Roof Coatings: Advice From a Roof Consultant

Introduction

If you’re responsible for a roof, you may be thinking about using a roof coating to make your roof last longer. I was a roof consultant advising corporate and institutional clients for over 20 years. My company managed their roof assets; we recommended strategies and actions that would maximize the value of those roof assets using life cycle cost analysis and our roofing expertise. We specified and scheduled roof maintenance, roof repairs, and roof replacements. We extended the useful service life of the roofs beyond the standard design life while reducing overall expenditures. Our clients got more roof for less money. And we rarely recommended roof coatings.

Note: This article is primarily concerned with use of roof coatings to extend the service life of low-slope (or “flat”) roof systems. This article is about proper roof coatings, not roof treatments or roof “rejuvenators”.

The use of roof coatings on pitched, shingled roofs is not something I would ever recommend.

Roof Coatings on Shingled Roofs

This is simply a bad idea and goes against the guidance of every reputable shingle manufacturer. In almost no case will a roof coating be suitable for a shingle roof. According to the Asphalt Roofing Manufacturers Association:

“Coatings may negatively impact the performance characteristics (including the fire classification, algae resistance, impact resistance, etc.) of the roof assembly”

and:

“The problems reported after asphalt shingle roofs have been field coated include shrinking of the coating, which may result in unsightly curling and/or cupping of the shingles or loosening of the granule surfacing of the asphalt shingles. In addition, non-permeable roof coatings may create a vapor-retarding layer by sealing the voids around and between the shingles. If this occurs, it may contribute to moisture accumulation within the roofing system.”

The moisture that will accumulate in the roof system generally comes from interior humidity. Heating and air conditioning lead to different levels of humidity and temperature between the inside of the house and the outside air. These differences lead to condensation. If you coat the roof, you will have created a vapor barrier, and that moisture will have nowhere to go. It will remain trapped in the wood roof sheathing, laying the groundwork for dry-rot and mold.

Also note that the International Residential Code (IRC), Section R905.1 specifically says that you have to follow the manufacturer’s instructions:​

“Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer’s installation instructions.”​

Whether manufacturer guidance on roof coatings is a tip or an instruction can be debated, but it should be taken into account either way.

Another good source for impartial information about the roof coating products marketed for use on asphalt shingles is the article Myth Busting: The Risks and Unverified Benefits of Field Coating Asphalt Shingles in Professional Roofing magazine (published by the National Roofing Contractors Association).

For homeowners considering roof coatings as a way to extend the life of their shingles, a better approach is regular maintenance, proper attic ventilation, and dealing with minor repairs right away.

Will a Roof Coating Extend the Life of Your Roof?

I’ve worked with a lot of property managers and facility directors and once in a while they’d ask me whether a roof coating would be a good way to get more life out of their roofs. A few of them seemed to have fallen under the spell of a roof coating salesman and become convinced that putting a coating on their roof would let them push back a roof replacement by 10 years and save them all kinds of money. It always amazes me how much some people want to believe what a salesman tells them even when I explained all the things the salesman isn’t telling them. It really is like they’re under a spell.

Roof coatings can be a good idea, sometimes. A roof coating might be able to extend the roof’s service life. Maybe. It really depends on the very specific attributes of the individual roof. Sometimes a roof coating can be a terrible idea because it’s just a flat out waste of money that you’ll regret later. A roof still has to be in good condition when the coating is applied in order for you to see a real benefit. If your roof is at the point where you’ve already started thinking about scheduling a roof replacement, it’s pretty much too late for a coating to do any good.

That being said, there are other reasons to apply a roof coating besides trying to extend the life of your roof:

Energy Savings: Reflective “cool” roof coatings can significantly reduce roof surface temperatures by reflecting sunlight. This can help lower the cost of cooling the building, and it makes sense in places like Texas if you have an existing black surfaced roof like EPDM. Before you proceed in these cases, you should verify the Solar Reflectance Index (SRI) value of the exact roofing material product that’s in place on your building and see how much of a difference a coating will make. Check with the manufacturer’s technical department and see what they say.

Waterproofing: Many roofs, particularly asphalt built-up and modified bitumen roofs (and EPDM, to a lesser extent, because of the adhesive in the seams) do not perform well if water sits on the roof for long periods. Chronic ponding water like that can really damage these roofing materials over time, so a coating may be necessary to protect it. A properly designed and installed roof shouldn’t have this issue, but it doesn’t always work out that way. You want a coating that is designed to handle ponding water exceptionally well in these cases. Silicone is good for this.

Fire Resistance: There are specialty roof coatings that contain fire-resistant additives that can help improve a roof’s ability to resist fire, which may be desirable for buildings in wildfire-prone areas​.

Chemical Resistance: Some industrial and commercial roofs are exposed to concentrated chemical pollutants from exhaust vents that vent above the roof. Polyurethane and fluoropolymer coatings may offer additional protection in such environments​.

Corrosion Resistance: Steel roofs in humid or coastal environments are prone rust and corrosion. Some coatings can serve as an anti-corrosion treatment that will help extend the life of these metal roofs​.

You can read more about the different types of roof coatings here.

How Roof Coatings Work (or Don’t)

Roof coatings don’t somehow rejuvenate the roof by infusing it with new strength and vigor. A roof coating simply protects what is there at the time it is applied. If the roof is already near the end of its life, a roof coating will provide almost no value for the money.

A roof coating is not a roof. It should never be counted on as the main barrier between the weather and your building. Roof coatings depend on the underlying roof in order to function.

To emphasize this, I want to point out that building codes do not consider a coating to be a standalone roof system; the codes only recognize roof coatings as supplemental protection, not primary waterproofing​. This is why building codes have almost nothing to say about roof coatings except to repeat the minimum slope requirements for flat (low-slope) roofs and to list the ASTM material standards that apply​.

Roofing materials become weaker and less flexible as they age. Asphalt oxidizes over time, the asphalt molecular chains break down, and asphalt roofing becomes brittle. The plasticizers added to PVC roof membranes migrate out of the material. EPDM shrinks. Every roofing material weakens with age and exposure to the elements. The damage caused by UV radiation is biggest contributor to the deterioration associated with roof aging.

As a roofing material becomes more fragile over time, it becomes more and more likely to split, tear, and leak due to the expansion and contraction of the membrane while it undergoes normal daily thermal cycling. The roof membrane expands when it heats up during the day and shrinks when it cools down at night. A roof coating won’t help a roof that no longer has the strength to resist these cycles.

If the coating is applied, say, halfway through the life of the roof, it will prevent UV radiation from hitting the roof itself and that way it can slow down the processes that weaken the roof. By doing this, a roof coating will extend the life of a roof. That is the main benefit of a roof coating.

But if the coating is applied after the roof is already worn out, it does no good. If the roof is already failing, a coating will do little more than temporarily mask the symptoms while the underlying issues continue to worsen​. Imagine spending 15% to 25% of the cost of a new roof only to still have to replace the roof a year or two later. I’ve seen that happen.

In some cases a roof coating can do more harm than good. Coatings can actually trap moisture inside the roof system, leading to accelerated deterioration of roof insulation and fasteners. This is especially true if a coating is applied over a roof with existing leaks and wet insulation​.

Before you apply a roof coating, I strongly recommend that you have a professional roof consultant inspect the roof to determine whether the roof is in a suitable condition to benefit from a coating​. Not a contractor, and certainly not a coating salesman. And you should listen to your consultant.

The Roof Coating Industry

Roof coatings are minimally regulated by building codes, and while there are product standards (such as ASTM D6083 for acrylic roof coatings), enforcement is inconsistent. This allows substandard products and practices to proliferate and because of this, the roof coating industry is saturated with shady, unscrupulous coating salesmen, suppliers, and manufacturers.

Many roof coating companies are simply marketers who purchase cheap coating material from industrial chemical manufacturers with poor quality control, and then outsource the application work to poorly trained applicators.​

This doesn’t mean that there aren’t reputable roof coating manufacturers who produce quality materials and are honest about what a roof coating can and cannot do.​ It simply means that you need to be as careful when buying a roof coating as you would be if you were buying a used car.​

When I’m involved in coating projects, I carefully research the product and the company that makes it. As a rule of thumb, I generally want the coating manufacturer to have been in business for at least 20 years. I also make sure that the company that applies the coating is an actual commercial roofing contractor, not a company that just does coatings. And I want the contractor to have been in business for at least 10 years.

Roof Coating Warranties

Just about all roof coatings will come with a warranty. You can buy roof coatings with 5-year, 10-year, 15-year, and, in some cases, even 20-year warranties. The catch is that these warranties are material warranties that are limited to material defects.​ Material defects in the coating, not the roof.

A material warranty simply guarantees that when the coating material left the factory, it was free of defects.​

A material warranty does not cover the application of the coating. If the applicators put the coating on too thin, forget the reinforcing fabric at flashing locations, or apply the coating while the roof is wet, the warranty doesn’t cover it.​

A roof coating warranty does not cover the performance of the coating. It will never cover problems due to the performance of the existing roof, and that’s the real issue. If you have a 10-year warranty on your roof coating but the roof has serious problems and starts to fail in 3 years, your coating warranty won’t help you in the least.​ If your roof has blisters or areas with wet insulation, and the roof coating delaminates and falls off in those areas, the coating warranty won’t cover it.​

Roof coating warranties are, for the most part, something that roof coating salesmen can point to in order to convince you to buy their product.​ Roof coating warranties are practically worthless. I want to emphasize that. If you think that your roof coating warranty is going to cover you if your roof starts leaking, you are almost certainly wrong.​

An Actual Roof Coating Experience

We were hired by a Fortune 100 company to oversee a major re-roofing project at one of their largest manufacturing facilities. The facility has dozens of buildings and roof areas that total in the millions of square feet.

Some of those buildings had spray polyurethane foam roofs that had been installed on top of two layers of old built-up roofing. The job consisted of grinding off (scarifying) a few inches of the existing foam on a few of those roofs, cutting out and replacing wet insulation, and applying a new layer of spray foam, surfaced with a new silicone coating.

This job went very well, the new roofing was a high quality installation, and the client was set for another 20 years of good roof performance on those buildings. The following year they contacted us again about doing the same thing on a different and much larger roof area.

We had infrared and nuclear capacitance surveys of the roof performed to identify areas of wet insulation. This would normally be overkill, but there were three existing roof systems in place on the building, which made identifying wet areas within the roof particularly challenging. We started putting specifications together. We lined up contractors to bid on the work.

Then a roof coating salesman got hold of the facilities director. Right before the job was supposed to go out to bid, we got an email from the facilities director suggesting that he was now planning to simply re-coat the roof and asking us for our opinion on a certain brand of acrylic roof coating.

He pointed out that they were giving him a 10-year warranty and that the price would only be about 15% of what our proposed project would cost. He seemed very excited about that.

This was my response:

My Letter to the Facilities Director

Dear (Mr. Facilities Director) –

Regarding the spray polyurethane foam roofs:

We do not consider these roofs to be good candidates for a roof coating application, especially an acrylic roof coating. Here are our concerns:

1. Roof Coating Compatibility Issues

These roofs have an existing silicone coating. Silicone coatings are known for being incompatible with other coating chemistries. The following is a quote from the Spray Polyurethane Foam Alliance (the industry organization which certifies SPF contractors and establishes the standards that govern SPF roofing):

According to SPFA-102: A Guide for Selection of Elastomeric Protective Coatings Over Exterior Spray Foam Applications:

“Compatibility with other Elastomeric Coatings: Acrylics have been used with other elastomeric coatings; however, manufacturers should be consulted to ensure compatibility. Acrylics are not recommended to be used over existing silicone coating.”

2. Coating Over Wet Polyurethane Foam

These roofs have more than 800 locations where the foam is water-saturated. Roof coatings cannot be applied over a wet substrate. If a coating is applied over areas of wet foam, the coating will rapidly delaminate in those areas and fail.

Those wet areas are the exact areas that are currently most in need of remediation. Even with the graphic from the infrared survey as a guide, the coating contractor will not be able to identify areas of wet foam that have formed since that survey was performed.

If the roof is scarified and foamed, all wet areas will be identified and removed during the scarifying process.

There are also many locations where the existing coating has worn away to a considerable extent, so pressure washing the entire roof surface (which would be necessary) will likely lead to new areas of wet foam forming, and this would be right before they apply the new coating.

3. Coating Over Roof Blisters

These roofs have many, many areas where blisters have formed in the foam. Blisters expand and contract as the air inside them warms and cools. They also get bigger over time as the thermal cycling process repeats.

Acrylic coatings are relatively brittle and would likely fail in many blistered locations due to the expansion and contraction. The blisters would have to be identified and repaired during the coating process.

We are not confident that this could be done effectively by a roof coating company. This would not be an issue if the roofs were scarified and re-foamed by a roofing contractor.

4. New Spray Foam Application Before Coating

The existing foam in more than 800 locations (wet foam and blisters) would have to be cut out and replaced with new spray foam.

We do not know whether the coating contractor is qualified to perform this work. As these areas would most likely not be properly prepared (scarified), we doubt that the new foam in all of these areas would successfully adhere to the existing roof without new blisters forming soon after the application; this would damage the new coating.

5. Acrylic Roof Coatings and Ponding Water

These roofs currently have large areas where ponding water is an issue. Acrylic coatings are possibly the worst-performing coatings under ponding water conditions. Acrylic coatings have high permeability; when water sits on top of them for prolonged periods, the water eventually penetrates the coating and gets into the substrate, causing the coating to delaminate and fail.  

6. Roof Coating Warranty

Roof coating warranties almost always only cover the coating material itself as being free from manufacturing defects. It would not cover any problems caused by existing issues with the roofs. It would not cover coating failure due to ponding water, wet foam, blisters, etc. We do not think the coating warranty should be a factor at all in your decision as to how to proceed with this project.

Yours Truly, Jack Gray, etc.

The Rest of the Story

The facilities director thanked me for my input. Two days later he told us he was going to go ahead with the roof coating idea. We billed them for our work up to that point and had nothing more to do with that project.

I did eventually find out how everything turned out, though.

One of the roofing contractors on our standard bid list did a lot of leak repair work at that facility, and they had also been amazed that the facilities director would go ahead with the roof coating application despite their own recommendations against it.

I was on the phone with a project manager from that roofing contractor about six months later, talking about a totally unrelated roofing project, when he brought it up.

That new acrylic roof coating started to fail within three months (three months!). The areas where the coating delaminated and began falling off made up about 40% of the total roof area. The roof was shedding pieces of roof coating into the parking lot constantly.

The roof coating manufacturer, who had convinced the facilities director to use their product in the first place, refused to do anything about it. They pointed out that the warranty was just a material warranty and that the coating failure was solely due to the poor condition of the existing roof.

The facilities director had also been relieved of his duties, and was no longer the facilities director.

So that’s something to think about before you put your faith in a roof coating.