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Chimney cavity tray

We have an old extension that butts up against an external chimney. We are getting damp on the wall below the extension roof. The roof & flashing look OK. I have been told that water is penetrating the chimney brickwork and migrating to the room below (this happens when we get prolonged periods of rain). Can a cavity tray be fitted into the chimney? Some builders say no but one said yes.
I was thinking of waterproofing the chimney wall with tiles but cavity trays would be a cheaper option. Help appreciated.

2 Answers from MyBuilder Extension Builders

You do not say what the height of exposed chimney brickwork there is above the butted - up extension, but if not very much you could dress lead over it all, assuming you are satisfied there is no bad pointing/open joints.
Also rain gets down the stack if you do not have a suitable 'pot' on the top- check that as well or cap it off if chimney not in use.
Without a photo it is hard - also to consider IF the extension roof butts onto the stack there could be a problem with all the lead soakers whereby water rolling off the roof is getting onto the stack wall instead of being protected by the soakers.


Answered 15th Jul 2015

Is the chimney used at all or now redundant? if redundant as sounds as though it was once an old coal flu. then this damp could be caused by a number of issues??
it could be that the flaunching on top of the stack has been breached, in addition is the pot on top of the stack still open? or has a cowling been fitted.
if the pot is still open and there is no through ventilation, then it could be that rain water is penetrating the open pot and creating damp ingress from within the flue.


Answered 21st Jun 2017

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