Chimney extraction, air flow interuption.

My neighbour built a dormer window and loft extension that went above the height of my chimneys. Thier dormer is about five feet from our chimney. We have two gas fires and the fumes are extracted via chimneys. Now what is happening is that on the prevalling wind (SW) the air is going over their roof and dormer and over our chimeny (as the roof is now heigher) and causing a change in air pressure and forcing the fumes back down our chimney. I found some information about this issue a while ago which showed diagrams etc of what happens to the air circulation and extraction and when a construction goes above a chimney level. Does this come under building regs? Can anybody point me in the right direction please or offer advice. Thanks.
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It should have been picked up at building regs checking stage (if their designer actually showed your chimney on his plans) and at site inspection stage. Contact your local BC dept to see if a completion certificate has been issued or if there is any mention of this problem. Either way, ask for an officer to come and have a look and advise you.
The Party Wall Act would have applied here, and although its implementation by the neighbour is not compulsory, and he can not be penalised for not following its guidelines, it will still count in your favour if you pursue a civil claim.
You should get a suitably qualified gas engineer to give you a solution (possibly a different chimney pot or extension) and then speak to your neighbour about him fitting the bill for it.
dg

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Ok many thanks. I have managed to find some documents online showing the effects of developing close to a chimney and building above its height. The diagrams show that the air pressure changes causing downdraft. My next concern is that my neighbour is planning to build another dormer window at the back of the house in a position closer to my rear chimney stack which is used by the downstairs living room gas fire. This chimney stack has always been lower than the other which at present is affected. The second dormer will be about four feet away and several feet above.
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Then you should notify building control of your concerns as soon as you are aware work is planned.
You should also insist on the Party Wall procedure being followed. If work starts and you have/can not come to a solution, then you should seek an injunction on the works, which the Courts would be obliged to grant.
dg

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