by: Todd Miller - Isaiah Industries, Inc.,
Todd Miller is President of Isaiah Industries, Inc., a leading manufacturer of specialty residential metal roofing. His personal website, www.asktoddmiller.com, is a great resource for answers to your questions about roofing and ventilation.
Why is there reason to be concerned that residential metal roofing products are specified and used properly? First of all, the metal roofing industry continues to enjoy rapid growth. Current market share is estimated at 14% of the roofing market and, depending upon where you live and exactly what sector of the roofing industry you serve, you may feel like the market share is considerably higher than that. This is much higher than 15 or so years ago when market share nationally was only around 2%.
So, what is driving this growth? Increased awareness is playing a big role. A rising tide raises all ships. Property owners see more metal roofs and they want to become a part of the trend. They read about metal roofing on the internet and see photos of beautiful roofs. Once they learn about some of the other benefits of metal roofing, they don’t want to miss out on those either. I think that what we’re seeing in metal, especially in the residential arena right now, is part of an evolution toward better building materials that has always existed and is going to continue to occur.
Those benefits that property owners appreciate include durability, wind resistance, and fire safety. We’re also seeing metal being selected for its low weight compared to other roofing materials, especially on older structures. There is also great interest in the energy efficiency of metal roofing, this being driven heavily by the federal tax credit that, for several years, was in place for reflective metal roofing. And, in general, homeowners really like the green benefits of metal roofing including not only the energy efficiency but also the recycled content of the metal, the 100% recyclability of the products at the end of their life, and the ability in many instances to install metal roofs over old shingles.
As a part of this increased use of metal roofing, we’re seeing more manufacturers and also more contractors entering the arena. And all of those new players come with some learning curve still ahead of them. Even the most experienced of us are always learning. That’s why education and information are so very important.
Many roofing contractors are interested in metal right now. In fact, if you go to just about any roofing contractor’s website, or look at the lettering on their truck, there is some mention of metal. Yet almost every day I hear of stories of contractors advertising metal who can’t answer the questions about metal roofing that are posed to them by architects or homeowners. It’s also not uncommon for me to hear that if a prospective customer asks them about metal, they just downplay it and steer them instead toward their “bread and butter” product, whatever that might be.
Property owners are also increasingly intrigued about metal roofing yet, with them, there’s something even more dangerous going on than just lack of information and not knowing where to go for education. The worst thing about property owners is that they assume all metal roofs are the same. Sadly, they don’t even know what to look for nor what questions to ask! So, they are often going along with recommendations from their contractor or their lumberyard or big box, even though they don’t really understand the product being sold to them. Their expectations may be way too high, sometimes leaving them badly disappointed when the product doesn’t look or perform as they had expected.
So, the end result of this lack of good training, good information, and appropriate resources is two things:
1) Products are being used incorrectly – they are being used on jobs and in ways for which they were never intended to be used; and
2) Products are often being installed incorrectly – fastened wrong, cut wrong, flashed wrong -- you name it. All of these are bad things that lead to unhappy customers.
So, that brings us to this topic of specifying the best possible option for every metal roof installation. Because it’s a bit like eating an elephant where you have to do it one bite at a time, I will review what’s available in metal roofing today including where it works and where it does not work.
There are numerous key considerations that must be considered on each and every project where a metal roof is being considered. Keeping these things in mind as the project is evaluated will allow the best metal roof option to be called for. Before we start digging into product details and limitations, let’s take a look at some of the Key Considerations when recommending a particular metal roof. These are the very important things to be aware of on every project before you decide which product will be best for that roof.
Roof Geometry. Are your salespeople – those out helping property owners assess their needs and determine an appropriate solution – experts at considering the overall shape or configuration of a roof? Are they trained and looking for things like flared gables – where the roof is wider at the top than the bottom? Are they thinking about water and potentially even snow and ice that will shed from upper roofs onto lower roofs? Are they looking for non-90 degree hips? Have they ever brought in contracts for jobs with complex things on them like eyebrow windows or barrel dormers … and they’d not really given any thought to how time consuming the proper installation of those areas will be? All of these things play huge roles in making sure the proper product is being specified and that the contractor has the resources to carry out the project specifically – meaning that the contractor is getting paid enough to do the job well. Being able to assess and evaluate roof geometry and how metal roofing will work with that geometry is critical.
Water Flow. This is another big one. You may think you’re doing great by specifying a snap lock standing seam with a 1.875” tall seam but then completely miss the 25’ rafter length on a second story that is going to drop all of that water onto a first floor roof, making it all land in one 15” wide standing seam panel on a 3:12 pitch. Do you know how many times I’ve been consulted on roofs where they couldn’t track down a leak and it was just because they had way too much water flowing down one standing seam panel, and it’s flooding out? When evaluating roofs and recommending roof systems, as I am sure you have all heard before, you must think like a rain drop.
Air movement. This is especially critical in areas with high wind potential. Most folks in the roofing industry know that the side of the roof that takes the brunt of uplift pressures in a severe wind event is not the side of the roof that faces the wind – it’s actually the back side of the roof which gets the effect of wind rushing over the roof and curling around on the back side, trying to lift the panels off the roof. Sometimes the geometry of the roof also contributes to high uplift areas in certain places. So, how do you deal with that? Well, in some cases, you can consider increasing fasteners or something in the areas that are most likely to have damage from high winds. Regardless, a roof must be built to sustain the winds it will endure. Understanding those wind dynamics is critical.
Attic Ventilation. While ventilation usually has more to do with how the roof is installed than what product is being installed, it’s still a critical consideration. Here are questions that your estimator or salesperson should be thinking about on every project. Are there special ventilation needs here beyond what is even required by code? Is there animal confinement going on? Do they have a lot of house plants? Ventless gas stove? Wet crawlspace or basement? Once you consider those, then you can begin to investigate … does the ventilation meet code? Is it evenly balanced between intake and exhaust or perhaps even a little pressurized in the attic due to a slightly higher level of intake? Do you need to add exhaust vents to the roof? Do you need to include a package with intake vents, or clean the insulation back from their intake vents? I don’t need to tell you about the number of lawsuits out there pertaining to mold in homes and other buildings. If you leave a home without proper ventilation, even if it was that way when you arrived, you’re at risk if mold develops in that structure and the homeowner and their insurance company start suing anyone and everyone who have ever touched that house. And, let me give you an extra warning here … let’s say the structure is not vented per code but they have never had a condensation problem before. Can a metal roof, if vented the same as the previous roof, cause problems that did not exist before? Actually, yes, it can. Because the metal roof will drop the roof deck temperature a couple of degrees from what it was previously, condensation might occur that did not occur before. And if that building is made more air tight in the future such as by adding a house wrap or new windows or doors, that will increase the amount of moisture that ends up in the attic, again increasing the risk of condensation occurring.
Trees Around The House. The first thing that trees around a house tell you is that there will be leaves or pine needles on the roof. So, as the roofer, how will those leaves and needles get off the roof without damage to the roof or without having them clog up your roof system? This is where specifying a roof system with only open valleys comes into play. If you install a roof system with closed valleys designed to carry water beneath the roof’s surface, those concealed waterways are going to clog up with debris and there are going to be major problems on the job. Rotted out eaves and other things.
What is another thing that trees tell me? That the roof is going to be prone to tree sap, or at least airborne fungus. So, I am going to want to specify a metal roof that has a coating on it that’s as resistant as possible to dirt and fungus. Otherwise, in a few years, you’re going to have a very unhappy customer and a situation that is a black eye for the metal roofing industry.
Aesthetics. Nine times out of ten, if you send me driving down a neighborhood street and tell me that there is a metal roof on a home on that street, I will be able to tell you which house it is on long before I can see the roof. How can that be? Because most metal roof customers care very much about the aesthetics – the beauty – of their homes. So, I will recognize the house based upon the landscaping, the manicured lawn, or perhaps a fountain or other lawn statuary.
So, if you have a prospective customer who cares about how their home looks, what are you going to do? Pull out the samples of your prettiest product. Maybe use Visualizer software from your manufacturer to help them see what their home will look like after the roof is completed. You’re going to do all you can to prove to them that their home will look phenomenal with your roof.
Here’s another interesting thing on aesthetics. I was contacted recently by a homeowner who was very unhappy that their contractor had sold them what they felt was an ugly metal roof. And they were so upset that they were trying to put a dollar amount on how much this ugly metal roof (and it really was not appropriate looks-wise for their home) was decreasing the value of their home so that they could deduct that from their final payment on the roof. They were playing with a number around $9000 when they contacted me.
Energy Efficiency. A big part of Needs Analysis with a property owner should focus on whether they’d like to make their home more energy efficient and, if so, how they’d like to accomplish that. Generally speaking, if they want to save energy in the winter, that is done by increasing the insulation on top of their home’s ceilings – holding the heat in. If the attic is vented according to code, which helps to prevent ice dams on roofs in the winter, then once that heat reaches the attic, it is exhausted out. Summer energy efficiency is achieved through reflecting heat away from the home, using thermal breaks to stop conductive heat transfer from the roof into the attic, and then, finally, by using ventilation to get rid of any heat that does make its way into the attic. Metal roofing meets these criteria well through the use of heat-reflective finishes, the integration of thermal breaks (small air gaps) between the metal roof and the roof deck, and by integrated ventilation. The thermal breaks I have mentioned work much the way the small airspace works between two pieces of glass in a thermal pane window. They stop conductive heat transfer. Metal shingles usually have an integrated thermal break. Vertical seam metal roofs can accomplish a thermal break by being installed on battens, if the product allows for that, or sometimes by using special clips that lift the panel slightly up off of the roof deck.
Weather Extremes. If you live in a hot climate, you will want to offer metal roofs with heat reflective coatings. If you live in an area prone to hurricanes, you’re going to do special things to prepare for wind events. In an area with lots of seismic activity? A low weight metal roof may be appropriate. Ice and snow – again, you will be looking at ventilation and at a roof system that won’t trap ice on the roof. You set yourself apart from your competitors, serve your customers with excellence, and ensure successful roofing projects by strongly considering the weather dynamics before recommending one metal roof type over another.
Other key considerations. When I train salespeople how to sell metal roofs, I teach them how to help homeowners set their Purchasing Criteria for the new roof. What are the homeowners’ hot buttons? What do they care about? What benefits will raise the value of the roof enough in their minds to justify the price? Is it durability, energy efficiency, added home value, beauty? Something else? What are the things they really want to accomplish with their roof investment? This is all determined very purposefully during the Needs Analysis part of your in-home presentation and, once you know these things, you can tailor your presentation to really build value in these areas. These things also become a critical tool that you will use when it comes time to close the deal because, as they weigh their decision, you can remind the property owners of the Purchasing Criteria they set, and what it will take to meet those goals.
Maybe this all seems like a lot to think about on every job. Maybe it seems like a lot to expect of your salespeople each time they meet with a prospective customer. But, is it really? I mean, after all, what are the risks if we don’t evaluate and assess these things – as well as many other things – in order to propose the roof system that will best serve the structure and its owners? Here are the risks. They aren’t small.
Worst case is you install a system that fails. Now, keep in mind, for most property owners, a metal roof is a significant investment. You do something that causes leaks to start popping up – perhaps even leaks that were never there before, and you have one unhappy customer. Worse, yet, what if those leaks are over their grand piano? Or their new gourmet kitchen? Anyone ever been there before? Anyone ever hear of an unhappy customer hitting social media and Ripoff Report to try to “take down” a contractor. I hope you have never experienced any of those things but, if you have, you know that it gets real ugly real fast. So, one risk to not properly evaluating the job and then recommending the right system is failure—call-backs, repairs, perhaps even replacement. Because, I have to tell you something – if you install a metal system on a roof that is flat-out inappropriate for that home or other building? There’s no fixing it … no amount of spit shine or elbow grease is going to make that metal roof that was intended for a 3:12 pitch roof work on even a 2.8:12 let alone a 1.5:12.
Next thing, of course, is an unhappy customer. Let’s say that what goes wrong is, by some miracle, something that you can easily fix. Even after the repair, you probably still have an unhappy customer. And, what’s more, because the metal roof was so unique, all the neighbors were watching. Now, they know that you messed up, too! Word travels fast, doesn’t it? And, an unhappy customer can easily mean you don’t get paid, you end up in court, and you don’t get referrals from that job! Worst case, just one messed up, ill-advised, improperly-specified metal roof, and you can create a situation that ruins a market for metal roofing for several years!
Okay, none of us wants any of that to happen, do we? So, in order to make sure that the right metal roof product is being used on each and every job, here are key things to consider:
The various profiles, or looks and style of metal roofing
Fastening and attachment Methods
By understanding the above things fully, then, based upon what you figured out during that earlier evaluation, you can know what sort of metal roof will be best for the project you’re on.
Let’s discuss Profiles first – the general designs or style of metal roofs. How a metal roof looks impacts the aesthetics of the project but it goes way beyond that as well. There are peculiarities of each style of metal roof which must be considered. One of those things is that every metal roof has a minimum required pitch. Do not ever install a metal roof at a pitch lower than that recommended by its manufacturer! Sadly, I see this done all the time – people think they can beef up the underlayment or do this or that in order to get by at a lower than required pitch. Don’t do it! Even if the homeowner begs you and says “pretty please with a cherry on top” and promises they will never hold you liable. Don’t do it. Minimum pitch requirements are there for a reason. They are serious. Manufacturers would love to sell product for all roof types but, in some cases, it just doesn’t work. You can’t fool a raindrop! And, as for that homeowner who promises to never hold you liable? He or she will be the first one to hold you liable!
I do want to make a quick general statement before we dig into Profiles. Some of the profiles we will discuss are structural, meaning that they can be installed without solid decking beneath them. They can be installed over battens or purlins. Most of the profiles we will be digging into,, though, are architectural, meaning they must be installed with decking. This should go without saying but never install an architectural panel – pone of the panels that requires decking – without decking.
One more thing I will say, for residential applications, even if you are installing a structural metal roof, I really, really, really urge you to have solid decking as a part of the system. The problem is that, inside of homes as well as some other structures, we create a lot of moisture in of a relatively small space. We create moisture from cooking, doing laundry, taking showers, house plants – all kinds of things. That amount of moisture, even if the attic is vented per code, can still be enough to raise air humidity levels to the point where condensation occurs if the cold back side of the metal roofing is directly exposed to the warm, moist attic air. This is the risk with structural panels on homes. Again, my advice, never install a metal roof on a residence or other small, moisture containing building without having solid decking in place.
So, I want to break Metal Roofing Profiles down into two general categories and then we will take a look at the fifty thousand or so sub categories. Those two general categories are Vertical Seam and Modular Panels. Vertical seam panels only run vertically on the roof, and generally will not have any horizontal seams or laps. Modular panels on the other hand, usually have horizontal seams as well. And these are the panels that often are designed and fabricated to look like shake, shingle, slate, or tile.
Let’s look at Vertical Seam panel profiles first. I will break them down into sub-categories.
The first sub-category is Exposed Fastener. These panels are sold in a variety of profiles. Common profiles include 5V Crimp, R Panel, and PBR Panel. They are defined by their consistent vertically running corrugations. The fasteners used in them are typically screws with a rubber washer and a cap head. Because of the fact that they are direct screwed to the roof rather than a series of interlocking panels, these are extremely wind resistant products. The down side is that the exposed screws can have problems over time, such as the fasteners backing out, the washers cracking and failing, or the screw holes wallowing out or elongating, also causing the panels to loosen. This type of panel has no allowance vertically for the metal’s natural expansion and contraction with temperature changes. So, the impact of that movement is borne by the fasteners and the fastener holes. This will impact the roof’s wind resistance as it ages as screws can loosen or even break and the fastener holes wallow out. These panels usually are steel and are rarely made from aluminum because of aluminum’s higher expansion rate. The aesthetics of these products are sought after for certain jobs but are not real common on higher end homes.
I mentioned 5V as a common Exposed Fastener profile. That particular panel and its distinctive look is very much associated with coastal Florida and island areas. Really, the wind resistance of these sheets directly screwed to the roof versus other metal roofs with any sort of interlock speaks for itself. However, the lack of allowance for expansion and contraction is a negative for these panels, and jeopardizes wind resistance in the future. Additionally, because these are what I call “entry level” metal roofs, meaning they are on the low end of the scale as far as price, we end up seeing a lot of lower grade steels and coatings work their way into these panels. I also sometimes see secondary metal – metal that’s been rejected for quality purposes – finding its way into these panels. In that case, it’s important to understand metals and coatings so you know what you’re getting. Exposed Fastener panels also just have an overlap on their sides. So, they are not going to be as water resistant as some other panels with more aggressive interlocks panel to panel. Sometimes in these panels, though, butyl tape or butyl sealant will be used in the overlaps to enhance the water resistance.
There is also a hybrid version of these panels which are tile profile exposed fastened panels. These panels run vertically and have exposed fasteners but they also have horizontal steps pressed into the panels to simulate the look of clay tile courses. The horizontal steps actually serve a very beneficial purpose. They help to take up the metal’s expansion and contraction so that thermal movement is not borne entirely by the fasteners and fastener holes. Each course or step acts like a little accordion if you will, meaning these panels do not have the fastener problems that we see with panels that do not have these steps.
Now, contrasting with Exposed Fastener products, the rest of the vertical seam panel types we are about to cover have concealed fasteners.
First, let’s look at standing seam roof systems, and we’re going to break it down into two categories – snap lock and mechanically seamed. Snap lock panels are exactly what they sound like – the vertical seams snap together. There are actually two types of snap lock panels. One is traditional which consists of hidden clips to secure the panels to the roof deck. The other is called a nail hem panel. It’s called that even though it is usually applied with screws. When I describe this particular profile, the best thing I know to say is to think of vinyl siding that runs vertically up the roof instead of horizontally on a wall.
The hidden clip version of snap lock, when properly installed, has full allowance for expansion and contraction, making it ideal for roofs with long rafter lengths. Additionally, the clip helps support and provide additional wind resistance to the seam itself.
The nail hem version, on the other hand, has slotted holes for the fasteners. It is critical that crews installing nail hem panels be properly trained in regards to driving in the screw fasteners. The screws must all go into the middle of the slots and they must not be torqued down so tightly as to prevent the expansion and contraction of the roofing panels. If the screws are not placed properly or if they are driven in too tightly, ripples, known as oilcanning, will be forced into the panels.
The clipped standing seam panels can usually be used down to 2:12 pitch while the nail hem panels usually require a 3:12 pitch. This determination is primarily a result of the height of the seams. The clip-fastened version can have sealant in the seams as well for extra protection. One thing to keep in mind in regards to any vertical seam panel with sealant in the seams – you’re going to have real problems if you ever try to take the panels apart. So, if there is any advance thought that a roof might ever have to be modified, perhaps to add onto or remodel the structure, you will later wish that it did not have sealant in the seams.
These types of standing seam are commonly available in both steel and aluminum. It is not unusual for them to be available with the high end PVDF finishes and also with the runner-up super polyester finishes. These panels are available with different seam heights though generally the clip fastened panels will have higher seams than the nail hem panels. Clipped panels will have seam heights typically from 1.25” to 2” and nail hem panels will have seam heights usually less than 1.25”. The height of the seam determines how much water each panel can handle before it floods out and water penetrates the lock. For this reason, again, clipped panels with their taller seams will be preferred for longer panel lengths and also for that scenario I mentioned earlier where a higher level roof may be dropping water into one or two panels of a lower roof.
The remaining type of clip fastened standing seam is a mechanically seamed standing seam. These metal roofs are designed for low pitch applications. When these pans are first installed on the roof, there is no lock to the seam. The pans are installed and secured using clips. Then a seaming machine is run down the length of the seam to create a watertight lock. In old days, rather than use a seaming machine, they would use crimping tools in order to crimp the seams shut by hand. Sometimes mechanically seamed panels will have sealant in the seams as well. This is the style of metal roof that is commonly installed on large commercial and industrial buildings. Mechanically seamed standing seams can often be used at roof pitches as low as 0.25: 12.
That covers the vertical seam panels. Let’s move on to modular panel metal roofing profiles.
Modular panels come in a variety of sizes and styles. Many but not all of them have concealed fasteners and many but not all of them have interlocks on all sides of the panels. We often see these panels used for residential applications. One thing about residential applications is that the homeowners typically care about longer term warranties. So, most manufacturers of these panels use higher end coatings and finishes rather than “budget grade” coatings. These allow them to offer more aggressive warranties.
Modular panels almost always require a minimum 3:12 roof pitch and, in a few cases, 4:12. Keep in mind that if you install a modular panel that has a 1” formed thickness at its downhill edge, and it’s a 12” high panel, then that panel is creating a negative 1:12 pitch all by itself. If you installed it on a 1:12 pitch roof, the panels are sitting flat on the roof deck – not a good way to get water off of the roof, is it?
One thing to keep in mind on modular panels is that they can take some extra care for walkability. The formed thickness lifts the metal up off of the roof deck and, whether the panel is steel, aluminum, or copper, that does mean some extra care must be taken when walking the roof in order to prevent causing visible damages. Generally, that extra care is in the form of walking on the areas of the panel which are closest to the roof deck.
If a homeowner has roof areas where they walk frequently, perhaps to wash dormer windows or put up Christmas lights or something, many of these panels have optional foam inserts that fill up the airspace with a high-density foam. That helps allow the panels to be walked on. Now, a couple of things to keep in mind. Some of these panels are heavily textured so that can help mask the appearance of minor indentations, far better, really, than what happens on many vertical seam panels where every indentation can be quite visible. Additionally, as is the case with all metal roofs and in contrast with most other roofing materials, these products will maintain their impact resistance and walkability as they age.
As I mentioned earlier, there are some different fastening and locking systems with these panels. Most modular panels do have concealed fasteners but a few have exposed fasteners. We see this primarily with some tile profiles and some of the older stone-coated steel systems designed to be installed over battens. Additionally, while most modular panels have interlocks on all sides, some have overlaps on the sides. I would caution you again to think about water flow. If a roof is designed such that water may flow or be pushed sideways across the roof as it flows down the roof, you do not want that water running into a side overlap between the metal roofing panels.
Let’s cover metals now. There is so much to be discussed here but we’re going to focus primarily on the differences that may make you want to use one metal rather than another metal on a particular project. But, I will still provide some basic details as well.
The steel used in roofing is typically either galvanized or Galvalume. Both of these metals have carbon steel at their core. They then have a corrosion-resistant metallic coating that has been applied to both sides of the steel to keep it from rusting. In the case of galvanized, that metallic coating is primarily zinc. In the case of Galvalume, that metallic coating is primarily aluminum.
For some folks, this raises a question of curiosity. We hear a great deal about the possibility of electrolysis or a galvanic action occurring when two different metals come in contact with each other. Why doesn’t this occur when we place, for example, a coating of aluminum on top of steel? The reason is that, in order for a galvanic reaction to occur, there must be a catalyst introduced. That catalyst is commonly a salt or water. As long as the aluminum completely covers the steel, no pin holes or scratches or wear marks, then a catalyst can’t be introduced between the two different metals and no galvanic reaction occurs. This is one reason why, with both galvanized and Galvalume steel, it is very critical that care be taken to not scratch the surface of the metal and to touch up any scratches that do occur.
There are different grades of both galvanized and galvalume steel. The grade is based upon the thickness of the corrosion resistant coating on top of the steel. G90 is a common grade of galvanized steel used in metal roofing. The 90 refers to the fact that 0.90 ounces of galvanization has been applied to every square foot of the metal. There are lower grades of galvanized steel being used including G60 which is common in the agricultural market. Please realize that, when you use a lower grade steel, you are shortening the expected life of the product.
In Galvalume, AZ 50 is a common grade for painted metal roofing. For Galvalume roofing that just has a clear acrylic coating on it, AZ 55, which has 10% more metallic coating for corrosion resistance, is common. One thing to keep in mind, when you hear about clear or acrylic coated galvalume, is that the clear coating has a life expectancy of less than 10 years before it will be washed away – probably more like 5 – 7 years. Once that occurs, it is only the aluminum coating that prevents the steel from rusting.
As a warning, if you encounter a steel roofing material and the price seems too good to be true, it probably is. It is either a lower grade steel, with a shorter life expectancy, or it is steel that has been rejected by another supplier and then re-sold as secondary metal. Sometimes that secondary metal can conveniently lose the “secondary” tag as it flows through producers and distributors.
Something to be aware of is the Metal Construction Association Certified Metal Roofing program. This is a program that some manufacturers have become a part of. Through this program, those manufacturers are able to certify that their raw material, and hence the metal roofs they form from that raw material, are of a certain quality level. They have QA procedures in place, for example, that allow them to track their raw material on every project back to its source, and ensure that secondary metal was not used. This program also looks at the coatings used on these products and is a great way for contractors to assure their customers of the quality of the product being sold to them. There is both a Standard and a Premium level of certification through the MCA program.
So, back to galvanized and Galvalume. Why would you want to use one product over the other? The aluminum used on Galvalume erodes away at a slower rate than does the zinc used on galvanized steel which is good. But, zinc has a better ability to self-heal any scratches as well as cut edges.
Think about this, both the factory cut edges and the field cut edges on any steel roof expose a bit of carbon steel. It is so critical that your installers always cut steel with a shearing action that leaves a sharp, crisp edge rather than with, say, a sawing action that leaves a jagged edge. You want as little of that raw carbon steel exposed as possible.
When it rains, zinc molecules from the exposed galvanization coating on the cut edge go into solution with hydrogen from the water. Those zinc molecules are then deposited on the raw edge of the steel, protecting it from further exposure to the elements. Something similar happens to minor scratches that occur as well in the surface of the steel.
However, whereas this is what zinc molecules do, aluminum does not do this. Therefore, in the Galvalume coating, there is some zinc to try to accomplish this cut edge protection. But, there is not as much zinc to do it as there is with galvanized steel.
So, again, Galvalume wears better ultimately but it doesn’t self-heal cut edges and scratches as well. Keep in mind that, as far as the ultimate wearability of the two metals, if they have a paint finish on them, that paint finish has to completely wear away before the metal itself is ever exposed and this becomes a potential issue. So, that means the most vulnerable spot is indeed the cut or factory edges of the metal.
Bottom line, if you’re in a highly abusive, harsh environment, or if you want a product that can survive without a paint finish, Galvalume is preferred. However, if you’re more concerned about cut edge protection, if you’re concerned about scratches on the metal, or if you’re concerned about doing a lot of forming of the metal which could potentially stretch the paint finish and expose the steel, galvanized is the better choice. Most vertical seam products that have minimal forming to the metal and minimal exposed cut edges, therefore, will be made from Galvalume. But, when you get into heavily formed modular steel panels such as shake and tile profiles where the metal is being stretched and contorted and where you have more cut edges because of the many smaller panels, galvanized is usually the metal of choice.
Aluminum is another metal option. It is more expensive than steel so it won’t reach the price point of a steel roof. It also inherently isn’t as strong as steel. In areas prone to real severe hail or extreme heavy snowloads and, in particular on buildings with snow loads that cascade from higher roofs onto lower roofs, steel can be a very good choice. But, aluminum can be more easily formed than steel, and it is completely rust resistant. So, we see aluminum as a great material for products that are more decorative and have a lot of forming done to the metal. Additionally, we see aluminum in harsh coastal environments or areas subject to severe acid rain, because it won’t rust. To help give strength and support to the final roof system, we will see aluminum panels sometimes having those foam backers installed beneath it that we discussed earlier. One thing we do not typically see is aluminum being used in unpainted form. Unpainted aluminum is very difficult to form because the top surface tends to get very grabby or sticky.
Next, there are some exotic metals available as roofing. Copper and zinc are the two most common. Both can make great roofs, though they do have higher price points than steel and aluminum. Copper is very good even in corrosive environments. As you know, it will change color over time, turning dark brown originally and then later developing the characteristic verdi gris green color. The green patina will cause run off streaks any place it touches, and actually the anti-microbial effect of copper (and zinc) ions may leave clean streaks on the roof. So, when you install a copper roof, you need to think about run-off control. For example, if you let copper run off into aluminum gutters, eventually the aluminum will sacrifice itself to the copper through galvanic action, and corrosion will occur. Also, if the copper runs across stone, stucco, etc., it will leave deposits of copper in the form of green streaks on that material. Some property owners may like that, and others may not. It is something that you as the roofing specifier must discuss with them before they make their roofing choice.
We are seeing more zinc being used as roofing. Very common in Europe for hundreds of years, zinc is not inexpensive but it can make a great roof. We’re seeing it specified a lot on public use and government buildings. One critical thing about zinc is that moisture trapped against the surface of the zinc is its enemy. So, commonly with zinc roofs, there is a spacer material used behind the roofing to promote drainage of any condensation or other trapped moisture. Even though it may seem like overkill to have this spacer, it is used because moisture trapped against the zinc will cause rapidly damaging corrosion to the zinc. Zinc producers will encourage these spacers even if a protective coating has been directly applied to the back side of the zinc itself.
Let’s move on now to the coatings that are typically on metal roofs. The attributes of the various finishes will strongly impact what finish you want on any particular job.
First, let’s talk about paint coatings. Wet paint consists of three basic things and dry paint consists of two basic things. The three components of wet paint start with the solvent – that is what makes it wet. Next are the pigments, often called the solids – that is what gives the paint its color. And finally, the resin – that is the “glue” if you will that holds the pigment in place and also holds it to the base metal. Dry paint, then, has just pigments and resin because the solvent – the wet stuff – has been evaporated out of it.
Various paint chemistries, therefore, are defined most easily by their pigment and by their resin -- the stuff that gives it color and the stuff that makes it all stick together.
So, if the two primary items are resin and pigment, there are two things that happen to the paint as it ages. One is that the resin breaks down. As the resin breaks down, the pigment starts to be exposed to more ultraviolet light and, worst case, the pigment starts to chalk. Did you ever run your hand down the aluminum siding on grandma’s house and get all that white stuff on your hand? That is because the resin has started to break down and, as a result, the pigment is being lost. So, you want a resin that resists breaking down, especially if you’re in a harsh weather environment with lots of sun because sun is very damaging on resin.
Next, you want pigments that do not change color quickly. Again, the resin helps protect the pigment but that will only take you so far. Pigments used in metal roof coatings today generally fall into two categories – ceramic pigments which are man-made, and organic pigments which come from nature. Believe it or not, this is one area where man has excelled over nature. The man-made pigments perform far better than the natural pigments.
The two most common paint systems being used in metal roofing today are polyesters and PVDF, which stands for polyvinylidenefluoride. Both of these coatings are applied when wet to the metal while it’s still in coil form through a process called roll coating or coil coating. So, yes, these products are painted before the fabrication work is done on the metal. In the roll coating process, done at speeds from 250 to 750 feet per minute depending upon the particular production line, the metal is cleaned first, followed by a chemical pre-treatment that prepares the metal surface to accept paint. A primer is then applied and baked on followed by the top coat – the color coat – which is also baked on. You have perhaps seen a few multi-colored coatings and those usually have a print coat on top of the color coat and often, for extra protection, a clear coat on top of that. Clear coats are also common on some of the higher end finishes including metallic colors. Clear coats do extend the life of the paint system through extra protection.
Let’s look in more detail at the polyester coatings first. Polyesters are named for the resin that is used in them. They have proven to be good over the years but eventually the resin does break down and chalking occurs. As this happens, the pigments are exposed to more ultraviolet light and so they begin to fade. The paint manufacturers have developed a higher grade of polyesters called super polyesters and basically what they have done with these is require them to use only ceramic, or man-made pigments. That boosts the performance considerably. In fact, some folks have made claims that, after five years of exposure, the performance of these coatings is not far off that of the highest grade of coatings, the PVDF coatings. However, weatherization studies taken out to year 10 and beyond do show a marked drop off in performance of even the super polyesters. As the resin breaks down, we start to see chalking and also color loss.
Now we come to PVDF coatings. The resin in these coatings is from the mineral fluorite which is a very hard translucent green stone. The mineral is ground up to powder consistency and, because it has thermoplastic properties, it can be used in coatings. There is nothing even on the horizon today that out-performs these paint resins for their ability to remain solid and resist wear and breaking down as they age. To control the quality of these coatings, only certain paint producers are licensed to buy and use the PVDF resin.
In order to use these resins, a paint producer must use only ceramic pigments – the man-made pigments. So, these coatings are ensured of both the best resin and the best pigments for the best performance. By the way, the vast majority of the ceramic pigments have now been tweaked to be “cool colors” – so that they reflect radiant heat even in darker colors. This is what allows these coatings to meet Energy Star standards.
So, which do you want when specifying a painted metal roof? Polyester coatings or PVDF? I have a personal clear preference and it is based upon the quality of the PVDF coatings. However, there is a price difference between the two. If you’re in a mild environment meaning moderate amounts of heat, sunshine, and rain, and the property owner is not calling for top performance and the best possible warranty, polyester coatings can fit the bill nicely. However, in most situations, the PVDF finishes are going to meet the needs of even very demanding climates and clients. The PVDF chemistry provides the slowest erosion rate and the best fade resistance. I want to add, too, if the project is calling for a specialty finish such as a very bright, vibrant, saturated color like a red or a blue, or if the coating is a metallic, there is no doubt that the PVDF coating is what you will want.
I will add here that we are starting to see some work being done in metal roofing with PVDF coatings in powder form rather than the wet-applied coatings we have been discussing. These powder finishes are applied electrostatically and baked on after the metal roofing has been formed. The powder coats allow for texture to be built up on the surface of the metal and they also can allow for the blending of multiple colors.
There is another type of metal roof coating that we see being used, primarily on modular shake, shingle, and tile, and that is what we call a stone coating. Stone coatings are similar to the aggregate stones used on asphalt and fiberglass shingles, except they have been applied to a steel base. Like the powder coatings I just mentioned, the metal is fabricated first, and then cleaned, an adhesive is applied, and then the stones are applied, followed by a clear acrylic overglaze. Stone coated steel products, for consumers, create a nice bridge from asphalt shingles to metal. They have a great look and can include blended colors.
I want to now touch on a couple of additional things and provide you with some resources for your ongoing research.
First, I touched on this earlier – flared gables. These are common on log homes as well as some California and chalet designs. The ridge of the roof is wider than the eave. This situation can be tricky for some metal roofs. So much water – and debris – flows into the gables as it runs down the roof that it overwhelms many typical gable trims. So, what you need for these applications is a special flared gable trim. Not all metal roof manufacturers offer this, so you need to know that before specifying a particular metal roof for a flared gable.
Next, let’s talk quickly about solar attachment. I have never seen a metal roof that could not have solar panels attached to it. However, many of them will require fasteners through the metal roof, very similar to what is done with asphalt shingles. The primary exception is clip fastened standing seam panels. For these systems, the brackets for the solar panels can be clamped to the raised seams, with no fasteners penetrating the metal panels. If someone knows they will add solar to their roof in the future, standing seam would be a great option, even if they choose to use standing seam only where the solar panels will be installed, and then perhaps use a more decorative metal shingle or something on the rest of the home.
Finally, I can’t say a ton about this because warranties vary greatly from manufacturer to manufacturer but it’s important to know what sort of warranty will meet your customer’s needs best. How long of a warranty? Prorated or non-prorated? Transferable or not? These are all great questions … make sure that you know the warranties of the products you are selling.
This article has covered a great deal. Here’s the bottom line, though … if you’re going to be selling and installing metal roofs, make sure that those salespeople or others in your company who are helping to select and specify metal roofs understand as much as possible about the various metal roof systems and why one is superior to another for certain applications. They need to be able to help select the best product design, metal, and coating for each and every application.
The good news is, there are resources available to help with this education. First, align yourself with a quality metal roof manufacturer or two and take advantage of any and all training they offer. Next, here are some trade associations and other things that may help you.
Residential Metal Roofing Executive Report is published twice a month and it is full of help in marketing, selling, and installing metal roofing. I write many of the articles for it. You can subscribe free online at www.executive-report.com.
Metal Construction Association has many great articles and links and technical papers available at metalconstruction.org.
Metal Roofing Alliance has great links to leading manufacturers, as well as good information on the benefits of metal roofing. The website is metalroofing.com
An event held each year in March now focuses just on residential metal roofing, bringing together contractors and speakers from across the country for inspiration, sharing of best practices, and networking. Called the Metal Roofing Summit, the website is www.metalroofingsummit.com
My company also does training for metal roofing contractors, both for sales and installation. You can find information on those opportunities at www.midyeartraining.com and www.Isaiahindustries.com. As you connect with other manufacturers, you will find that they offer training opportunities as well.
Finally, please do not hesitate to contact me. I am always happy to answer questions, or even get involved in helping you market and sell successful metal roofing projects. You can reach me through my website at asktoddmiller.com and you can email me at email@example.com.