the work is done properly!
It is quite unu