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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 flat roof?

Roof Coating

It’s the question we get most often about single-ply membrane, EPDM, TPO, PVE and asphalt 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, it’s 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 asphalt 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?

The process of installing a roof coating system will generally go like this:

  • Inspect existing roof, perform necessary repairs
  • Clean the existing roof of all foreign matter that could affect adhesion
  • Depending on the type of system being installed, seams will be reinforced or a fully fabric reinforced membrane will be built
  • Final topcoat applications
  • Inspections for warranty process

If your commercial flat 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 roof? If your existing roof is in decent condition, depending on the system, warranty length, etc., the average 10,000+ square foot roof will fall in the $2.80 - $4.00 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.

 

Flat Roof Coating in Four Steps

 

Step 1: Inspection & (Potentially) Insulation Repair

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 large sections of ponding water or soft spots, they will likely perform core sample testing to determine if the insulation under your current membrane is saturated. At times an Infrared survey will be suggested to determine how much of the roof insulation is wet. Here’s how that works (it’s kind of fascinating):

When the sun goes down, a contractor will use an infrared camera to view temperature changes in your roof. During the day, any wet insulation will attract heat and hold it after sunset while the rest of the roof will cool much faster. These temperature-based pictures will offer a visual map of where and how much of your insulation is saturated and will need replacing before moving forward with your new fluid applied membrane.

Note: If your roof needs insulation replacement prior to roof coating, repair costs will be in addition to the new system cost. A responsible contractor will help educate you on how much of the roof should be repaired before a coating system is no longer a viable option. For example, if more than 25% of your roof’s insulation is needing replacement, we recommend that you should start thinking about a traditional roof install with a full tear off. If less than 25% of your insulation is wet, then typical repair costs can range from $.50 - $2.00 per square foot for labor and materials.

Typical insulation repair consists of:

  • Making a cut on three sides of the area to be replaced and folding back the current membrane on the uncut side.
  • Removing the damaged saturated insulation.
  • Cleaning the decking beneath and possibly applying rust primer if the metal deck is starting to rust, or installing new metal decking if structural integrity has been compromised.
  • Installing new, like-kind insulation
  • Folding the existing membrane back over the repair, mechanically fastening this repair and seaming it all up together

 

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.

Your contractor should use cleaning agents along with a minimum of 3000PSI (pounds per square inch) pressure washing to clean things up. 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 roofs, 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 4: Initial Waterproofing & Second Inspection

Initial waterproofing will be the next step in your fluid applied membrane or roof coating system install. Depending on the materials being installed and the manufacturer’s guidelines, your contractor may use one of two different approaches:

  • Approach one is to install a base coat of material to the roof at a specific mil thickness, then install a polyester mesh fabric in the wet coating, and finally another coat of material over the fabric, sandwiching the fabric between two layers of coating. This is call a “wet-on-wet” application. Here, each row of fabric overlaps by 4”-6” in a process that builds a fiber-reinforced monolithic membrane across the entire roof substrate. This type of full-coverage reinforcement on a 10,000+ sqft roof will range in cost from $1.00 - $2.00 per square foot.
  • Approach two involves only reinforcing the seams of the existing membrane. This can be achieved via the process in approach one, or by installing fabric-backed butyl seam tape and coating the tape. This type of seam-only reinforcement on a 10,000+ sqft roof will range in cost from $2.25 - $4.45 per linear foot of seams.

After one of the above applications is complete, a knowledgeable and responsible contractor will do an inspection of the roof. During this inspection they will look for “fish mouths” (spots where the fabric or tape opened slightly which may allow for water to penetrate), trouble spots around drains and any penetrations, then use additional flashing materials from the manufacturer to reinforce these common problem areas. Generally, flat roofs do not leak in the open “field” of the roof; they leak at seams, penetrations, drains, 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 4: 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 manufacturer’s 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 applications on your 10,000+ sqft commercial building will range from $1.40 - $2.50 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, let’s 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 flat 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 roof with a 10-15 Year material and warranty system will average between $2.80 - $4.00 per sqft. So, total cost will be somewhere between $28,000 - $40,000.

Considering that a new, traditional membrane will cost $5.00 per sqft up to $11.00 per sqft if a full tear-off is required…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 metal roof and are wondering about the cost of coating it? Check out our connected article: “How Much Does it Cost to Coat a Metal Roof?”