While roofing defects make up one of the most common items found in an inspection report, a large portion of them deal with chimneys. If you find caulking, tar or other sealants on the chimney and they are not sealing the counter flashing or the flue as it penetrates the cap, it is an incorrect install. Period… In my area there are very few brick chimneys that are flashed correctly. Let’s discuss where they went wrong.
Cap
Let’s start at the top and work our way down. The most effective cap will be cast in place concrete. This cap must be crowned to divert water away from the flue. Provisions must be made to divert water away from the flue penetration, The flue pipe must extend a minimum of 2 inches above the cap material and be sealed and flashed as shown in the diagram.
Many chimney caps in our area are cement wash caps, which is basically mortar built up to create a crown, the issue is that as this mortar cures and ages it always cracks and deteriorates at the edge due to the mortar being so thin. This leads to
moisture intrusion and damages the brick below. If you see spalling brick in the upper 3-4 courses of brick, you will likely find either a cracked cap or an inadequate seal at the flue pipe.
The Chimney Wall
While the most important aspects to brick chimneys is the cap and the flashing, expansion and contraction can cause mortar joint issues with the chimney wall. On home inspections I regularly find deteriorated mortar joints and spalling brick. Spalling brick are brick that the face has cracked and separated or is gone completely. There are two conditions that can cause this. The use of structural mortar and moisture penetration of the cap and/or chimney wall. The brick will expand and contract daily, the use of structural mortar will not allow for this
movement and causes damage. The other cause is water, the single biggest enemy of any home. When water penetrates the brick and freezes it can cause spalling damage as well. Deteriorated mortar joints can also lead to spalling damage. An annual examination of the overall chimney condition as well as all mortar joints is recommended to identify any areas of possible moisture intrusion.
The Flashing
So not long ago I was asked: “I just have one question. Are there ANY chimney flashings around here that are installed correctly!?” My answer: “Not many”. “How can that be? Roofers must be licensed, right?” Nope. But licensing wouldn’t likely solve the issue. Many homeowners install their own roofing materials to save money, while that may be OK for the overall roof, the installation of a chimney and wall flashings is not as easy as it may look unless you know what you’re doing.
For a shingle roof the chimney sidewall must incorporate a step-flashing. 6 inch wide aluminum must step down with each shingle course to adequately keep the roof sheathing dry. The flashing at the high side chimney wall should extend past the corners or be bent and sealed on the outside of the step flashing. The upper chimney wall must also incorporate a cricket if this dimension exceeds 30 inches. When I inspect the flashing I am looking for any sealant, if the chimney or flashing is sealed to the shingles with asphalt 
cement, caulk, or tar, it is an incorrect install. These sealants will crack and separate during freeze/thaw cycles. They may also cause thermal fracturing of the shingles. The chimney and roofing materials expand and contract at different rates and must be allowed to move, especially during the spring and fall. One exception is at the counter-flashing. Many times the aluminum is inserted into the mortar joints then sealed with caulking. Since this flashing is not connected to the roofing surface this is allowed to move with the expansion and contracted of the chimney and allows the step-flashing to move independently. Any corrosion observed on these flashings should also be sealed.
Maintenance
So, on an annual basis it is a good idea to check your cap, chimney wall, and flashings for obvious areas of movement, potential leak locations, and any changes in the overall condition. Periodic sealing of concrete cracking may also be necessary. Remember a small roofing leak can lead to thousands of dollars in damage if not caught early enough.
I should also add that if you don’t feel comfortable on you roof or if you have a steeper roof pitch, STAY OFF THE ROOF! Hiring a professional with the correct equipment is by far cheaper than and injury from a fall and the hospital bills that would follow.
That is all for now. I hope you found this article helpful.
-AZ
Aaron M. Zuehlke is the owner and inspector at Zuehlke Inspection Service, LLC, a full-service home inspection company serving Southern Wisconsin. Specializing in Home inspection, Radon Testing, Mold Testing/inspection and Residential Thermal Imaging. He can be reached by email at Aaron@Zuehlkeinspections.com or by calling the office at 608-931-7485.