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Repairing or Removing Shared Chimney Stacks

Friday, 25th November 2016 | by: Justin Burns

We looked at typical defects to chimney stacks on the blog a few years ago so today I wanted to cover a related topic – what the legal responsibilities of the owners are when it is a shared chimney stack that has been affected.

Chimneys tend to be more exposed to the weather than other parts of a property and therefore prone to defects such as eroded pointing, spalled brickwork and cracked flaunching. When repairing defects of this type, providing safe access by means of scaffolding or a cherry picker will make up a significant proportion of the cost. For this reason there are obvious benefits in the whole of a defective shared stack being repaired at the same time but as each owner is responsible for the maintenance of their half neither can force the other to participate.

Shared chimney stacks are not ‘party’ i.e. the two owners do not have rights over the whole structure – there is likely to be a party wall within the stack separating the flues of the two owners but that is not normally the defective element as it is protected from the weather.

That is all fairly straightforward but it gets more complicated when one or both of the owners decide to remove the stack entirely; either because the defect is significant or as part of loft conversion works. Obviously, chimney stacks are only removed when the connected fireplaces are no longer in use.

The whole of a shared stack can only be removed if both owners are in agreement – if it is on account of defect the cost will generally be split but if it is being done as part of improvement works to one property the owner benefitting from those works will generally carry the cost. Because removing a shared stack is not a right under the Party Wall etc. Act 1996 no notice is required. Having said that, if it is being done as part of a project that is otherwise covered by the Act the appointed surveyors will tend to include it in their discussions (if not in the award) and possibly agree the details of how the adjoining owner’s roof structure and covering are made good.

If one of the owners does not want the stack removed it is still possible for the other owner to remove their ‘half’ but that gives rise to further complications.

Unlike removing the whole of a chimney stack, removing just half of it is notifiable under the Party Wall Act as masonry will be cut away from the party wall within and that party wall will be exposed to the elements where it was hitherto enclosed (both are rights provided by section 2(2) of the Act). A Party Structure Notice should be served at least 2 months prior to the works commencing.

The party wall surveyors will consider 2 key factors:

The Slenderness Ratio

Tall slender structures are vulnerable to the wind and can deflect in extreme conditions. This is covered in Approved Document A of the Building Regulations. The height of the remaining section of chimney stack, as measured from its intersection with the roof, should be no more than 4.5 times its width provided that the density of the masonry is at least 1500kg/m3 (London stocks are approx. 1850kg/m3).

Making Good the Remainder of the Stack

The newly exposed party wall within the stack will need to be either pointed or rendered to protect it from the weather. If the stack is visible from the front of the property pointing would be the preferred option as it’s more attractive but it’s also very time consuming to remove the cut bricks from the front and rear and tooth in replacements.

If rendering, any residual soot should first be removed and stainless steel stop beads used to the corners to achieve a neat finish.

The works can only commence once the appointed surveyors have agreed and served the party wall award which will also cover details of any access required.

On period properties the surveyors would normally request that a CCTV survey of the adjoining owner’s flues is undertaken prior to the work and again afterwards to ensure they have not been compromised. It would also be prudent to temporarily seal any open flues within the adjoining owner’s property; even if they have been swept regularly there’s a good chance that vibration caused by the works could loosen dust and debris clinging to the sides of the flue.

If you have an issue with a shared chimney stack that you would like to discuss with our surveyors you are welcome to contact us by email or on 020 7183 2578.