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Surveying Chimneystacks

Chimneystacks are particularly exposed to the elements and are a common source of damp defects in older buildings.  Early chimneystacks (commonly built up to the 1950’s)  were usually built without a damp proof course/tray within the stack and damp penetration commonly occurs and is problematic to fully eliminate. A number of competent roofing contractors we have spoken to, actually advise us the only way to ensure damp penetration will not occur and to obtain a warranty is to reconstruct the chimneystack which is a very expensive option.

Other common issues we encounter with chimneystacks is a lack of or dated/inadequate lead flashings and soakers to  abutments. The remedy for this is to install new soakers and flashings around the stack. A lack of top protection to chimneypots is also a common source of internal damp defects. Defective pointing and  flaunching (mortar applied to the top of the stack around the chimneypot) is another issue we regularly encounter.Sometimes sub-standard bricks are used to construct the stacks and this leads to spalling of the brickwork due to freeze/thaw effect. If minor spalling has occurred brick repair/replacement can be carried out, however, if significant spalling has occurred it is likely to be more economical to reconstruct the chimneystack.

Spalling to brickwork and lack of lead flashings and soakers to abutments.

Spalling to brickwork and lack of lead flashings and soakers to abutments.

In recent times the use of water repellents or coatings is becoming a popular course of remedial action to prevent damp penetration. The coating is applied to the exterior of the stack and bonds with the masonry to provide a water resistant barrier. In our experience such coatings are effective, but only for a limited time (3-5 years) and it is necessary to periodically reapply the coating.

Leaning is another common defect in older chimneystacks. The lean is usually due to the prevailing wind and differing wetting/drying cycles causing mortar erosion and salt crystallisation to raise the joints. In addition, sulphate attack can occur in chimneys due to sulphates from the cement used in the mortar and sulphates deposited due to the combustion process condensing on the cold side of the stack and attacking the mortar. The degree of deflection is not normally sufficiently serious to justify rebuilding and we often recommend that the stack is restrained using metal clamps, however, if the lean is to severe then the only option is to reconstruct the stack.

Leaning Chimneystack

Lean to chimneystack.

If you are buying an older property with a chimneystack we strongly recommend you instruct a RICS surveyor to carry out a full building survey which will identify any issues with the chimney and recommend suitable remedial action. In addition, any contractor you use to carry out work on a chimneystack should be registered on a competent person scheme and/or registered with a trade association such as the National Federation of Roofing Contractors (NFRC).

Luke Thorburn MRICS South West London Surveyors Ltd