Roof Flashing: Seven Types, and the One North Carolina Dropped
Most roof leaks are not shingle leaks. They happen where the roof stops being a plain slope: against a wall, around a chimney, through a pipe, down a valley. Here is every type of flashing, what the code pins down for each, and the one North Carolina leaves to the manufacturer.
The short version
Where roofs actually leak
And why the code is specific about some of this and silent about the rest.
A shingle sheds water across an uninterrupted surface. That is the whole job. Everywhere the surface is interrupted, something else has to carry the water, and that something is flashing. Which is why a roof with good shingles and bad flashing leaks, and a roof with tired shingles and good flashing often does not.
The building code is unusually specific about three of these and says almost nothing about the rest. For asphalt shingles it requires flashing to be applied in accordance with its own section and the shingle manufacturer's printed instructions, which means the manufacturer's document is part of the code rather than a suggestion alongside it.
So the list below is ordered by how much the code actually pins down, most specified first. We would rather order it by which flashing leaks most often, but nobody publishes that, and making it up would be the dishonest part of this page.
The seven
Every type of roof flashing, and where it goes
Ordered by how much the code specifies, most first. The order is computed from that one key.
1. Base flashing, the most specified flashing in the code
The code sets a metal thickness for this one Where a roof plane runs into a wall or a chimney, underneath the counter flashing.
The lower half of a two-part joint. The code sets a floor on what it can be made of: corrosion-resistant metal at a minimum nominal 0.019 inch thickness, or mineral-surfaced roll roofing weighing at least 77 pounds per 100 square feet. Those are minimums rather than recommendations, and they are among the few flashing numbers the code states outright.
The catch. Base flashing is only half a joint. On its own it leaves the top edge of the metal exposed to anything running down the wall.
2. Counter flashing, also called cap flashing, the half that makes the joint watertight
The code sets a metal thickness for this one Let into or surface-mounted on the wall above the base flashing, lapping over it.
The upper half. It covers the top edge of the base flashing so water coming down the wall is thrown out onto the base rather than behind it. The code holds it to the same corrosion-resistant metal at a minimum nominal 0.019 inch thickness.
The catch. On masonry this is the piece that gets skipped, because doing it properly means cutting a groove into the mortar joint rather than running a bead of sealant along the top of the base metal and calling it done. Sealant is not flashing.
3. Valley lining, the most prescriptive section in the whole flashing code
The code sets a metal thickness for this one Down the trough where two roof planes meet, installed before the shingles.
A valley carries water off two slopes at once, so the code is unusually specific. Lining goes in before the shingles. An open metal valley has to be at least 24 inches wide, in a metal from the code's own table, and the table sets a minimum thickness for each one. An open valley can instead use two plies of mineral-surfaced roll roofing, an 18 inch bottom ply under a top ply of at least 36 inches. A closed valley, where shingles carry across the trough, can use a single ply of smooth roll roofing at least 36 inches wide, and a self-adhering polymer-modified bitumen underlayment meeting ASTM D1970 may be used in place of the lining.
The catch. Valleys collect debris as well as water, which keeps them wet for longer than any other part of the roof. The lining is doing real work there, and it is hidden, so nobody finds out it was skimped on until there is a stain on a ceiling.
4. Drip edge, the one North Carolina does not require
The code sets dimensions but no thickness Along the eaves and up the rakes, at the very edge of the deck.
An L-shaped strip that throws water off the edge of the deck instead of letting it run back onto the fascia. The model code sets the dimensions: adjacent segments lapped at least 2 inches, a vertical leg of at least 1.5 inches extending at least a quarter inch below the sheathing, at least 2 inches back onto the roof, and mechanical fasteners no more than 12 inches apart. It also sets the order, which catches people out: underlayment goes over the drip edge at the eaves and under it at the rakes.
The catch. In North Carolina it is not independently required. The State Fire Marshal's engineering division was asked directly whether a drip edge is required on a residential shingle roof and answered no, if the manufacturer's installation instructions do not require one, because section R905.2.8.5 was deleted. That makes the shingle manufacturer's printed instructions the document that decides it, and most of the major manufacturers do require one.
5. Kickout flashing, the cheapest piece of metal on a roof and the costliest to omit
The code names no numbers and defers to the manufacturer At the very bottom of a roof-to-wall joint, where the roof edge meets the wall and the gutter begins.
A small diverter that takes everything the wall-to-roof joint has collected and throws it out into the gutter instead of letting it continue down behind the siding. It is the last piece in a run of step flashing and it is the one most often left off, because the run of step flashing looks finished without it.
The catch. When it is missing, the water does not show up on the roof. It shows up as rot behind the trim and a stain running down the wall below the joint, often years later and several feet from the actual cause. The code names no dimensions for it, which is part of why it goes missing.
6. Pipe boot, also called vent flashing, the flashing with the shortest life
The code names no numbers and defers to the manufacturer Around every plumbing vent, flue and pipe that comes through the roof.
A flanged collar that seals the gap where a pipe passes through the deck. The flange is metal or plastic and the part that actually seals against the pipe is usually a rubber or synthetic collar. The code groups these under its catch-all for other flashings and defers to the manufacturer's printed instructions rather than setting a number.
The catch. The rubber collar is the part that fails, and it fails from sunlight rather than water, so it goes on a schedule of its own that has nothing to do with how old the shingles are. A roof with twelve good years left can have a boot that is finished, and it is one of the most common causes of a leak on a roof with no other problems.
7. Step flashing, the joint that cannot be done with one piece of metal
The code names no numbers and defers to the manufacturer Up the side of a dormer, chimney or wall where it meets a sloping roof.
Not one piece but a stack of L-shaped pieces, one per course of shingles, each lapped over the one below so water is handed down the slope from piece to piece like tiles. That stepped arrangement is the only way to flash a sloping joint, which is why a single bent strip of metal up a sidewall is a defect rather than a shortcut. The code sends you to the shingle manufacturer's printed instructions for how it goes in.
The catch. Because each piece is nailed and then covered by the next shingle, step flashing cannot be inspected or replaced without lifting shingles. It is also the joint most often sealed with caulk by somebody chasing a leak, which hides the problem for a season and makes the real repair bigger.
Code requirements read on UpCodes at the asphalt shingle flashing section, 1507.2.8, the commercial twin of the residential R905.2.8. These are the model code figures. North Carolina amends the model code, and the one amendment that changes a homeowner-facing answer is below. Sources read 27 October 2026.
Leak you cannot find?
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Valley metal
What an open valley has to be made of
The code's own minimum thicknesses for an open metal valley lining. Thickest first.
Metal
Minimum thickness
Zinc alloy
0.027 in
Aluminum
0.024 in
Copper, cold-rolled
0.0216 in
Galvanized steel
0.0179 in
Copper, high-yield
0.0162 in
Figures from UpCodes, asphalt shingle flashing, valleys. Galvanized steel is listed at 26 gage, G90. The lining of an open metal valley also has to be at least 24 inches wide.
Those are floors, not targets. The reason to care about the number is that a valley stays wet longer than any other part of a roof, because it collects the debris as well as the water, and the lining is buried where nobody will look at it again for twenty years.
The North Carolina answer
Drip edge is not required here, and that is not the end of it
This is the one place where the national guidance and the North Carolina answer come apart.
Every national page on this subject will tell you the code requires a drip edge. In North Carolina that is not what the state says. The Engineering Division of the NC Office of the State Fire Marshal was asked the question directly and published the answer:
Question: Is a drip edge required when using asphalt shingles on a residential dwelling?
Answer: No, if the manufacturer's installation instructions do not require a drip edge per Section R904.1. Section R905.2.8.5 was deleted.
NC Department of Insurance, Office of the State Fire Marshal, Engineering Division, "Drip Edge on Residential Dwellings", dated 28 February 2020 against the 2018 NC Residential Code. We are quoting it with its date rather than calling it current law, because the 2024 edition has been delayed more than once and the published sources disagree about when it takes effect.
Read it carefully and it does not say a drip edge is optional. It says the requirement moved. Section R904.1 makes roof assemblies subject to the manufacturer's installation instructions, and the major shingle manufacturers require a drip edge in theirs. So on most roofs the answer is still yes, by a different route.
What it does mean in practice is that you cannot settle an argument about your roof by pointing at the state code. The document that decides it is the installation instruction sheet for the shingle that is going on your house. Every roof we install gets a drip edge regardless, because the alternative is water running back onto the fascia we are about to warranty.
Questions
Roof flashing questions
What homeowners ask when a leak will not behave.
What is roof flashing?
Metal, or occasionally reinforced membrane, at every place where a roof stops being a plain slope: against a wall, around a chimney, through a pipe, down a valley, along an edge. Shingles shed water across an uninterrupted surface and that is all they do. Everywhere the surface is interrupted, something else has to carry the water, and that something is flashing. It is why most roof leaks are flashing leaks rather than shingle leaks.
Is a drip edge required in North Carolina?
Not by itself. Asked whether a drip edge is required when using asphalt shingles on a residential dwelling, the Engineering Division of the NC Office of the State Fire Marshal answered: no, if the manufacturer's installation instructions do not require a drip edge, because section R905.2.8.5 was deleted. That interpretation is dated 28 February 2020 and written against the 2018 NC Residential Code. In practice it moves the question rather than settling it, because R904.1 makes the manufacturer's installation instructions binding, and the major shingle manufacturers call for a drip edge in theirs. Any roof we install gets one.
Can flashing be repaired, or does it have to be replaced?
It depends which one. A pipe boot is a genuine standalone repair and a sensible one. Counter flashing on masonry can often be redone without touching the roof. Step flashing is the hard case, because every piece is nailed under a shingle, so getting at it means lifting the shingles above it and those shingles may not reseal if the roof is old. That is the point where a flashing repair turns into a slope.
Why does my roof leak when it only rains sideways?
That pattern points at flashing rather than shingles almost every time. Water falling straight down is handled by the slope. Water driven horizontally gets under edges and behind wall joints, which is exactly where drip edge, step flashing and kickout flashing are doing their work. A leak that only appears in wind-driven rain is a leak at an interruption.
Is caulk an acceptable way to fix flashing?
As a way to get through a weekend, yes. As a repair, no. Sealant has a life measured in a few years and the joint it is covering has a life measured in decades, so the repair fails again on its own schedule and usually somewhere slightly different. Worse, caulk along the top of a base flashing hides the fact that the counter flashing was never installed, so the real defect never gets found.
Does flashing have to be the same metal as my gutters?
It does have to be compatible with whatever it touches and whatever drains onto it. Dissimilar metals in contact with water between them corrode, and the pairing that causes the most trouble on a house is copper draining onto aluminum or onto galvanized steel. Runoff is enough; they do not have to be touching. It is a question worth asking before someone puts copper flashing above aluminum gutters.
Keep reading
Related guides and calculators
Leaks, repairs, and the details underneath the shingles.
What goes under the shingles, and where the code wants ASTM D1970.
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