Roof flashing types: what each one does and where roofs leak

Roof flashing, and why the field is not where it leaks

Roof flashing is the metal or membrane that seals every spot where the field roofing stops being one continuous surface. The valleys, the edges, the walls and curbs the roof runs into, the pipes and vents that poke through it. Anywhere the shingles or the membrane have to end, turn, or wrap around something, a piece of flashing carries the water across that joint and keeps it out of the building.

The field of the roof, the wide-open run of shingles or membrane, almost never leaks on its own. It is made to shed water and it does. Water gets in where the field meets something else: a wall, a chimney, a drain, the edge. That is the flashing, and that is the whole game. The flashing is the leak control, not the field.

Think of every flashing as solving the same problem in a different place. The roof is a waterproof plane until it has to deal with a vertical surface, an opening, or an edge. The flashing is how you handle the interruption without letting water find the seam. Get the flashing right and the roof lasts decades. Get it wrong and the field can be perfect while the building still gets wet.

Where does a roof actually leak?

A roof leaks at its flashings, not in its field. The NRCA and most of the trade put the large majority of roof leaks at the flashings, terminations, and penetrations rather than the open membrane or the field of shingles. Anyone who has chased water through a ceiling for twenty years already knows this in their bones: you start at the nearest detail, not in the middle of the roof.

The reason is simple. The field is made by machine and laid in a repeating pattern that sheds water by design. The flashings are made by hand, at the hard spots, often late in a shift, around objects that were placed by other trades. Every flashing is a one-off decision where the geometry changes and the water has to be redirected. That is where the mistake lives.

So when you inspect, when you bid a repair, or when you design the roof, you spend your attention where the water gets in. The chimney, the skylight, the wall, the valley, the edge, the pipe. The companion guide on roof penetration flashing details walks the boots, curbs, drains, and pourable pockets in depth. This guide is the map of every flashing type and where each one belongs.

The flashing principle: water sheds over, never under

Every flashing on the roof obeys one rule: each piece overlaps the piece below it, so water always runs over a lap and never into one. This is the same logic that makes shingles work. The upper course covers the top edge of the lower course, water sheds down the face, and there is no open seam pointed uphill for water to climb into.

Flashing is just that logic applied at the hard spots. The metal that goes up a wall is covered at its top by a second piece that laps over it, so the joint between them sheds water down the face instead of catching it. The membrane that turns up a curb is capped by a counterflashing that overlaps it. The valley metal runs under the field on both sides so the field sheds onto the metal, not behind it. Over, over, over, all the way down to the edge.

Reverse a lap and you have built a funnel. A flashing installed under the course that should cover it, or a counterflashing tucked behind the base instead of over it, points an open joint uphill and collects every drop that runs down to it. That single reversed lap is one of the most common flashing failures there is, and it leaks the first time it rains hard. The flashing has to shed water by its geometry. The sealant is a backup, covered later, never the plan.

What is the difference between base flashing and counterflashing?

Base flashing is the part that carries the roof up a vertical surface. Counterflashing is the cap that covers the top of the base flashing and sheds water down over its face. They are a pair, and a watertight wall or curb detail needs both. The base does the waterproofing; the counter protects the top edge of the base from water getting behind it.

Base flashing is the roof material itself turned up the wall or curb. On a low-slope roof it is the membrane carried up the vertical, commonly at least 8 in above the finished roof per the NRCA recommendation. On a steep-slope roof the base function is handled by the underlayment and the step or apron flashing carried up under the wall covering, with the visible turn-up commonly 4 in or more. Either way, the base flashing is the layer water actually rides up and away from the joint.

Counterflashing is the metal cap over that turn-up. It either sets into the wall, tucked into a saw-cut groove called a reglet, or mounts to the face of the wall as a surface-mounted counterflashing held with fasteners and a sealant line. The counterflashing laps down over the top of the base so the base's exposed edge is never the first thing the water hits. Leave the base flashing capped with nothing but a bead of caulk and you have skipped the counterflashing, and that detail leaks from the top down as the caulk ages.

What is step flashing?

Step flashing is the set of individual L-shaped metal pieces woven into a sloped roof where it runs alongside a wall, one piece per shingle course. Each piece is bent down the middle, commonly around 10 in long with roughly 4 in lying on the roof and 4 in standing up the wall. The piece is set so the shingle course below it laps over the roof leg, and the course above laps over it, while the wall covering and the counterflashing come down over the vertical leg.

The weave is what makes it work. Because the roof rises one course at a time along a sidewall, the elevation of the joint changes step by step, so a single continuous piece would either gap or fight the courses. The stepped pieces shingle the joint the same way the field shingles the roof: each step sheds onto the course below it, and there is no open seam pointed uphill. This is the steep-slope sidewall detail, where a slope runs up beside a wall. The companion guides on shingle roofing cover how the courses and the step pieces interlock.

Step flashing fails in predictable ways. The classic mistake is replacing it with one long bent piece of continuous flashing run behind the siding, which reads as faster but cannot follow the courses and traps water at every lap. The other is caulking step flashing in place instead of weaving it, so the pieces are held by sealant rather than by the lap geometry. Both leak. When you tear off a leaking sidewall, you usually find reused, bent, or caulked step flashing that was never woven right in the first place.

Where a sidewall step-flashing run ends at the eave, the last piece is the kick-out, and it is the single most commonly missed flashing on a house. The kick-out is a step flashing with a flared lip bent out at the bottom that throws the water running down the wall out past the wall line and into the gutter. Leave it off and every storm sends that concentrated runoff straight down behind the siding at the wall-to-roof junction, where it rots sheathing and framing out of sight for years before anyone sees a stain inside. The fix is cheap on a new roof and expensive once the wall is wet, so the kick-out goes on at the bottom of the step run, sealed at its inside corner, and the siding and any housewrap lap over its vertical leg.

Headwall, apron, and sidewall flashing

Where the top of a slope runs into a wall, that is a headwall, and it gets apron flashing: a single continuous piece bent over the top edge of the roofing and up the wall. Because a headwall sits at one constant elevation across its whole length, a continuous apron works there, unlike a sidewall. The apron laps over the roofing below it and up under the wall covering above, so water sheds off the slope, onto the apron, and down the face.

The apron has to go over the roofing, not under it. The common error is tucking the bottom leg of the apron under the last course of shingles, which traps water against the back of those shingles instead of shedding it onto them. Run the apron over the field so the slope drains onto the metal, then cap the top with the wall covering or a counterflashing. Under the shingles is backwards, and it ponds water exactly where the wall meets the roof.

A sidewall is the other case: the slope runs up alongside the wall instead of dying into it. On steep-slope roofs the sidewall gets step flashing, woven per course as described above. On low-slope roofs a sidewall is a base flashing carried up the wall and counterflashed. The terms describe geometry: headwall is the top of the slope into a wall, sidewall is the side of the slope along a wall, and the flashing changes to suit which one you have.

Valley flashing: open, closed-cut, and woven

Valley flashing handles the channel where two roof slopes meet and dump their water into one line. It is the busiest water path on a steep-slope roof, carrying the runoff from both planes, so it gets either a metal liner or a layer of the roofing itself worked across the valley. There are three common methods, and they differ in whether metal stays exposed.

An open valley runs a continuous metal liner down the center, with the shingles cut back on both sides to leave the metal exposed as the visible water channel. It is the method that sheds the most water and clears debris best, which is why it is favored on steep pitches, in heavy-rain and heavy-snow country, and where two large planes converge. A closed-cut valley runs the shingles from one slope all the way across the valley, laps the other slope's shingles over them, and trims that top layer back along a line just off the valley center, with metal or membrane underneath. A woven valley interlaces the courses from both slopes across the valley with no cut line. Both closed methods hide the metal; the open valley shows it.

Whatever the method, there is a waterproof layer under the valley before any shingle goes down, commonly a metal liner or a self-adhered membrane, because the valley concentrates water and ice. The failures are a valley liner that is too narrow, fasteners driven through the center of the channel where the water runs, or a closed-cut line trimmed too tight to the center so water washes under the cut edge. Keep the fasteners out of the water path and keep the channel wide enough for the drainage area it serves.

Drip edge, rake edge, and the perimeter edge metal

Edge metal is the flashing at the perimeter that controls water at the eaves and rakes and ties the roof edge down against wind. On a steep-slope roof this is the drip edge: an L-shaped or T-shaped metal run along the eaves and up the rakes that kicks water off the edge and into the gutter instead of letting it wick back under the roofing and rot the fascia and deck. At the eave the underlayment laps over the drip edge; at the rake the drip edge goes over the underlayment. Recent editions of the residential code require a drip edge on shingle roofs, so confirm it against the adopted edition and local amendments.

On a low-slope roof the perimeter metal is the gravel stop or edge metal: a flanged metal edge that the membrane terminates into, holds the roofing back from the edge, and on a gravel-surfaced roof keeps the aggregate from washing off. Fascia metal covers the vertical face of the edge. The fascia is the perimeter trim at the edge of the roof, and the edge metal wraps and protects it.

Roof edges are a wind problem as much as a water problem, and the edge is where wind uplift starts to peel a roof. The wind-design standard for low-slope perimeter edge metal is ANSI/SPRI ES-1, with related testing under FM 4435, and many codes now reference it for the fascia, drip edge, gravel stop, and coping. Size and fasten the edge metal to the wind load for the building, because an edge that lifts in a storm opens the whole perimeter, and confirm the requirement against the adopted code.

Coping: the cap on a parapet wall

Coping is the cap that covers the top of a parapet wall, the wall that rises above the roof around the perimeter. The parapet has an exposed top that would soak up water and dump it into the wall and the building, so the coping caps it with metal or stone, sheds water to one or both sides, and keeps the top of the wall dry. It is the flashing for the one surface that faces straight up at the sky.

Good coping has a slope built into it so water drains off rather than ponding on top, joints that are covered or sealed so water does not run into the gaps, and a drip on the underside of each leg so water releases off the edge instead of running back under and staining or rotting the wall face. Coping is also a wind-uplift item under ANSI/SPRI ES-1, with its own pull test, because a parapet cap that lifts in a storm is both a leak and a flying hazard.

Under the coping you commonly want a continuous through-wall flashing, covered next, to catch any water that gets past the coping joints and weep it back out before it reaches the inside. The coping sheds the bulk of the water; the through-wall flashing is the second line under it. A parapet capped with nothing but caulked joints and no flashing underneath is a wall waiting to leak at every seam.

What is through-wall flashing?

Through-wall flashing is a concealed waterproof layer built into a masonry wall that catches water inside the wall and directs it back out through weep holes. Masonry is not waterproof. Brick, block, and the mortar between them absorb and pass water, so a masonry wall is designed to let some water in and then drain it out at controlled lines, and the through-wall flashing is the line that collects it and sends it back outside.

It goes in during construction at the spots where water collects: the base of the wall, shelf angles, window and door heads, and under the coping at a parapet. The flashing runs through the full thickness of the wall, turns up at the back, and laps out at the face. Just above the face edge sit the weep holes, small open gaps in a mortar joint that let the collected water drain out. No weeps, or weeps that get mortared shut, and the water the flashing collected has nowhere to go but inward.

Through-wall flashing is the strongest version of a wall termination, but you only get it if it was designed and built into the wall. On an existing building you usually inherit whatever is there, which may be surface-mounted counterflashing and a reglet instead. When a masonry wall leaks and the roof flashing checks out, look at whether the wall has through-wall flashing and working weeps, because a parapet or a wall base with no through-wall drainage path leaks regardless of how good the roof is. The companion guides on masonry walls cover the weep and drainage detailing in depth.

Pipe, vent, curb, and skylight flashing

A pipe or vent through the roof gets a pipe flashing: a boot, jack, or collar that seals the round penetration. On a steep-slope roof this is usually a one-piece flashing with a flat base that shingles into the courses and a collar or rubber gland that seals to the pipe. On a low-slope roof it is a prefabricated boot welded or bonded to the membrane and clamped to the pipe with a draw band. The base shingles in like any flashing, and the top seals to the pipe.

A curb is a raised frame that a rooftop unit, a fan, or a skylight sits on, and curb flashing carries the roofing up the curb sides like a small wall: a base flashing up the curb, a termination at the top, and a counterflashing or the equipment's own flange capping it. The curb is the biggest single flashing on many commercial roofs, and its four corners are the weak points. A skylight gets the same treatment, either a manufacturer's flashing kit on a steep-slope roof or a flashed curb on a low-slope roof, sized and lapped so the slope sheds around it.

Pipe boots, curbs, drains, and odd-shape penetrations are the heart of the companion penetration-flashing guide, which covers the prefab-boot-first hierarchy, the hot-pipe high-temp boot, the drain clamp ring, and the pourable pocket of last resort. This section names where each sits in the flashing family. The detail is that water-shedding base plus a protected top, the same as every other flashing, applied around a hole instead of along a line.

Pitch pans and pourable sealer pockets

A pitch pan, also called a pourable sealer pocket or pitch pocket, is an open metal or molded box flashed to the roof around an odd-shaped penetration and filled with a pourable sealant that cures around the shape. It is the detail you reach for when nothing else fits: a bundle of small tubes, an angle iron, a shape no boot or wrap can seal cleanly. It is also the most chronic leaker on the roof, which is why it is the last resort, not the default.

The reason it leaks is that the sealant shrinks as it cures and again as it weathers, so it settles below the rim, dishes, ponds water in the dip, and eventually cracks or pulls away from the penetration. A pitch pan that nobody tops off becomes a funnel pointed into the building. It belongs on the maintenance schedule by name, built with a crowned cap pour that sheds rather than a flat fill that holds water.

Use it only when a fabricated flashing genuinely cannot be made, not because it is quick. The companion penetration guide covers how to build and maintain one, and the better answer wherever possible is to change the penetration so it can take a real boot or wrap instead. The pitch pan seals shapes nothing else can, and it costs you maintenance forever in exchange.

Expansion joint flashing

An expansion joint is a deliberate gap that lets two parts of a building move independently, and the roof has to bridge that gap without tearing. You cannot run roofing flat across it, because the building moves and the roofing is not built to cycle. The flashing is a raised cover: a curb or cant on each side of the gap with a flexible bellows spanning between them, and the roofing flashes into the metal flanges on each side as an ordinary base flashing.

The bellows is the moving part, a flexible loop over a foam core that compresses and stretches so the movement stays in the cover and never reaches the roof flashing. Built up off the deck, the cover sheds water to both sides; run flat, it becomes a dam right where the most movement is. The companion penetration-flashing guide covers the expansion-joint cover in more detail. The point for this overview is that it is a flashing type with one job no other flashing has: to seal a joint that is supposed to move.

What is a cricket on a roof?

A cricket, also called a saddle, is a small peaked structure built on the uphill side of a chimney, curb, or wide penetration to split water and snow and divert it around the obstruction instead of letting it pile up against the back. It is part flashing, part framing: a ridge that rises from the roof and sheds to both sides, surfaced with metal or with the roofing material itself.

It exists because anything wide that sits in the flow of water dams it. Water and snow back up against the uphill face, sit there, and test that flashing constantly, and on a steep roof a wide chimney without a cricket gets a permanent wet streak and a debris pile behind it that eventually rots the deck. The residential code requires a cricket or saddle on the ridge side of any chimney wider than 30 in measured across the slope, and the trade commonly recommends one at 24 in and up. Confirm the trigger against the adopted code edition.

On a low-slope roof the same problem behind a wide curb is solved with a cricket built out of tapered insulation that splits the water around the unit. The companion guide on roof crickets and tapered insulation covers building the slope. The thing to carry from here: if a wide object sits in the path of the water, it needs a cricket behind it, or its flashing sits underwater no matter how well it was made.

Chimney flashing: the full assembly

A chimney is the detail that uses almost every flashing type at once, which is why it leaks so often. It needs an apron at the downhill face, step flashing up both sides, a cricket and its flashing at the uphill face, and counterflashing tucked into the masonry over all of it. Miss any one of the four sides and the chimney leaks at that side.

Work it side by side. The downhill face gets an apron flashing that sheds the slope's water out around the chimney base. Each side gets step flashing woven into the courses, exactly as a sidewall. The uphill face gets a cricket to divert water around the chimney, with its own flashing, because the uphill face is where water piles up worst. Then a counterflashing is set into a reglet cut into the brick or stone and lapped down over the top of all the base and step pieces, so the masonry sheds onto the metal and the metal sheds onto the roof.

Chimneys leak for two repeat reasons. The counterflashing is surface-caulked to the brick instead of cut into a reglet, so it lets go as the caulk ages. And there is no cricket behind a wide chimney, so water dams against the back and finds its way in. When a chimney leaks, check the uphill side and the counterflashing first; that pair is the failure in most cases.

Flashing materials: the metals and the membrane

Flashing splits into two material worlds. On steep-slope roofs the flashing is sheet metal: galvanized steel, aluminum, copper, stainless steel, and historically lead. On low-slope roofs much of the flashing is membrane that matches the field, single-ply boots and corners on a TPO, PVC, or EPDM roof, or modified-bitumen flashing plies on an asphalt system, with metal still used at edges, copings, and counterflashings.

Each metal has a lane. Galvanized steel is the low-cost workhorse, painted or bare, but the zinc coating wears and it eventually rusts at cut edges and scratches. Aluminum is light, will not rust, and is common for drip edge and edge metal, but it is soft and corrodes in contact with masonry and treated lumber unless separated. Copper lasts the longest, solders cleanly, and shows up on high-end and historic work, but it is expensive and it stains and attacks other metals in runoff. Stainless steel is the most durable and the most expensive, used where failure is not an option. Lead is malleable and forms easily around shapes, the old standard for pipe collars and chimneys, now used less because of handling and environmental concerns.

Membrane flashing follows the field membrane and has to match its chemistry. A TPO roof gets TPO flashing, a PVC roof gets PVC, so the boot, corner, and curb wrap weld into one material with the field. The flashing-grade membrane is often unsupported, without the internal scrim of the field sheet, so it stretches to form corners and shapes the reinforced field sheet cannot. The companion membrane-selection guide covers the chemistries. The rule across both worlds: the flashing material has to be compatible with what it ties into, or the joint between them is the leak.

Sealant is the backup, not the flashing

Caulk is not flashing, and the single most common flashing mistake in the trade is treating it like it is. Sealant has a service life measured in years, it shrinks, it cracks, it loses adhesion as it weathers and the joint moves, and a roof built to last decades cannot depend on a bead of caulk to keep water out. The flashing has to shed water by its shape and its laps. The sealant is the secondary measure that protects an edge or a fastener, not the thing holding the water back.

You see the failure everywhere: a counterflashing surface-caulked to a wall with no reglet, a pipe sealed with a glob of mastic and no boot, a step flashing held by sealant instead of woven into the courses, a pitch pan relied on as a permanent seal. They all work the day they are installed and they all fail on the same schedule the caulk does, usually a few seasons in, after the crew is long gone and someone else owns the leak.

Use sealant where it belongs: capping a termination bar, sealing the kerf of a reglet, dressing a fastener head, backing up a lap that is already shedding water on its own. Where you find yourself reaching for caulk to make a detail watertight that has no proper flashing under it, stop and build the flashing. Caulk is maintenance. The flashing is the detail.

Dissimilar metals and galvanic corrosion

Put two different metals in contact with water between them and the more active one corrodes, fast. This is galvanic corrosion, and it eats flashings that were specified without thinking about what they touch. It takes three things: two different metals, a path between them, and an electrolyte, which on a roof is just rainwater. Remove any one and it stops, but on a wet roof the water is always there.

The pairings that bite are known. Copper is hard on aluminum, steel, and zinc, so a copper flashing draining onto a galvanized gutter or in contact with an aluminum edge corrodes the cheaper metal severely. Galvanized steel fasteners in stainless, or zinc against stainless, go the same way. Copper sits fine against lead and stainless steel, which is part of why those combinations show up on long-lasting work. The other trap is runoff: even with no contact, water running off a copper roof onto galvanized metal downstream carries enough copper to corrode it.

The fixes are not complicated. Keep dissimilar metals from touching, and where they must be near each other, separate them with a membrane, building paper, a coating, or a non-conductive sealant so there is no metal-to-metal path. Match fasteners to the flashing metal, never galvanized screws into copper or stainless flashing. And watch the drainage direction so a more active metal never sits downstream of a copper one. This is the corrosion caution that turns a thirty-year flashing into a ten-year one when it is ignored.

The reglet and the termination bar

Two pieces of hardware show up at the top of almost every wall and curb flashing: the reglet and the termination bar. A reglet is a groove that holds the top of a counterflashing. It is either a saw kerf cut into a masonry mortar joint, with the metal sprung into the cut and the cut sealed, or a manufactured reglet built into the wall to receive the flashing. The reglet keeps the top edge of the counterflashing tucked into the wall and out of the weather, which is why a regletted counterflashing outlasts a surface-mounted one.

A termination bar is a metal strip screwed through the top of a membrane base flashing into the wall or curb at close spacing. It mechanically holds the membrane so it cannot sag or peel down, and it is capped with a bead of sealant over the fastener heads and the membrane edge. The term bar is a low-slope and membrane detail; the reglet is the masonry counterflashing detail. Both do the same job in their world: they fix and protect the top edge of the flashing, the spot water most wants to get behind.

Neither is the finish by itself. A term bar still needs a counterflashing or cap over it so water sheds over the bar instead of at the fastener line, and a reglet still depends on the sealant in the kerf, which is a maintenance item with a service life. Surface-mounted counterflashing is the fallback where you cannot cut a reglet, cheaper but more dependent on the sealant and the fasteners, so it needs watching. Where it leaks, the top edge is almost always where it started.

Where do you look for a roof leak?

You look at the flashings, in the order water hits them, before you ever look at the field. A leak shows up inside at a spot that is rarely under the actual breach, because water runs along the deck and the framing before it drops through the ceiling. So you start uphill of the stain and you work the details: the nearest penetration, the wall above it, the chimney, the skylight, the valley, the edge.

Run the same list every time. Pipe boots and their collars, because the rubber cracks and the sealant fails. Chimney counterflashing and the cricket behind it. Skylight flashing and its corners. Step flashing at every sidewall, looking for caulk where there should be weave. Valley centers for fasteners in the water path and trimmed-too-tight cuts. Wall terminations and copings for failed reglet caulk. Drains and clamp rings on a low-slope roof. The field of the roof is the last place you look, and it rarely makes the list.

The wet detail does not always show from above. On a low-slope roof an infrared scan after sundown reads the warm, wet insulation around a leaking penetration, and a moisture survey finds the trapped water the eye misses. On a steep-slope roof a controlled water test, hosing the suspected detail from the bottom up with someone watching inside, isolates which flashing is the breach. The companion leak-diagnosis guides cover the test methods. The principle holds: chase the detail, not the field.

Re-flashing: the most common roof repair

Re-flashing a failed detail is the most common roof repair there is, because flashings are where roofs fail. A field of shingles or membrane with twenty years left in it can sit over a chimney, a wall, or a pipe whose flashing is shot, and the fix is to rebuild that one detail, not the roof. Most leak repairs are a re-flash, not a re-roof.

Do it right and you cut the failed flashing out and build a new one to the proper detail. Strip the old metal or membrane, address whatever rotted under it, and install fresh flashing that laps and sheds correctly, woven step flashing back into the courses, a counterflashing cut into a fresh reglet, a new boot shingled in. The temptation is to skip all that and smear the old failed detail with roof cement or caulk, which buys a season and then leaks again, often worse, because now the water is trapped under the patch.

The repair that holds is the one that fixes the geometry, not the one that covers it. On a re-roof, the same logic is the whole point: the most common re-roof leak is new field tied into old flashing that was already failing, so the field is perfect and the roof still leaks at the same detail it always did. Reflash the penetrations, walls, chimneys, and edges as part of the re-roof, because those are what were leaking before the new field went on.

Two worlds: steep-slope metal and low-slope membrane

Flashing comes in two flavors depending on the roof, and the names map across but the materials and methods differ. Steep-slope roofs, the shingle, tile, metal, and shake roofs you see pitched, flash mostly with sheet metal: step flashing, apron, valley metal, drip edge, and counterflashing, each piece shingled into the courses so the field sheds onto it.

Low-slope roofs, the flat and near-flat commercial roofs, flash mostly with membrane that matches the field, plus metal at the edges and copings. The base flashing is the membrane turned up the wall or curb, commonly to at least 8 in, capped with a termination bar and a counterflashing, and the penetrations get membrane boots welded or bonded into the sheet. The companion membrane-selection guide and the penetration-flashing guide live in this world.

The same principle runs both worlds: a water-shedding base carried up the vertical, a protected top edge capped over it, every piece lapping the one below. A foreman who understands base-over-field and counter-over-base can read a flashing detail on either kind of roof, because the geometry is the same even when one is folded copper and the other is welded thermoplastic. The materials change with the slope. The logic does not.

What to document

The flashing record is what defends the roof when a leak shows up and the question is whether the detail was built right. Flashings get buried under courses or capped with metal the day the crew leaves, so the log made on the roof is the only proof of what is underneath. A warranty claim and a callback both turn on it.

Capture each flashing by type and location: what it is, where it sits, the base-flashing height where that applies, whether corners are prefab or field-made, the material and how it was capped, and the inspection result. Note every pitch pan and every reglet-sealed counterflashing, because those are the maintenance items. Tie the package to the manufacturer's details on a low-slope roof and to the code-required items, like the cricket over a wide chimney, on a steep-slope one.

Common mistakes

• Relying on caulk or roof cement to make a detail watertight instead of building a flashing that sheds water by its shape.
• Leaving base flashing capped with sealant and no counterflashing over its top edge.
• Reverse-lapping a flashing, running it under the course that should cover it, so the joint points uphill and collects water.
• Replacing woven step flashing with one long continuous piece, or caulking step flashing in place instead of weaving it per course.
• Tucking an apron flashing under the last shingle course instead of over the roofing.
• Skipping the cricket behind a wide chimney or curb, so its flashing sits underwater on the uphill side.
• Surface-caulking a chimney counterflashing to the brick instead of cutting it into a reglet.
• Pairing dissimilar metals, or letting copper runoff land on galvanized metal, and watching the cheaper metal corrode.
• Mismatching membrane flashing to the field membrane, a TPO boot on a PVC roof, so the joint never welds.
• Inspecting the field for a leak and ignoring the flashings, where the water actually gets in.
• Patching a failed flashing with cement instead of re-flashing the detail to the proper geometry.

Field checklist

Standards and references

No single document governs all roof flashing, so you cite the one that controls the detail in front of you. On a low-slope roof the membrane manufacturer's published details and warranty govern the flashing, full stop: the base-flashing height, the boots and corners, the terminations, and the approved sealants. Confirm every figure here against the actual product literature, and treat the warranted accessory list as the authority on what part goes where.

The NRCA Roofing Manual is the trade reference for flashing construction details and is where the commonly cited 8 in low-slope base-flashing height and the figure putting most roof leaks at flashings come from. Treat its numbers as recommended industry practice and confirm the current edition. SMACNA's architectural sheet metal guidance covers the metalwork: copings, counterflashings, gravel stops, and reglets. ASTM material specifications define the flashing metals and membranes and the test methods behind them. Asphalt-shingle flashing details follow the shingle manufacturer's instructions and the asphalt-roofing manufacturers' guidance.

Codes carry the requirements that are enforceable. The International Building Code and International Residential Code cover roof flashing, drip edge on shingle roofs, the cricket trigger over wide chimneys, and roof drainage, and recent editions reference ANSI/SPRI ES-1 for perimeter edge-metal wind resistance, with related testing under FM 4435. The code is adopted and amended by jurisdiction, so confirm the requirement against the adopted edition and any local amendments. Where a manufacturer's warranted detail is stricter than a rule of thumb, the detail controls.

Units, terms, and conversions

Flashing has a deep vocabulary, and the same piece reads differently across a detail drawing, a product sheet, and a spec, so the terms are worth pinning down.

Base-flashing height is given in inches above the finished roof, commonly at least 8 in on low-slope work and 4 in or more on steep-slope. A reglet is the saw-cut groove a counterflashing tucks into; a termination bar is the metal strip that fastens a membrane flashing's top edge. Step flashing is woven per shingle course at a sidewall; apron flashing is the continuous piece at a headwall. A cricket and a saddle are the same diverter. A pitch pan, pourable sealer pocket, and pitch pocket are the same last-resort detail. Edge metal, drip edge, gravel stop, and fascia are all perimeter flashings, with the wind standard ANSI/SPRI ES-1 covering fascia, drip edge, gravel stop, and coping.

Base flashing

The roof material turned up a wall or curb that waterproofs the joint, commonly at least 8 in above a low-slope roof

Counterflashing

The metal cap over a base flashing that sheds water over its top edge so water cannot get behind it

Step flashing

Individual L-shaped pieces woven one per shingle course where a slope runs alongside a wall

Apron / headwall flashing

A continuous piece run over the roofing where the top of a slope meets a wall

Drip edge

Perimeter metal at eaves and rakes that kicks water off the edge and ties the roof down against wind

Coping

The sloped cap covering the top of a parapet wall, a wind-uplift item under ANSI/SPRI ES-1

Through-wall flashing

A concealed waterproof layer in a masonry wall that collects water and weeps it back outside

Reglet

A saw-cut groove in masonry that receives and holds the top of a counterflashing

Cricket / saddle

A small peak built uphill of a chimney or curb that diverts water around it

Pitch pan

A pourable sealer pocket flashed around an odd penetration and filled with sealant; the last-resort detail

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