How Do You Properly Flash a Brick Chimney?

Many issues on your residential roof stem from leaks occurring around your chimney, and the culprit is often the chimney flashing. This is an overview of the process of properly flashing a brick chimney as part of an effective roof system. This article is primarily focused on flashings that are tied into a composite asphalt shingle roof, as that is the most common roof type found in the US – however, the general flashing process is similar for other roof types as well.

Understanding the proper method of flashing a brick chimney is important to know not only if you are installing a roofing system and need to conduct the flashing yourself, but also to know if the job was done properly on a home you are considering purchasing, to identify if there is a flashing problem when trying to locate a roof leak, or simply to know if the flashing job was done properly if you recently had a roof repair or replacement done. Finally, identifying and knowing about proper chimney flashing is important to know what maintenance might be needed over the next few years on your brick chimney.

This article is split into two parts:

Part 1: How to Identify Issues with Existing Brick Chimney Flashing

• • • • The two types of brick chimney flashing
      • Signs you may have a bad chimney flashing
      • Things that could cause a roof leak at/near a chimney that AREN’T a flashing problem

Part 2: How to Properly Flash a Brick Chimney

• • • • Components and Materials
      • Installation Process

Part 1: How to Identify Issues with Existing Brick Chimney Flashing

Chimneys, especially brick chimneys, are the number one leak site of residential roofing systems. Here’s what we’ll cover to learn more about how chimneys are supposed to look and how flashing systems work:

• • The two types of brick chimney flashing
  • Signs you may have a bad chimney flashing
  • Things that could cause a roof leak at/near a chimney that AREN’T a flashing problem

First, there’s two types of brick chimney flashings:

“Cut-in” or “Mortared-in” Counter Flashing:

Surface-Mount Counter-flashing

The top of the counter flashing is embedded in a mortar line of the masonry chimney

If it doesn’t have a stair step mortar and counter flashing and it has a surface mount counter flashing, the only thing preventing the water from entering behind the brick and the flashing is the bead of caulking. So if you have a surface mount counter flashing versus style, is has now become a maintenance issue; you would have to have somebody come look at your chimney and redo the caulking every five years

 

THE WHY: Signs you may have a bad chimney flashing: How to identify the current or potential roofing system leaks near your brick chimney.

• • You have a leak. Okay, sounds obvious, but this doesn’t necessarily mean it’s a flashing problem, it could come from the cap or the masonry itself
  • You have an excessive amount of caulking and/or roofing cement over your flashings. Tar
  • You see rust or deterioration of the metal flashings
  • The metal is bent or curled away from the masonry

If the chimney flashings are installed correctly and the metal is in good condition, it usually indicates that there might be an issue somewhere else in the chimney structure. Things that could cause a roof leak at/near a chimney that AREN’T a flashing problem:

• • Deteriorated mortar lines – look for loose, cracking, or missing mortar
  • Chimney chase cover on top of the chimney could be rusted or damaged
  • Rains lasting 4-5 consecutive days will often cause small leaks around masonry chimneys because brick and mortar itself are both porous, and will eventually saturate
  • Cracked crown (is that the name). On a brick chimney, they usually just put cement on a crown, and if you look on the top of it sometimes that could be cracked all the way through, sometimes like a half an inch crack there. (A crown is only relevant if you don’t have a chimney chase topper). A temporary solution there in the meantime might be to coat with Uniflex

 

Part 2: How to Properly Flash a Brick Chimney

**Disclaimer. This really is a job best left to the professionals, especially for cut-in flashings that connect into a chimney at the mortar line. The cost and consequence of roof leaks into your home make this job high consequence. Furthermore, because of the potential safety and damage risks involved, most municipalities require any roofing work to have a building permit and inspection by the governing building authority. That said, here’s the components and process:

Components and Materials

When installing a chimney flashing on a brick chimney there are 5 main components:

• • Cricket or saddle flashing located on the topside of the chimney
  • An apron flashing located on the bottom side of the chimney
  • Step flashing located on the sides of the chimney
  • Counter flashing embedded into mortar joint
  • Install Ice & Water barrier underneath the flashing for added protection against water intrusion