Metal roof chimney flashing has to float with the panels, seal to the panel profile instead of being nailed through it, and be made from a metal that will not corrode the roof, because a 100 ft steel panel grows about 0.78 inch over a 100 °F temperature swing and an aluminum one about 1.56 inches, per Metal Sales. Get those three things right (movement, attachment and metal pairing), add a cricket where IRC R1003.20 requires one, and the joint can stay dry for the life of the roof.
By The Roofing Brief Team. Last reviewed: October 2026.
Metal roof chimney flashing decision table
| If your chimney or roof is… | Then | Threshold or rule | Source |
|---|---|---|---|
| A masonry chimney wider than 30 in parallel to the ridge, not at the ridgeline | Build a cricket | Required; height per Table R1003.20 (for example 1/4 of width at 6:12) | IRC R1003.20 |
| On standing seam panels | Use a curb or seam-attached flashing | No fasteners through the panel field | Panel maker details |
| On exposed-fastener or corrugated panels | Lap trim over the panel, fasten at the ribs | Butyl tape plus inside and outside closures | Panel maker details |
| A round Class A pipe, 3 to 6.25 in outside diameter | Use a metal-roof pipe boot | Dektite DF104, roof pitch 0 to 40 degrees | Dektite |
| A Galvalume roof under copper flashing, pipe or gutter | Change the copper or isolate the runoff | Copper runoff corrodes Galvalume | MCA technical bulletin |
| Being sealed on Galvalume | Use butyl or neutral cure silicone | No acetic-cure (vinegar smell) or amine sealants | Cleveland-Cliffs GALVALUME data |
How is chimney flashing on a metal roof different from a shingle roof?
On a shingle roof, step flashing tucks under each course and gets nailed to the deck; HomeGuide describes it as L-shaped pieces that alternate with the shingles. Those nails should match the flashing metal, as our guide to nails for flashing explains. On a metal roof there are no courses to weave into and you cannot fasten flashing through the field of a panel without creating a leak and locking the panel in place. Instead, flashing seals to the panel profile (a standing seam, an exposed-fastener rib, or a corrugation) with butyl tape, closures, and a counter flashing that floats over the base so the panel can expand and contract underneath.
The result is that metal-roof chimney flashing is usually custom formed or ordered as a pre-made curb or kit, and it lives or dies on details that have nothing to do with a shingle install: sealant chemistry, panel attachment and dissimilar-metal contact. GALVALUME producer Cleveland-Cliffs specifies neutral cure silicone, butyl or styrene butadiene rubber sealants on GALVALUME and rules out sealants containing acetic acid or amines.
The four parts of a chimney flashing system
Every chimney flashing job, metal roof or not, is built from four parts installed in a set order so water always laps onto a lower piece, never behind it. On a metal roof each part is formed from coil stock matched to the roof or ordered as a manufacturer kit, such as the 3 ft Pro-Rib chimney flashing kit sold at Menards with inside and outside closure strips.
| Part | Location | Job | Metal-roof note |
|---|---|---|---|
| Apron (base) flashing | Downslope face of chimney | Sheds water onto the panels below | Sits on top of the panel, sealed with butyl tape at the rib |
| Step or side flashing | Both sides, running up the slope | Carries water down past the sidewalls | Formed as a continuous pan or soldered/lapped pieces, not woven shingle-style |
| Back pan or cricket | Upslope side | Splits water around the chimney | A back pan for narrow chimneys, a peaked cricket for wide ones |
| Counter (cap) flashing | Set into the masonry | Covers the top edge of the base flashing | Floats over the base so the panel can move; embedded in a cut reglet, not surface-caulked |
The counter flashing is the part most DIY jobs get wrong. HomeGuide’s chimney flashing guide (February 2026) describes the top edge of counter flashing as embedded directly into the chimney’s mortar joints. Let it into a saw-cut reglet and fold it down over the base flashing, hanging free; a bead of caulk on the brick face is not a substitute for the reglet.
How does flashing attach by metal panel type?
Attachment is the biggest split in metal-roof chimney work, and it depends on the panel profile. Standing seam hides its fasteners and must not be penetrated in the field, so flashing clamps or seals to the raised seam. Exposed-fastener (R-panel, PBR) and corrugated panels seal at their ribs with butyl tape and closure strips under the trim, the parts a 3 ft Pro-Rib chimney flashing kit bundles. Our guide to solar panels on a metal roof covers how racking attaches to the same seams.
| Panel type | How flashing attaches | Sealing detail |
|---|---|---|
| Standing seam | Clamps or a curb that ties to the seams, no field penetrations | Butyl tape and a floating counter flashing; often a factory curb (for example a Sheffield Metals or Western States curb) |
| Exposed fastener (R-panel, PBR) | Trim laps over the panel and fastens at the ribs with gasketed screws | Butyl tape under the trim plus inside/outside closure strips at the ribs |
| Corrugated | Trim shaped to the wave, fastened at the crowns | Foam or profiled closure strips seal the gaps under the flashing |
For a round metal chimney or Class A pipe instead of a masonry stack, the base flashing is replaced by a pipe boot sized to the pipe diameter, with a storm collar above it. The Dektite metal roof range runs from the DF101 (0.25 to 2.5 in pipe) to the DF105 (4.25 to 7.5 in) for roof pitches up to 40 degrees, with an aluminum band in the base that is formed to the panel ribs. Dektite rates its EPDM boots for 239 °F constant at the roof line and its red silicone boots for 392 °F, so hot flues get silicone.
Why metal roof flashing has to float with thermal movement
A metal roof expands when it heats and contracts when it cools. Metal Sales gives the coefficient of thermal expansion as 0.0000065 in per in per °F for steel and 0.0000128 for aluminum, so aluminum moves about twice as much. If flashing is fastened tight to both the chimney and the panel, that movement tears the sealant, elongates the screw holes, and opens the joint.
| Panel run from fixed point | Steel, 100 °F swing | Aluminum, 100 °F swing | Source |
|---|---|---|---|
| 20 ft | 0.16 in | 0.31 in | Metal Sales coefficients (arithmetic ours) |
| 40 ft | 0.31 in | 0.61 in | Metal Sales coefficients (arithmetic ours) |
| 100 ft | 0.78 in | 1.56 in | Metal Sales |
The fix is to let the roof move independently of the chimney. Fasten the base flashing to the roof side only, keep the counter flashing hanging free over it, and never screw step or side flashing through the panel into the deck in a way that pins the panel. On standing seam this is why clamp-on curbs and clip systems exist: on a 40 ft aluminum run, the table above shows about 0.6 inch of travel the curb has to absorb.
Which flashing metal is compatible with which roof (galvanic corrosion)
Galvanic corrosion happens when two dissimilar metals are coupled by an electrolyte such as rainwater, and the less noble metal corrodes faster. The Metal Construction Association’s dissimilar metal corrosion bulletin (June 2016) says copper has “a very severe corrosive effect on steel, aluminum, and zinc.” The safe rule is to match the flashing metal to the panel, or isolate them so they never touch.
| Roof panel | Compatible flashing | Avoid |
|---|---|---|
| Galvalume (AZ50/AZ55 coated steel) | Galvalume, coated (Kynar/PVDF) steel | Copper, bare lead, raw aluminum in direct contact |
| Galvanized steel | Galvanized, coated steel | Copper and lead (they corrode the zinc coating) |
| Aluminum | Aluminum, coated steel with a barrier | Copper (severe), bare steel |
| Copper | Copper, lead-coated copper, stainless | Aluminum, galvanized, Galvalume downstream of it |
Copper is the worst offender because runoff carries it downslope: the MCA bulletin gives a copper roof or pipe draining onto a Galvalume surface as its example of runoff corrosion, so even a copper chimney cap above a Galvalume panel can corrode metal it never touches. The Cleveland-Cliffs GALVALUME product data also bars fasteners containing lead or copper and lead washers. Where mixing is unavoidable, separate the metals with an underlayment membrane or butyl tape and never stack copper upslope of the panel.
When does a metal roof chimney need a cricket?
A cricket is a small peaked saddle behind the chimney that splits water and debris around it instead of letting it pond against the upslope face. IRC R1003.20 requires a cricket where the chimney dimension parallel to the ridgeline is greater than 30 inches and the chimney does not intersect the ridgeline, and IRC R903.2.2 says cricket coverings shall be sheet metal or the same material as the roof covering. Table R1003.20 sets the cricket height (H) as a share of chimney width (W):
| Roof slope | Cricket height H | Example: 36 in wide chimney | Source |
|---|---|---|---|
| 12:12 | 1/2 of W | 18 in | IRC Table R1003.20 |
| 8:12 | 1/3 of W | 12 in | IRC Table R1003.20 |
| 6:12 | 1/4 of W | 9 in | IRC Table R1003.20 |
| 4:12 | 1/6 of W | 6 in | IRC Table R1003.20 |
| 3:12 | 1/8 of W | 4.5 in | IRC Table R1003.20 |
On a metal roof the cricket is formed from the same panel or coil stock, tied into the back pan, and flashed and counterflashed the same way as the rest of the chimney, which R1003.20 also requires. A cricket can still be worth adding on a chimney under 30 inches that sits low on a long slope; This Old House puts a chimney cricket at $700 to $1,300. For sizing and build sequence, see the dedicated chimney cricket install guide.
Factory curb kits vs site-formed flashing
You can either bend flashing on site from matching coil stock or order a pre-manufactured curb, kit or boot sized to the chimney and panel. Factory parts, such as a standing seam curb, a Pro-Rib chimney kit with matched closures, or a Dektite boot sized by pipe diameter, arrive with the right profile and a finish that matches the panel. Site-formed flashing is cheaper in parts and works on any profile, but it depends on the crew’s sheet-metal skill.
- Factory curb or boot: best for standing seam and round penetrations, matched finish, higher part cost, fewer field errors.
- Site-formed coil flashing: lower material cost, works on any profile, quality rides entirely on the crew’s sheet-metal skill.
- EPDM/silicone pipe boot: for round pipe only, sized by pipe diameter (Dektite DF101 to DF105 cover 0.25 to 7.5 in), paired with a storm collar; choose silicone where the flue can exceed 239 °F at the roof line.
What does it cost to flash a chimney on a metal roof in 2026?
HomeGuide (February 2026) puts chimney flashing repair at $300 to $1,800, with flashing material at $5 to $10 per linear foot for aluminum, $6 to $10 for galvanized steel and $15 to $30 for copper. Those are general figures, not metal-roof specific; expect a metal roof job to land toward the upper part of the range when it needs a custom curb, a cricket or panel rework. What you pay also tracks the panel metal, which the metal roof repair cost breakdown by metal type covers in more detail.
| Line item | Typical 2026 range | Notes and source |
|---|---|---|
| Chimney flashing repair, all roof types | $300 to $1,800 | HomeGuide, February 2026 |
| Aluminum flashing | $5 to $10 per linear foot | HomeGuide, February 2026 |
| Galvanized steel flashing | $6 to $10 per linear foot | HomeGuide, February 2026 |
| Copper flashing | $15 to $30 per linear foot | HomeGuide; avoid on Galvalume, galvanized and aluminum roofs |
| Cricket added | $700 to $1,300 | This Old House; scales with chimney width and pitch |
Ask for an itemized quote that names the flashing metal and gauge, whether a factory curb or site-formed pieces are used, and whether a cricket is included, since those three lines move the price most. A 4 ft by 3 ft chimney has about 14 linear feet of perimeter, so copper at HomeGuide’s $15 to $30 per foot comes to about $210 to $420 against $70 to $140 in aluminum at $5 to $10 (arithmetic ours). For the sourced ranges on a standard roof, see our guide to chimney flashing replacement cost on shingle roofs.
Installing metal roof chimney flashing: the order that matters
The install order is what makes flashing waterproof, because every piece has to lap onto the one below so water runs over a joint, never into it. This is the sequence on a masonry chimney, with the IRC R1003.20 or maker rule for each step that has one.
- Set the base: lay the apron flashing across the downslope face, on top of the panel, bedded in butyl tape at the rib, with outside closures under it on ribbed panels, as in a Pro-Rib kit.
- Run the sides: form and lap the side flashing up both walls, sealing to the panel profile with tape and closures, fastened to the roof side only so the panel keeps its 0.16 to 0.78 inch of travel (steel, 20 to 100 ft runs).
- Build the back: install a back pan for a chimney 30 inches wide or less, or a cricket sized by Table R1003.20 for a wider one, tied into the side flashing.
- Cut the reglet: saw a groove into the mortar joint around the chimney for the counter flashing.
- Set counter flashing: fold the top edge into the reglet, seal the reglet with a sealant Cleveland-Cliffs lists as GALVALUME-compatible (butyl or neutral cure silicone), and let the flashing hang free over the base so the panel can move.
- Seal and inspect: tool sealant only where the detail calls for it, then check every lap for correct overlap direction.
If the existing flashing is failing rather than new, diagnose the failure mode first: staining below copper (the MCA notes copper salts stain and corrode the roof surface), torn sealant at fasteners and a counter flashing caulked to the brick face each point to a different fix, as does a missing cricket on a chimney over 30 inches wide. The metal roof leak repair guide walks through finding and sealing a leak by source, and bad chimney flashing covers the warning signs before it leaks inside.
Common metal roof chimney flashing mistakes
Most metal roof chimney flashing leaks trace back to six avoidable errors, clustered around thermal movement, penetrations and metal pairing.
- Pinning the panel: fastening flashing through the panel field so thermal movement tears the joint.
- Surface-caulked counter flashing: caulk on the brick face instead of a cut reglet, which fails in a few years.
- Dissimilar metals touching: copper or bare aluminum against Galvalume or galvanized, driving galvanic corrosion.
- Reverse laps: an upper piece tucked behind a lower one, funneling water under the flashing.
- Relying on sealant alone: sealant is a backup to correct laps and closures, not the primary seal.
- Skipping a cricket: no saddle on a chimney over 30 inches wide, so water and debris pile against the upslope wall.
For how these parts fit into the whole roof, the metal roof components guide names every accessory, and Galvalume metal roofing explains the ASTM A792 AZ50 and AZ55 coatings that decide which flashing metals are safe against your panel.
Frequently asked questions
Can you put chimney flashing on a metal roof yourself?
A skilled DIYer can flash a round pipe with a sized metal-roof boot, such as a Dektite DF104 for 3 to 6.25 inch pipe, and a storm collar. Flashing a masonry chimney on a metal roof is harder because it needs custom-formed pieces, a cut reglet, correct laps, matched metals, and a cricket if the chimney is over 30 inches wide. On standing seam, a field mistake often means pulling panels to fix.
What is the best flashing material for a metal roof chimney?
Match the flashing to the panel. A Galvalume or galvanized roof takes Galvalume or coated (Kynar/PVDF) steel flashing. An aluminum roof takes aluminum flashing. A copper roof takes copper or stainless. The Metal Construction Association says copper has a very severe corrosive effect on steel, aluminum and zinc, including through runoff, so keep copper off and upslope of coated-steel and aluminum roofs.
Does a metal roof chimney need a cricket?
Under IRC R1003.20, a cricket is required when the chimney is wider than 30 inches parallel to the ridge and does not meet the ridgeline. Table R1003.20 sets its height, for example 1/4 of the chimney width on a 6:12 roof, so a 36 inch chimney needs a 9 inch cricket. On a metal roof, IRC R903.2.2 allows the cricket to be covered in sheet metal or the roof material.
Why does chimney flashing leak on a metal roof?
The usual causes are thermal movement tearing a joint that was fastened too tight (a 100 ft steel run moves about 0.78 inch over a 100 degree swing), a counter flashing caulked to the brick instead of set in a reglet, dissimilar metals corroding, reverse laps, or a missing cricket on a chimney over 30 inches wide. Diagnose the failure mode before resealing.
How much does it cost to flash a chimney on a metal roof?
HomeGuide puts chimney flashing repair at $300 to $1,800 (February 2026), with flashing at $5 to $10 per linear foot for aluminum, $6 to $10 for galvanized steel and $15 to $30 for copper. A metal roof job tends toward the upper part of the range when it needs a custom curb or panel rework, and This Old House puts an added cricket at $700 to $1,300.
Can you flash a chimney on a standing seam roof without penetrating the panels?
Yes, and you should. Standing seam panels are meant to move and hide their fasteners, so flashing clamps or ties to the raised seams and uses a curb that lets the panel slide underneath. Butyl tape and a floating counter flashing seal the joint; on a 40 ft aluminum run the curb has to absorb about 0.6 inch of travel per 100 degree swing. Screwing flashing through the field of a standing seam panel pins it, tears at the fastener as the panel moves, and causes leaks.