Quick answer: You can install a spray polyurethane foam roof. Spray foam has an R-value of 6.5 per inch of thickness. If all you have is a deck, then you can install almost 4 inches of foam (although we don’t recommend this much foam). If polyiso is available, a combination of polyiso board and spray foam can get you to an R-25. The warranty for a spray foam roof depends on the thickness of the protective coating that’s installed over the foam. To get a 20-year warranty, 30 mils of coating need to be installed.
So, you have a commercial building, and you need to get to an R-25. And you need to get a 20-year warranty.
You can get these figures with any roofing system available.
Because of the polyiso shortage, many contractors and building owners are looking for new ways to get these numbers.
In this article, we’ll answer some of the questions you might have, such as:
- What is a spray polyurethane foam roofing system?
- What are the ballpark costs of spray foam?
- How does a spray foam roof get to an R-25?
- How does a spray foam roof get a 20-year warranty?
- How durable is a spray foam roof?
And so you’re aware, we only write articles based on true events and experiences. Every piece of content written at West Roofing Systems is produced in-house. Every article is reviewed and edited by a roofer/salesman with 30+ years of experience in the field.
West Roofing Systems has been spraying foam and coating systems since 1979.
What is a spray polyurethane foam roofing system?
There are four parts to a spray polyurethane foam roofing system:
Spray foam would be fluid-applied over your existing roof. Since spray foam will degrade within 72 hours from UV rays, the foam is protected with an elastomeric coating, such as silicone.
The silicone is installed in two separate coats.
To increase impact resistance, aesthetics, and to highlight walkways (if needed), ceramic granules are embedded into the topcoat of coating.
NOTE: The installation is one part, the other part is preparing your existing roof for installation. Proper preparation involves careful analysis of your existing roof, including seam adhesion strength and how much of the insulation is wet or saturated.
What are the ballpark costs of spray foam?
The ballpark cost of a spray foam roof is $4 – $7 per square foot. There are many variables in pricing, such as:
How much of the existing roof will need to be removed and replaced before installation?
Core samples and infrared inspections can show that wet insulation is present. These areas need removed and replaced with a similar material before any roofing system is installed.
How much spray foam will be installed?
Sometimes certain R-value targets need to be hit. This can include as much as 3-4 inches of foam. Others don’t have R-value requirements. In this case, 1-2 inches of spray foam would be installed.
How long of a warranty are you seeking?
A 20-year warranty needs more coating installed than a 10-year warranty.
Where is the location of your building?
- How far away are you from the contractor?
- Are you in L.A. or N.Y. where prices are generally higher?
- Is the building 1-story or 20-stories in the air? Additional safety measures may be needed on a taller building.
- Is the roof in a downtown or very busy area? If so, this can increase the difficulty of the project setup and increase the risk of overspray.
How many square feet is your roof?
A 1,000 sq. ft. roof will cost more per sq. ft. than a 100,000 sq. ft. roof based on economies of scale.
There are fixed costs that go into any roofing project such as mobilization and safety setup that occur on any size roof. A larger roof can have higher production rates, lowering the cost per sq. ft.
How does a spray foam roof get to an R-25?
There are a few ways a spray foam roof can get to an R-25.
The first way is to only use spray foam. Spray polyurethane foam has an R-value of 6.5 per inch of thickness.
25/6.5 = 3.85
If you install roughly 3.85 inches of spray foam on a roof, you will have an R-25.
NOTE: With the current shortage of polyiso board, this is a good alternative. The usual max thickness is around 3 inches of foam. Only under rare occurrences do we go more than 3 inches thick with foam. In some cases, the roof looks undesirable with close to 4 inches of foam.
A second (and more common) way is to install spray foam over an existing roof that already has an R-value.
Perhaps the existing roof has a deck, two inches of tapered polyiso board, and a single-ply membrane on top.
This roof probably has an R-value of 11. The R-value will need to increase by 14 to get to an R-25.
14/6.5 = 2.15
If you install roughly 2.15 inches of spray foam over the existing roof, you’ll be at an R-25.
NOTE: A coverboard (or polyiso board) may need to be installed to provide a fully-adhered membrane for spray foam to adhere to.
How does a spray foam roof get a 20-year warranty?
The warranty length on a spray foam roof is in correlation with the amount of coating that’s installed over it.
- For a 10-year warranty, 20 mils of coating will be installed.
- For a 15-year warranty, 25 mils of coating will be installed.
- For a 20-year warranty, 30 mils of coating will be installed.
It’s important to note that a “mil” is one-thousandth of an inch.
A spray foam contractor or the manufacturer of the coating will use certain tools that will measure this level of thickness.
If it’s light, more coating needs to be installed.
Manufacturers know that if 30 mils of coating are installed, at an absolute minimum, it will last 20 years.
NOTE: West Roofing Systems has been in the spray foam and coating industry for 40+ years. In those years, we’ve never seen coating not last the desired warranty duration. The only times it doesn’t last is if it’s installed wrong, too light, or there’s no routine maintenance on the roof.
How durable is a spray foam roof?
A spray foam roof has a compression strength of 50-60 pounds per square inch (PSI).
Spray foam roofs can be walked on. If there’s a large amount of foot traffic, a double broadcast of granules can be embedded into the topcoat to produce walkways.
Spray foam roofs can be damaged with hail (just like any other roofing system). Hail damage will not cause a leak due to spray foam’s closed-cell properties.
A spray foam roof does have issues with sharp objects. Dropped tools and screws can puncture a spray foam roof.
However, punctures are easily repaired. The area is cut out, dried, coating or sealant fills the hole, and the area is smoothed out.
This is why is important to have routine maintenance. Routine maintenance will ensure that small repairs don’t turn into large repairs.
NOTE: Think about routine maintenance like your car. If you don’t change the oil, tires, or brakes, how long will your car last versus doing simple repairs?
What should you do now?
If you need a commercial roof with an R-25 and a 20-year warranty, I’d reach out to multiple contractors.
Because they each can have a different solution to get you that R-value and desired warranty.
Then weigh your options and choose the best solution.
I wanted to point out that West Roofing Systems has been developing the most cost-effective solutions for commercial roofing problems since 1979.
That could be spray foam, coatings only, wait a few years because the roof has multiple years left, only foam a few sections to stay within budget, etc.
And if you’re new to spray polyurethane foam roofing, please check out our cheat sheet that will answer most of the common questions people have about foam.