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A chimney crown is the first thing that protects your chimney from outside abuse from rainwater to snow, and everything in between.  Due to its location and purpose, a chimney crown plays an important role in keeping your chimney safe.  Knowing about the chimney crown and its maintenance is necessary if you want to keep your chimney safe from moisture and deterioration.  However, most people are unaware of its importance and don’t maintain it.  Due to this most chimney crowns get damaged and form cracks from which moisture can enter your chimney can cause great harm.

What Is A Chimney Crown?

A chimney crown is a huge slab of concrete, stone, or metal, that covers the top layer of brick of a chimney.  Its primary purpose is to seal the chimney and keep the brick and mortar structure protected from moisture.  With a thickness of at least two inches, the chimney crown usually slopes to the side to direct rainwater and snow away from the chimney.  If properly constructed, a chimney crown can last quite a long time. However, if the crown has poor construction, its lifespan will be significantly reduced and it’ll start to deteriorate, which can cause serious (and costly) damage to your chimney.

Think of your chimney crown as a rain cap.  Whereas your chimney cap covers the flue, the crown actually covers the entire top of the chimney.  The primary purpose of a chimney crown is to protect your chimney from deterioration from time or weather exposure.  When a chimney crown is properly built, you’ll have a slab of concrete or mortar about 2-3 inches thick, extending over the chimney about 2-3 inches.  This design helps direct the water away from your chimney and onto the roof without damaging the bricks and mortar of the chimney structure.

The cement or stone crown at the top of your chimney plays a crucial role in preserving the health of your fireplace’s ventilation system.  Bricks and mortar tend to act like a sponge, naturally absorbing moisture.  Unlike a sponge, when the moisture in masonry freezes and thaws, it breaks down.  This freeze amd thaw cycle can weaken the structural integrity of your chimney and cause thousands of dollars in damage.  Protecting the health of your chimney crown can extend the life of your chimney and prevent the need for expensive repairs.

A chimney crown is a cap at the top of your chimney that covers the bricks and mortar or stones that make up the structure of the chimney.  Its purpose is to prevent moisture from seeping into the chimney’s masonry where it is most exposed to the elements: at the top.  It also extends over the edge of the chimney by a few inches so that rain and snow will run off onto the roof or the ground instead of falling straight down to the base of the chimney which would cause extra wear and tear to the flashing.

Chimney crowns are usually made of concrete that has been covered by a waterproofing sealant. Though they can also be made of metal or stone. A properly designed chimney crown will have a minimum slope of 3 inches per foot of run and will extend over the side of the chimney by a minimum of 2 ½ inches.

Importance Of A Chimney Crown

A masonry chimney is made up of brick, mortar, and stone.  When a masonry chimney is exposed to water, the moisture seeps inside the mortar, causing it to deteriorate.  Thus, the mortar and bricks crack, putting the structural integrity of your chimney at stake. Since moisture deteriorates the mortar, the chimney bricks loosen and cause the chimney to crumble.  Furthermore, when water enters the chimney, other parts of the chimney get exposed which can rust, corrode, and ultimately malfunction, affecting the efficient working of the chimney.  When the water reaches the firebox, it makes it harder to start a fire and also leads to condensation which further exposes the brick and mortar structure to moisture.  Thus, to protect your masonry chimney against water damage, a chimney crown (made from concrete) is constructed over the last bricklayer on top of your chimney. Since it protects the brick and mortar of your chimney against water damage, a chimney crown can be credited for increasing the overall lifespan of your chimney.

Difference Between Chimney Crown And Chimney Cap

People often confuse the chimney crown and chimney cap because they have somewhat similar roles and are both located at the top of the chimney. The difference, however, is that while a chimney crown is constructed atop the last layer of chimney bricks, the chimney cap sits on top of it.

A chimney cap essentially covers the chimney flue and keeps water, dust, debris, small animals, and birds from entering the chimney. Both, the chimney cap and crown, together protect the flue and the chimney from outside harm.

There are several main reasons why a chimney crown can become cracked or broken:

Natural wear and tear

Overtime, the waterproofing sealant on the chimney cap will become less effective.  If the crown is not retreated with sealant, water can seep into the concrete.  When it freezes and thaws inside the concrete, it can begin to crack creating pathways for moisture to seep into the masonry.  Overtime, the waterproofing sealant on your crown will become less effective. Bricks and mortar are porous materials.  That means they absorb water fairly easily.  If the chimney crown is not retreated with sealant, water can seep into the concrete.  When the water freezes, it expands inside of the brick and mortar. As it expands, it chips away at the brick and mortar.  Then, with extra space from the cracks, more water is able to penetrate, freeze, and create larger cracks.  This creates pathways for moisture to seep into the masonry.

Improper construction

If the chimney crown doesn’t have a steep enough slope or isn’t made of the correct materials, it is more likely to crack or break.  We’ve seen a lot of newer homes, built within the last 5-10 years that have cracked chimney crowns.  The main issue from this is that the builder didn’t build the chimney crown properly.  That means that the builder didn’t put a steep enough slope on the crown to help push away the water.  Or the builder didn’t use the right materials.  Both of these options help contribute to quicker deterioration.

Shifting and settling

Homes shift and settle as the foundation sets and ground shifts. The chimney crown can become cracked during this process.  Older chimneys that were built properly with the right materials can still have cracked chimneys.  After several years you could have some cracks, both inside and out of your house.  A general rule of thumb is that it takes about 2 years for your house to settle enough where cracks in the plaster inside are minimal.  It’s safe to assume that the same time frame and rule of thumb apply to the outside of your house, including your chimney’s crown.  After a few years, if you don’t have annual inspections (which you should), you ought to get on top of your roof (bring a step ladder up too) and take a look.

Concrete Shrinkage

Many crowns are made of concrete. That’s what we use to build the crown.  Some chimney companies use mortar.  This is usually okay.  But we opt for concrete because it’s stronger and able to withstand weather better.  But the problem with concrete is that as the moisture content evaporates, it dries and ages. This can cause concrete shrinkage.  Severe concrete shrinkage is known to cause the crown to crack. 

Cracks and damage to your chimney crown are hard to see from the ground. The best way to ensure your chimney crown is in good condition is to schedule an annual chimney cleaning and inspection. An annual chimney inspection and cleaning isn’t only important to check the health of your chimney crown. It is recommended by the Chimney Safety Institute of America (CSIA) and National Fire Protection Association because it is essential for preventing fires and carbon monoxide poisoning as well as expensive repairs.