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Patrick Stilwell

By: Patrick Stilwell on October 15th, 2020

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How much does it cost to coat a metal roof?

Roof Coating

It’s the question we get most often about standing seam and screw down “R” or corrugated panel roofs: How much does it cost to install a fluid applied membrane or roof coating system? It makes sense. At Custom Coatings, we’ve been covering the roofs of industrial sites, commercial facilities and more since 1991, and if we know one thing, we know that all businesses want to stay dry without spending a fortune.

As with many things however, the answer to “How much will it cost?” is “It depends.” Let’s break down some of the variables (without naming any specific coating products).

First, however, because we are all about education here, a primer in fluid applied membranes.

 

What is a Fluid Applied Membrane or a Roof Coating System?

A roof coating system is a barrier that starts out life as a liquid (unlike a hard surface roof, which might be made of shingles or metal). A traditional single-ply roof membrane (another roofing option) sounds similar and also starts life as a liquid, but is created in a factory, cut to length on a roll, brought out to the job, and glued or attached to the building.

Now for the good stuff: A roof coating system or fluid applied membrane is built on the roof in the field. That’s important, because roofs built in the field can be seamless. Traditional roofs will have seams due to how they are cut in the factory and installed. A roof coating system however, can be one solid, monolithic sheet over the roof. No seams means much less potential for leaks, and fixing or avoiding leaks is why you’re installing a new roof in the first place, right?

Note that the only way to install a traditional roof on top of an existing metal roof is to first install a layer of foam – which means more work and more mess. The process of installing a roof coating system on your metal roof however has a few steps, but costs less (we’ll tell you more later). The steps:

  • Inspect existing roof and perform necessary repairs
  • Clean the existing roof of all foreign matter that could affect adhesion
  • Tighten, replace and add new fasteners to ensure the roof is tight
  • Seal all seams, fasteners and penetrations
  • Apply intermediate and finish coats
  • Inspections for warranty process

If your commercial metal roof is in reasonably good condition, it can be restored with a new fluid applied membrane or roof coating system and last a long time, boosted by a full material and labor warranty option.

 

So, how much does it cost to install a fluid applied membrane or roof coating system on your commercial metal roof? If your existing roof is in decent condition, depending on the system, warranty length, etc. The average 10,000+ square foot metal roof will fall in the $1.85 - $3.75 per square foot range for a 10-15 year material and labor warrantied system.

 

Now, let’s get into the nitty gritty of getting the job done.

 

Metal Roof Coating in Six Steps

 

Step 1: Inspection

During the initial survey of your roof, a qualified and experienced estimator will walk your roof and evaluate its current condition. If the contractor finds that some of the metal is rusted or weak, depending on the severity, they may suggest some of the metal be replaced. Other things your estimator will do are closely investigate all fasteners, seams, penetrations, pipe boots, valleys and any other transitions. Metal roofs do not typically leak in the “field” or open areas, they leak at all the above listed places.

 

Step 2: Cleaning and Preparation

The number one reason for roof coating failure cited by the National Roofing Contractors Association and countless other entities is improper preparation and cleaning of the existing roof substrate.

Most manufacturers do not have specific cleaners for metal roofs, but a good rule of thumb is that your contractor should use some cleaning agents along with a minimum of 3000PSI (pounds per square inch) pressure washing. Before washing, remember to also ask them how they will be proactive in preventing driving water into your building. There are strategic techniques to power washing metal roof, over and above simply blasting the surface with high pressure water.

 

The cleaning phase of your 10,000+ sqft roof will range in cost from $.30 - $.50 per square foot.

 

Step 3: Repairs

Addressing rust and/or metal replacement will be next. If your metal roof has any holes from rust or other punctures, your contractor will repair those holes prior to moving forward. If your roof is a typical “R” Panel (or other standard corrugation profile), then your contactor will likely get new metal to replace larger holes. If holes are minor, then your contractor may opt to scab a small, new metal flashing repair over the existing roof instead. Either repair is acceptable, and both will provide a sound substrate for your Fluid applied membrane or roof coating system to be applied. If your metal roof has any rust, your contractor will either apply spot treatments of rust inhibitive primer or potentially fully rust prime your entire roof.

 

Step 4: Tightening & Initial Waterproofing

The first step in making your roof water-tight is tightening, replacement and/or addition of fasteners. This is super important, because no matter what, your roof panels have gotten loose over the years. (Why? Thermal shock. Read more here.) If any existing fasteners that have backed out are able to be tightened, then your contractor will do that. Unfortunately, however, most often a larger diameter fastener is needed to securely go back into the same hole and tighten the roof, so new fasteners or additional “stitch” screws may be needed to close gaps and fully tighten things up.

Once your roof substrate is tight, the real waterproofing can begin.

Depending on the materials being installed and the manufacturer’s guidelines, there could be a wide discrepancy in how this phase will go down. Some manufacturers will have your contractor apply some form of waterproofing material to every single part of your roof that has the potential to leak (i.e. fastener heads, horizontal seams, vertical seams, valleys, penetrations, flashings and transitions). Other manufacturers will only specify that the horizontal seams be waterproofed.

Not only do manufacturers have different thoughts about where to apply waterproofing, but also in how their waterproofing is applied. For instance, one manufacturer may ask that your contractor simply brush on their sealant to a certain mil thickness on the horizontal seams only. Another manufacturer will specify that your contractor must install a three-course reinforced waterproofing membrane over all the seams – liquid sealant, poly fabric and another coat of liquid sealant. It can get complicated. Because of the differences in how a roof is waterproofed, the pricing to install the waterproofing phase is also wide.

On average, your 10,000+ square foot metal roof will cost between $.35 - $1.25 per sqft to install the waterproofing layers.

Step 5: Second Inspection

After all the above-mentioned repair and waterproofing are complete, a knowledgeable and responsible contractor will do a secondary inspection of the roof. During this walk-around, they will look for “fish mouths” (a spot where the fabric or tape opened slightly which may allow for water to penetrate), trouble spots around seams and any penetrations. The contractor will then use additional flashing materials from the manufacturer to reinforce these typical trouble spots. Again, metal roofs don’t typically leak in the open “field” of the roof; they leak at seams, penetrations, fastener heads, transitions and curbs. By fully addressing all these potential trouble spots early in the coating process your contractor can be confident that your new fluid applied membrane will withstand the test of time.

 

Step 6: Top Coating Installation

Different manufacturers will require different applications of their products, from single to multiple layers. Top coating applications can be applied by sprayers or rollers. If your contractor opts to roll the coating on your roof, ask them how they will ensure the material is being applied to the proper mil thickness since your roof is not flat. No matter how it is applied, your contractor must take mil thickness measurements incrementally to ensure the product is being applied at the manufacturers required thickness. The final application of the topcoats will protect all the repairs, existing roof membrane, seams, penetrations and waterproofing layers. The finish coating is the final waterproofing layer between your building and the elements.

The final topcoat application on your 10,000+ sqft commercial building will range from $1.00 - $2.00 per square foot.

 

Final Variables: Warranties and Other Assurance

Warranty requirements and costs will vary widely depending on the type of material, the manufacturer and who installed the system. Note that while it is possible for someone to go buy a roof coating product on their own, it is not possible for them to get a warranty on it by performing the work themselves.

For the purpose of this article, lets talk about the cost of a full material and labor warrantied fluid applied membrane or roof coating system. Manufacturers who offer these extremely valuable and comprehensive warranties are quite selective about who can install their system. So, ask your contractor for their credentials, certifications and what manufacturer brands endorse them. The cost of the warranty is relatively small compared to the full roof coating system install, so don’t skimp, and make sure your selected contractor is eligible to offer the warranty promised.

Moving on: Typically, the mil thickness of the final topcoat application goes into determining the length of the warranty offered. The cost of the warranty is determined by the coating manufacturer. The industry standard for a manufacturer’s 10 Year material and labor warranty is $.07 - $.11 per sqft. The standard for a 15 Year Material and Labor Warranty is $.13 - $.17 per sqft.

One note: There is a key difference between roof coating system warranties and traditional roofing warranties.

The first and most relevant thing is that fluid membrane warranties are renewable. At the end of the initial warranty term, your contractor can inspect, clean and apply a fresh layer of the topcoat only to your roof at a small fraction of the initial install cost. The full material & labor warranty will then renew for an additional 10+ years depending on the manufacturer. The average material, labor & warranty cost for this renewal in today’s dollars is between $1.00 - $2.00 per sqft. Traditional roof warranties are not able to be renewed in this fashion.

The second key factor to look at with warranties is that traditional roofs may come with a 20 or 25 year “warranty” up front. If you will read the fine print however, you will discover that warranty is prorated after a certain time frame and it is materials-only after a short, initial term of 2-5 years. Coverage for labor expires after a short time, and then if you have a leak, you will still pay for the labor to have it repaired. A roof coating system however, will come with a Full Material and Labor Warranty for the life of the system, and even better, your warranty can be renewed repeatedly every 10+ years.

Taking these two key warranty factors into consideration, we can honestly and confidently tell you that if properly maintained, this will be the last roof you ever install on your building.

 

Sealing It Up

Installing a fluid applied membrane or roof coating systems on a metal roof takes a few steps, includes a number of variables and the ultimate cost depends on a number of choices and possibilities.

Like any roofing project however, a solid strategy executed by a competent contractor and supported by a quality manufacturer’s product is essential in providing a long-lasting solution for your building.

Now, the math you’ve been waiting for:

Knowing the above variables, for a 10,000+ square foot commercial metal roof with aa 10-15 Year Material and Warranty System will average between $1.85 - $3.75 per sqft. So, total cost will be somewhere between $18,500 - $37,500.

Considering that a new, traditional foam or TPO membrane will cost $4.00 - $5.00 per sqft and new metal would cost $5.00 - $6.00 per sqft…a roof coating systems can provide a cost conscience alternative while also ensuring your roof itself is covered (by a good, renewable warranty) for its life.

Have additional questions? We’re here to help. Contact us at info@customcoatingsinc.com or visit our website to fill out a contact form. Have a flat roof and are wondering about the cost of coating it? Check out our connected article: “How Much Does it Cost to Coat a Flat Roof?”