Roof Coating Comparison of Foam Vs. Silicone

What is the best type of roof coating?

A roof coating is a great alternative to re-roofing. If your roof is still in sound structural condition but requires protection against time and the elements, then it is a great candidate for roof coating. Read our pages about spray polyurethane foam and silicone roof coating to get an overview of each material. This post will address common differences and similarities between the best roof coating types. A look at the roof coating pros and cons between foam and silicone coating materials to help you make a decision on what type of roof coating is best for your unique needs.


Requirements for Foam and Silicone


Commercial roofing substrate analysis. Testing existing roof conditions before roof coating application.

Checking the existing roof substrate for materials used and existing water damage.


SPF – Foam is typically used in commercial buildings with flat or low-slope roofs although there exists a small percentage of residential projects requesting foam coatings. The existing substrate can be tar and gravel, asphalt, concrete, fiberglass, glass, metal, wood, or even a home’s shingles. No primer system is required unless rust is present, but a primer is recommended over any metal substrate. Application temperature minimum 50°F, maximum 160°F with 80% or less humidity, and less than 15mph wind velocity.

Silicone – Like foam, silicone is commonly applied over flat or low-slope roofs of commercial buildings. Compatible substrates are asphalt, concrete, fiberglass, glass, metal, wood, SPF and other previously coated substrates. Silicone requires a primer application over most substrates. Application temperature minimum is 33°F, maximum 85°F and should not be used when the air temperature is within 5°F of the dew point.


Roof Coating Pros and Cons: Spray Foam Polyurethane and Silicone


SPF Pros

  • No CFCs, HCFCs or other gasses harmful to the ozone layer.
  • SPF is an added insulation layer. R-6.5 at 1” thick, R-25 at 3.5” thick.
  • A reflective, “cool roof” coating.
  • GacoRoofFoam 2733 meets ASTM E108 Class A rating for external fire exposure.

SPF Cons

  • “Do it yourself” applications can leave shallow paths that hold ponding water.
  • Cannot hold ponding water without proper sealant layer.

Silicone Pros

  • Will not decay, chalk, or crack under intense UV rays.
  • Can be used to repair leaks.
  • A highly reflective, “cool roof” coating.
  • Waterproof, even with ponding water.

Silicone Cons

  • Cannot be used on tar and gravel.
  • Does not provide any added R-value.

When used together, these two coating options cancel out each other’s R-value and ponding water cons.


Roof coating comparison. Commercial roofing project progress with a layer of spray polyurethane foam sealed with silicone roof coating in Stuart, Florida, by Alliance Group Roofing and General Contractors.

SPF sealed with silicone for a commercial roof project in Stuart, Florida.


Cost Comparison


Silicone roof coating product applied on Port St Lucie commercial flat roof for weatherproofing.

Limited roof access, existing damage, and the amount of object we need to seal around can affect the cost of sealing a roof.


A spray polyurethane foam application must be sealed. The types of sealers available vary and will affect the cost. Below is a generalized per square foot price of the typical cost of these roof coatings in the South Florida area. This rough estimate does not take into account unique factors such as the amount of necessary prep work and repair, the amount of ducts and other penetrations, roof access issues, or other unique circumstances that would make the coating installation more challenging.

SPF + Silicone = $5.50 / Sq. Ft.

Silicone = $3.00 / Sq. Ft.


How Long Does a Roof Coating Last

SPF – Foam will need maintenance just about every year to remove excess debris and generally check for any damage. At this time, the roof should be cleaned. Because foam can be damaged from frequent contact or physical abuse, a walk pad installation is highly recommended for maintenance workers needing access to roof components. You can expect an SPF roof to last 20+ years.


Silicone roof coating on a South Florida commercial building 1 year after roof coating application.

This photo shows 1 year of accumulated dirt and grime after the silicone application. Alliance Group returned to the Delray Oaks condo complex job site in South Florida for maintenance and clean-up work.


Silicone – Silicone requires very little maintenance, but this does not mean it is completely maintenance free. As with any roof, regular yearly inspections should be made to detect debris and damage. The roof should be cleaned of accumulated debris and mildew in order to maximize its reflective property. If damage has occurred to the silicone layer from people, animals, windblown debris, or abnormal use, the area can be spot treated with additional silicone or recovered entirely. A walk pad is recommended to protect the roof coating from foot traffic. The estimated material life is 50+ years. See this post for information about Gaco Western’s silicone roof coating warranty.


Factors That Decrease Foam and Silicone Effectiveness

Foam and silicone roof coating problems are limited but do occur. Adhesion and product life can be greatly affected by the roofer applying the product. This can be caused by failing to clean the roof thoroughly before applying any coating product. Discrepancies in how either SPF or silicone coatings are mixed are a big factor in how well they will perform throughout their working life. An inadequate application technique can cause problems such as improper drainage and weak insulating values. Roof coatings are best done by an experienced professional. Alliance Group is a certified Gaco installer. Our crew is experienced with roof coating applications and we continue to execute these jobs on a regular basis, so you can trust us with your project.

Give us a call and we’ll give you a quote for your commercial building. (800) 822-7663