Chimneys are notorious for leaking and usually the problem is poorly installed or defective flashings. It is fairly easy to spot of you have missing or split lead flashings by having a look in your loft. If you can see daylight or signs of damp around the chimney breast then this is a good indication that the flashings are failing.
You should really replace the flashings if you suspect they have deteriorated or are missing. Chimney flashings are one of the worst areas for being ‘bodged’ many so called roofers will do anything for fast repair and fast money. unfortunately it isn’t always easy to see what’s been done around your chimney. Quick fixes such as bitumen tars or other weather proof type paints will only last in the short term. New flashings will last for many years and you can be assured there will be no further problems in that area. Flashings are installed to close the gap between the roof covering and any joining walls or brickwork usually there will be a lot of water in these areas so it will pay to make sure the job is done right. Typically chimney flashings are made from lead sheeting as it is a good material to cut and shape into position. Tin, Zinc and Copper flashings were used in older buildings but lead is more common.
There are 4 positions where flashings are installed on a chimney, the front, two sides and the rear. The front flashing or apron for its technical name is a large single piece of lead which is turned up the front of the stack and fixed into a brick work joint then dressed over the tiles or slates below. The side flashings called ‘step’ flashings are installed in two parts if it is a slate roof or concrete roof with a flat tile. The first stage is to install soakers under every course of flat tiles or slates up the side of the chimney. These are pieces of lead that go underneath the slate and turn up the side of the chimney. Next the ‘step’ flashing is cut and fitted to go over the sides of the soakers.The final piece of leadwork is the back gutter and this is installed underneath the course of tiles and turned up the back of the chimney stack and into a course of bricks.
This of course is only a brief description, it is quite a technical process to get the flashings fitted correctly and looking good. It requires a fair amount of skill.
When the flashings are installed in the correct order and all the joints are repointed where the lead turns into the brickwork it creates a water tight seal around the chimney stack. Care is taken to cut and shape (dress) the leadwork and it creates a finish which is very pleasing to the eye.
Being in such an exposed position chimney flashings should be the highest quality possible and the correct procedure for fitting new lead flashings should be followed. In the case of renewing lead flashings around your chimney it is recommended that you employ the services of a reputable roofer.
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