spray foam installed on a roof instead of polyiso board

What is a Good Alternative to Polyiso Board Insulation?

Greg PalyaSpray Polyurethane Foam Roofing

With recent shortages of materials in every industry, companies are looking for alternatives to keep business going.

In commercial roofing, polyiso board is a common type of insulation that many companies use.

A great alternative to polyiso board insulation is spray polyurethane foam.


  • It can be used on mostly any roofing substrate or deck
  • The slope can be easily customized
  • It has closed-cell properties
  • It has a better R-value than polyiso
  • It’s available

If you have any questions about spray polyurethane foam, please contact us and we’ll respond ASAP.

West Roofing Systems has been applying spray foam on commercial buildings since 1979.

This post has been reviewed by an SPFA-certified, spray foam roofing specialist with more than 30 years in the industry.

Let’s go into each of the bullet points above in more detail.

Bonus: At the end of the article are typical questions companies ask us when they first hear about spray foam. You know…the skeptical ones ?

Spray foam can be used on mostly any roofing substrate or deck

If your roof deck is concrete, wood, metal, spray foam can be applied. Spray foam will fully adhere to the deck and since it expands, will fill in any tiny crevices.

If you didn’t know, spray polyurethane foam is fluid-applied.

If you’ve never seen spray foam applied before, watch this video:

As far as spray foam being applied to existing roofing substrates, spray foam can go over:

  • EPDM
  • TPO
  • Metal
  • Smooth or Granulated Modified Bitumen
  • Gravel Built-up

In existing roofs where the substrate isn’t fully adhered, a cover board will need to be installed.


Spray foam’s adhesion to the roof is only as good as what it’s attached to.

An example would be an EPDM roof that is mechanically attached at the seams. In this case, a cover board will be fully adhered to the EPDM roof, then foam can be installed.

NOTE: Cover boards are inexpensive (30-40 cents per sq. ft.) and they provide a little insulation boost with an R-2.

Slope can be easily customized with spray polyurethane foam

Lots of roofs utilize polyiso board because it can be tapered. This means that the slope of the roof is created through the insulation (the polyiso board).

If polyiso isn’t available, what other options do you have?

Since spray foam is fluid-applied, the slope is easily created by the thickness of the application.

An easy example would be 2-3 passes of foam at the perimeter and 1 pass near a drain. Within seconds, spray foam can create a customized slope.

NOTE: A customized slope using polyiso board can be expensive. Utilizing spray foam’s ease and speed of application will get the job done more cost-effectively.

Spray foam has closed-cell properties

Spray foam is not only a great alternative to polyiso board, but in most cases, it’s an upgrade. We’ve covered slope, but what about if something penetrates it?

Let’s say a hailstorm comes through and damages the roof.

If the hail penetrated the membrane and exposed the polyiso board, any future precipitation will saturate it.

Say a month goes by and it rains five times. That’s five rainstorms worth of precipitation that will expand vertically and horizontally in your roofing system.

The issue with polyiso board is that it’s open-cell. This means it’s not waterproof. It will absorb water and allow the water to travel through it.

This is very similar to how water travels along a paper towel. While water may only enter a paper towel at the corner, eventually the entire paper towel is soaked.

Spray foam is closed cell.

This means the complete opposite of what was explained before.

If hail damages a spray foam roof and leaves the foam exposed, water will sit in that hole and not move.

A contractor can simply cut around the hole, dry the area, and fill the exposure with caulk or sealant. No other damage is done to the roofing system. No water has traveled and affected other areas.

Spray foam has a better R-value than polyiso board

Polyiso board has an R-value of 5.5 per inch of thickness.

Spray foam has an R-value of 6.5 per inch of thickness.

Sometimes spray foam contractors use polyiso board for repairs or to build a very high R-value before the foam is installed.

Spray foam is available

At West Roofing Systems, we are installing spray foam daily (weather pending). A company reached out to us and stated that polyiso board is not available and we’re looking for an alternative.

As of now (August 2021) spray foam is available and polyiso (according to another company) is not.

Other questions about spray foam and polyiso board

Like most, this might be the first time you’re considering using spray foam as an alternative to polyiso board.

Here are some other questions (and answers) you might have:

How durable is spray foam?

Spray foam has a compression strength of 50-60 PSI. You can absolutely walk on it. If you need to frequently service rooftop machinery, walkways can be installed by adding a double broadcast of granules into the topcoat of coating.

Can we see a sample of the spray foam roofing system (spray foam, basecoat, topcoat, and granules)?

Yes. West Roofing Systems has samples of the spray foam roofing system that we can send you.

What is the longevity of spray foam roofing?

A spray foam roof can be the last roof you ever install on your building. That’s because the coating that protects the foam can be renewed over and over again.

Say you get a foam roof that comes with a 10-year warranty. On a 10-year warranty, 20 mils of coating will be installed over the foam.

After 10 years, the coating will naturally wear away to 7-8 mils. The roof is cleaned, more coating is applied, and a new warranty is granted.

The foam never gets touched and doesn’t lose any performance over time.

What is the operation on how spray foam is installed?

Most spray foam contractors use a 24-foot box truck that has 55-gallon containers inside. There are two of them, the A-side and the B-side. The material is heated and pumped from the box truck that will sit near the building through a hose. A hose runs up to the roof where the applicator sprays the material. The only thing on the roof is the roofers, the hose and spray gun, and possible windscreens if it gets too windy.

A coating rig is parked near the building as well. In the same manner as the box truck, they will be pumping coating through a hose to an installer on the roof. They will be coating over what the spray foam installer has laid down only minutes ago.

How fast can spray foam be applied – start to finish?

It depends on the details of the job, but if a roof is prepared and it’s a good weather day (over 50 degrees F, no rain, not windy), about 8,000 – 10,000 sq. ft. can be foamed and coated per day.

What are the installation requirements to apply good foam?

To apply good foam, it needs to be 50 degrees F and rising, dry, and not much wind. Although windscreens and spray foam booths can be used to combat windy conditions.

How long is the hose that goes from the box truck to the applicator?

400-600 feet.

What is the cost per square foot?

Ballpark cost is $4 – $7 per square foot. This depends on many variables, such as:

  • Where is the roof located? There are transportation costs for labor and materials
  • How much foam is needed? 1.5” to 3” can make a big difference in cost
  • How long is the warranty going to be? Longer warranty = more coating = more cost
  • How difficult is the project? Is it 1 story high, 20 stories high? Is a lift needed?

For a project with tight deadlines, is located far from our locations, requires a large amount of foam and coating, and is overall a very difficult project, this could cost as much as $15 per sq. ft.

Have any other questions? If so, contact us today!

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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.