How Much Does It Cost to Renew a Flat Roof?

Greg PalyaSilicone Roof Coatings, Spray Polyurethane Foam Roofing

The average cost to renew a flat roof is $5 – $10 per square foot. The cost varies on many factors, such as:

  • The size of the roof
  • Desired R-value and warranty length
  • The amount of tear-off
  • What roofing system is installed
  • The number of penetrations
  • The distance away from the roofer

And many more factors, which we’ll get into.

And just so you’re aware, West Roofing Systems has been in commercial roofing since 1979. We install spray foam roofs and roof coating systems, which are used 99.99% of the time for roof renewals.

This article has been reviewed, edited, and approved for publishing by one of our salespeople with over 30 years of roofing experience.

Let’s get started!

What factors affect the cost of renewing a flat roof?

Roof Size

The smaller the roof, the more it’ll cost per square foot. It’s because of indirect costs, such as admin salary, rent, and equipment costs, that are the same for every job.

Think of it like buying a 24-pack of Pepsi versus one can.

A can is probably sold for $1. A 24-pack will likely be around $12, or 50 cents per can.

Silicone roof coating system installed over a school

More R-value and extended warranties

Both have to do with the amount of product used on the job.

More product = higher costs.

For example, a spray foam roof has an R-value of 6.5 per inch of thickness.

An R-10 requires spray foam to be installed at an average of 1.5 inches of thickness.

An R-13 requires spray foam to be installed at an average of 2 inches of thickness.

More R-value = more spray foam that’s installed = higher costs.

The same goes for longer warranties.

On spray foam roofs, the warranty is determined by the thickness of the coating used to protect them.

The warranty for roof coating systems on their own is determined by coating thickness as well.

For example:

  • 20 mils of coating grant a 10-year warranty
  • 25 mils of coating grant a 15-year warranty
  • 30 mils of coating grant a 20-year warranty

More coating = longer warranty = higher costs.

The amount of tear-off

No roofing system should be installed over damaged membrane or wet insulation when re-roofing. Therefore, these areas need to be removed and replaced.

There’s a cost difference between a roof with 2% wet insulation versus the same roof with 20% wet insulation.

You have to consider:

  • the labor hours to tear-off
  • the cost of transporting those materials to a landfill
  • landfill costs
  • purchasing new materials for replacement
  • and the labor hours to install

Quick Tip: Never install a roof over wet insulation. Some contractors will cut corners on this to reduce costs. Don’t fall for it! The trapped water will move up, down, or stay the same. If it moves up through evaporation, it could cause blisters in the new membrane. If it moves down, it could damage your deck and come into your building. And if it stays where it’s at, it could produce mold.

Choice of Roofing System

The roofing system you choose to re-roof your flat roof with will cost differently. Here are the ballpark costs for the most popular systems:

Quick Tip: Get a quote for each roofing system. Some roofing systems might not require a complete tear-off. Avoiding the complete tear-off is the #1 way to reduce the cost of a roof renewal.

The number of penetrations

Penetrations are anything that comes through the roof. The most common are skylights, drains, and HVAC units.

Penetrations are brutal to roof around if the roofing system’s installation method is interfered with.

For example, single-ply roofs are rolled-out sheets. Any penetration stops the installation. The membrane needs to be cut, adhesives and termination metal are used, and then the installation can continue.

These interruptions add labor hours to a project.

NOTE: It may take 30 minutes for a single-ply roof to be installed around an HVAC unit, while it would take 2 minutes for any fluid-applied roofing system.

Some roofs have hundreds of penetrations:

spray foam roof at Maryland Court - Michigan - 2022


Spray foam roof at Mercer County Career Center in Mercer, PA

Roofing systems such as spray foam and coating systems are fluid-applied, which are very easy to install around penetrations.

Distance from the roofing contractor

Labor hours for travel, gas, wear and tear on company vehicles, and possible hotel stays play a role in the total cost.

The further away you are from the roofing contractor, the more expensive your project’s cost will be.

This doesn’t mean always choosing the contractor closest to you. That’s a terrible move!

The reason?

The quality of the installation is most important. A roof that lasts 20+ years with only routine maintenance will be more cost-effective versus one that was $1000 cheaper today, yet leaks in 3 years and needs repaired repeatedly.


The main points to take away from this article are:

  • The average cost of a roof renewal for a flat roof will likely be $5 – $10
  • Get a quote for different roofing systems
  • Never roof over wet insulation
  • Never choose a roofer only because they are closer than someone else.

Need more insights into the pros and cons of commercial roofing systems? Please download our free guide below.

New call-to-action

About the Author

Greg Palya

Greg Palya is the Digital Content Manager of West Roofing Systems, Inc. He has a B.S. in Marketing from the University of Akron and an MBA in Marketing from Walsh University. When he's not trying to teach others about spray foam roofing and silicone roof coatings, you can find him on the basketball court or golf course.