For roofing crews, foremen, and estimators — not a homeowner how-to

Flashing workmanship is arithmetic before it is craft.

Steep-slope asphalt, slate, wood and tile · residential and light commercial

Most of what separates a detail that runs twenty-five years from one that calls back in nine is decided by four numbers: the exposure, the piece length, the lap those two produce, and where the fastener sits inside it.

30-second answer

What actually decides whether a flashing detail lasts?

Flashing lasts when its geometry sheds water without help. Three things decide that on site: each piece laps over the one below in the direction water runs, the metal-to-metal lap covers the fastener, and sealant supplements a joint that already works. The published instructions for the specific shingle set the dimensions — and departing from them moves the risk onto you.

Safety first

Flashing work concentrates the crew at the rakes, eaves, valleys and wall corners — reaching, working one-handed, and often off a ladder.

Every detail on this page lives at a rake, an eave, a valley, or a roof-to-wall corner. Those are the places a crew reaches past the plane, works one-handed with a brake or a pair of snips, and leans off a ladder to set a kickout. OSHA 29 CFR 1926.501(b)(13) requires that each employee engaged in residential construction activities 6 feet (1.8 m) or more above lower levels be protected by guardrail systems, safety net system, or personal fall arrest system unless another provision of that paragraph provides an alternative. Steep roofs fall under 1926.501(b)(11) at the same 6-foot trigger.

The residential provision does allow a written fall protection plan under 1926.502(k) where conventional systems are infeasible or create a greater hazard, but the standard states plainly that there is a presumption that it is feasible and will not create a greater hazard, and that the employer carries the burden of establishing otherwise. A plan is a documented argument, not a default.

Fall protection is an employer obligation, not a personal choice. If your state runs its own OSHA-approved plan, its rule may be stricter than the federal one and it is the one that applies to you. Fall protection on roofing work is covered separately in fall protection on roofing work.

Learning paths and saved lessons

At a glance

The numbers this page turns onSection link

Every dimension below comes from a named published document. None of them is a universal rule, because none of them is: the instruction for the specific product on the specific roof controls, and where two respectable sources disagree — and below, two of them do — the product instruction is the one that decides who carries the risk.

Step-flashing lap: piece length minus shingle exposureConsecutive pieces are offset up-slope by exactly one exposure, so this is the whole of it. Nothing else on the roof changes the number.
Minimum piece length (CertainTeed rule of thumb): exposure + 2 in“As a general rule of thumb, the minimum length of flashing should be 2″ more than the shingle exposure.” Master Craftsman Shingle Applicator’s Manual, 16th edition, ch. 6.
Minimum metal-to-metal overlap (CertainTeed): 2 in between consecutive piecesStated separately in the same list. It is the same requirement as the rule of thumb, written twice.
Where the fastener goes (CertainTeed): the uppermost 2 in of the piece“Step flashing fastener(s) should be placed in the uppermost 2″ area of the step flashing piece, to avoid leaks.” The 2 in lap and the 2 in fastener band are dimensioned to each other.
NRCA suggested step flashing: 7 in long × 8 in wide, for standard-sized asphalt shinglesProfessional Roofing, May 2005, “manual elements”. The published metric equivalents are 178 mm and 203 mm.
Model-code minimum (IRC R905.2.8.3, 2015 through 2024): 4 in high × 4 in wideMODEL text, and stable across editions: the Building America Solution Center quotes it from the 2015 IRC, CertainTeed from the 2018, and the 2024 IRC still reads “not less than 4 inches in height and 4 inches in width”. It dimensions the legs and not the length along the slope — the dimension that decides the lap. Not law anywhere until adopted, and adoptions amend.
Flashing cement, IBHS FORTIFIED: 8 in wide at open-valley edges; maximum 1/8 in thickA maximum, not a minimum. Cement is specified in width and thickness because more of it is a defect, not extra insurance.
Reglet depth (CertainTeed): 1 in minimum into masonry; 1-1/4 to 1-1/2 in preferredWith a 3/8 to 1/2 in reverse fold acting as a spring-loaded hem lock. The fold is what holds the metal; the sealant is not.

Tradeoffs

Where this page is right, and the jobs where it is wrongSection link

The position here is that flashing is a lapped, mechanically-held assembly sized to the covering, and that sealant supplements it. That is right most of the time on a steep-slope roof. Here is where it is not.

Best when

Asphalt shingles, slate, or wood on a wall or a chimney — the coverings NRCA names for individual step flashing rather than a continuous L.
A tear-off, where the wall side is open and the water-resistive barrier can be re-lapped over the flashing legs instead of under them.
A metric-dimension laminate, where the exposure is 5-5/8 in and a 7 in piece is 5/8 in short of the manufacturer's own minimum.
Any detail where a warranty claim is plausible later — because the record of what was installed to which instruction is what the claim turns on.
Masonry sound enough to take a saw cut, where a reglet buys a joint that does not depend on a bead.

Think twice if

The covering is tile. NRCA says the same detail applies to slate, tile and wood, but that “because of the unique shape of many tiles, continuous channel flashing is used for tiles.” Step flashing is not the universal answer.
The covering is standing-seam metal or a membrane. The Building America Solution Center is explicit: “when installing metal or rubber membrane roofs, use continuous flashing rather than pieces of step flashing.”
You are about to condemn continuous counterflashing. Continuous base flashing under a shingle roof is the defect. Continuous counter flashing over it is a published alternative that CertainTeed says avoids “water leaks along the vertical joints in high wind” and “the entry of wind-driven, fine-grained snow.”
The masonry is historic, soft, deteriorated, or due for repointing or relining. Cutting a reglet into it is a mason's call and possibly a preservation one, not a roofer's afternoon.
The existing counterflashing is sound. CertainTeed's own reroofing guidance is that at walls and skylights “it might be possible to save the counter flashing if it is in good condition” — with the caveat that reused metal has to last the life of the new roof.
The courses were deliberately adjusted. A crew planning a headwall will “adjust the exposure slightly (and evenly) in the previous courses”; the lap arithmetic below uses nominal exposure and stops being exact where the exposure is not.

What changes the answer

The exposure of the specific shingle. It sets the offset, and therefore the lap, and therefore the minimum piece length. It is a product number, not a trade number.
What the published instruction for that product says, which outranks every general figure on this page including the ones taken from NRCA.
What is above the roof: siding that lifts and re-laps, masonry that takes a cut, stucco that does not come off, or a wall assembly that has to be opened by another trade before the flashing can be integrated correctly.
The adopted code edition in that jurisdiction, its amendments, and whether the inspector looks at flashing on a reroof permit at all.
Whether the wall's water-resistive barrier can be lapped over the flashing legs. If it cannot, the flashing is a shelf, and no dimension on this page fixes that.
Climate: salt, freeze-thaw, deep snow and wind-driven fine snow each change the metal, the lap you want, and whether stepped or continuous counterflashing is the better call.

The mechanism, stated for people who install it

Water leaves a roof by being handed downhill, one lap at a timeSection link

This is not new to anyone reading it. It is stated here because every specific decision below is a consequence of it, and because the shortcuts all consist of breaking it in a way that is invisible on the day.

Two step-flashing runs at the same 5-5/8 in shingle exposure, flattened into the plane of the wall so the lap can be measured directly. Panel A uses 7-5/8 in pieces; the 2 in lap that produces is exactly the 2 in band the fastener is supposed to sit in, so the metal above covers every nail below. Panel B uses 5 in pieces at the same exposure; five is less than five and five-eighths, so the pieces never touch and the fasteners sit in the open channel. The difference between the two panels is one dimension on a purchase order. A full text description is available to screen readers.Original diagram, Understanding Roofing. Dimensions derived from the CertainTeed Master Craftsman Shingle Applicator's Manual, 16th edition.

CertainTeed puts it in one sentence at the opening of its flashing chapter: Roof flashing works like shingles: it overlaps and sheds water. The sentence that follows is the one worth keeping — when correctly designed and installed, flashing can only be defeated by water running uphill — because it names the actual design target. You are not building a seal. You are building a surface on which every joint faces downhill, and then you are accepting that snow, ice, and wind-driven rain are the three conditions that make water run the other way.

Everything that follows is an application of that. A detail fails when a joint faces uphill, when a fastener is on the wet side of a lap, or when a lap is short enough that a small amount of uphill travel clears it. The first is a sequencing error, the second is a placement error, and the third is an arithmetic error — and the third is the one that gets installed by competent people, because nothing about it looks wrong.

Two pieces that get confused, and one that gets skipped

CertainTeed’s own vocabulary note is worth repeating because proposals and callbacks both turn on it: Step flashing is sometimes called “base flashing” and cap flashing is sometimes called “counter flashing.” Often, exterior wall siding serves as cap flashing. Base flashing belongs to the roof and moves with the deck. Counterflashing belongs to the wall or the chimney and moves with it. The manual gives the reason the two are separate rather than one piece: don’t fasten the cap flashing to the roof deck or to the step flashing, since they are meant to move independently of each other to accommodate any structural movement.

That is why fastening a counterflashing through into the deck is not a belt-and-braces improvement. It converts a designed sliding joint into a rigid one across two assemblies that move at different rates, and the joint opens somewhere else.

For what each flashing location is and what it is called, the reader-side page is roof flashing. For what the failures look like once they are running, see flashing failures. This page assumes both and talks about the hands.

The original asset

The lap is the piece length minus the exposure. That is the whole calculation.Section link

Step flashing is the one detail on a steep-slope roof whose adequacy is fully determined by two numbers that are both known before the truck is loaded.

Consecutive step-flashing pieces are offset up the slope by exactly one shingle exposure, because one piece goes in per course. So if a piece is L inches long along the slope and the covering is laid at an exposure of E inches:

metal-to-metal lap = L − E

Nothing else affects it. Not the pitch, not the wall, not the leg heights, not how carefully the pieces are set. CertainTeed publishes the same fact from the other direction as a rule of thumb — the minimum length of flashing should be 2″ more than the shingle exposure — and separately requires that the pieces of flashing must overlap each other by at least 2″. Those are one requirement stated twice: L ≥ E + 2 is the same statement as L − E ≥ 2.

Why two inches, and not some other number

Because two inches is also where the nail goes. The same manual instructs that step flashing fastener(s) should be placed in the uppermost 2″ area of the step flashing piece, to avoid leaks. Put the two rules beside each other and the design intent is visible: the 2 in lap is sized so that the 2 in fastener band of the piece below sits entirely under the piece above. The lap band and the fastener band are the same band.

That is why 1-3/8 in of lap is not “nearly enough.” It is 5/8 in of the fastener band left in the open channel between the wall and the shingle — the exact place water runs when it gets behind the cladding.

Metal-to-metal lap produced by a step-flashing piece of a given length at a given shingle exposure. Every cell is the subtraction L − E, computed by this site. “ok” means the lap meets CertainTeed’s published 2 in minimum; “short” means it does not; “gap” means the pieces never touch and the joint is backed only by underlayment.
Step piece length (along the slope)	at 4 in exposure	at 5 in exposure	at 5-5/8 in exposure	at 8 in exposure
5 in	1 in — short	0 in — no lap	5/8 in gap	3 in gap
6 in	2 in — ok	1 in — short	3/8 in — short	2 in gap
7 in	3 in — ok	2 in — ok	1-3/8 in — short	1 in gap
7-5/8 in	3-5/8 in — ok	2-5/8 in — ok	2 in — ok	3/8 in gap
8 in	4 in — ok	3 in — ok	2-3/8 in — ok	0 in — no lap
10 in	6 in — ok	5 in — ok	4-3/8 in — ok	2 in — ok

Read this table one item at a time

5 in

at 4 in exposure: 1 in — short
at 5 in exposure: 0 in — no lap
at 5-5/8 in exposure: 5/8 in gap
at 8 in exposure: 3 in gap

6 in

at 4 in exposure: 2 in — ok
at 5 in exposure: 1 in — short
at 5-5/8 in exposure: 3/8 in — short
at 8 in exposure: 2 in gap

7 in

at 4 in exposure: 3 in — ok
at 5 in exposure: 2 in — ok
at 5-5/8 in exposure: 1-3/8 in — short
at 8 in exposure: 1 in gap

7-5/8 in

at 4 in exposure: 3-5/8 in — ok
at 5 in exposure: 2-5/8 in — ok
at 5-5/8 in exposure: 2 in — ok
at 8 in exposure: 3/8 in gap

8 in

at 4 in exposure: 4 in — ok
at 5 in exposure: 3 in — ok
at 5-5/8 in exposure: 2-3/8 in — ok
at 8 in exposure: 0 in — no lap

10 in

at 4 in exposure: 6 in — ok
at 5 in exposure: 5 in — ok
at 5-5/8 in exposure: 4-3/8 in — ok
at 8 in exposure: 2 in — ok

Derived arithmetic, not a source claim: every cell is length minus exposure. The 2 in threshold used to label the cells is CertainTeed’s published minimum for CertainTeed shingles; another manufacturer may publish a different one, and its number governs its product. The exposures in the column headings are the ones CertainTeed names for its own product families. The table assumes nominal exposure and square-set pieces, and it says nothing about leg heights, which are a separate requirement.

The published minimums are the same arithmetic, run backwards

CertainTeed publishes a table of minimum step-flashing lengths by product family. Subtract two inches from each and you recover the exposure of the shingle it is for — which is a good sign that the rule of thumb is not a rule of thumb at all but the actual derivation, and a good way to check whether a length you have been handed is right for a shingle that is not on the list.

CertainTeed's published minimum step-flashing lengths, the exposure each one implies, and whether that exposure is confirmed elsewhere in the same manual.
Product family	Published minimum length	Implied exposure (length − 2 in)	Exposure as stated elsewhere in the manual
Presidential, Presidential TL	6 in	4 in	4 in — the application chapter states shingle applications are on 5 in and 15 in offsets with a 4 in exposure.
Landmark Series, all three-tab strip shingles (English size)	7 in	5 in	5 in — the manual refers throughout to square-tab asphalt strip shingles at a 5 in exposure.
Landmark Series, metric dimension	7-5/8 in	5-5/8 in	5-5/8 in — stated in the same paragraph as the rule of thumb, as the worked example.
Highland Slate, Grand Manor, Carriage House, Belmont	10 in (12 in for the first Carriage House piece)	8 in	8 in confirmed for Highland Slate, described as an oversized 18 in × 36 in designer shingle with an 8 in exposure. Not separately confirmed in this manual for the other three.

Read this table one item at a time

Presidential, Presidential TL

Published minimum length: 6 in
Implied exposure (length − 2 in): 4 in
Exposure as stated elsewhere in the manual: 4 in — the application chapter states shingle applications are on 5 in and 15 in offsets with a 4 in exposure.

Landmark Series, all three-tab strip shingles (English size)

Published minimum length: 7 in
Implied exposure (length − 2 in): 5 in
Exposure as stated elsewhere in the manual: 5 in — the manual refers throughout to square-tab asphalt strip shingles at a 5 in exposure.

Landmark Series, metric dimension

Published minimum length: 7-5/8 in
Implied exposure (length − 2 in): 5-5/8 in
Exposure as stated elsewhere in the manual: 5-5/8 in — stated in the same paragraph as the rule of thumb, as the worked example.

Highland Slate, Grand Manor, Carriage House, Belmont

Published minimum length: 10 in (12 in for the first Carriage House piece)
Implied exposure (length − 2 in): 8 in
Exposure as stated elsewhere in the manual: 8 in confirmed for Highland Slate, described as an oversized 18 in × 36 in designer shingle with an 8 in exposure. Not separately confirmed in this manual for the other three.

Column 2 is quoted from the manual. Column 3 is this site’s arithmetic. Column 4 is quoted from elsewhere in the same document, and says plainly where the confirmation is missing. The agreement across three product families is what makes the rule usable on a fourth — but only as a starting point, because the instruction for that fourth product is what actually governs.

What a crew does differently with this

Reads the exposure off the shingle’s own instruction sheet before the flashing is ordered, not off habit. English-size and metric laminates are 5/8 in apart and look identical in a stack.
Buys step flashing in the length the arithmetic asks for, per job, rather than keeping one size on the van for everything.
Sets the fastener high — in the upper part of the piece, inside the band the next piece will cover — and, on a short-lapped legacy detail found mid-job, understands that moving the nail up cannot recover a lap that is not there.
Measures one installed lap early in the run rather than at the end, because the error is systematic: if the first one is short, all thirty are.

The distinction that gets collapsed

Continuous flashing: one of the two is the defect, and it is not the one people nameSection link

“Continuous flashing” describes two different pieces in two different positions. One of them is a defective substitute. The other is a published alternative that is sometimes better than what it replaces.

Continuous base flashing under a shingle roof

This is the shortcut: a single long L-shaped piece run up the wall and out onto the deck, with the shingle courses butted against it and usually a bead of sealant along the top. It is quick, it takes one person, and it looks tidy.

NRCA states the reason it fails in one clause. Step flashing is recommended for asphalt shingles, slate and wood roof systems instead of a continuous L-shaped flashing piece so water is directed onto the top surface of the roof covering and not the underlayment. Read that carefully, because it is not the argument most people give. The problem is not that a continuous piece leaks along its length. The problem is where it puts the water it collects: the continuous piece drains onto the deck side of the covering, under the shingles, onto the underlayment — which is a secondary layer being asked to act as the primary one, continuously, for the life of the roof. Individual pieces, lapped in shingle fashion, hand the water out onto the top of the covering instead.

There is a second reason, and CertainTeed states it as a fastening rule without naming continuous flashing at all: Avoid driving nails through metal flashing that covers two sides of adjoining underlaying materials, such as different pieces of roof decking or between vertical and horizontal planes. It is very difficult to permanently seal the punctures in these situations and, over time, expansion and contraction of the flashing can cause the flashing to buckle. A continuous L is, by definition, one piece of metal spanning a vertical plane and a horizontal one, fastened across the join. Individual pieces are, among other things, a movement joint every course.

Continuous counter flashing over a shingle roof

This is a different piece, in a different position, and it is legitimate. CertainTeed presents it as an optional counter flashing technique using a continuous metal piece instead of the typical staggered (stepped) counter flashing, and gives the reason to prefer it: stepped counterflashing can lead to water leaks along the vertical joints in high wind or permit the entry of wind-driven, fine-grained snow. The step flashing underneath is still individual, per course. Only the weather-side cap is continuous.

So when someone says “continuous flashing is a red flag,” the right follow-up is which piece. Continuous base flashing under a shingle roof is a defect. Continuous counter flashing over one is a choice, and on a windward wall in a snow climate it is often the better choice.

And on roofs that are not shingles

The Building America Solution Center states the exception without hedging: when installing metal or rubber membrane roofs, use continuous flashing rather than pieces of step flashing. NRCA adds tile: because of the unique shape of many tiles, continuous channel flashing is used for tiles. Step flashing is the correct detail for lapped small-unit coverings. It is not a universal principle, and applying it to a standing-seam roof is its own defect.

Reglet, surface mount, and the bead

Counterflashing: what is actually holding it upSection link

Both published methods are mechanical. In both of them the sealant is the last thing installed and the first thing that will need renewing.

CertainTeed’s reglet procedure is worth reading as a sequence rather than as a picture, because the order tells you what is doing the work. Cut a groove a minimum of 1″ deep into the masonry (1-1/4″ to 1-1/2″ is preferred). Form the metal with a reverse fold of 3/8″ to 1/2″, which will act as a spring-loaded hem lock in the groove. Run sealant into the reglet, set the metal, let it cure, then run a final bead of sealant/caulk on the exposed area of the reglet to seal the metal-to-masonry joint. And form a pinch bend at the lower edge, which will ensure a tight fit against step flashing and add rigidity.

The hem lock is what holds the metal. It is a spring in a groove. Remove the sealant entirely and the flashing is still mechanically engaged; remove the hem lock and no amount of sealant makes it a joint. The bead is there to close a gap between two hard materials that will never move together, and it is a consumable.

Surface-mounted counterflashing is the manual’s stated alternative to that, and the detail it draws has the same shape: a hemmed caulking lip for the sealant, compressive tape sealant behind the metal to span irregularities, and a bead at the top. The manual does not dimension the fastening in that figure, and how a surface-mounted piece is held to a particular masonry wall is a job-specific call rather than something this page can publish. The principle is unchanged though: something mechanical holds the metal, and the sealant is closing a gap between two materials that will never move together.

There is a third thing that gets called surface-mounted counterflashing and is neither of these: a strip of metal held to the wall by the bead alone, or no metal at all and a bead run along the top of the step flashing. That is not a method with a shorter service life. It is a maintenance item installed where a joint should have been, in a position nobody will service.

Which is worth naming, because a customer may arrive holding it. The consumer-facing pages on this site list surface-mounted counterflashing on a chimney among the things to look at harder — see roof flashing. That is not a claim that the method is defective, and it does not contradict what is written here. It is a statement about what can be told apart from a driveway: a formed, taped, fastened surface-mounted piece and a strip stuck on with a bead look identical from the ground, and the second is the more common of the two. If you use the method, what stops that judgement landing on your work is the written scope and the photographs taken before the staging comes down — not an argument on the day.

One clearance number worth keeping, because it is the reason pre-formed counterflashing sometimes will not sit down: the manual asks for a 3/4″ separation from the step flashing corner bend to the bottom edge of the counter flashing, to account for the thickness of the shingles laid over the step flashing.

Safety first

Cutting a reglet is silica work, and it is regulated as such.

29 CFR 1926.1153 applies to all occupational exposures to respirable crystalline silica in construction work except where exposure stays below the stated action level. Cutting a mortar joint with a handheld power saw is squarely inside it. The Table 1 engineering control for handheld power saws, any blade diameter, is to use saw equipped with integrated water delivery system that continuously feeds water to the blade and to operate and maintain tool in accordance with manufacturer’s instructions to minimize dust emissions. Used outdoors, no respirator is specified for four hours or less and APF 10 beyond that; used indoors or in an enclosed area, APF 10 either way.

Whether the standard applies to a particular employer on a particular day depends on the work, the employer, and whether the state runs its own OSHA-approved plan. Nothing here is a compliance determination.

Bring the wet-cut saw and the water supply to the job, or do not plan on cutting a reglet that day. Table 1 is one compliance route; the standard’s exposure-control-plan, housekeeping, training and medical surveillance provisions are separate from it.

Where a roof-to-wall run ends above a wall

Kickout: the smallest piece with the longest consequence chainSection link

What makes this one worth its own section is not the difficulty. It is that omitting it damages something other than the roof, over years, invisibly, and the damage is not yours to see.

At the bottom of a roof-to-wall run, water leaves the intersection channel and the wall face above it and arrives at a corner. If nothing turns it out, it runs down the cladding and into the joint behind it. The consequence chain runs cladding, water-resistive barrier lap, sheathing, framing, cavity insulation, interior finish — and none of the early links is visible from the roof or from inside. The Building America Solution Center’s instruction on an existing house is not “add a kickout” but carefully inspect the side wall at the roof eave for possible deterioration from bulk water leakage and repair as needed. The roofing part is the cheap part.

Diagnosis and the repair scope for a house that has been going without one are on flashing failures. What belongs here is fabrication.

NRCA’s one-piece detail, and what it asks of the siding

NRCA’s published approach to the eave-to-wall interface is not a bolt-on diverter. It is a soldered one-piece step flashing at that interface, fabricated with a kickout at the downslope edge, installed over the starter course and under the first exposed course of shingles. Two consequences follow, and both are scope rather than skill:

The kickout has to clear the cladding. NRCA specifies that the dimension of the kickout should equal or be slightly larger than the thickness of the wall covering. A diverter that projects less than the siding is thick is delivering water to the back of the siding, which is the failure it was installed to prevent. That means the siding thickness is a number the flashing is dimensioned to, and it is known before the job.
The siding has to be notched. A vertical notch in the siding is required for the installation of this unique piece of step flashing. Which means the wall trade is involved, or you are, and either way somebody is cutting cladding. That is a conversation to have while pricing, not while standing on a ladder with a piece of soldered copper.

NRCA also allows that it may be prudent to install sealant along the top and vertical edges of the exposed portion of the kickout to help prevent water intrusion. Note the position of that sentence: after the geometry, on the exposed edges, as a supplement. It is not the detail.

Worth naming honestly: the three sources here do not speak with the same force. NRCA fabricates it into the flashing. BASC instructs you to install kick-out flashing at the end of a roof-wall intersection to divert water away from the wall and into gutters and to ensure it is large enough to handle expected stormwater flows. CertainTeed’s manual offers it as a tip — you may want to install a kick-out diverter at the eaves’s edge of the sidewall. One trade association, one federal program, and one manufacturer, at three different strengths. If you want it to be in the job, it goes in the written scope; it will not get there by inference.

The decision made before the first course crosses

Valleys: the cut side is decided by watershed, not by slopeSection link

The shorthand — cut the steeper side — agrees with the published rule on plenty of roofs and disagrees on plenty of others, because the published rule is not about slope at all.

In a closed-cut valley, CertainTeed’s rule is stated in terms of water volume, not pitch: the shingles on the deck with the least area of watershed are the shingles which should be applied first, to go under the other shingles on the adjoining deck. The shingles on the adjoining deck (the deck with the greatest amount of watershed) are the shingles which should be cut. The plane carrying more water crosses on top and is cut back; the plane carrying less runs underneath, whole.

The manual then publishes two cases specifically because they cut against intuition:

If a 10/12 roof section forms a valley with a 4/12 roof section, and the 10/12 section is one-third the area (water volume) of the 4/12 section, you should cut the shingles on the 10/12 side. The steeper plane gets cut here — but because it carries less water, not because it is steeper.
If an 8/12 roofing section forms a valley with a 10/12 roofing section and the 8/12 roof has one-third the area (water volume) of the 10/12 section, put the cut on the 8/12 side. Here the shallower plane gets cut, for the same reason.

In both, the answer follows area. Which means the decision is an estimating decision as much as an installation one — the areas are known from the takeoff, and marking the cut side on the plan costs nothing and stops it being decided by whoever reaches the valley first.

The execution numbers that go with each method

For closed-cut work, the manual asks for the lining centered under the valley, the first course carried across at least 12″ onto the adjoining plane, no fasteners within 6 in of the centerline, the cut struck 2 in back from the centerline, and cut 2″ diagonally off the upper corner of each trimmed shingle (at an approximate 45° angle) to direct water into the valley. The stated purpose of that clip is worth reading as a negative statement about the alternative: if a 45-degree clip is what directs water into the valley, an unclipped square corner is what does not, on every course.

There is also an alternate closed method in which the shingles on the second plane are laid vertically against the cut line, and it carries an explicit restriction: This application cannot be used with shingles that have cut-outs, such as a typical 3-tab strip shingle. Method availability is product-dependent.

For open valleys, two constraints matter at the point of ordering. First, thick shingles do not close: open valleys are strongly recommended for the heavy laminates because of the thickness and multiple-layer construction of these types of shingles, they are not designed to conform easily with the angle or shape of a valley. Second, when installing open valleys, only metal valleys are recommended. Mineral-surfaced roll roofing is not considered to be sufficiently durable to last for the warranted life of today’s shingles. The manual publishes a table of metals it considers equivalent to 16 oz copper for that use; the point for a crew is that the metal is specified, not chosen on site.

Reused valley metal is the one reuse the same manual will not entertain: Even though valley flashing may appear to be sound, plan to remove and replace it. Small cracks in old valley flashing are hard to detect, and it is not worth risking a possible leak because of it.

Boots, flanges and collars

Penetrations: the flange laps like a shingle, and the collar is on a different clockSection link

Two separate things are happening at a pipe. One is a lapped sheet-metal detail built on the same rule as every other lap on the roof. The other is a piece of exposed elastomer, and the two do not age at the same rate.

The lap order, which is the same rule as everywhere else

Both the manufacturer and the federal guidance describe the same sequence, and it is worth stating as a sequence because it is entirely about which piece goes under which. CertainTeed describes the finished detail as appearing with the lower part of the flange overlapping the lower shingles, and the side and upper shingles overlapping the flange. The Building America Solution Center, for an existing roof: a formable self-adhered membrane collar around the pipe first, then install the metal flashing collar over the membrane flashing collar and overlap the metal collar onto the lower layer of the asphalt shingles, then continue installing shingles around and above the pipe. These shingles will cover the upper edge of the metal flashing collar.

Downslope edge on top of the covering. Upslope and side edges under it. It is the step-flashing rule again, in two dimensions instead of one: every edge faces the way the water is going.

The failure that follows from getting it wrong is not subtle in mechanism, only in timing. A flange whose upper edge sits on top of the shingles above it is a scoop, and a flange nailed through on its upslope side has put fasteners in the wettest part of the detail.

The collar is the shortest-lived thing in the assembly

Set aside the sheet metal. The elastomeric collar or boot that seals against the pipe is one of very few components on a shingle roof that is simultaneously a polymer, fully exposed to sun with no covering over it, and mechanically stretched around something that expands and contracts on its own schedule. Most of what surrounds it is either mineral-surfaced, covered by metal, or lapped under something else.

We are not going to give you a number of years, because there is not a defensible one to give. The service-life figures that circulate for boots come from contractor marketing pages, not from a testing body, and no publicly verifiable dataset for them could be found. What can be said is what determines it: the polymer, the orientation and shading of that particular pipe, the surface temperatures that roof reaches, whether anything shields the collar from direct UV, and whether the detail depends on the collar alone or on lapped metal that would still shed water if the collar split.

Which points at the design decision rather than the number. If the collar is the only thing between the pipe and the deck, you have installed a component with a life you cannot state into a roof with a life you have quoted. The detail that survives is the one where lapped metal, and not the elastomer, is what is actually shedding the water at the flange — so that a split collar is a maintenance visit rather than a leak. CertainTeed’s own field tip points the same way: to prolong the life of a newly installed collar, you can remove the neoprene from another new collar and install it over the existing vent collar to function as a “counter-flashing.” That is a crew inventing a counterflashing for a component that did not come with one, which is a fair summary of the problem.

Supplement, not waterproofing

Sealant: where the published instructions actually put itSection link

The honest version of this is not “never use sealant.” It is that every legitimate use of it in these documents arrives with a location and a dimension — and that a bead with neither is usually standing in for something.

Look at what the specifications actually say and a pattern falls out. Sealant and flashing cement appear constantly — and every time, they are placed somewhere specific, at a stated size, doing a bounded job:

Dimensioned, with a maximum. IBHS FORTIFIED, as reproduced by the Building America Solution Center, calls for shingles at open-valley edges to be set in a minimum 8-inch-wide strip of flashing cement and the cut side of closed valleys in a minimum 2-in.-wide, ⅛-in.-thick strip, with the maximum thickness of flashing cement at ⅛ in. A maximum. More is out of spec.
With a stated failure mode for overuse. The CertainTeed manual repeats the same caution across product chapters: Excessive use of roofing cement can cause shingles to blister. The extra bead is not neutral.
Matched to the materials. Use caulks and sealants designed for the materials involved. Urethanes are suited for metal and masonry applications. SBS, SBR or rubber-based caulks are ideal for shingles and metal flashing. And for the reglet specifically, choose a sealant/caulking that is specifically designed for use with masonry.
Installed last, over a joint that already works. In the reglet sequence the final bead goes on after this sets up — after the spring-loaded hem lock is engaged and cured in. The joint is complete before the bead is applied.

The working test on site is therefore not “is there sealant here” but “if this bead were not here, would water still be shed?” If yes, it is a supplement doing its job. If no, a maintenance item has been installed in place of a joint, in a location nobody will service, and its service life is now the detail’s service life.

One place NRCA takes the argument further than a bead-and-fastener habit would: it recommends soldering the joints of its one-piece step flashing for longevity and durability of its weatherproofing ability instead of joining the seams by overlapping, sealing and installing fasteners, and the stated reason is access — it is difficult to access the flashing piece if there is a maintenance issue. The logic is worth generalising: the harder a joint is to get back to, the less it should depend on anything consumable.

The specification that is one line long and easy to leave out

Metals and fasteners, at the moment of installationSection link

The mechanism of galvanic corrosion is covered elsewhere on this site. What belongs here is the pair of choices a crew makes without noticing that it is choosing.

CertainTeed’s installation rule is short enough to be a shop rule: use fasteners of the same metal as the flashing material they will penetrate. For example, use only copper nails with copper flashing. Use aluminum (or galvanized) nails with aluminum flashing. Also, do not combine dissimilar metals in your flashing system. Where a combination cannot be avoided — they must be isolated with underlayment, bituminous paint or another non-conducting material.

The two ways a crew creates a couple by accident are worth naming because neither feels like a decision:

The nail box. One box of galvanized roofing nails serves the whole job, including the three copper pieces at the chimney. The metal was specified in the proposal; the fastener was not, so it defaulted.
Runoff, not contact. Metals do not have to touch to couple. New aluminum installed downslope of an existing copper valley or under a copper gutter is in the runoff path from the copper. That is a layout question, decided by where the new metal goes, and it is worth a minute at the start of a repair.

NRCA’s framing of metal selection is the one to carry into an estimate: the type and thickness of the metal should be commensurate with the anticipated service life of the asphalt shingle roof system. A flashing that outlives one covering and not the next is a decision, made when the metal was chosen, whether or not anyone made it deliberately. In salt air that decision gets much less forgiving — coastal salt corrosion covers the environment; the galvanic series and the thermal-movement arithmetic are on flashing failures.

Considerations

What changes this on a real buildingSection link

Code and jurisdiction

There is no nationwide building code for site-built construction. The code figures on this page are model provisions, and none of them reaches you from the publisher: we could not open the official model text ourselves, because codes.iccsafe.org refuses automated requests. The CertainTeed manual and the Department of Energy’s Building America Solution Center each quote the sidewall-flashing minimum from the 2018 and 2015 IRC respectively, and the current edition was read through the same third-party code aggregator this site’s other code-carrying pages use.

The three readings agree. The Building America Solution Center attributes 4 in by 4 in to the 2015 IRC, CertainTeed to the 2018, and the 2024 IRC at R905.2.8.3 still reads “base flashing against a vertical sidewall shall be continuous or step flashing and shall be not less than 4 inches in height and 4 inches in width.” That the figure is stable across a decade of editions is a reason to trust the number. It is not a reason to treat it as current law anywhere. Your jurisdiction’s adopted edition, its amendments, its effective date, and its inspector govern. Look them up before you treat any of it as a requirement on a permit.

MODEL text, read secondhand — through two manufacturer and government guides for the 2015 and 2018 editions, and through a third-party code aggregator for the 2024. None of those is the publisher and none of them is adopted law. Record the jurisdiction, adopted edition, amendments, effective date and official URL yourself, and confirm with the authority having jurisdiction. Nothing here is a compliance determination for any job.

Climate

Cold changes which counterflashing you want. CertainTeed offers continuous counter flashing specifically as an alternative to stepped counterflashing because stepped units can lead to water leaks along the vertical joints in high wind or permit the entry of wind-driven, fine-grained snow. On an exposed wall in a snow-and-wind climate that is a real reason to change the detail, and it is the opposite of a shortcut.

Cold also changes the eave. Where meltwater backs up behind an ice dam, the flashing at the eave is being asked to resist standing water rather than running water, and the assembly that handles that is the ice barrier, not the metal.

Slope and drainage

Slope changes how far water travels uphill under a lap, which is why CertainTeed says its 2 in wall leg may not be adequate and that for additional protection in areas that experience heavy rain or snow storms, or on low slope roofs, step flashing with greater height should be used. On the shallow end of steep slope — CertainTeed labels below 4:12 down to a minimum of 2:12 a low-slope application with its own underlayment requirement — the leg heights and the lap both want to go up, not down. What that application actually requires is set by the published instruction for that product and by the adopted code in that jurisdiction, and neither is decided here.

Wind

Wind performance is a property of a tested assembly on a specific building, not of a flashing detail. What the detail changes is whether the edge metal is fastened at the spacing the adopted code and the tested assembly call for, and whether the counterflashing is engaged mechanically rather than held by a bead. Neither of those is a wind rating.

Nothing on this page is a wind-design determination. Basic wind speed, exposure, height, geometry, pressure zone, enclosure, risk category, attachment, and the tested assembly all matter, and a marketing mph number is not a code determination for any building.

Fire

Fire classification belongs to a tested assembly — deck, underlayment and covering together under a defined test — and not to any single component. No flashing choice on this page carries a class, changes one, or preserves one.

If a fire classification matters on a job, the question is which tested assembly was specified and whether what you installed is that assembly. The flashing metal is not the answer to it.

Salt and dissimilar metals

CertainTeed’s installation-side rule is short enough to run a crew on: use fasteners of the same metal as the flashing material they will penetrate. For example, use only copper nails with copper flashing. Use aluminum (or galvanized) nails with aluminum flashing. Also, do not combine dissimilar metals in your flashing system. Where a combination is unavoidable, the manual’s remedy is isolation: they must be isolated with underlayment, bituminous paint or another non-conducting material. The mechanism and the galvanic series are set out on flashing failures, and the corrosion environment near saltwater on coastal salt corrosion.

Maintenance

Two things in every flashing detail are maintenance items rather than permanent construction: sealant, and anything elastomeric that is left exposed to sun. Everything else — the laps, the reglet, the hem lock, the soldered joint — is built to be left alone. A detail that puts a maintenance item in a position nobody will ever reach is a detail that has quietly become permanent.

Warranty and repair

What the customer thinks they bought, and what you are actually carryingSection link

This is the place where a contractor's interest and a homeowner's interest genuinely diverge, and it is worth being straight about rather than pretending otherwise.

The instruction is the contract term, not a suggestion

A manufacturer’s workmanship coverage is written against its own instructions, and the exclusions are narrower and more specific than “bad work is not covered.” Two examples, both quoted from the CertainTeed manual and both about CertainTeed’s own programs: its SureStart Plus 5 Star warranty for workmanship coverage excludes any and all defects, damage or failure of shingles caused by application of shingles over decks not in accordance with applicable building code or acceptable building practices or not in accordance with the written instructions of the manufacturer. And in its roof-deck chapter the same manual lists, among the things a shingle manufacturer will not take the responsibility for, defects, damage or failure of shingles caused by applications that are not in strict adherence with the written instructions of the manufacturer. GAF’s Timberline application sheet put the same allocation in one line: Any deviation from printed instructions shall be the responsibility of applicator and/or specifier.

Read that as an allocation of risk rather than as a threat. The instruction is the boundary of what the manufacturer will answer for. Outside it, the answer is you. Those are three sentences out of two documents about two manufacturers’ programs, and they are quoted as examples of how the allocation is written — not as a summary of what any warranty on your job covers. The document issued for that product, in that state, is the one that decides, and this page is not it.

The divergence, plainly

Every shortcut on this page is cheaper, faster, and invisible from the ground on the day it is installed and for several years after. A continuous L instead of thirty step pieces. Reused flashings on a tear-off. No kickout. A surface-mounted counterflashing held by a bead instead of a cut reglet. Boots pushed on and caulked. A homeowner comparing three numbers cannot see any of it, which is exactly why the low number can be low. That is a real conflict, and it does not go away because everybody involved is decent.

What that means for a bid, in both directions

The useful consequence for a contractor is not that customers should be trusted less. It is that a bid that includes the detail is not obliged to match a bid that omits it, and the only way to be paid for the difference is to write the difference down: metal type and gauge, piece length against the shingle’s exposure, kickout present or absent, counterflashing method, valley method, whether existing flashings are reused. Pricing that scope is covered in pricing and margin.

Reuse is a decision with a rule attached

CertainTeed’s position is that step flashing should be replaced when re-roofing (unless the flashings are in like-new condition), that counterflashing at walls and skylights can sometimes be saved if it is in good condition but that reused flashing should last for the life of the new shingle roof, and that valley metal should be replaced regardless because small cracks in old valley flashing are hard to detect, and it is not worth risking a possible leak because of it. Reuse is legitimate; unexamined reuse is not.

Repairability

Flashing is repairable in proportion to how it was fastened. A reglet-set counterflashing can be dropped and reset. A soldered one-piece assembly cannot be opened without unsoldering it — which is precisely why NRCA prefers soldering instead of joining the seams by overlapping, sealing and installing fasteners, and says so on the grounds that it is difficult to access the flashing piece if there is a maintenance issue. You are trading serviceability for a joint that does not need servicing. Make that trade on purpose.

The consumer-side view of what these documents cover is in roofing warranties.

A warranty is a contract between a reader and whoever wrote it. What it covers, what voids it, whether it transfers, and how it is enforced are set by that document and by the law where the reader lives. Read the actual warranty for the product and the installer in front of you — not a summary of one, including this one.

Before the tear-off

Questions to settle before the crew is on the roofSection link

None of these is a question for the customer. They are questions for the supplier, the manufacturer's technical line, and the estimate — and every one of them is cheaper to answer on the ground.

What is the exposure of the shingle we actually ordered?
It is the input to every other number on this page. A metric-dimension laminate and an English-size strip shingle are 5/8 in apart, and 5/8 in is the whole difference between a compliant lap and a short one.
What length is the step flashing in the van, and does exposure + 2 in clear it?
One box of flashing does not serve every shingle. If the answer is 7 in and the shingle is metric, the manufacturer's own minimum is 7-5/8 in and you are 5/8 in short before anyone climbs a ladder.
Can the wall's water-resistive barrier be lapped over the flashing legs on this job?
The Building America Solution Center is explicit that the barrier must be “layered over the step flashing to provide a complete drainage system.” If the cladding will not come off far enough to do that, the flashing becomes a shelf and the metal work is beside the point. That is a scope conversation, and it happens before the contract.
Is there a roof-to-wall run that ends above a wall, and is a kickout in the price?
It is a small piece with the longest consequence chain on the building, it is routinely omitted, and BASC's instruction on an existing house is to “carefully inspect the side wall at the roof eave for possible deterioration from bulk water leakage” before assuming the repair is a roofing repair.
Which side of each valley is the cut side, and why that side?
The default rule is watershed, not slope, and CertainTeed publishes two worked cases where the steeper plane is the one that gets cut. If nobody has decided this before the shingles start, it gets decided by whoever reaches the valley first.
Are we cutting a reglet, and who is doing the silica controls?
A handheld power saw in masonry is regulated construction work under 29 CFR 1926.1153. The Table 1 control is a saw with an integrated water delivery system that continuously feeds water to the blade, operated per the manufacturer's instructions. That is a tool and a water supply on the truck, not a decision at the wall.
What metal, what gauge, and what fastener metal — written down?
Fastener metal has to match the flashing it penetrates. It is a one-line specification and its absence is what produces a corroded fastener in copper five years later.
Which flashings are being reused, and who has looked at them?
Reuse is legitimate and sometimes correct. Reuse decided by whoever is on the roof at the time is not a decision, and if the reused piece fails inside the new roof's life, the callback is yours.

Require these in writing

Shingle product and its published exposure, named, not implied.
Step-flashing length, leg dimensions, metal and gauge — against that exposure.
Kickout present or absent at every roof-to-wall run that ends above a wall, and what is being done about the wall below it if it has been going without one.
Counterflashing method: reglet-set, surface-mounted, or existing metal reused and on what evidence.
Valley method by valley, with the cut side identified and the reason.
Penetration flashings: which are being replaced, which are being reused, and what the collars are made of.
Fastener metal, stated separately from flashing metal.
Whether the wall's water-resistive barrier is being re-lapped, by whom, and what that requires of the cladding.

What goes wrong

What gets believed, and what actually goes wrongSection link

Common misconceptions

Common belief
Continuous flashing is always the shortcut and stepped is always right.
What is actually true
Two different pieces are being confused. Continuous base flashing under a shingle roof is what NRCA warns against, because it directs water onto the top surface of the roof covering and not the underlayment only when it is stepped. Continuous counter flashing over the shingles is a published, deliberate alternative that CertainTeed recommends where wind-driven fine snow gets past stepped joints. And on metal and membrane roofs, BASC calls for continuous flashing outright. The rule is not stepped-good, continuous-bad.
Common belief
More sealant is cheap insurance.
What is actually true
It is specified in width and in maximum thickness because it is not. IBHS FORTIFIED asks for cement strips at valley edges at a maximum thickness of flashing cement of 1/8 in., and CertainTeed repeats a caution through the whole manual: Excessive use of roofing cement can cause shingles to blister. Cement is a placed component with a dimension, not a material you use up.
Common belief
A 7 in step flashing is the standard size, so it is fine.
What is actually true
It is NRCA’s suggestion for standard-sized asphalt shingles, and it is exactly right for a 5 in exposure. On a metric-dimension laminate at 5-5/8 in it gives 1-3/8 in of metal-to-metal lap, against the shingle manufacturer’s own 2 in minimum. Two respectable published figures, disagreeing at one specific product — and the product instruction is the one that decides who pays.
Common belief
The nail placement rule is about not puncturing the wet part.
What is actually true
It is about the lap. CertainTeed puts the fastener in the uppermost 2″ area and separately requires the pieces to overlap each other by at least 2″. Those two numbers are the same number: the lap is sized so that the fastener band of the piece below sits entirely under the piece above. Shorten the lap and the rule stops working, whatever you do with the nail.
Common belief
If it does not leak at the end of the job, the detail is right.
What is actually true
Nothing on this page fails on day one. A short lap, a missing kickout, a nail in an open channel and a reused valley metal with a hairline crack all pass a hose test and a final walkthrough. They are distinguishable from correct work only by measurement at the time of installation, which is why in-progress checks exist and post-hoc inspection does not substitute for them.

How it actually fails

Short lap on a metric shingle: One box of 7 in step flashing used on a 5-5/8 in exposure. The lap is 1-3/8 in, the fastener band is 2 in, and the bottom 5/8 in of that band is in the open channel between the wall and the shingle.What you can see: Nothing, for years, and nothing distinctive when it starts: water travels along framing before it appears, so the stain reports where it ran to rather than where it entered. A short lap is normally found by measuring one at the next tear-off, not by diagnosing a symptom.
Water-resistive barrier lapped outside the flashing legs: The wall was closed in before the roof, or the cladding was not opened far enough on a reroof. Every upturned leg becomes a shelf feeding water behind the barrier. BASC’s requirement is the opposite order: the barrier is layered over the step flashing to provide a complete drainage system.What you can see: Sheathing damage behind sound-looking flashing. The metal work inspects as correct because it is.
Second layer laid over step flashing that was left buried: On a roof-over, the existing step flashing stays where it is and the new course is cut in against the wall. The old metal now discharges into the space between two layers rather than onto a surface, and the new covering hides whether it does or not. Stated as a mechanism, not as a measured finding: no source read for this page quantifies how often it happens or how fast the deck goes. What the CertainTeed manual does publish is the position that step flashing be replaced when re-roofing (unless the flashings are in like-new condition), and a blunt test for the rest — ask yourself whether the existing flashing will last at least 20 years. If not, replace it.What you can see: Nothing, while the second layer is on. It is found at the next tear-off, at the wall run, and the interior usually shows nothing until late.
Counterflashing fastened through to the deck: The two halves of the detail are designed to move independently; fixing them together transfers differential movement into whichever joint is weakest.What you can see: Opened joints, elongated fastener holes, or a counterflashing that has pulled its own leg out of the wall.
Collar aged out while the covering is mid-life: The elastomeric collar is the part of that detail sitting in full sun with no covering over it, stretched around a pipe that moves on its own schedule. Nothing about the shingles around it has to have failed for the collar to have.What you can see: Splitting or cracking at the collar where it grips the pipe. Because the collar is the visible part, this is one of the few flashing failures that can be identified from a ground-level photograph rather than inferred.
Valley cut on the wrong side: The cut side was chosen by slope or by convenience rather than by watershed, so the plane carrying more water is running onto a cut edge instead of under a whole one.What you can see: Nothing visible that distinguishes it from a correctly cut valley. It is established by comparing the two plane areas against which side was actually cut — which is exactly why the decision belongs on the takeoff and not to whoever reaches the valley first.

Sources and further readingSection link

Understanding Roofing / Published August 27, 2026

Scope and limitations

It does not publish a service-life number for any flashing detail, and specifically not for pipe-boot collars.
The figures that circulate for boot life come from contractor marketing pages, not from a testing body or a neutral dataset, and no publicly verifiable source for them could be found.
What is written here about collars is about the mechanism and the variables, not about years.
It does not publish a cost figure.
Flashing is priced by linear foot at each location, by metal and gauge, and above all by what has to be removed to reach it, and no defensible dataset separates those from the rest of a roofing job.
The lap arithmetic is exact only where the shingle is laid at its nominal exposure.
Courses adjusted to land a headwall, a run stretched to clear a chimney, or a mixed reroof over an existing exposure all break the assumption, and the piece has to be measured against the actual course spacing on that roof.
The step-flashing lengths and the rule of thumb are one manufacturer's published minimums for its own products.
They are not a trade standard and they do not govern another manufacturer's shingle.
The instruction for the product on the job is what controls.
It quotes model-code dimensions at one remove, because the publisher’s own text could not be retrieved: the 2015 and 2018 wording is quoted by two guides and the 2024 wording was read on a code aggregator.
It records no jurisdiction and no effective date, and therefore states no code requirement for any address.
It is not a compliance determination under OSHA or any state plan.
Whether a specific standard applies depends on the work, the employer, and whether the state runs its own OSHA-approved plan.
No employer's obligations are decided here.
It does not cover low-slope membrane flashing, tile-specific channel flashing, or architectural metal roof detailing beyond noting that each takes a different approach from the one described here.

Master Craftsman Shingle Applicator's Manual, Sixteenth Edition — Chapter 6, Flashing: Valleys, Walls, Chimneys, etc.; Chapter 4 workmanship exclusion; Chapters 14 and on product exposures
CertainTeed (Saint-Gobain). Code No. 13-03-1741-NA-EN, printed 03/23 / Sixteenth edition, March 2023
The 2 in minimum overlap between step-flashing pieces; the “minimum length of flashing should be 2″ more than the shingle exposure” rule of thumb and its worked metric example; the published minimum lengths by product family; the uppermost-2-in fastener rule; the 3 in deck leg and 2 in wall leg minimums and the statement that 2 in may not be adequate on low slopes or in heavy weather; “roof flashing works like shingles” and “can only be defeated by water running uphill”; the instruction not to fasten cap flashing to the deck or the step flashing; reglet depth, the 3/8–1/2 in reverse fold and the sealant sequence; the surface-mounted counterflashing alternative; the continuous-counterflashing rationale in high wind and fine snow; the closed-cut valley rule that the lesser-watershed plane goes under and the greater-watershed plane is cut, the 12 in cross-over, the 6 in fastener exclusion and the 2 in clipped corner; the two worked judgement calls on which side to cut; the open-valley recommendation for thick shingles and metal-only valley lining; the vent-pipe flange lap order; the galvanic scale and the same-metal fastener rule; the reroofing positions on replacing step flashing, saving counterflashing and replacing valley metal, and the twenty-year test for whether existing flashing is reusable; the caution against driving nails through flashing spanning vertical and horizontal planes; the caution against excessive roofing cement; the caulk- and sealant-selection note; the 3/4 in clearance from the step-flashing corner bend to the bottom edge of the counterflashing; the kick-out diverter tip; the SureStart Plus 5 Star workmanship-coverage exclusion; and the separate shingle-warranty exclusion for applications not in strict adherence with the manufacturer's written instructions.
Manufacturer instructions, product-specific. They govern that manufacturer's products and nothing else. Read as retrieved from a retailer's document library rather than from CertainTeed's own site; the current instruction sheet shipped with the specific product controls, and it can differ from a manual printed in 2023.
“Manual elements” — step flashings, Professional Roofing, May 2005
National Roofing Contractors Association / May 2005
That individual pieces of metal flashing are installed at the end of each shingle course; that step flashing is recommended for asphalt shingles, slate and wood “instead of a continuous L-shaped flashing piece so water is directed onto the top surface of the roof covering and not the underlayment”; that continuous channel flashing is used for tiles because of tile shape; NRCA's suggested 178 mm by 203 mm step flashing for standard-sized asphalt shingles; the soldered one-piece step flashing with an integral kickout at the eave-to-wall interface, the requirement for a vertical notch in the siding, and the kickout dimension equalling or slightly exceeding the thickness of the wall covering; that the piece is installed over the starter course and under the first exposed course; that metal type and thickness should be commensurate with the anticipated service life of the roof system; and the preference for soldering over overlapping, sealing and fastening because of maintenance access.
A 2005 magazine page reproducing a figure from the fifth edition of the NRCA Roofing and Waterproofing Manual. The article itself says the figure is enhanced relative to the manual and directs readers to the NRCA Steep-slope Roofing Manual, which is behind a paywall and was not read. Later NRCA editions may differ. The 7 in by 8 in figure is read here from the published metric values, 178 mm and 203 mm.
Step and Kick-Out Flashing at Roof-Wall Intersections
U.S. Department of Energy, Building America Solution Center (PNNL)
That step flashing pieces are “overlapped in a shingle fashion”; the 4 in up the wall and 4 in onto the deck figures, as quoted from the 2015 IRC; that the water-resistive barrier is “layered over the step flashing to provide a complete drainage system”; the purpose and sizing intent of kickout flashing; and that continuous flashing rather than step flashing is used on metal and rubber membrane roofs.
Government technical guidance, not adopted law. Its code citations are to the 2015 and 2018 IRC — model editions that a jurisdiction may not have adopted, and may have amended.
Flashing of Roof-Wall Intersections in Existing Homes
U.S. Department of Energy, Building America Solution Center (PNNL)
The 4 in high by 4 in wide step-flashing dimension attributed to 2018 IRC R905.2.8.3; that step flashing is used with shingle roofs and continuous flashing with metal and rubber membrane roofs; that best practice is to install counterflashing over the top edge of the step flashing; and the instruction, on an existing house without a kickout, to inspect the sidewall at the eave for deterioration from bulk water leakage before repairing.
Guidance for existing homes, not adopted law, and its code citation is to a model edition. It does not establish what any jurisdiction requires.
Asphalt Shingle Roofs
U.S. Department of Energy, Building America Solution Center (PNNL)
The IBHS FORTIFIED Roof flashing-cement requirements it reproduces: an 8 in wide strip at intersections and both sides of open valleys, a 2 in wide strip on the cut side of closed valleys, and a maximum flashing-cement thickness of 1/8 in; and the general requirement to install flashing at penetrations and roof-wall intersections integrated with the roofing and wall underlayment and coverings.
The cement dimensions are FORTIFIED program requirements as reproduced by DOE, not a building-code requirement and not a universal practice. FORTIFIED is a voluntary designation; whether it applies to a job depends on whether the job is being built to it.
Flashing of Penetrations in Existing Roofs
U.S. Department of Energy, Building America Solution Center (PNNL)
The layered sequence at a pipe penetration — a self-adhered membrane collar around the pipe, then the metal or rubber flashing collar over it lapping onto the lower shingle course, then the upper shingles covering the collar's upper edge — and the use of backer rod and urethane sealant in the hole around the pipe.
It carries no service-life information for collars and none is claimed from it. Its metal-thickness statement defers to local building code rather than naming a figure.
29 CFR 1926.501 — Duty to have fall protection
U.S. Occupational Safety and Health Administration
The 6 ft trigger and permitted systems for steep roofs under (b)(11) and residential construction under (b)(13); the availability of a written fall protection plan under 1926.502(k) where conventional systems are infeasible or create a greater hazard; and the standard's stated presumption of feasibility, with the burden on the employer.
Federal OSHA text. Applicability depends on the work and the employer, and roughly half the states run their own OSHA-approved plans whose requirements may be more stringent. Nothing here is a compliance determination for any employer.
29 CFR 1926.1153 — Respirable crystalline silica
U.S. Occupational Safety and Health Administration
That the standard applies to occupational exposures to respirable crystalline silica in construction work except below the stated action level, and the Table 1 entry for handheld power saws: a saw with an integrated water delivery system that continuously feeds water to the blade, operated and maintained per the manufacturer's instructions, with no respirator required outdoors for four hours or less and APF 10 beyond that or when used indoors or in an enclosed area.
Table 1 is one compliance route among several and its full conditions, including the housekeeping, exposure-control-plan, medical-surveillance and training provisions of the standard, are not reproduced here. State-plan states may differ. Not a compliance determination.
Timberline / Prestique Application Instructions, English — information sheet updated 2007
GAF-Elk Corporation, read via the InterNACHI course library / Updated 2007
The single line quoted from it: “Any deviation from printed instructions shall be the responsibility of applicator and/or specifier,” as an example of how a manufacturer allocates the risk of departing from its instructions; and its wall-flashing note that one piece of step flashing is used for each course.
A superseded document. GAF's current Timberline instructions could not be retrieved — both documents.gaf.com and gaf.com return 403 to automated requests — so nothing about current GAF practice, exposures, valley methods or nailing is asserted from it. It is cited only for the risk-allocation sentence and the per-course statement, and the current instruction sheet for the specific product controls.
2024 International Residential Code, Chapter 9: Roof Assemblies — R905.2.8.3, sidewall flashing
International Code Council (MODEL text), read through UpCodes / 2024 edition
That the current model edition still reads “base flashing against a vertical sidewall shall be continuous or step flashing and shall be not less than 4 inches in height and 4 inches in width and shall direct water away from the vertical sidewall onto the roof or into the gutter” — the same 4 in by 4 in minimum the 2015 and 2018 editions carry as quoted secondhand elsewhere on this page.
An aggregator, not the publisher and not adopted law: cited only for wording that was actually read on it, because ICC's own Digital Codes site returns HTTP 403 to automated requests. The section dimensions the two legs and says nothing about the length of a step-flashing piece along the slope, which is the dimension this page is about. Confirm the wording against the edition your jurisdiction adopted, its amendments and its effective date.

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