Step flashing vs l flashing

Step flashing vs l flashing DEFAULT

Anyone remotely associated with construction,  In order to make sure that buildings are properly protected against the elements, you will always need to consider metal flashing. Understanding the importance of custom metal flashing in construction will be key in order to ensure the longevity of the building. At New Standard Building Materials, we work hard to develop proper metal flashing regardless of the intended use. We find that a lot of people doing their own flashing tend to confuse two of the leading types of such: l-flashing and z-flashing. Here is a brief breakdown of what each kind of flashing does, what their differences are, and in which cases they should be used.


What Is Z-Flashing?

In construction terms, z-flashing refers to a “Z” shaped piece of metal that provides a transition between two different materials. The particular shape allows the channels to act as a receiver for panels, ridge caps, and headwall flashing. In flashing the transition between the different materials, the pieces assist in preventing water penetration. They do so by purposefully directing the water away from the vulnerable points in the roofing and facilitating its drainage. Since it is custom-made, the channels are fabricated in order to perfectly fit the necessary roofing, as well as the specific angle, size, and profile. Overall, it’s all about properly adjusting the channels to anticipate potential threats to the integral parts of the roofing and the structure.

What is L-Flashing?

L-flashing, similarly to its z counterpart, is a versatile type of flashing generally used to uniformly strengthen the finish on a ninety-degree surface. This way, the flashing can protect the structure from moisture infiltration in the vulnerable spots where the walls meet the roof. Like other flashing beams, these are integral components of just about any construction due to their role in protecting the structure against water damage. Should you not implement flashing in these spots between your roof and your wall will be left practically defenseless against damage from the elements, immediately limiting the lifespan and compromising the integrity of the structure.

When to Use Each?

It’s not going to be a matter of when to use z-flashing vs when to use l-flashing but it’s, instead, going to be about where. It’s all going to depend on the angle of the flashing itself. Angular roofs will require flashing that can adapt to the uneven surfaces, while l-shaped pieces will be best used as flashing in the cases of the right angles where the walls meet the roofs. In the end, each contractor will make their own call at the time of applying metal flashing.

Custom Metal Flashing

We at New Standard Building Materials are proud suppliers of quality building materials to the Seattle area. In the interest of providing our customers with the best products available, we carefully select our source materials and enforce quality manufacturing throughout the ensuing process. We understand just how important it is to make use of only the best materials at the time of building, so we refuse to ever neglect any stage of the process. For more information on our products or custom quotes for materials, you can always give our team a call at (206) 268-0663. We are here to help you get the l and z-flashing channels for your construction.

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The development of the International Codes is a continuous process, with each code volume being revised on a three-year cycle. Changes are submitted and approved and can then be reviewed in subsequent cycles. Controversial changes get people and the building industry thinking, which is what happened recently with the way code looks at sidewall flashing in asphalt-shingle installations.

Step flashing Through History

Step flashing has been required for asphalt shingles at roof-to-wall intersections as far back as the 1986 CABO. With this method, L-shaped pieces of metal that are a couple of inches longer than the shingle overlap are installed on top of each shingle adjacent to the sidewall, and the flashing is then laced into each course. Step flashing ensures that any water that migrates underneath a shingle will still end up on top of the flashing that is covering the shingle below. The water can then drain away safely.

In addition to the CABO reference, the requirement for step flashing at sidewalls appeared in the first edition of the International Residential Code (2000 IRC) and remained unchanged through the 2009 edition.

Every asphalt-roofing manufacturer’s installation instructions that I have ever seen specify step flashing as the preferred way to flash the roof-to-wall juncture. And in section 905—which covers the installation of all roof coverings—of the 2015 IRC, the first sentence requires compliance with the code and the manufacturer’s installation instructions. But things changed in 2012.

Enter Continuous Flashing

In the 2012 IRC, the section that covered sidewall flashing was much expanded, and for the first time, it included continuous flashing as an approved method for roof-to-sidewall flashing with asphalt shingles. Continuous flashing has always been used at a headwall (an intersecting wall at the top of a roof plane and perpendicular to the slope). In this case, continuous flashing is simply a single piece of flashing placed behind the exterior cladding and weather-resistive barrier on the wall and then extended out over the shingles. The flashing can be left exposed, or installers can adhere a “beauty strip” of asphalt-shingle material to the flashing to make it less visible from the ground.

No Clear Directions

To complicate matters, the new provision allowing the use of continuous flashing at sidewalls is rather vague and provides few installation details beyond the need for the vertical leg of the flashing to be at least 4 inches tall and for the flashing to divert water away from the side wall using some sort of kick-out flashing.

Installation details for continuous flashing are also missing from the asphalt-shingle manufacturers’ installation instructions. After decades of sidewall step flashing being installed beneath the shingles, continuous flashing is most likely to be installed below the shingles as well. But some installers may assume that continuous flashing should be installed above the shingles, as is done for headwall flashing. The IRC offers nothing to clarify this issue.

Continuous flashing at sidewalls is standard practice for clay tile and slate shingles (see “Roofing With Tile,” 06/15). In those applications, the continuous flashing installs under the roofing. Those roof coverings are meant to provide protection from bulk water movement only, with the expectation that moisture will find its way beneath the roofing and that the underlayment will provide the final protection.

Industry standards and manufacturer installation instructions for clay and slate also specify that the continuous sidewall flashing have a J-roll along the edge under the shingles and over the roof deck. The small roll along the long edge of the continuous flashing helps to ensure that water will flow down to the bottom of the flashing and not migrate sideways and off the flashing.

This roll is effective for clay and slate roofing because those products are usually elevated on horizontal battens. Asphalt shingles, however, are not rigid like clay or slate, and a J-roll would likely telegraph a hump to the finished surface. Additionally, asphalt shingles would not protect the J-roll from getting flattened by someone walking on the roof. But the IRC does not mention a J-roll along the edge of continuous flashing in an asphalt-shingle application.

Regional applications

Based on anecdotal evidence I’ve gathered, continuous flashing is used regularly only in drier regions of the country, such as the desert Southwest. Mike Guertin touches on continuous flashing in his roofing demos for JLC Live, and his insights for installing continuous flashing are provided in “Installing Continuous Flashing”.

After all this information was discussed (with plenty of opposition) in the 2012 hearings and again in 2015, the measure was still approved. But because this new subject is not clearly spelled out in the code, I would encourage you to do a little homework before trying to change the decades-long practice of using step flashing with asphalt shingles. Review the installation instructions of the product you are installing and perhaps contact a technical representative at the manufacturer for guidance for an alternative installation method that uses continuous flashing. Then follow whatever details the manufacturer provides.

Also I’d review the adopted code, as well as any amendments, to see if your local jurisdiction has accepted this practice. But perhaps the easiest solution is to leave well enough alone and continue using the tried-and-true step-flashing method.

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Step Flashing vs. Continuous Flashing

[quote=“peterk”]Instead of using step flashing, I used a continuous piece of 10" aluminum which I bent into an L shape. Am I asking for trouble, or is this a reasonable practice?

The place where this is installed is what I would call a confined rake. You could also call it meeting a vertical side wall, as the vertical wall would be at your side as you faced the roof while shingling.

This confined rake is also covered by a two foot overhang from an eave above, and never really gets wet. In addition, the siding was removed and Grace Ice & Water shield was applied one foot up the side wall all along the rake.

A fellow who shingles told me that continuous flashing would leak, and that I did the job wrong. My thinking is that continuous flashing is still a common practice around chimneys, and was once the primary practice. While I appreciate step flashing is very popular and convenient, I don’t think it invalidates old school continuous flashing.[/quote]

You step-flash rake edges along base of walls, chimneys, etc. L-flashing is a quick way of doing it, but it is wrong and often times leaks.

What is Roof Flashing \u0026 How to Install it

Mastering Roof Inspections: Flashing, Part 2

by Kenton Shepard and Nick Gromicko, CMI®



The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail. 


Places where roofs and walls intersect are very common. They’re called headwalls and sidewalls.



A headwall is a level junction where a roof meets a wall.

This illustration shows proper flashing at a headwall condition.

Headwall flashing should extend up behind the exterior wall covering and down over the roof-covering material, as you see here.

This is true no matter what type of roof-covering material is installed.

Flashing should overlap the roof-covering material, but on asphalt shingle roofs, for aesthetic reasons, the part of the headwall flashing that extends down over asphalt shingles is often covered with a course of shingle tabs.

Don’t mistake this condition for headwall flashing routed beneath the shingles and call it a defect.

No minimum headwall flashing dimensions are provided that are applicable to every manufacturer and jurisdiction, so you’re only concerned with seeing that headwall flashing is installed in a manner that will keep the water out.  Common flange sizes are 4 inches by 5 inches. Headwall flashing typically comes bent to 120°  and can be fairly easily flattened for roofs with shallower pitches.

Occasionally, you’ll see a roof which has had 90°-sidewall flashing installed as headwall flashing. These don’t bend well to accommodate roofs with steeper pitches, and you’ll often see gaps beneath the flashing. Wind-driven rain can enter at these gaps, causing roof leaks.


A sidewall is a junction between a wall and a sloped portion of a roof.

Except where walls are brick, the vertical part of the sidewall flashing should extend up behind the exterior wall covering, just like with headwalls.

The horizontal part of the flashing will vary, depending on the type of roof-covering material

Step Flashing

Sidewalls on roofs covered with asphalt shingles, wood shingles, shakes and slate should be flashed using step flashing, like you see here.

Step flashing consists of short pieces of flashing, each installed to overlap the shingle in the course below, and to be overlapped by the shingle in the course above. All shingle manufacturers require step flashing at sidewalls for both asphalt, wood and slate.

If you see continuous, one-piece flashing like this used as sidewall flashing with shakes, shingles or slate, it’s a defective installation, no matter how often you see it.

Here’s an example of an asphalt shingle roof with continuous flashing installed.

This is an example of a defective installation where an asphalt shingle roof meets a stone sidewall. Instead of installing the step flashing between shingles, the flashing rests on top of the shingles.




It’s not unusual to see sealant installed when sidewall flashing is missing. Sealant will eventually dry, shrink and crack.

You’ll see sealant substituted for flashing in a lot of different areas on roofs. When you see it, you should recommend replacement with proper flashing, or annual inspection and re-application of an appropriate sealant, as necessary.

Tile Requires Pan Flashing 



Tile roofs should have continuous pan flashing installed at sidewalls, and it’s sometimes difficult to confirm. You can probably lift the butt of the lowest tile enough to see. Pan flashing is continuous flashing that has a lip on the flange which extends beneath the tile so that the horizontal part of the flashing acts as a water channel.

Step Flashing Sizes

Step flashing size requirements vary according to manufacturer. Manufacturers' requirements can vary anywhere from 2 inches to 10 inches, and you probably won’t be able to see the sidewall flashing completely, anyway. The vertical side will be hidden behind the exterior wall-covering material.

You aren’t required to confirm compliance with manufacturer’s installation requirements, but you should be able to confirm that step flashing is installed by looking at the exposed portion and making sure that it extends up behind the exterior wall-covering material.

Sidewall Gap

In both headwall and sidewall conditions, unless the exterior wall is brick, you should see a gap of at least 1½ inches between the bottom of the exterior wall-covering material and the top of the roof-covering material.




You’ll often see exterior wall coverings installed right down on top of the shingles. Without a gap, the exterior wall covering can wick up moisture from the roof.  This can lead to decay, delamination, peeling paint, and other problems. This condition is especially common on roofs with multiple layers of shingles.

The gap can be present but difficult to see on tile roofs. You can see it in this photo if you look at the base of the sidewall just to the left of the downspout termination.

Looking at this same area, you’ll see that several tiles are cut short. Unless the pan flashing is fairly wide, this may allow enough moisture entry to cause a leak, and it should be mentioned in your inspection report. You’ll also notice poor installation at the inside corner, and a broken tile at the ridge.

You’d want to check this area carefully to evaluate the chances for moisture getting past the tile. At the inside corner, the headwall flashing that extends out over the tile was not installed high enough.

If you don’t see a gap, you will not be recommending correction, but you should mention in your inspection report that the exterior wall covering has inadequate clearance from roof-covering materials.



Vs flashing flashing step l


How to Install Flashing on a Roof - Mastering the Roof by GAF


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