The Roofing Resource Blog

Metal Roof Coatings Vs Metal Roof overlays systems - What's the difference?

Thu, Jul 16, 2020 @ 11:39 AM | Perry

For many building owners, a metal roof coating seems like the logical next step to take when trying to stop leaks on a metal roof, especially if  other targeted repair attempts in the past have failed and the metal roof leaks. 

At first glance a metal roof coating appears to be the path forward to an economical and quick solution to stop the leaks without having to replace the entire metal roof and disrupt either your business’s operations or your tenants. 

Metal roof coatings sound great, you get to leave the existing metal roof in place and still fix the leaks, What could be better? And besides that, what other choice do you have? 

Most building owners find themselves stuck between an Expensive and unaffordable metal roof replacement option  or a metal roof coating option.

In this blog we’ll introduce you to another metal roof repair option you probably haven’t considered called a metal roof overlay system and we’ll compare and contrast it to metal roof coatings. After reading this article you should walk away with a much better understanding of metal roof repair and knowledge of several possible ways  to stop the leaks on your building. 

  Table of Contents 

  1. Different types of metal roof coatings and different types of metal roof overlay systems 
  2. Application Issues- weather play a big role
  3. No new flashings around pipes, HVAC units, or Skylights
  4. Similar in cost, Not in Value, What’s the price difference?

Metal Roof Coating

Metal roof coatings and metal roof overlays  are similar in several ways such as they both leave the existing metal in place, there’s no tear off and replacement of the existing roof, both are much less expensive than full roof replacement would be , and neither the metal roof coating nor the metal roof overlay disrupts the buildings daily activities so the building can stay up and running through out the process.

Different Types Of Metal Roof Coatings And Different Types Of Metal Roof Overlays

Just as there are several types of metal roof coatings on the market today such as acrylic based, polyurethane based, Elastomeric, and siliconized coatings, there are also two distinct types of metal roof overlays:

metal roof over meal roof overlay

As mentioned in the beginning of the article, building owners seem to have no problem finding their own way to metal roof coatings as a repair option, however the metal roof overlay systems option isn’t as self evident  or as obvious as a possible solution to metal roof repair.

In Fact, we find most building owners aren’t even aware that you could install another metal roof on top of your existing metal roof, (metal over metal retrofit) , or that you could install a TPO/PVC flat roofing membrane overtop of your existing metal roof, (Metal roof retrofit).

Moving forward, it’s worth noting that metal roof coatings are easier  to compare to the TPO/PVC membrane over metal option than the metal over metal roof overlay. 

Metal roof coatings and TPO/PVC over metal roof retrofits are similar in class and also in the price installed even though the TPO/PVC over metal has much better long term performance. The comparison is fair, more like apples to apples, and we see this comparison play out in the real world everyday as building owners consider their metal roof repair options and their budgets.

Metal over metal roof retrofits are harder to compare to because they are in a category of their own. A new metal roof installed over your existing roof is long lasting, durable, and includes all new trims and commercial guttering. A metal roof coating is akin to a thick paint. The two are hard to compare but it’s still valuable to you as the reader to know what options are available to you and we’ll look at the average cost for metal over metal roof overlay later in the article so you’ll have an idea if it fits into your budget. 

3 Major Reasons Why A Metal Roof Coating May Not Be The Right Solution For Your Building

1. Application Issues- Weather Plays A Huge Role In The Successful Installation And Performance Of Metal Roof Coatings But Metal Roof Overlay Systems Can Be Installed Year Round

Roof Insulation

The first major difference between a metal roof coatings and a metal roof overlay system  is that the roof coating can only be installed in the right temperatures.  Some metal roof coatings can be installed in temperatures as low as  40 degrees and rising whereas other coatings must have 60 to 65 degrees and rising temps. These temperature restrictions reduce the installation window of metal roof coatings in many climates around the country. 

It may or may not be the right time for your business  or your budget to tackle metal roof repairs when the temps and weather conditions are right but metal roof coatings offer little flexibility when it comes to temperatures.

In addition  to temperature restrictions,  other weather and environmental conditions must be considered like Humidity, dew point temperature, frost, dew,  and condensation.

In order for the metal roof coating to adhere correctly to your building’s metal roof, the surface must be clean, dry, and free of loose debris or any other contaminants. 

Metal roof coatings that require multiple coats to be applied have varying dry times between applications that range from 16-24 hours out to 3-5 days again depending on air temps, surface temps, humidity levels etc.  

The ability for a metal roof coating to keep your building dry and its long term performance is very much tied to the conditions it is installed in. Less than ideal environmental conditions = less than ideal overall performance of the coating.

None of these weather, temperature or environmental factors come into play with metal roof overlay systems. The TPO/ PVC membrane can be installed over an existing metal roof  in a wide range of temperatures especially when being installed “mechanically  attached” as there is no glue, sealants, or anything that needs “dry time”. And the metal over metal roof overlay can also be installed in cold temps with no thought about humidity, dew point, or adhesion problems.

The main idea behind most metal roof coatings is that as multiple layers of coating are applied, you are “ building a waterproof membrane right on top of the existing metal roof. The problem is that building the water proof membrane on the existing metal needs to be done during ideal temperatures and weather conditions that seldom occur. 

A metal roof overlay system, especially the TPO/PVC roofing membrane over metal is not being “built or applied” in the field but rather installed. The membrane is already created, all that needs to happen is for it to be installed correctly. 

There is a major difference between a metal roof coating being used to create a membrane vs. having a membrane or new metal panel already made and having it installed  over the existing metal roof. 

2. No new Flashings around Pipes, HVAC units, or gaskets between Trims

Metal Roof Leak

Metal roof coatings largely fail to solve the 3 of the Top 5 reasons why metal roofs leak

And it’s one of my biggest problems with coatings, you don’t get new flashings. 

Metal is a super durable and long lasting material,  after all that's why it's made it into roofing. And metal roofing rarely leaks just out in the middle of the roof somewhere for no reason. Leaks are almost always centered around Pipes, seams in the metal sheets, behind  HVAC units, or on the screws or trims. 

So it’s reasonable to want special care given to the most leak prone areas of the  roof, but metal roof coatings come up short in these critical areas. All you get around the pipes and behind the units is more coating which in many cases causes water to become trapped and pond behind the pipes or units and makes the leaks even worse. 

Metal roof overlay systems come standard with all new flashings around pipes,  HVAC units, and they recover old leaking trims, not just paint them white. 

3. Similar in Cost Not in value- what’s the price difference 

Duro-Last metal roof retrofit system

Metal roof coatings and TPO/PVC membrane over metal roof retrofits are similar in cost  but not in value. Both Metal roof coatings and TPO/PVC retrofits in the MidWest will cost in the $3.00 - $5.00  dollar range per sq. Ft. installed depending on the building size and field conditions.

But the roofing membrane over metal  and the metal over metal roof system both come with new insulation which adds R value to your building, reducing heating and cooling cost, while the metal coating does not add any R -Value to a building.

The TPO/ PVC membrane over metal options are 20 yr solutions whereas the longevity of the coating will vary greatly depending on the conditions it was applied in, the number of coats applied, and  the adhesion of the coating to the existing metal roofing, all of which are unknown factors. 

The TPO/ PVC membrane over metal system comes standard with  added roof insulation, all  new flashings and trims, and can be installed in a wide range of temperatures at most times throughout our year. 

The roofing membranes used to recover metal buildings  have been tested and  are proven to last, but each time a metal roof coating is “built on site” it’s a unique product and untested in the unique environment and weather conditions it was applied in. Your building’s roof becomes the test site, and you or your building occupants hope it passes the test long term.

As mentioned, Metal over metal roof overlays are not really similar at all to a metal roof coatings but they are worth knowing about and understanding. The metal over metal retrofit is a great option for building owners who want to forget about leaks for the next 40 years or so and get on with their business.  So how much more should you expect to spend on a metal roof overlay?  There are many factors that drive a metal over metal recovery like panel length, building size, and labor cost in your geographical location, but what we see in our area on average is somewhere between $7 and $11 dollars a sq. ft. installed. Watch a video that further explains cost (Click here)

It's not all about price but price is important and so is working within your company’s budget to resolve leaks on your metal roof. Use the price ranges given here only as a guide. We suggest getting actual quotes from roofing contractors in your area for the metal roof repair option you feel is the best fit for your building. 

If you need help finding  a roofing contractor who does  metal over metal roof overlays near you, feel free to contact us at

At the end of the day  there’s no one size fits all solution to metal roof repair. Each job is unique and you find the right fit for your building, your budget, and your long term goal for the property. 

Understanding your options will better equip you to make the right decision about your building. We hope we’ve helped you in this article and thank you for reading.

Metal over metal overlay