Directory of Traditional Building Skills - Mourne Heritage Trust

Large chimneys are divided into multiple flues which are separated from each other by thinbrick divisions called ‘feathers’. Flue gases gradually eat away at the brick and can cause the‘feathers’ to crack and eventually collapse, blocking a flue or opening a smoke passage fromone flue to the next. Birds’ nests, accumulated soot and broken ‘feathers’ can combine to blockor even destroy a chimney. Tell tale signs are smoke coming out of more than one chimney potwhen only one fire is lit or smoke coming out of one fireplace when the only fire lit is in theroom next door. Coal that is not being burnt correctly in a closed fire will produce invisible andhighly toxic flue gases of odourless carbon monoxide which can spread throughout the houseif left unchecked. It is always a wise precaution to have chimneys swept annually and toconsult a ‘chimney doctor’ if you are lighting fires for the first time or are aware that theremight be a problem.If it is necessary to rebuild a chimney, the original corbelled courses around the top should bereplicated and either the old pots or matching new pots reinstated. Excellent reproductions oftraditional terracotta pots are available. Redundant flues must be fitted with a ventilated cap tothe pots and a grille built into the chimney breast to prevent damp and condensation. Evenunused chimneys add great presence to a house and the temptation to demolish them when thecentral heating is installed should be resisted.See also Appendix 1: Further reading – p. 149Interior of disused formaer National School, Newry, County Down127