Updated: Feb 19
Everyone wants a good deal, and understandably so. You work hard for your money and you want to make it stretch as far as it possibly can, me too! This is exactly why you should be wary about purchasing that metal roof that you found "cheaper" somewhere else.
Some styles of metal roofing, particularly through fastened systems like Tuff-Rib, sometimes get labeled as "barn metal" or "barn tin". This is because not all through fastened systems are the same even if they may look identical. This leads some people to inappropriately group all through fastened systems into a category that isn't fit for residential roofing. The truth is, properly installed through fastened systems have provided homeowners with outstanding protection for decades with minimal maintenance when those homeowners chose a quality through fastened system (and a good installer). What should you look for when purchasing your metal roof? Why do two products seem to look the same and even have the same paint warranty but the prices be so different? What information do you really need to make sure you're purchasing a quality metal roof? Let's take a look.
Not all paint warranties are the same. Even if they're the same.
There has been a recent uptick in small metal roofing manufactures and distributors deceitfully advertising a "40-Year Warranty" on painted metal roofing products. Their prices can seem to be much lower than other established competitors too. Why is that? Are the established metal roofing manufacturers just price gouging? I can't speak for everyone, but that is generally not the case. There is a lot of work involved in preparing steel for use as a residential roofing product and that leaves opportunity for dishonest or otherwise uneducated businesses to bypass important processes that ensure your metal roof will stand the test of time.
Under your metal roof's paint system should be a quality primer and something called a substrate. The substrate provides a protective barrier between the raw steel and the paint coating on the panel. There are a variety of substrates on the market that serve different purposes, and not all of them are suitable or designed for residential use on your home.
Galvalume®. The ambiguous substrate.
If you've already done any self educating on metal roofing you've probably heard of Galvalume. If you haven't you've probably at least heard of galvanized which sounds similar, and it is. Galvanized metal is steel with a zinc coating that helps protect it from the elements. This is the shiny, spangled, silver looking metal on your grandpa's barn. While it serves a purpose, it is inferior to quality Galvalume coatings for residential applications. Galvalume is a mixture of zinc and aluminum (and a little bit of silicon) that provides superior rust-through protection against the elements. Galvalume is a very popular substrate for metal roofing materials. Steel is Galvalume coated before being primed and eventually painted with a quality powder coat before being sold to you to be installed on your roof. So that's it, right? As long as your metal roof has Galvalume under the paint you're good to go, right? Wrong. Sadly, to make things a little more complex, not all Galvalume is the same. In fact, some Galvalume... isn't even Galvalume. Let me explain.
Different types of Galvalume have different thicknesses, weights and consistencies. These are represented by designators like the ones you seen in the chart above (AZ50, AZ35). These designators tell us a lot about the quality of that substrate. The examples you see here show the differences between AZ50 Galvalume and AZ35 Zinc-Aluminum.
NOTE: AZ35 is not considered Galvalume® by most mills . Anything less than AZ50 is marketed as ASTM A 792 55% Aluminum-Zinc Alloy-Coated Sheet rather than Galvalume®.
AZ50 and AZ35 are popular substrates in the metal roofing world but they may achieve different results. Both of these substrates can technically be coated with a "40-Year paint" allowing companies to advertise a 40-year paint warranty for a considerably lower price. The problem is that quality metal roof paint coatings were not designed to be applied to AZ35 substrates for residential applications. Here's why:
AZ35 Does not meet International Residential Code requirements.
That's right. Coating weights less than AZ50 do not meet International Residential Code requirements. Choosing a material with a 40-year paint that uses an inferior substrate like AZ35 or AZ40 will offer less edge rust protection and protection against through rust. .
Looking at the graphic above we can see some the differences between AZ35 and AZ50. AZ35 weighs less than AZ50, is substantially thinner, has no corrosion warranty, doesn't meet International Code Requirements and technically isn't even Galvalume®.
In conclusion, do your due diligence in researching surprisingly cheap through fastened metal roofing products boasting 40-year paint warranties. They may be just that, cheap. A good paint system does you far less good on a bad substrate. If you purchased a metal roof with an AZ35 or AZ40 substrate, you may find yourself with a failing roof system that looks inferior and needs repaired and replaced before it's life should be expired. When choosing your metal roof the paint system is very important (another post coming on that) but it isn't the only thing you should consider. You should also look at the substrate to make sure it is AZ50.
Director of Marketing & Development, Best Buy Metals