Chimney locations on a roof system are notorious for creating leaks and need special care in order to ensure there is no water intrusion to your living space. There are different types of chimneys that are used in a residential environment. We will address each type of chimney and how it should be handled.
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This is a chimney that consists of a ceramic flue, surrounded by a brick veneer. This is the most typical type of chimney. When constructed and designed properly, a masonry chimney should have copper counter flashing metal set into the courses of brick to counter flash the base metal flashings of the roof system. It is important for the counter and base flashing to be done in two separate pieces so they move independently when the wood structure expands and contracts, and the masonry chimney does not. Large chimneys (wider than 12”) should have a cricket installed on the rear high side or back of the chimney to facilitate the movement of water around the chimney.
When replacing your roof it is a good idea to replace the base flashing system that is integrated with the shingles. If the original counter flashings set into brick are in suitable condition they can be reused. More times than not we find these counters to be worn, tarred up, or miss-installed from the time it was built. In these cases we replace the counter flashing system by removing the existing system, cleaning the brick surface of tar and caulk. We will then use a diamond blade masonry-cutting tool and create new riglets in the chimney just above the original flashing line to accept the counter flashing. New counter flashings are fabricated and pinned into the cut riglets and sealed with structural silicone.
A few other things may need to be done to a masonry chimney to ensure the chimney remains watertight and structurally sound. Masonry chimneys are usually built with what is called a “slush cap”. This is cement that is put on the top of the chimney and is crowned to allow water to run off. This functions as your chimneys roof. It is common to find this cracked and loose after many years of being exposed to the weather. It is also not uncommon to find the mortar and bricks on the exposed exterior to be loose of deteriorated.
If this condition is present, we will disassemble the slush cap and loose bricks and reset the bricks and cap in a new Type S mortar. Tuck pointing mortar joints can also be done as necessary. Once the chimney has been re-flashed and any masonry repairs made we treat all the masonry components of the chimney with a clear silicone base spray to limit the amount of water that can be absorbed into the brick and mortar. This is crucial to prevent leaks and damage to masonry during freezing conditions. A chimney cap installed on open flues is also a good idea to prevent water and animals from entering the open flue.
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Many houses were constructed with a metal or ceramic flue to exhaust the heating equipment or fireplace. These pipes will have a pre-fab chimney housing installed on the exteriors of the roof. These units generally have a 20-year life and it is imperative that the exterior kit be replaced if you are installing a new roof and if it is expected to remain watertight for the life of your new roof. When installing a new pre-fab kit, the assembly is carefully dismantled leaving only the actual vent pipe. The pipe will remain and the new purchased kit will be assembled and tied into the existing pipe. The new kit will consist of new roof flashing, 4 wall box housing, stainless cap and pipe extension that drops into the existing pipe. Installed correctly, this unit should last the life of your new roof system.
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This type of chimney also uses a metal pipe that is installed thru a wood framed chimney. A framed chimney chase type of chimney is base flashed the same way you would flash a wall or dormer, using step and apron flashing. The sidewalls of the framed chimney are generally treated with some form of siding that matches the house. The biggest problem we find with this type of chimney is generally how the cap is designed and installed. Poor design and installation leads to leaks, wood damage and staining on the chimney structure.
The best way to handle the cap on this type of chimney is a one-piece stainless steel chase chimney cap; we make these caps with shop-fabricated unit with soldered corners and flue pipe ring. The cap is also shop bent to create a pitch so water will not lie on the top portion of the chimney. Installed correctly this cap will remain watertight, wind tight and stain free for a lifetime.
If your chimney needs service, or if you have any questions, don’t hesitate to contact NY Roof Repair online or give a call at 1 (800) 766-3776.