Do you have a leak around your chimney? Has a roofer recommended that you have your chimney flashing inspected? Are you concerned about your brick chimney causing leaks? Determining whether you have a roofing problem, a masonry chimney problem, or chimney flashing problem may require expert advice or even leak testing. This page is dedicated to discussing leaking issues with brick chimneys and solutions.
Three critical areas of the masonry chimney can cause leaking into your home.
First, we need to discuss the essential chimney flue cap
The first and simplest cause of leaks associated with the chimney is a chimney flue left uncovered without a flue cap. Without a cap, a masonry flue is an open hole catching rain… here is critical information on the necessity of a chimney cap.
This a great example of a chimney cap with a porous crown.
A porous crown allows water entry which will damage mortar allowing loosening and deterioration to the masonry directly below the crown, including natural stone, brick, or in this case, cast stone.
We will Briefly Discuss the Critical Role of your Chimney Crown
Another cause of a leaking masonry chimney is a porous and cracked crown which is not shedding water off the top of the chimney, but instead is letting infiltrating water work its way down the inside of the brick and mortar chimney. This invasive water not only destroys mortar and brick, but as damage accumulates, sufficient invading water can outflank the counter flashing and can create a leak inside the home.
A crown is tapered to shed water from the underlying brick. Bricks themselves are placed flat and square. If there are cracks in the crown, water does not run off but infiltrates the brick and mortar below. We have more information on crowns here.
This cracked crown is allowing water to infiltrate brick and mortar below. Water causes mortar cracks to expand with freeze thaw cycles. Porous types of bricks become saturated, and upon freezing, can cause brick spalling. Deterioration rates accelerate if the degradation is allowed to continue. Early comprehensive repairs can eliminate or control the major expense of dismantling a chimney for repairs and will head off any leaks attributable to defective and deteriorated brick and mortar. This crown needs to be rebuilt, many spalled brick need replacing, some mortar joints need repointing, and a chimney cap added.
This rebuilt concrete crown looks similar to a new mortar crown, gently sloping to shed water away from the top of the chimney. (Note that the metal cap shown also prevents rainwater from entering the chimney flue, which can cause damage to interior chimney components.)
This rebuilt crown is constructed of concrete which lasts much better than mortar. See the preceding image with seriously cracked mortar. Again a reminder, make sure you also see the information on crowns if you think this is your issue.
Metal Chimney Flashings Play a Critical Role in Keeping Water out of Your Home
There are two basic types of counterflashing- the step counter flashing and a continuous counter flashing. Both work well when the brick and mortar is in sound condition. See the illustrations below.
This is a good, sound cut-in reglet joint on a chimney at the peak of the gable roof. The brick and mortar are sound from what we can see in the image and water will shed right over these brick and right over the cut-in reglet.
Here is a repaired cut-in reglet joint. The original mortar covering the reglet joint separated from the sheet metal. Brick Doctor cut out the mortar and added a sanded elastomeric joint which can absorb the differential movement of a long section of metal and basic brick and mortar as the structure heats and cools. This natural force is created by differential temperature coefficients.
Here is a good example of stepped counter flashing built right into the chimney. Unfortunately, the brick above this counter flashing has cracked, allowing invasive water to enter the brick and migrate down, bypassing the counterflashing.
Here the mortar has been ground out and bricks replaced as necessary to eliminate the cracked mortar and broken brick. This repair has restored the ability of this vertical section of chimney to shed water down and over the counter flashing.
The above images show structural cracks in the body of the chimney bricks, before and after repairs. Brick and mortar cracking need prompt attention, as they create entry points for water.
It’s important to differentiate between leaks caused by a problem with the masonry fireplace from potential leaks through the roofing assembly itself. Proper flashing is also critical.
A deteriorated mortar joint around the counterflashing can also allow invading water to outflank the counterflashing and cause a leak. Deterioration of the chimney crown is often the beginning factor which causes damage to other chimney components.
The deterioration continues until eventually it allows infiltrating water to accumulate into a visible leak into your home. For more information, click for fundamental issues regarding masonry crowns and masonry chimney flashing.
Porous brick and mortar over a continuous counter flashing is never properly repaired by simply applying caulk. Moisture in and behind masonry can cause spalling and bricks which accumulate salts can cause efflorescence and other water-born stains.
Irregular stone masonry requires a continuous counter flashing to facilitate construction. Here, Hairline cracks between stone and mortar create water entry points above the counter flashing on this fieldstone masonry chimney. Water does not run across a crack but gravity and capillarity draw it into the crack. Water in mortar can freeze and melt and pry fieldstone and mortar apart. Absorbed water may also dissolve and deteriorate weak mortar.
Primary Head Flashing can also be a Leak Source.
The primary head flashing is interlayered with the underlayment and roofing materials as the waterproofing transition between the roofing assembly and the metal head flashing.
These two images here are a reconfiguration of the images above, to highlight the head flashing. The head flashing is wider than the chimney and sheds runoff out, around the step flashing.
Notice corrosion on the head flashing where water and debris can accumulate. The brick mason’s responsibility ends at the counter flashing, which transitions water flowing off the brick over onto the primary flashing components…in this case, the head flashing.
The head flashing is basically flat and water can run off, or puddle here, or until it evaporates. Chimneys over 30 inches wide require a cricket, illustrated below. You can also see the brick cracking here which compromises the ability of the brick and mortar to shed water over the counterflashing.
In Texas, chimneys wider than 30″ require a cricket upslope.
In Texas, chimneys wider than 30″ require a cricket upslope, because more water has to be diverted over a longer area. While the flat metal head flashing is cheaper; it is simply not fundamentally sound for a large chimney. Other problems magnify with length as well. Windblown debris can create damming at that crevasse and accentuate problems.
The chimney cricket adds slope around the chimney and is a preferred technology to the flat head flashing. This is the best design for shedding water and preventing debris build-up, although more expensive to build. (Note this illustrates water flow over a cricket, but the step flashing on the illustration is not accurate.)
The chimney cricket adds slope around the chimney and is a preferred technology to the flat head flashing. There is good slope for drainage, no standing water, and no deterioration of metal. With quality mortar repairs, a proper sound and sloping crown, and a proper chimney cap, this configuration of a masonry chimney will perform without issues for many years or until the roofing assembly needs replacing.
There is also a flashing transition around the downslope side of the Chimney, which usually is not a source of a problem.
Because it is downslope, it is not usually a factor with chimney leaking problems; unless of course, the brick and mortar have problems which allow invasive water to circumvent this portion of the metal flashing assembly.
For more help diagnosing the source of leaks around your chimney, click here.
You can eliminate masonry components as a possible leaking problem of a chimney when masonry repair work is done properly by conscientious masonry professionals.
On occasion, brick problems can be subtle–poorly bonded mortar and brick can allow water to wick between brick and mortar. This leaves obvious traces that an experienced brick repair specialist can observe and diagnose. Poor bonding between counterflashing and brick and mortar can allow moisture to bypass the counterflashing. Masonry experts familiar with these issues can readily spot this problem and explain a proposed solution.
Poor construction of the flashing assembly and the haphazard placement of bricks here (note the many voids in the mortar) means extensive repairs are needed here. These mortar problems are quite obvious, yet even a few such holes, voids, or gaps in the mortar joints can result in further deterioration and interior damage.
Your brick mason solves problems with the counterflashing and the brick and mortar above the counterflashing. Your Roofer is responsible for the installation of the head flashing. The head flashing is assembled into the underlayment and the roofing shingles, and under the counter flashing metal to shed water around the chimney.
What can the homeowner do to make sure the chimney is watertight?
If the roofing is sound, a competent masonry repair expert familiar with all relevant chimney components should be able to diagnose any potential masonry problems. Pictures of the chimney can be provided upon request, illustrating the masonry problems and their proposed solutions. Bottom line- chimney problems need attention as soon as possible. The risk of water penetrating into the house only increases with time, along with the resulting damage. Any water infiltration issue typically gets more difficult and more expensive the longer it goes unnoticed.
Need Help diagnosing a chimney leaking issue?
Over the years, Brick Doctor has restored thousands of brick chimneys with leaking issues. Let us know if we can help you.
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