What Are Flashings?
Flashings are shaped metal components used to weatherproof the junctions, transitions, and penetrations on a building envelope. Anywhere that two surfaces meet — where a roof meets a wall, where a pipe passes through cladding, where two roof planes intersect — there is potential for water ingress. Flashings are the primary defence against this.
In New Zealand, the Building Code (clause E2 — External Moisture) sets clear requirements for weathertightness. Flashings are one of the key components that ensure a building meets these requirements. They direct water away from vulnerable joints and towards the drainage path, preventing moisture from entering the building structure where it can cause timber rot, corrosion, and mould.
Whether you are building a new home, reroofing, or carrying out maintenance, understanding the different types of flashings and the materials they are made from will help you specify the right product for the job.
Types of Flashings
Each flashing type is designed for a specific location on a building. Here is a breakdown of the most common types used in New Zealand construction.
Apron Flashings
Apron flashings are installed where a roof slope meets a vertical wall, such as at the base of a chimney or where a lean-to roof connects to the main building wall. They form a continuous weatherseal along the straight junction between the roof surface and the wall cladding, directing water onto the roof sheeting rather than into the joint.
Barge Flashings
Barge flashings cover the exposed edge of roofing at the gable ends of a building. They protect the ends of the roof purlins and underlays from wind-driven rain and give the roof edge a clean, finished appearance. Barge flashings are one of the most visible flashings on a building and are typically colour-matched to the roofing material.
Ridge Cappings
Ridge cappings sit along the peak where two roof planes meet at the top. They cover the gap between the two sheets of roofing, preventing water and wind from penetrating at the highest point of the roof. Ridge cappings come in various profiles to suit different roof pitches and roofing profiles.
Valley Flashings
Valley flashings are installed in the internal angle where two roof planes intersect. Valleys carry a high volume of water during rain, making them one of the most critical flashing locations on any roof. They must be correctly sized, lapped, and fixed to handle the water flow without leaking.
Window and Door Flashings
Window and door flashings are installed at the head, sill, and jambs of window and door openings. They divert water away from the opening and back onto the face of the cladding. These flashings are essential for meeting E2 requirements and are a common point of failure in leaky building investigations.
Parapet Cappings
Parapet cappings cover the top of parapet walls — the upstanding walls that extend above the roof line on flat or low-slope roofs. They protect the exposed top of the wall from direct rain penetration and are designed with drip edges on both sides to shed water clear of the wall face.
Drip Edge Flashings
Drip edge flashings are installed at the eaves or lower edge of a roof. They direct water off the roof edge and into the gutter, preventing it from running back under the roofing or along the fascia. A properly formed drip edge also helps prevent capillary action drawing water back up under the roof sheeting.
Cover Flashings
Cover flashings are secondary flashings that overlap another flashing or junction to provide an additional layer of weather protection. They are commonly used at the top of an upstand or where a primary flashing is let into a wall. Cover flashings are typically fixed to the wall and lap over the top of the primary flashing below.
Step Flashings
Step flashings are individual overlapping pieces used where a sloping roof meets a vertical wall at an angle — the classic example being along the side of a chimney on a pitched roof. Each step piece is layered with the roofing courses so that water is directed off the roof at every step, rather than relying on a single continuous piece.
Penetration Flashings
Penetration flashings seal around pipes, vents, flues, and other services that pass through the roof or wall cladding. They must accommodate the shape and size of the penetration while maintaining a watertight seal. For roof penetrations, these flashings often include a sleeve or collar that sits tightly around the pipe and a skirt that laps over the surrounding roofing.
Flashing Materials Compared
The material you choose for your flashings affects durability, appearance, and suitability for different environments. Here is how the most common materials used in New Zealand compare.
Colorsteel (prepainted steel) is the most widely used flashing material in residential construction. It comes in the full range of roofing colours, so flashings can be matched to the roof and cladding. The factory-applied paint system provides good corrosion resistance for most New Zealand environments, though performance will vary depending on the corrosion zone.
Zincalume is an aluminium-zinc alloy coated steel with a distinctive metallic appearance. It is commonly used where a painted finish is not required, or as a base material for on-site painting. Zincalume offers good corrosion resistance but is not recommended for direct contact with concrete, mortar, or treated timber without appropriate isolation.
Galvanised steel has a zinc coating applied by hot-dip galvanising. It is a traditional material that works well in mild environments but has lower corrosion resistance than Zincalume or Colorsteel in aggressive conditions. Galvanised flashings are commonly used in agricultural and industrial applications.
Aluminium is lightweight and naturally corrosion-resistant, making it well suited to coastal and high-humidity environments. It is softer than steel and easier to form on site. However, aluminium must not be placed in direct contact with dissimilar metals or alkaline materials such as fresh concrete, as this can cause galvanic corrosion.
Stainless steel offers excellent corrosion resistance across virtually all New Zealand environments, including severe marine zones. It is more difficult to work with than mild steel and is typically specified for high-performance or long-design-life applications where other materials would not last.
Copper develops a distinctive green patina over time and is one of the most durable flashing materials available. It is used in heritage restorations and architectural applications where its appearance is desired. Copper is expensive relative to steel options and, like aluminium, requires care to avoid galvanic corrosion with dissimilar metals.
How to Order Custom Flashings
When ordering custom flashings, providing clear and complete information ensures you get the right product first time. Here is what we need from you.
Profile sketch or drawing: A cross-section sketch showing the shape of the flashing. This does not need to be a formal CAD drawing — a clear hand-drawn sketch with dimensions marked is fine. Include all bends, angles, and return edges.
Dimensions: Mark all leg lengths (the flat sections between bends) and the overall developed width. Specify the finished length of each piece and the quantity required.
Angles: Note any angles that are not 90 degrees. If the flashing needs to match a specific roof pitch, include that information.
Material and gauge: Specify the material type (Colorsteel, Zincalume, galvanised, aluminium, etc.) and the gauge or thickness required. If you are unsure, let us know the application and we can recommend the appropriate specification.
Colour: For Colorsteel flashings, provide the colour name or code. If you need the flashings to match existing roofing or cladding, let us know the product and colour so we can source the correct coil.
You can submit your flashing order through our online quote form, email your drawings to us, or drop into our Onehunga workshop to discuss your requirements in person.
Common Mistakes with Flashings
Even well-intentioned installations can fail if basic principles are overlooked. These are some of the most common mistakes we see.
Incorrect lapping direction: Flashings must always lap in the direction of water flow. If upper flashings do not overlap lower flashings correctly, water can be directed behind the flashing rather than over it. This is particularly critical with step flashings and valley flashings where the lapping sequence is essential to performance.
Wrong material for the environment: Using standard galvanised flashings in a severe coastal environment, or placing aluminium in direct contact with treated timber, are common material selection errors. The NZS 3604 standard and roofing manufacturer guidelines specify minimum material requirements based on corrosion zone. Choosing the wrong material can lead to premature failure and costly remediation.
Insufficient fixings: Flashings that are under-fixed can lift in high winds, allowing water to penetrate. Conversely, fixings placed in the wrong location — such as in the flat pan of a valley — can create leak points. Fixings must be placed in accordance with the manufacturer's specifications and the relevant New Zealand standards.
Inadequate sealant use: While flashings should be designed to shed water mechanically, sealant is sometimes required at specific locations. Using the wrong type of sealant, or relying on sealant as a substitute for proper flashing design, is a frequent source of failure. Sealant degrades over time and should never be the primary line of defence against water.
Not accounting for thermal movement: Metal expands and contracts with temperature changes. Long runs of flashing that are rigidly fixed at both ends without provision for movement can buckle, distort, or pull fixings loose. Slotted fixing holes and expansion joints should be incorporated on longer flashings.
Get Your Flashings Right
Flashings are a small component of any building project, but they carry a disproportionate responsibility for keeping the structure dry. Getting the type, material, and installation details right is essential for long-term weathertightness and compliance with the NZ Building Code.
At Coating Lab, we manufacture custom flashings to order from our Onehunga workshop. Whether you need a single run of barge flashings or a full set of roof flashings for a new build, we can fold and finish them to your specifications. Get in touch for a quote or call us on 09 218 6436 to discuss your requirements.
Frequently Asked Questions
Flashings are shaped metal components installed at junctions, penetrations, and transitions on a roof or building envelope to direct water away and prevent leaks. They are a critical part of meeting the NZ Building Code requirements for weathertightness. Without properly installed flashings, water can enter the building structure and cause rot, corrosion, and mould.
The best material depends on the environment and application. Colorsteel is widely used for residential roofing due to its colour-matched finish. Zincalume suits unpainted applications. Stainless steel or copper may be required in severe coastal or corrosive environments. Contact Coating Lab for personalised advice on your project.
Yes. Coating Lab manufactures custom flashings to order. Provide a profile sketch or drawing with dimensions, angles, material type, and colour, and we will fold and finish them to your specifications. You can submit details through our online quote form, email us, or visit our Onehunga workshop.
Apron flashings are continuous pieces installed where a roof meets a vertical wall in a straight line. Step flashings are individual overlapping pieces that follow the slope of the roof where it meets a wall at an angle, such as along the side of a chimney. The choice depends on whether the junction runs parallel to or at an angle across the roof slope.
Contact us with a profile sketch or dimensioned drawing showing the cross-section, lengths required, material type, and colour. You can submit this through our online quote form, email your drawings to workshop@coatinglab.co.nz, or drop into our Onehunga workshop to discuss your requirements in person. Call us on 09 218 6436 if you have questions.