(316) 927-2233Virtually all sloped roofs have some amount of visible metal flashings that become part of the overall look of the roof. Flashings are typically aluminum or steel, but can also be copper, and historic lead flashings (once almost ubiquitous) are still found on roofs today although no longer installed. Larger and custom-fabricated roof flashings, such as metal chimney crickets, valley pans, or large dormer aprons are more often fabricated out of steel for durability on the larger surface areas.
Among steel options, the two most common types found in roofing are galvanized and bonderized. Stainless steel is occasionally found on roofs as well, but with roughly double the cost and a mirror-like finish, typically not wanted on roofs because of glare.
What Is the Difference Between Bonderized and Galvanized Flashing?
Composition: Galvanized vs Bonderized
Galvanization is the process of dipping raw steel into a protective zinc coating, which helps shield the metal from moisture and prevents rust. Widely available and cost-effective, galvanized is the default option chosen by most roofers for steel flashings in the US.
Bonderized flashing builds on that by adding extra coating layers, phosphate and chromate, that allows paint to effectively bond with the metal —so you get the same strong protection, plus a clean, finished look that can match your home’s exterior. The added manufacturing step does at some cost, and also dulls the sheen and changes the color (if unpainted) to more of a warm brownish metal.
Both galvanized and bonderized are perfectly adequate flashing materials – weldable into custom forms, corrosion-resistant, durable, and expected to outlast the shingles and other components of a roof. The decision between one and the other is largely one of design/aesthetic preference.
Identification: Galvanized vs Bonderized Steel
In our experience, people are more familiar with the look of galvanized steel. When new, galvanized steel is smooth, shiny, silver, and has slight color texture like subtle camouflage splotches called spangling formed as the zinc coating has cooled and crystalized. Over time, typically 2-5 years of being outside, galvanized steel loses it’s shine and dulls to a medium grey instead of silver. The surface typically ages to a slightly rough texture as well.
Bonderized flashing can be painted to match any color you need thanks to a chromate coating that neutralizes the chemical reaction that usually happens between paint and galvanized steel. This means that the paint adheres smoothly and lasts longer. Once painted, the color usually lasts as long as the roof. If the metal in question is painted steel, it’s probably (hopefully) bonderized. Powder-coated and painted aluminum is also very common on roofs, but typically only for pre-fabricated materials such as valley flashing, step flashing, drip edge, and gutters. Custom-fabricated flashings, such as those around chimneys, dormers, crickets, and dead valleys, usually have to be welded steel in order to be strong enough. The easiest way to tell the difference between aluminum and steel if both are painted is to touch a magnet to it. Aluminum is non-ferrous and will not attract a magnet, whereas a magnet will stick to steel.
Bonderized steel can also be left unpainted, and often is intentionally left that way. If left unpainted, bonderized steel has a satin sheen when new and warmer bronze color. Over a few years, unpainted bonderized steel ages to a dull brown. Some people like this color as it matches warmer-toned shingles and looks more natural. However, the oxidation process for the first few years can be uneven, looking blotchy or ‘rusty (though it isn’t corrosive nor rust) until the metal achieves it’s final aged look.
The photo above shows an example of new galvanized flashing. On an area hidden from the ground, such as chimney crickets, galvanized metal is cheaper if looks are not a concern. However, galvanized metal can cause serious glare in the right lighting if there are windows above or if the angle of the metal will reflect sunlight like a mirror into a neighbors window. This will dull over time, but always be shinier than bonderized metal.
This photo is an example of bonderized counter-flashing on a chimney. In this specific case, the homeowner chose not to paint the flashing, which will result in a darker, matte finish that will match the roof.
Design/Curb Appeal of Bonderized Flashing
While both materials are highly durable and are expected to outlast other components of a roof, bonderized steel offers the advantage of being paintable and (even if left unpainted) avoiding glare. In our experience, many customers don’t think about the metal selections on their roof unless they have a neighbor whose shiny galvanized flashings shine sunlight directly into a window. As asphalt shingles reflect very little light, shiny flashings contrast a lot against the rest of the roof.
We still find that on the majority of homes we visit for inspections and repairs, galvanized is the default option. Certainly new homebuilders, whose primary interest is in keeping costs low, choose galvanized. Other times, we find painted galvanized metal, but since galvanized steel isn’t meant to be painted, they had to use special primers and treatments, adding time, cost, and long-term maintenance.
Installation is the same for both materials. As an installer, we are happy to put in either – meaning it is a personal design choice by the homeowner or building owner. When presented with a choice though, we often find that homeowners and building owners choose to use bonderized metal for custom flashings. Whether they get painted to match the other flashings (valley metal, headwall, drip edge, gutters) is up to the homeowner or building owner.
Cost Difference for Roof Flashings: Galvanized vs Bonderized
Bonderized flashings are slightly more expensive. Bonderized steel material is slightly more expensive to start with because of the additional treatment layers to manufacture it. However, when talking about custom steel fabrication for chimney crickets, pans, or other larger flashings on a home, the metalwork labor is most of the cost to custom bend and weld the flashing. On a $1,000 custom flashing, for example (galvanized), making the same piece out of bonderized might cost $1,075.
Will Bonderized Flashing Rust?
Bonderized flashing is that it is slightly more resistant to rust than galvanized flashing. However, both steel types are expected to outlast the other roofing materials if un-damaged.
However, bonderized metal does have a reputation for staining during it’s weathering process. It can have an inconsistent look for a few years with white blotches or darker stains. Eventually, the whole material will turn to a dull bronze color, but this “white rust” can alarm folks who think something is wrong with the metal. This is not a corrosive deterioration, just part of the chemical reaction as the bonderized metal is exposed to water and air.
Does Bonderized Flashing Add Value to A Roof?
Just like quality installation, we consider bonderized flashings to be a very inexpensive ‘upgrade’ to many homes for a more cohesive look to the whole roof. It offers long-lasting durability and if paired with the right shingle or roofing material colors, can enhance your home’s curb appeal, making it a smart investment. Most people consider bonderized metal to have a better-looking aging process, as it turns into a consistent bronze color rather than a dull steel color, helping preserve/add value over time.
The painted metal flashings here on the cornice headwall are an example of using flashings to accent the appearance of the home overall.
This is an example of a roof that uses painted bonderized flashing for the custom-made flashings around the chimney. Visible from the street, shiny galvanized metal would stand out a lot against the dark roofing here, in this case, a synthetic/composite slate.
Why Don’t All Roofing Companies Install Bonderized Flashing?
Galvanized metal is typically the default option – simply because it’s a term everyone knows, and is found everywhere. Bonderized flashing may cost a bit more than standard options, but it’s often chosen by roofing companies committed to helping accent the look of a home or building. Homes that require custom-welded flashings may be dependent on the suppliers of the metal fabrication: either a partner company to the roofing contractor or made by the same company. Galvanized sheet metal is easier to get, and is typically carried at any local metal supplier, so lead times may be less. However, with a little planning ahead, bonderized metal is similar in price and allows more flexibility to design a custom look for the home.
Some homes need more flashing than others, and while it’s usually tucked away, certain roof designs leave it fully visible. In those cases, the shiny, reflective surface of standard galvanized metal can stand out and not always in a good way. Roofers can also mix materials if cost is a concern – using galvanized materials where not visible from the street, such as a dead valley.
Bonderized flashing helps solve that problem. If you like the look, it can be left unpainted or painted; either way, its matte finish reduces glare and may blend in better with your roof so it doesn’t draw unwanted attention.
As an installer, we don’t have a bias one way or another – and simply want homeowners to be aware of the options out there for flashing metals. Wherever you are in your project, we encourage you to explore the details and design options available for your roof, and to ask your contractor about what is available in your market. As always, if you’re in the greater Wichita/central Kansas region, feel free to reach out; Rhoden Roofing offers free inspections and roof consults.
