What are the best techniques for a roofer to properly flash a chimney to prevent leaks?

For a roofer, the key is to treat chimney flashing as a layered water-shedding system, not as a bead of caulk around the chimney. The most reliable assembly uses base/apron flashing, step flashing, and counterflashing, with a cricket or backer flashing on the upslope side where appropriate.

Best practices

1. Start with the roof-to-chimney underlayment

• Strip the area back far enough to inspect the deck.
• Repair deteriorated sheathing first.
• Integrate the roof's water-control/underlayment layer with the chimney flashing.
• In climates subject to ice dams, use the specified ice-barrier membrane around the chimney.

2. Use proper step flashing on both sides

• Install an individual L-shaped piece with each shingle course.
• The horizontal leg goes under the shingle; the vertical leg runs up the chimney.
• Lap each successive piece over the one below so water always drains outward rather than behind the flashing.
• Avoid relying on exposed fasteners through the vertical portion of the flashing.

3. Make a substantial apron flashing at the downslope face

• The apron carries water coming down the roof around the front of the chimney.
• Form the corners carefully; chimney corners are particularly vulnerable because sheet metal has to transition between multiple planes.
• Good metalwork is preferable to trying to compensate for poor folds with sealant.

4. Use a backer flashing or cricket on the upslope side

• This is one of the most important details on larger chimneys.
• A cricket diverts water around the chimney, rather than allowing a large volume of water, snow and debris to accumulate against its uphill face.
• NRCA guidance recommends a cricket for chimneys 24 inches wide or greater; smaller penetrations may use a backer flashing depending on the design.

5. Install real counterflashing

• This is where many otherwise decent chimney jobs fail.
• Counterflashing should overlap the vertical legs of the base/step flashing and be integrated into the masonry, commonly by installing it into a mortar joint or properly formed reglet.
• The counterflashing forces water running down the brick to discharge onto the underlying flashing rather than behind it.
• Don't depend on surface-applied caulk as the primary waterproofing mechanism.

6. Pay special attention to the four corners

• Corners are common leak points because they require complex folds and can create small openings/pinholes.
• Properly folded corners, mechanically secured seams, and carefully designed overlaps are much more durable than simply filling gaps with sealant.

7. Use compatible metals and good fabrication

• Copper, galvanized steel, galvalume, lead and lead-coated copper are commonly used, depending on the roof and local practice.
• Avoid incompatible combinations that can cause galvanic corrosion; aluminum is generally a poor choice directly against masonry mortar.

8. Use sealant as secondary protection—not the flashing system itself

• A quality sealant can protect the top edge of counterflashing and certain seams.
• But a chimney that is "waterproofed" primarily with roofing cement or caulk is likely to develop problems as the sealant ages.
• The metal should be shaped so gravity and overlapping layers do most of the waterproofing.

A good mental model

Think of the assembly as:

roof underlayment → apron/backer → step flashing → shingles → counterflashing → masonry

Every upper layer should shed water onto the layer below it. There shouldn't be a point where water can run behind the flashing and into the roof assembly.

For a professional installation, I'd also follow the roof-covering manufacturer's flashing details and the locally adopted building code, because dimensions, cricket requirements, ice-barrier requirements, and materials can vary by roof system and jurisdiction. The NRCA's chimney-flashing guidance is a particularly useful benchmark for workmanship.

If you're actually flashing a chimney right now, I can also give you a roofer-oriented step-by-step installation sequence, including how to cut/fold the apron, step flashing, corners, cricket, and counterflashing.

Properly flashing a chimney requires a two-layer system—step flashing and counter flashing —along with critical water-diversion components . Relying on sealant alone is a recipe for failure; a professional installation relies on a mechanical seal integrated with the chimney masonry and roof deck.

Core Techniques for Leak-Proof Chimney Flashing

- Expose the roof decking around the chimney base and install a high-temperature self-adhering ice and water membrane.
- Wrap this membrane 2 to 3 inches up the vertical face of the chimney to create a continuous waterproof sub-layer before any metal touches the deck.[](https://www.youtube.com/watch?v=9jJgV_k4nFs&t=24) [[1]](https://www.youtube.com/watch?v=9jJgV_k4nFs&t=24)

- Use individual L-shaped metal pieces (90° bends) for the sides of the chimney.
- Install one piece of step flashing for every single course of shingles, making sure each piece overlaps the one below it and extends at least 3 to 4 inches out onto the shingle flat and up the chimney wall.
- Fasten each piece to the roof deck with a single nail at the top edge (avoid nailing directly into the brick vertical wall).[](https://www.youtube.com/watch?v=9jJgV_k4nFs&t=24) [[1]](https://www.youtube.com/watch?v=9jJgV_k4nFs&t=24)

- For any chimney wider than 30 inches situated on a moderate-to-steep slope, a roof cricket must be constructed behind it.
- This peaked, triangular diversion structure forces cascading rain and melting snow to part cleanly around the sides of the chimney rather than pooling and stagnating against the back wall.

- Never surface-mount counter flashing with just caulk. Use an angle grinder to cut a horizontal groove (reglet) about 1 inch deep into the mortar joints of the brick𝑐.1.1.2.
- Insert the top edge of the custom-bent counter flashing lip directly into this ground-out mortar joint, securing it with masonry anchors or lead plugs.
- Point up the joint with fresh mortar or high-grade polyurethane sealant to lock the metal mechanically into the brickwork. The counter flashing drops down over the step flashing by at least 3 inches.[](https://www.youtube.com/watch?v=d8aYTKqjwvQ&t=1) [[1]](https://www.youtube.com/watch?v=d8aYTKqjwvQ&t=1)[[2]](https://www.youtube.com/watch?v=9jJgV_k4nFs&t=24)

- At the lowest corner where the roof meets the vertical chimney wall, install a **kickout (diverter) flashing**.
- This forces runoff outward and away from the sidewall/step transition so water doesn't run down behind the siding or pooling at the bottom corner edge.[](https://www.youtube.com/watch?v=C0WqVERJ3QI&t=12) [[1]](https://www.youtube.com/watch?v=C0WqVERJ3QI&t=12)

If you're planning a specific project, let me know:

• What is the chimney's exterior material (brick, stone, or stucco)?
• What roofing material is being used (asphalt shingle, metal, or tile)?

I can tailor these instructions with material-specific nuances or material choices (like copper vs. aluminum).

Proper chimney flashing is less about caulk and more about creating a shingle-style drainage system with independent layers of metal. The most reliable approach is a combination of base/step flashing, a back-pan or cricket where appropriate, and counterflashing.

Best practices

1. Start with a sound chimney and roof deck

• Remove old, deteriorated flashing rather than trying to bury it under new material.
• Inspect the chimney masonry, mortar joints, roof sheathing, and underlayment.
• Repair loose/cracked masonry or deteriorated mortar before flashing. Flashing can't compensate for a structurally defective chimney.

2. Install a proper water-resistant underlayment

• Run compatible leak-barrier/self-adhered membrane around the chimney, following the roofing manufacturer's requirements.
• Don't rely on membrane alone; it is supplemental protection, not a substitute for properly formed metal flashing. GAF's current guidance, for example, calls for leak barrier up the chimney sides in its shingle systems.

3. Use new step flashing at the sides

• Install one piece of corrosion-resistant step flashing for every shingle course.
• Each piece should extend sufficiently up the chimney and onto the roof. As a typical benchmark, GAF specifies at least 5 inches up the chimney and 5 inches over the shingle face, while Owens Corning specifies dimensions based on shingle exposure. Always follow the particular shingle manufacturer's instructions and local code.
• The flashing should be integrated with the shingles so water always flows over the next lower layer—not behind it.

4. Handle the lower/front edge with a properly formed apron/base flashing

• The bottom flashing needs to direct water onto the shingles rather than allowing water to run behind them.
• Form the corners carefully; poorly folded corners are common leak points.
• Avoid depending on surface-applied sealant to make up for bad metalwork.

5. Pay special attention to the chimney's uphill/back side

• This is often the most important part of the installation because water and debris accumulate behind the chimney.
• A back-pan/backer flashing should be properly sized and turned up the chimney and sufficiently up the roof.
• For larger chimneys or steeper roofs, install a cricket to divert water around the chimney. GAF recommends crickets particularly for chimneys wider than 24 inches and on roofs steeper than 6:12; requirements can vary by roofing system and jurisdiction.

6. Install true counterflashing

• The counterflashing is the second half of the chimney flashing system and covers the upper edge of the base/step flashing.
• For masonry chimneys, cut into a mortar joint and insert the counterflashing rather than simply smearing sealant over the joint.
• GAF's installation guidance calls for counterflashing to be embedded or mechanically secured and sealed at the joint.
• Counterflashing should overlap the step flashing by at least 2 inches according to GAF's current field guide.

7. Don't fasten flashing in ways that create unnecessary leak paths

• Keep fasteners out of areas where water will be flowing whenever the manufacturer's system allows.
• Some shingle manufacturers specifically instruct installers not to fasten step flashing to the vertical masonry/wall surface.
• Follow the flashing manufacturer's fastening requirements for the particular metal and assembly.

8. Use sealant as a secondary component—not the primary waterproofing

• A bead of high-quality compatible sealant at the appropriate counterflashing/masonry joint is useful.
• Do not "flash" a chimney by simply caulking around its perimeter. Sealants age; properly lapped metal flashing provides the durable drainage path. GAF specifically warns that relying on caulk instead of a step- and counterflashing system can lead to failures.

9. Use compatible, durable metal

• Galvanized steel, aluminum, copper, or other approved corrosion-resistant materials may be appropriate depending on the roof system and chimney.
• Be careful about dissimilar-metal corrosion, especially when combining copper, galvanized steel, aluminum, or treated materials.

10. Finish by checking the drainage path

• Every lap should shed water downward.
• No exposed horizontal seam should face uphill.
• Corners should be fully closed.
• Shingles should lie flat around the flashing.
• Counterflashing should be tight to the masonry.
• Check that the cricket/back-pan actually diverts water around the chimney rather than creating a pocket behind it.

A good way to think about it

The finished assembly should effectively be:

Roofing → step/base flashing → counterflashing → masonry

with water always encountering the next layer as it travels downhill.

The single biggest mistake is treating chimney flashing as a caulking job. A well-installed system uses formed metal and overlapping layers to shed water; sealant is there to supplement those details, not replace them.

If you're evaluating a roofer's work, I can also give you a 10-point chimney-flashing inspection checklist showing exactly what to look for before paying for the job.

Properly flashing a masonry chimney requires a two-part system—step flashing (base flashing) and counter flashing —along with a strategic layer of waterproofing underneath. Relying on caulk alone is a recipe for failure; true protection comes from gravity-shedding metal overlaps and proper integration with the roof deck.

Core Techniques for Chimney Flashing

1. Install High-Performance Underlayment First
   • Wrap the base of the chimney with a self-adhering ice and water shield.
   • Run the membrane up the vertical walls of the chimney by at least 3 to 4 inches and extend it outward onto the roof deck. Care for the corners carefully by folding and sealing tabs rather than cutting raw holes into the material.
2. Layer Step Flashing (Base Flashing) Interlocked with Shingles
   • Never use one giant piece of metal for the sides. Use individual L-shaped step flashing pieces.
   • Install each individual piece of step flashing over each shingle course, overlapping the previous piece by at least 3 inches.
   • Nail the horizontal flange of the step flashing only to the roof deck , never directly to the chimney brick. The chimney and the house settle at different rates; rigid attachment will tear the metal or warp the seal.
3. Incorporate a "Cricket" on Wider Chimneys
   • If a chimney is wider than 30 inches (measured across the slope of the roof), building a cricket (saddle) behind it is essential.
   • A cricket diverts rainwater and melting snow around the obstruction rather than letting a massive dead pool of water pile up against the uphill face of the chimney, which inevitably overwhelms standard flashing over time.
4. Install a Kickout Flashing at the Lower Corners
   • At the bottom baseline where the sidewall meets the roof slope, install a kickout flashing (diverter).
   • This tiny, crucial bend kicks water outward and away from the sidewall/gutter intersection, preventing water from running down the siding or soaking the corner of the structure.
5. Cut Reglets and Insert Counter Flashing
   • Counter flashing protects the top edge of the step flashing. Do not surface-mount it with just adhesive if you can avoid it.
   • Use an angle grinder to cut a horizontal groove (a reglet ) about 1.5 inches deep into the mortar joints of the chimney, running around the slope.
   • Insert the top edge of the custom-bent counter flashing into the reglet, secure it with lead plugs or masonry anchors, and seal the groove completely with high-grade structural polyurethane or silicone masonry sealant.

Are you working on a brand new installation or repairing an existing leaking chimney ? If you're dealing with a specific leak, tell me where water is showing up inside (e.g., the firebox, the attic line, or drywall around the chase) to narrow down the fix.

A properly flashed chimney is less about caulk and more about creating a layered water-shedding system that lets the roof and masonry move independently. The most reliable installations use base flashing, step flashing, counterflashing, and (when needed) a cricket.

1. Start with a sound chimney and roof deck

Before installing metal:

• Repair cracked mortar joints, deteriorated brick, or loose chimney caps.
• Replace rotted roof sheathing around the penetration.
• Remove old failed flashing rather than covering it with new metal.
• Use a compatible high-quality underlayment or self-adhered membrane around the chimney corners and uphill side.

2. Install the base flashing system correctly

A good chimney flashing assembly has several parts:

• Apron flashing (downslope side): A continuous piece of metal that runs across the bottom of the chimney and turns up the face.
• Step flashing (sides): Individual L-shaped pieces installed one per shingle course, woven into the shingles as the roof is installed. Each piece should shed water onto the shingle below.

Best practices:

• Use properly sized step flashing (many professionals prefer larger pieces for better coverage).
• Keep fasteners out of areas where water can enter. Fasten only where the next layer covers the penetration.
• Do not rely on exposed screws and caulk as the primary waterproofing method.

3. Install counterflashing into the chimney

This is one of the biggest differences between a temporary repair and a durable installation.

Proper counterflashing:

• Is cut into a mortar joint or reglet in the chimney.
• Is embedded mechanically into the masonry.
• Overlaps the step flashing below.
• Allows the chimney and roof to move independently.

Avoid simply fastening a metal strip to the chimney face and smearing the top edge with caulk; that commonly fails as the masonry and roof move at different rates.

4. Build a cricket on the uphill side when needed

A chimney sitting below the roof ridge can trap water, leaves, and snow on its uphill side. A properly framed and flashed cricket diverts water around the chimney instead of letting it pond against the masonry.

A good cricket:

• Has proper slope.
• Is covered with compatible underlayment.
• Has metal flashing integrated with the roof system.
• Directs runoff away from the chimney corners.

5. Pay attention to corners

The front corners and uphill corners are common leak points.

Good techniques:

• Fold or solder metal transitions rather than leaving open cuts.
• Overlap pieces in the direction water flows.
• Use compatible sealants only as secondary protection, not as the main waterproofing layer.

6. Choose appropriate flashing materials

Common choices include:

• Copper (long life, easy to form and solder)
• Lead-coated copper
• Galvanized steel
• Stainless steel in harsh environments

Avoid mixing incompatible metals that can cause corrosion, and be cautious with aluminum against masonry.

7. Final inspection points

Before leaving the job, verify:

• Water has a clear path around the chimney.
• Counterflashing is tight and mechanically secured.
• No exposed fasteners are in drainage paths.
• Step flashing is woven correctly with shingles.
• Corners are sealed and folded properly.
• A hose test (performed carefully from low to high areas) does not reveal leaks.

The key principle: the metal should shed water by design; sealants should only reinforce the assembly, not substitute for proper flashing geometry.

Properly flashing a chimney requires a two-part metal system (base/step flashing and counter-flashing) working alongside a solid waterproof underlayment . The golden rule of roofing applies here: always work from the bottom up so that every overlapping layer sheds water like an umbrella.

Essential Techniques for a Leak-Proof Chimney

1. Install Ice and Water Shield First
   • Before any metal touches the deck, wrap the chimney base with a high-temperature self-adhering ice and water barrier. Run it at least 6 to 12 inches up the vertical brick faces and out onto the roof deck. This acts as a critical secondary moisture defense.
2. Build a Cricket (Saddle) on the Upslope Side
   • If a chimney is wider than roughly 30 inches, a cricket is mandatory. This small, peaked triangular structure built on the high side of the chimney prevents rain and snowmelt from pooling behind the masonry, forcing water to safely divert around the sides. Cover the entire cricket with the self-adhering membrane before shingling.
3. Install the Front Apron and Interweave Step Flashing
   • Front Apron: Place a continuous piece of base flashing at the lower downhill side of the chimney, extending it up the front face and out over the underlying shingle course.
   • Step Flashing: Along the sides, use individual L-shaped metal pieces (aluminum, copper, or galvanized steel). Interweave one piece of step flashing with each consecutive course of shingles, overlapping each piece by at least 2 inches. Nail the top flange of the step flashing to the roof deck, never directly into the vertical brick.
4. Cut a Reglet and Embed Counter-Flashing
   • Avoid relying solely on surface-mounted metal and caulking against the brick, as sealants eventually dry out, crack, and fail under thermal expansion.
   • Use an angle grinder to cut a horizontal groove (a kerf or reglet) roughly 1 to 2 inches deep into the mortar joints above the top edge of the step flashing.
   • Insert the top edge of the custom-bent counter-flashing into the cut, secure it with masonry anchors or lead wedges, and re-point the joint with fresh mortar or high-grade polyurethane concrete sealant to mechanically lock and waterproof the top edge. The counter-flashing must drop down to overlap the step flashing by at least 3 inches.

Community Perspectives

“A long gone roofer I knew summed up the procedure bottom(s) up! Like the shingles get laid, always flash bottom up. He also hated anything that didn't act like an umbrella. Designers seem to enjoy cutting holes in theirs.”

“For chimneys, always grind and embed the metal into the mortar joints. Surface-mounted flashing that relies only on caulk will eventually dry out and leak. Getting these specific details right is exactly what separates a roof that lasts decades from one...”

Are you currently planning a brand new installation , tracking down a persistent leak on an existing chimney , or working with an unusual roof/masonry material (like tile or natural stone)? Tell me more so I can tailor the advice.

Proper chimney flashing is less about piling on sealant and more about creating a layered drainage system that sheds water even after sealants age or masonry moves.

The best-practice approach

1. Inspect the chimney and roof first

   • Replace damaged/rotted roof decking before flashing.
   • Check mortar joints, cracked bricks, chimney crown, and existing flashing.
   • Remove old flashing rather than simply covering it.
   • Make sure the chimney is structurally sound and the masonry joints are suitable for receiving counterflashing.

2. Use a multi-piece flashing system

   A durable chimney detail generally consists of:

   • Base/apron flashing at the downslope face.
   • Step flashing along both sides, interwoven with each shingle course.
   • Back-pan/cricket flashing at the upslope side.
   • Counterflashing over the base and step flashing.

   Building Science describes this as the basic transition between the roof's water-control layer and the chimney, with step flashing integrated into the shingles and counterflashing overlapping the underlying flashing. bsesc.energy.govwww.nrca.net

3. Install step flashing one course at a time

   Don't use one long piece of flashing simply caulked to the chimney. Individual step-flashing pieces should be integrated with each shingle course so water always flows over the next layer rather than behind it. NRCA specifically identifies individual pieces at each shingle course as the standard step-flashing approach.

4. Make the upslope side the priority

   Water tends to accumulate and get driven against the chimney on the high side. A properly constructed back pan or cricket should collect that water and divert it around the chimney.

   In Florida, this is particularly important. The 2023 Florida Residential Code requires a cricket when the chimney is more than 30 inches wide parallel to the ridge and doesn't intersect the ridge.

5. Use proper counterflashing

   This is where many otherwise good chimney jobs fail. Counterflashing should be mechanically integrated with the masonry rather than relying on a bead of caulk at the chimney/metal interface.

   For masonry, a common high-quality detail is to cut a reglet into a mortar joint, insert the counterflashing, mechanically secure it, and seal the joint appropriately. IIBEC recommends a reglet roughly 1 inch minimum, with 1½ inches preferred, and describes bending the flashing to create a capillary break and a hemmed drip edge.

6. Don't rely on a shallow saw cut

   This is an important professional distinction. Simply cutting a shallow slot into the face of a brick and stuffing metal into it can look like proper counterflashing without actually connecting to the masonry's drainage plane. NRCA and Building Science both caution that conventional saw-cut counterflashing can be inadequate where water can penetrate behind the outer masonry.

   Where the chimney is being rebuilt, through-wall flashing integrated into the masonry is the more robust solution.

7. Keep dissimilar metals compatible

   Use flashing compatible with the roofing and masonry materials. Avoid creating galvanic corrosion by putting incompatible metals directly together. For a high-quality job, the roofer should follow the flashing manufacturer's compatibility requirements.

8. Use sealant as secondary protection—not the primary waterproofing

   Sealant should seal joints, reglets, laps, and appropriate transitions, but the geometry of the flashing should shed water without depending on caulk. Florida's roofing standard, for example, specifies properly detailed counterflashing joints and sealant rather than treating sealant as the entire flashing system.

A detail I'd consider a "red flag"

If a roofer says, "We'll put some flashing around it and seal the edges with roofing cement," I'd want considerably more detail before approving the work.

A good chimney-flashing job should have a clear answer for where water entering at the top of the chimney intersection goes, how it gets around the sides, and how the counterflashing remains effective after sealant eventually deteriorates.

For a reroof, I'd specifically ask the roofer to show you their planned side step-flashing, upslope cricket/back-pan, apron flashing, and masonry counterflashing/reglet details before the shingles go down.

To properly flash a chimney and guarantee a leak-free seal, a roofer must use a two-part flashing system layered from the bottom up . This method ensures that the roof and the chimney chimney can move independently without tearing the metal, while forcing water to shed like an umbrella over the shingles. Relying solely on caulk, roofing cement, or single-layered metal will eventually lead to failure.

The industry-best techniques and installation sequences are outlined below.

1. Preparation and Deck-Level Waterproofing

Never install metal flashing directly over bare wood or standard felt paper.

• Strip to the Deck: Remove all old flashing, shingles, and rotted wood to create a clean, nailable surface.
• Apply Ice & Water Shield: Install a self-adhering, rubberized membrane around the perimeter. Bring it at least 6 inches up the chimney walls and 12 inches out onto the roof deck. This acts as a secondary waterproof barrier if water ever gets past the metal.

2. The Bottom-Up Installation Sequence

Flashing must be integrated with the shingles row-by-row, starting from the lowest down-slope point.

[ Chimney Brick ]
              || 
       +------|| <--- Counter-flashing (Cut into Reglet)

       |      ||
  +----|--+   || <--- Step Flashing (Weaved with Shingles)

  | Shingle | ||
================= <--- Roof Deck & Ice/Water Shield

• Install the Apron (Base) Flashing: Place a single wide piece of metal at the bottom base of the chimney. It sits on top of the shingles on the downslope side and extends up the chimney face. Secure it with clips or nails high enough up so you are not piercing the lower roof deck.
• Weave Step Flashing on the Sides: As shingles are laid up the sides, place an L-shaped piece of step flashing with every single course of shingles.
  • Each step piece must overlap the lower one by at least 2 to 3 inches.
  • Nail the flashing only to the roof deck, never to the masonry. If nailed to both, structural settling or thermal expansion will tear the metal apart.
• Install a Cricket (Saddle) on the High Side: If the chimney is wider than 30 inches, code requires building a small peaked roof structure (a cricket) on the upslope side. This prevents water and snow from pooling behind the chimney and diverts it around the sides.

3. Proper Counter-Flashing (The Reglet Cut)

Counter-flashing covers the top of the step flashing to prevent water from running down the brick face.

• The Right Way (Reglet/Mortar-Cut): Use a diamond-blade grinder to cut a 1 to 1.5-inch deep groove (a reglet) directly into the mortar joints or brick. Bend the top edge of the counter-flashing metal at a 90-degree angle and insert it firmly into this groove.
• The Wrong Way (Surface Mounting): Never simply surface-mount metal against the brick and seal the top edge with caulk. As the house expands and contracts, the caulk will pull away from the brick within a few seasons, creating an active leak path.
• Lock and Seal: Fasten the metal inside the reglet using lead wedges, then fill the remaining groove completely with high-grade, UV-resistant polyurethane or silicone masonry sealant.

4. Critical Water-Diverting Details

• Incorporate Kick-out Flashing: At the very bottom corners where the chimney meets the roof edge, bend the final piece of flashing outward to form a "kick-out". This aggressively forces streaming water away from the wall siding and onto the open roof or into the gutter.
• Hem the Edges: For premium performance, fold the bottom 1/2 inch of the counter-flashing under itself 180 degrees to form a hem. This strengthens the metal edge, keeps it straight, and stops wind from blowing water up under it.

If you are currently evaluating a specific chimney layout, tell me:

• What roofing material are you using (e.g., architectural shingles, metal, slate)?
• Is the chimney made of brick/masonry or is it wood-framed with siding?
• Is the roof steep or low-slope?

I can provide custom tail-end bending dimensions or specific material pairing recommendations (like copper vs. aluminum) based on your project.

Flashing a chimney correctly requires a multi-layered, water-shedding system of metal step flashing and counter flashing. Here are the essential techniques and sequential steps to ensure a watertight seal:

1. Clean and Prepare the Surface

• Remove old material : Tear away all old flashing, mortar, and roofing felt around the chimney base down to the bare roof deck and masonry.
• Inspect the masonry : Check for cracks or loose bricks and repoint the mortar joints if necessary before installing any metal.

1. Install the Ice and Water Shield (Underlayment)

• Wrap the base : Apply a self-adhering polymer modified bitumen membrane (ice and water shield) extending at least 6 inches up the chimney wall and 12 inches out onto the roof deck.
• Seamless corners : Ensure corners are folded and sealed without cutting shortcuts that could let water track underneath.

1. Layer the Step Flashing (Step-by-Step)

• Cut individual pieces : Use L-shaped individual step flashing pieces rather than one continuous long piece. Each piece should be roughly 5 inches by 7 inches with a 90-degree bend.
• Integrate with shingles : As each course of shingles is installed up the side of the chimney, place a piece of step flashing over the shingle and nail it to the roof deck (never nail it directly into the vertical brick wall).
• Overlap correctly : Each upper step flashing piece must overlap the one below it by at least 3 inches.

1. Install the Front Apron Flashing

• At the low side (downslope) : Install a continuous apron piece at the bottom (downslope side) of the chimney over the underlayment and underlying shingles, extending up the face of the chimney and overlapping the bottom row of shingles.

1. Install the Cricket (for wide chimneys)

• Divert water : If the chimney is wider than 30 inches, build a framed and metal-clad cricket (saddle) on the upslope side to actively divert water and snow around the obstruction rather than letting it pool behind the flat brick wall.

1. Cut Reglet and Install Counter Flashing

• Grind a reglet : Use a masonry grinder to cut a horizontal groove (reglet) about 1 4 one-fourth 1 4 to 1 2 i n c h deep into the mortar joints, roughly 1 to 2 inches above the top edge of the step flashing.
• Insert counter flashing : Insert the top edge of the metal counter flashing into the regletted groove and bend it down to overlap the step flashing by at least 3 inches.
• Seal the joint : Fill the reglet groove with high-grade polyurethane or silicone masonry sealant to lock out driving rain.

If you'd like, I can also share:

• Common mistakes roofers make that cause premature leaks around chimneys
• The best choice of metals (copper vs. aluminum vs. galvanized steel) for longevity

Let me know how you want to proceed.

The most reliable chimney flashing is a layered drainage system, not a bead of caulk. For a roofer working on a typical asphalt-shingle roof, the key techniques are:

1. Start with the underlayment

   • Remove enough roofing to inspect the deck and existing flashing.
   • Run the roof underlayment correctly into the chimney intersection.
   • In cold climates, use an appropriate self-adhered ice/water membrane around the chimney, integrated with the roof's water-control layer.

2. Use individual step flashing on the sides

   • Install a separate L-shaped piece with each shingle course rather than trying to make one long piece of flashing.
   • Each piece should be layered so water always flows over the flashing and onto the shingle below.
   • The step flashing should generally be substantial enough to provide adequate coverage above the roof and up the chimney; dimensions need to be appropriate to the roofing system and local requirements.

3. Install proper base/apron flashing at the bottom

   • The downslope side needs an apron/base flashing that carries water away from the chimney and onto the shingles.
   • Don't depend on sealant to make the bottom transition watertight; the metal should be shaped to drain water mechanically.

4. Build a proper head flashing at the uphill side

   • The upslope portion is particularly important because water accumulates against the chimney.
   • Ideally, install a cricket/saddle behind the chimney to split and divert water around it. NRCA recommends a cricket for chimneys 24 inches or wider.
   • The cricket needs its own properly integrated flashing and counterflashing.

5. Counterflash the masonry

   • This is one of the biggest differences between a good chimney flashing job and a temporary repair.
   • The counterflashing should cover the upper edge of the base/step flashing and be mechanically integrated into the chimney, typically by cutting into a mortar joint/reglet rather than simply fastening it to the face of the brick.
   • Seal the reglet appropriately, but don't make caulk the primary waterproofing mechanism.

6. Pay special attention to the four corners

   • Chimney corners are difficult because several planes of sheet metal intersect there.
   • Carefully formed corners, folded/hemmed edges, and designs that direct water away from corner joints can substantially reduce dependence on sealant. A newer "winged" flashing approach specifically addresses these vulnerable three-plane corners.

7. Don't rely on exposed caulk

   • Sealant is useful as secondary protection, particularly at joints and reglets.
   • It shouldn't be the thing keeping the chimney from leaking. Proper overlaps, bends, mechanical attachment, and drainage should do that job.

8. Respect metal compatibility

   • Choose flashing material appropriate for the roof, chimney masonry, fasteners, and environment. Common professional materials include galvanized steel, stainless steel, copper, and lead.
   • Avoid creating galvanic-corrosion problems by combining incompatible metals.

The basic water-shedding sequence

Think of the assembly as:

roof deck → membrane/underlayment → base flashing → step flashing integrated with shingles → counterflashing integrated with masonry

Every upper layer should shed water onto, rather than behind, the layer below. The U.S. Department of Energy's Building America guidance describes the same basic three-part system—base, step, and counterflashing—with the elements layered to drain incident rainwater.

Biggest red flags: one-piece flashing simply caulked to the chimney, step flashing missing between shingle courses, counterflashing screwed to the brick face without a proper masonry joint/reglet, no cricket behind a wide chimney, exposed fasteners in drainage paths, and relying on roofing cement as the primary waterproofing.

If you're evaluating a roofer's work, the counterflashing and the uphill cricket/head-flashing detail are probably the two areas I'd inspect most carefully.