A chimney punches a big, square hole through your roof. Water flows around it from every direction. In a climate where it rains for six months straight, that hole becomes the most common source of roof leaks we see across the Fraser Valley.

We are Kory and Johnny Peters, and between the two of us we have re-flashed, repaired, or rebuilt chimney flashing on hundreds of homes from Hope to Abbotsford. Before roofing, we worked as Red Seal Boilermakers in the oil sands, fabricating metal systems that had to be watertight under pressure. Chimney flashing is the same discipline applied to your roof: cut it right, bend it right, seal it right, and water stays out for decades.

This guide covers what we do and why we do it. If you are a handy homeowner, it will help you understand the process. If you decide the job is beyond your comfort level, we are a phone call away.

Why the Fraser Valley Destroys Chimney Flashing

The Fraser Valley receives 1,500 to 2,000 millimetres of rain per year. Homes in Agassiz, Harrison, and Hope sit in the wettest pockets. Fog rolls off the river and condenses on metal surfaces. Morning dew forms even when it has not rained overnight. That constant moisture creates conditions that eat through flashing systems designed for drier parts of the country.

Here is what we see repeatedly on Fraser Valley roofs:

• Moss growth on the north side of chimneys. Moss holds moisture against the flashing for months, accelerating corrosion and lifting sealant.
• Mortar deterioration in older chimneys. Many homes in Chilliwack, Rosedale, and Agassiz have chimneys built in the 1960s-1980s with mortar that has softened from decades of rain. Counter flashing cannot hold in crumbling mortar.
• Galvanic corrosion from mismatched metals. When a previous roofer used aluminum flashing against a steel chimney cap, the two metals corrode each other. We see this constantly on re-roof jobs.
• Caulk-only "repairs." The number one failure mode. Someone ran a bead of caulk where counter flashing should be. It holds for a year or two. Then the rain wins.
• No cricket on the upslope side. Leaves, needles, and moss accumulate against the chimney back. Water pools. The flashing eventually gives.

The Anatomy of Proper Chimney Flashing

There are four distinct components, and every one of them must be correct. Miss one and the system fails.

1. Ice and Water Shield (The Failsafe)

Before any metal goes on, we apply self-adhering ice and water shield membrane to the deck around the chimney. It extends 12 inches out on all sides and 6 to 8 inches up the chimney face. In BC, this is not an optional extra. If any metal flashing ever lifts or corrodes, this membrane is the last line of defence keeping water out of your house.

2. Base Flashing (The Apron)

A single piece of metal covers the downslope face of the chimney. It bends 90 degrees — flat on the deck, then up the chimney face 4 to 6 inches. It extends 6 inches past each side of the chimney. Water flowing down the roof rides over this piece and keeps moving.

3. Step Flashing (The Shingle-by-Shingle Seal)

Individual L-shaped metal pieces, typically 8 by 10 inches, installed along each side of the chimney. One piece per shingle course. Each piece overlaps the one below by 3 inches. The genius of step flashing is that water hitting any point on the chimney side flows over one piece, onto the shingle below, over the next piece, and so on — all the way to the gutter.

The critical rule: step flashing gets nailed to the roof deck, never to the chimney. The chimney and roof move independently — thermal expansion, settling, wind loading. Nail flashing to both and the metal tears.

4. Counter Flashing (The Mortar-Embedded Cap)

Counter flashing is the piece that makes the whole system work. It is an L-shaped metal strip with the top leg cut into the chimney's mortar joint (1.5 inches deep) and the bottom leg hanging over the step flashing by at least 3 inches. Water running down the chimney face hits the counter flashing and drips onto the step flashing below. Without counter flashing, water runs behind the step flashing and into the house.

5. The Cricket (The Water Diverter)

On the upslope side of the chimney, a peaked structure called a cricket diverts water around the chimney instead of letting it pool against the back wall. BC building code requires a cricket for chimneys wider than 30 inches. In the Fraser Valley, we install one on nearly every chimney regardless of size, because the volume of rain and debris accumulation makes it worth the investment every time.

How We Flash a Chimney: Step by Step

Step 1 — Strip and Inspect

We remove shingles 12 inches out from every face of the chimney. Old step flashing, base flashing, and counter flashing come out. We chisel old mortar from the counter flashing joints and wire-brush the chimney clean.

Then we inspect. Older Fraser Valley chimneys often have problems that are hidden under the old flashing: cracked bricks, soft mortar, efflorescence staining. If the mortar is too far gone to hold new counter flashing, we repoint the joints before proceeding. Skipping this step means the new counter flashing pulls out within a few years.

Step 2 — Ice and Water Shield

We apply membrane to the deck 12 inches beyond the chimney on all sides, running it 6 to 8 inches up the chimney face. Seams overlap 6 inches. Every edge gets pressed flat. In BC, this backup layer is non-negotiable.

Step 3 — Base Flashing

We measure the chimney width, cut the base flashing to extend 6 inches past each side, and bend a clean 90-degree angle on our metal brake. The flashing sits against the chimney face 4 to 6 inches up. We nail along the bottom edge (covered by shingles later) and seal the chimney joint with roofing cement.

Step 4 — Step Flashing

Starting at the bottom corner on each side, the first piece overlaps the base flashing by 3 inches. Each subsequent piece overlaps the one below by 3 inches. We nail each piece to the deck with two nails placed high so the next shingle covers them. We never nail to the chimney.

We install the corresponding shingle course over each step flashing piece as we go. The pattern is: shingle, step flashing on top, next shingle on top of that. Water rides over each layer cleanly.

Step 5 — Build the Cricket

On the upslope side, we frame a peaked diverter from 2x4s. The ridge height is one-third of the chimney width. We sheathe it with plywood, cover it in ice and water shield, then install sheet-metal cricket flashing that extends 6 inches up the chimney and 12 inches onto the roof deck. Step flashing runs along the cricket sides using the same technique as the chimney sides.

In our experience, the cricket is what separates a flashing job that lasts 5 years from one that lasts 30. In the Fraser Valley, the amount of needles, leaves, and moss that collects behind a chimney without a cricket is remarkable. That debris holds water. Water finds a way in.

Step 6 — Counter Flashing

This is the step that requires masonry skill, and it is where most DIY and low-quality professional jobs fail.

We mark horizontal mortar joints 4 to 6 inches above the step flashing. Using an angle grinder with a masonry blade, we cut each joint 1.5 inches deep across the full width of the chimney side. We clean the joints with a wire brush and compressed air.

We fabricate L-shaped counter flashing pieces with a 1.5-inch top leg and a 4 to 5-inch bottom leg. The top leg slides into the cut joint. The bottom leg overlaps the step flashing by 3 inches minimum. Where counter flashing pieces meet, they overlap each other by 2 inches.

We pack Type N mortar tightly into the joint around the embedded flashing, then tool it smooth to match the existing mortar profile. After curing, this counter flashing is locked in place for decades.

Step 7 — Shingle and Test

We reinstall shingles around the chimney, maintaining proper overlap over the step flashing. Cut shingle edges get sealed with roofing cement to prevent water wicking.

Then we water test. We run a hose over the chimney for 15 to 20 minutes while someone checks the interior. In the Fraser Valley, we sometimes get the luxury of the next rainstorm arriving within hours to provide a real-world test.

Fraser Valley-Specific Considerations

Mistakes We See on Fraser Valley Re-Flash Jobs

After 500+ roofs across the valley, these are the chimney flashing failures we encounter most often:

Caulk instead of counter flashing. This is the single most common failure. A previous roofer ran a thick bead of caulk where counter flashing should be embedded in mortar. In BC's UV-and-rain cycle, that caulk fails in 2 to 4 years. We have lost count of how many of these we have re-done.

Step flashing nailed to the chimney. The roof and chimney are two separate structures that move independently — thermal expansion, wind loading, settling. When flashing is nailed to both, the metal tears and water gets in. We see this on roughly one in three re-flash jobs.

No ice and water shield underneath. Some roofers skip the membrane to save time. In the Fraser Valley, that is gambling with your interior. The membrane is your backup when the 40-year-old chimney mortar finally lets a drip through.

Mixing metals. Aluminum flashing against a steel chimney cap, or galvanized flashing touching copper pipes. Galvanic corrosion eats through the weaker metal in a few years. We see this surprisingly often on homes that had different contractors touch the chimney and the roof.

Counter flashing cut too shallow. The mortar joint needs to be cut 1.5 inches deep. We have pulled counter flashing out of joints that were cut half an inch deep — barely enough to hold the metal in place, let alone seal it against driving rain.

When to Call a Professional

Chimney flashing is arguably the most demanding single task in residential roofing. It requires both roofing expertise and masonry skill. If any of the following apply, we strongly recommend professional installation:

• Your chimney mortar is soft, crumbling, or missing in spots
• The chimney has structural cracks in the bricks
• Your roof pitch is 6:12 or steeper (difficult to work safely near a chimney)
• You do not own or have experience with an angle grinder
• Your chimney is wider than 30 inches and needs a cricket
• Previous flashing repairs have failed repeatedly

At Dads Roofing, chimney flashing is work we take seriously. Kory and Johnny bring boilermaker-grade metal fabrication to every chimney we touch. We cut counter flashing joints to proper depth, we embed metal in fresh mortar, and we build crickets that actually divert water. We have flashed chimneys on homes from Hope to Abbotsford, from brand-new builds to century-old farmhouses. We warranty our work because we trust our methods.

Frequently Asked Questions

Chimney leaking? Flashing pulling away from the mortar? Call (778) 539-6917 — Kory and Johnny will get it sorted.