Chimney Leaks: What to Do if You Have One & How to Prevent Them

The Types of Damage Caused by Water Penetration & Chimney Leaks

Another question we often hear is, ‘How bad is a chimney leak, really?’

Ultimately, water in your chimney can cause:

When you consider the amount of damage that water can do to a masonry or prefabricated chimney, and how quickly it can cause the need for extensive repairs, it’s clear that a chimney leak can be really bad.

Russ, our Director of Education, gives a quick (but great) overview of what water can do to your chimney in the following video…

Is There Any Way to Prevent Chimney Leaks?

The good news is that a little preventive and routine maintenance can keep chimney leaks (and the costly repairs they often demand) at bay.

How can you prevent chimney leaks in the future?

#1 Take good care of your chimney crown or chase cover

Every masonry chimney should have a slab of concrete, called a crown or chimney wash, at the top of the chimney stack. On a prefabricated or metal chimney, this important component is made of metal and is called a chase cover.

A well-built crown will provide a downward slope that directs water away from the flue to the edge of the crown. The overhanging drip edge directs the run-off away from the chimney and helps prevent brick and mortar erosion. On a prefabricated chimney, the chase cover should also be sloped and designed to encourage water to run off and away from the chimney.

If well-built and maintained, both chimney crowns and chase covers will prevent water from pooling on top of the chimney and provide protection against water damage and penetration in the area between the flue and the masonry, metal, or wood surround.

The trouble is that these components often get neglected. And because they’re not indestructible themselves, they can deteriorate with time and neglect, making them less effective at protecting the rest of the chimney against water penetration and leaks.

Additionally, most masonry chimneys are built with an inadequate crown constructed from common mortar mix that will crack, chip, or deteriorate from weather exposure. Likewise, chase covers that come stock on prefabricated chimneys are often made of sub-par metal materials that are quick to corrode, dent, and even cave in.

A proper crown should be constructed of a Portland cement-based mixture and cast or formed so that it provides an overhang that projects beyond all sides of the chimney by a minimum of two inches. The flue liner tile should also project above the crown a minimum of two inches. A proper chase cover should be made of a durable metal (not cheap sheet metal) and custom-fitted to the chimney chase.

If you have your chimney crown or chase cover inspected every year and checked for proper construction, proper installation, and signs of weather or water damage – and you keep up with repairs as needed – you shouldn’t have to worry about water making its way in through the crown or chase cover.

#2 Invest in a good chimney cap

We often get asked, ‘Do I really need a chimney cap?’ The answer is, without a doubt, yes. Chimney caps, also called rain covers, are probably the most inexpensive preventive measure that a homeowner can employ to prevent water penetration and damage to the chimney.

Here’s why: Chimneys have one or more large openings (flues) at the top that can collect rainwater and funnel it directly into the chimney interior. If there’s no cap at the top of each flue, there’s nothing to protect the flue against water penetration and leaks.

In fact, a commonly sized flue without a cap has the potential to allow large amounts of rain or snow into the chimney during just one winter, when damaging freeze/thaw cycles are common.

Simply by adding a chimney cap to your chimney – one that’s properly sized, fitted, and made of durable, corrosion-resistant materials (like stainless steel or copper) – you’ll give your chimney a barrier of defense that will protect the flue liner, the damper, and any other interior components against water damage.

You can also get a custom chimney cap that will cover multiple flues, a large portion of the chimney, or even the entire chimney top. Full coverage chimney caps may cost more initially, but this added protection can go a long way in preventing leaks and keeping repair costs low over the years.

Psst! That’s not all that chimney caps do. Chimney caps have long been recognized as an important chimney safety and damage prevention component. In fact, Underwriters Laboratories (UL) specifies that any chimney lining system that is to be listed to their test standard must include a chimney cap. Chimney caps also keep animals and birds out of your chimney and function as spark arrestors (preventing sparks from landing on the roof or other nearby combustible material).

#3 Keep your flashing watertight

Flashing is the metal seal between the roofing material and the chimney. Flashing prevents rainwater or snow melt from running down the chimney and into living spaces where it can damage ceilings and walls and cause rot in rafters.

The flashing is the expansion joint between two dissimilar materials. It is designed to allow both the roof and the chimney to expand and contract at their own rates, without breaking the waterproof seal in either area.

If you make sure your flashing is properly installed, waterproofed, and in good condition each and every year, you shouldn’t have to worry about leaks making their way in through this otherwise vulnerable area of the home.

#4 Repair deteriorated mortar joints and brick

Proper mortar joints have no gaps or missing mortar and are shaped in a way that directs water out of the joint. Deteriorated mortar joints on the chimney exterior, on the other hand, are entry spots for water. When mortar deteriorates from exposure to weather, it becomes much more absorbent, meaning it will wick water into the chimney with each rain or snow.

A common repair for deteriorated mortar joints is called repointing or tuckpointing. In this process, the existing mortar joint is cut to an appropriate depth and the joint is repacked with new mortar. The joint is then cut to form a concave surface that will direct water out of the joint.

A good repointing job done with the proper materials will give the chimney a much longer life span (by keeping water out) and will often enhance its appearance as well.

#5 Install a cricket

No, we’re not talking about the crickets you find in your garage near the end of summer…

A cricket is a water deflector that serves to direct rainwater away from or around the chimney. Crickets are recommended for chimneys more than 30-inches wide – and they’re especially important for chimneys on steep roofs.

If the chimney is located on the low side of the roof and water run-off is directed against the chimney, the installation of a cricket will provide additional protection against water leaking into the home and chimney.

So, if a chimney professional recommends a cricket for your chimney, it’s probably a good idea to move forward with installation. This little component can make a big difference and keep leaks and water damage at bay.

#6 Waterproof your chimney

As we talked about earlier, pretty much all components and materials on a masonry chimney can be damaged by water. And since most masonry materials are porous and will absorb large amounts of water naturally (acting much like a sponge), it won’t take long for an unprotected chimney to wick moisture to the chimney interior.

Thankfully, several products have been developed specifically for use as waterproofing agents on masonry chimneys. These formulas are 100% vapor-permeable, which means they allow the chimney to breathe. Therefore, water that has penetrated the chimney (and vapors produced when the chimney dries out or is in use) are allowed to escape, while the waterproofing agent prevents water from entering from the outside.

These products also prevent freeze/thaw, mold/mildew growth, efflorescence, spalling brick, and other common water-related issues and damage, and they usually have a five- to ten-year warranty – which means you might not have to worry about water damage or chimney leaks for a solid decade!

Note: Defective mortar joints or improper brick and mortar can greatly increase the natural tendency of your chimney to absorb and convey water to the chimney’s interior – making the destructive process even more rapid.

Wait, why not just use a clear sealant or paint from a big box store to waterproof your chimney?

Because these products will most likely trap water vapors and moisture inside the chimney, leading to further deterioration. Avoid this scenario by leaving chimney waterproofing to an experienced chimney professional with the right products for the job.

Note: While most stone is not affected by water penetration, large amounts of mortar are required to bond the stone together properly. Therefore, a stone chimney – just like a brick chimney – should be protected from the effects of water penetration.