Chimney Flashing Parts Explained: Apron, Step, Counter, Back Pan and Cricket
Five components, one overlap rule. Learn what each piece does and in which order they go on.
- Intermediate
- Reading guide, 15 minutes
- Updated
The short answer
Chimney flashing has four metal parts over a self-adhered membrane. The apron covers the downslope face and laps over the shingles. Step flashing runs up each side, woven into the shingle courses. The back pan or cricket on the upslope side divides water around the chimney. Counter flashing is set into the masonry and laps over the others from above. Every layer laps over the one below so water always sheds outward.
A chimney blocks the path of water running down the roof. Water hits the upslope face and has to go around, and it runs down the sides and pools against the downslope face. Every one of those four faces needs its own flashing, and the pieces have to overlap like the scales of a fish so the water never finds a seam facing upward.
Most chimney leaks come from a missing part, a part lapped backwards, or a part that was replaced with sealant. Knowing what each piece does makes the whole assembly easy to read, whether you are building it or looking at an old one. Each part has its own guide, linked below, and the older chimney flashing overview gives the big picture.
Tools
- Tape measure
- Tin snips (straight cut)
- Hand seamer
- Sheet metal brake
- Angle grinder with a diamond blade, for reglets
Materials
- Galvanized, prefinished steel or copper sheet
- Ice and water shield
- Roofing nails, 1-1/4 inch
- Polyurethane or hybrid polymer sealant, for masonry joints only
Safety first
- Chimneys are usually at or near the ridge, the highest and steepest spot on the roof. Work tied off. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury.
- Grinding mortar joints makes silica dust. Use a shrouded grinder with a vacuum and a respirator rated for fine dust.
- Masonry can be loose at the top. Do not lean on a chimney or use it as a handhold.
Step by Step
Step 1: Know the apron (base) flashing on the downslope face
The apron sits on top of the shingles in front of the chimney. Its lower edge laps over the shingles by at least 4 inches, and its wall leg turns up the masonry by 4 to 6 inches. The ends extend past the chimney corners so the side step flashing can lap onto them. It is installed first, because everything above it laps over it. See how to install chimney apron flashing.
Step 2: Know the step flashing on each side
Each piece sits on a shingle, takes one nail in the roof leg and is covered by the next course. Its wall leg turns up the masonry at least 4 inches. The first piece laps over the side of the apron. The result is that water running down the side of the chimney lands on a piece of metal and is handed out onto the shingle, course by course. See how to step flash a chimney.
Step 3: Know the back pan or cricket on the upslope face
A back pan is a small sloped metal saddle that runs across the upslope face, turns up the masonry, and sheds water out to each side. It suits narrow chimneys. A cricket, also called a saddle, is a small peaked roof framed behind the chimney. The BC Building Code requires a cricket (chimney saddle) where the upslope side of the chimney is more than 750 mm, about 30 inches, wide, unless taller flashing is used as the code allows. See how to install a chimney back pan and how to build a chimney cricket.
Step 4: Know the counter flashing set into the masonry
It is cut into a mortar joint, called a reglet, at least 1 inch deep, or surface mounted on a siding-clad chimney. It covers the wall legs of the apron, step flashing and back pan by at least 4 inches. It is separate from the base flashing so the chimney and roof can move independently and so the roof can be replaced without rebuilding the masonry joint. See how to install chimney counter flashing and how to cut a reglet.
Step 5: Follow the overlap order
Water flows downhill, so every upper piece must lie over the one below it. The apron goes on the shingles first. The step flashing laps over the apron ends. The back pan or cricket metal laps over the top step flashing pieces. The counter flashing caps everything from above. Each joint is a lap, not a seam, and sealant is used only as a backup.
Read an old chimney the same way: start at the bottom and look for any piece that faces the wrong way.
Step 6: Check the membrane under the flashing
Self-adhered membrane goes down first, lapping up the chimney face about 4 inches and out onto the deck about 12 inches all round. The metal flashing then goes over it, and the field underlayment laps over the membrane on the deck. If the flashing leaks, the membrane is what stops the water reaching the deck. See how to install ice and water shield.
Base Flashing vs Counter Flashing
Base flashing is the lower layer: the apron, step pieces and back pan that sit on the roof and turn up the chimney. Counter flashing is the upper layer that covers the top of the base flashing. The two-layer split lets the roof and chimney move apart slightly without tearing the flashing, because the counter flashing slides over the base flashing rather than being fixed to it.
Where Each Part Fails
- Apron: lifted at the corners, nail holes in the wall leg, or sealed shut where it should be lapped.
- Step flashing: reused and rusted, too short for the shingle exposure, or nailed through the wall leg.
- Back pan or cricket: missing entirely on a wide chimney, or built too flat so water and snow pool.
- Counter flashing: loose in the reglet, sealant failed, or mortar crumbled behind it.
- Membrane: not turned up the masonry, or punctured by nails.
Common Mistakes
- Replacing lapped metal with caulking. Sealant cracks and pulls away within a few seasons. The lap does the work.
- No counter flashing. A single piece of metal stuck to the masonry with sealant is not a flashing.
- Lapping pieces backwards. A lower piece over a higher one makes a channel into the roof.
- Skipping the cricket or back pan. Water and snow dam up behind the chimney and find every gap.
- Nailing the wall legs. Nails through the turned-up leg into the masonry or framing tear when the roof and chimney move apart.
- Blaming flashing for a cracked crown. Water from the top of the chimney looks like a flashing leak from inside.
When to Call a Professional
Chimney flashing involves cutting masonry, working at the ridge and building interlocking metal. It is among the highest-risk flashing details on a roof. If any part of a chimney flashing is missing, the roof is steep, or the chimney is tall, have a roofer do it.
If you are not sure whether the leak is from the flashing or the masonry, a roofer can test each part in turn. See how to diagnose and fix a leaking chimney.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
Chimney Flashing Parts Explained: Questions
What are the parts of chimney flashing?
Chimney flashing has an apron on the downslope face, step flashing up each side, a back pan or cricket on the upslope face, and counter flashing set into the masonry over the top of the others. Self-adhered membrane goes underneath all the metal. Each piece laps over the one below it so water is always carried out onto the roof.
What is the difference between base flashing and counter flashing?
Base flashing is the lower layer on the roof, made up of the apron, step flashing and back pan that turn up the chimney. Counter flashing is a separate upper layer, set into the masonry, that laps over the top of the base flashing. The two layers let the chimney and roof move slightly without tearing the flashing.
What is a chimney saddle or cricket?
A cricket, also called a saddle, is a small peaked roof built on the upslope side of a chimney. It splits the water running down the roof so it flows around the chimney instead of ponding behind it. The BC Building Code requires one where the upslope side of the chimney is more than 750 mm (about 30 inches) wide. Narrower chimneys use a simpler back pan.
What is chimney apron flashing?
Apron flashing is a single piece of metal on the downslope face of the chimney. Its lower edge laps over the shingles, and it turns up the masonry by several inches. It extends past the corners so the step flashing on the sides can lap onto it. It is installed first, because every other piece laps over it.
Related Guides
All Chimneys guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
Want someone to look at your roof?
Kory & Johnny have roofed homes across the Fraser Valley since 2016. Free inspections, honest estimates, no pressure.
604-728-0146Text UsEmailServing Hope, Agassiz, Chilliwack, Rosedale, Abbotsford & the entire Fraser Valley