MJA Roofing:: Roofer and Roofing Services in St Neots, Huntingdon, St Ives, Ramsey, Peterborough, BedfordCambridgeshire and Bedfordshire
Chimneys and flues are subjected to intense heating and cooling cycles,
condensation and aggressive chemical reactions caused by hot flue gases. Above the
roof line the chimney stack is exposed to the full force of the weather. To withstand such
conditions, maintenance and repairs need to be of the highest standard, and it is important that design elements of such
significance are conserved properly. Yet works are often badly executed by unqualified contractors using inappropriate
materials and ill-conceived methods. The result can be damaging to the character and fabric of the building,
and may even be dangerous.
A combination of erosion, acid attack and salt crystallisation are liable to cause a chimney to lean. The BRE Good Repair
Guide says any chimney that leans more than 1mm in 100mm is unsafe. Where the shaft wall is half a brick thick,
a lean of 35mm could be tolerated.
Thermal expansion of the flue lining can cause vertical cracks to appear in the structure of the chimney, particularly where
the flue is hidden within the thickness of a wall and where its actual presence has in any case introduced a point of
weakness. Where this is the most likely cause of failure (and not settlement for example), the usual remedy is to install
a flue liner ) which will provide some thermal insulation for the wall structure. Then point-up and make good the crack.
DEMOLISHED CHIMNEY BREASTS
In houses and flats which have been poorly converted it is often discovered that the chimney-breasts have been removed
in habitable rooms to create more living space, without removing the stack above. This is a classic error, committed
either through laziness or for the more laudable reason of wanting to retain the original roof scape. I
n either case, if the remaining stack has not been properly secured both it and the walls below it will be unstable.