At Fichtner Services we get hundreds of phone calls per week about roof leaks. Of these phone calls, the culprit that we hear most often is chimney issues. Water is coming down either the inside or outside of the chimney, the inside of the flue, or showing up somewhere lower down the roof line from the chimney. We always check the roof and flashing first for installation and maintenance issues, but more often the leak is due to the concrete chimney cap or the brick and mortar itself.
Top Causes for Chimney Leaks
Chimney leak cause number one: Roofing and flashing installation errors or maintenance problems.
Being that we are roofing contractors, our initial inspection of the chimney and search for the leak will be for the correct installation of the roofing materials and flashing. Whether it be shingles, cedar, slate, rubber, metal panels; the roofing material always has to tie into the sides of the chimney vertically. This is commonly done with the use of metal flashing, which can be aluminum, copper, steel or lead. Due to workability and cost, aluminum is most common in this area.
The flashing ties the side of the chimney together with the roof material by being bent at an angle and then woven and overlapped with the roof material. This flashing, which is step flashing and apron flashing, is then overlapped by a counter-flashing. The counter-flashing is either turned into and caulked to a groove called a reglet or has a lip bent to support a caulk joint which is referred to as a Philadelphia bend.
If any of the flashing overlaps, roofing materials and flashing isn’t installed correctly or is old and failing, then the system usually needs to be torn out and reinstalled. However, at the point where the flashing ties into the brick or stone chimney, there is a caulk join that periodically needs to be re-caulked so the leak might simply be a maintenance issue.
Chimney leak cause number two: The flue pipe is open.
If the flue pipe has no cover over it, then rain falls straight down the flue. That rain is most commonly collected in the smoke shelf but that can get a buildup of debris such as leaves and overwhelmed by long heavy rains. Most commonly this type of leak will result with water showing up inside the fire box and possibly out onto the floor. The best and easiest solution for this problem is to put a cover over the flue. The cover should keep 90% of the rain out of the flue except in rains associated with strong winds.
Chimney leak cause number three: The concrete cap is porous and allows water into the chimney.
Not everyone believes this, but brick and mortar are porous! When water runs over and down the concrete cap, brick or stone and mortar joints, it gets absorbed little by little like a very dense sponge. If you were to drip water onto the top edge of a vertical sponge, it will eventually drip out of the bottom of it. This is the same with the masonry chimney. Some are worse than others due to cracks, porousness of the material, etc.
We have found that the best way to prevent this absorption is to cover the top of the chimney with a sheet metal cap and to also spray-seal the masonry with a 5% silicone solution made by Drylok. In most cases, the combination of the cap and silicone spray, has completely stopped water intrusion into the home.
If you have a roof leak and suspect that the chimney may be to blame, contact us to schedule a roof checkup.