What Types of Roofs Can You Install Spray Foam Roofing Over?

spray foam re-roof

Spray foam roofing can be applied over most any type of roofing deck, either new construction decks or existing membranes.  The following is a list of acceptable roof decks and substrates:

New Construction Decks

Existing Roof Membranes

  • Minimum 15/32″ 4-ply structural plywood
  • Galvanized corrugated metal decks
  • B decking
  • Standing seam metal decks
  • Lightweight concrete
  • Structural concrete
  • Built-up roofing gravel removed
  • Fiberglass mat cap sheet
  • Modified bitumen
  • Smooth built-up roofing
  • Fiberglass shingles
  • Concrete tile
  • EPDM
  • Single ply
  • PVC
  • TPO (with modifications)

Although spray foam has been around for almost 50 years, it is still considered non-traditional in the world of roofing materials. As a building owner, knowing that spray foam roofing may be installed without removing the whole roof might just make your day. No tear off means less expense, less down time and less waste in a landfill. Spray foam will reduce energy expenses and that should make the comptroller’s day as well.

As spray foam can be applied over any type of roofing deck or system, a few main considerations should be stressed:

The existing substrate needs to be fully-adhered to the insulation or deck, or else a cover board needs to be installed so the foam can be applied to a fully-adhered layer.

The existing roof and underlying insulation needs to be dry, which core samples and an infrared inspection will identify those areas.

The existing substrate (if not using a cover board) needs to be clean and dry. This is usually done with power washing. This is very important for the spray foam to adhere and cure how it was meant to.


Spray foam can be installed over a commercial metal roof. How the installation begins is to first clean the existing roof with a power washer to remove debris and dirt.

With most metal roofs having rust, a roofing contractor will use a rust inhibitor primer, which will stop the oxidation process in rusting metals which have been exposed to oxygen and water.

If this step is skipped, rust will continue to grow on your metal roof which will accelerate the rate of decline in your roof’s projected lifetime.

Once the primer is installed, foam can begin to be installed.

NOTE: with metal roofs having crimped panels, tiny holes can be created throughout the years with the roof expanding and contracting due to weather fluctuations. With spray foam being liquid applied that expands, the foam will fill these areas, which will stop water from entering your building.


Spray foam cannot be installed over an existing TPO roof unless there is a  cover board.

Since TPO is heat-welded at the seams, the roof is not completely adhered to the insulation below.

Spray foam can only be applied to a fully-adhered substrate, so the addition of a cover board over the TPO roof makes that true.

The first step is to identify any indications of saturation underneath the existing TPO roof. These are done by pulling core samples and by doing an infrared inspection.

Once those areas are removed and replaced with similar materials that the roof currently has, the cover board can be installed, and then the spray foam installation can begin.

NOTE: a great benefit of installing spray foam over TPO is that you won’t have to worry about seams in the future. Seams break apart over the years due to harsh weather and wind, and once they do, water has a clear path into your insulation. With spray foam being monolithic and one continuous layer, seams will be eliminated from your current TPO roof.


Yes, spray foam can be applied over an existing EPDM roof. However, EPDM roofs have three different types of attachments, which affect the spray foam installation.

Type 1 is a fully adhered EPDM roof. This means that the EPDM has been applied over the insulation with an adhesive. Since the roof is fully adhered, foam can be applied. A primer/cleaner may be used depending on the condition of the existing roof.

Type 2 is a mechanically-attached EPDM roof. Mechanically-attached means there are rows of plates and screws at the seams of the membrane which fasten the roof down. Since this type of EPDM roof is not fully adhered, cover board needs to be installed first, then the spray foam.

Type 3 is ballasted EPDM roof. Ballasted means that the EPDM is only fastened down at walls and curbs. Then a thick layer (minimum 10 lbs./sq. ft.) of rocks and stones are laid over top.

For a spray foam roof installation, the rocks need to be removed using an industrial vacuum system. Then a cover board needs to be installed over the EPDM. Then the foam installation can begin.

NOTE: As mentioned before, spray foam roofs are seamless. Besides where the rubber sheets are fastened together, another area that commonly lets water in is around penetrations. With an EPDM roof, the rubber needs to be custom cut to fit around the boot that’s installed. You can see there are many overlapping areas, which have gaps. These gaps are filled when installing foam, which fully encapsulates the entire area around a penetration.

Spray Polyurethane Foam

Yes, you can install spray foam over an existing spray foam roof. This is what’s called a recoat. A recoat is needed every 10-20 years depending on the amount of coating that was initially installed.

Over the years, the initial 20-30 mils of coating that protects the foam roof from degrading UV rays, is worn down naturally to around 7-10 mils of coating.

A spray foam roofing contractor will power wash the coating, washing away all the loose granules, and then re-install the coating back to the original 20-30 mils…with new granules being broadcasted into the 2nd layer of coating.

There are many issues with broadcasting granules into a single coat of coating over a spray foam roof.

NOTE: The recoat process is why the spray foam roofing system is renewable and can last indefinitely. Some roofs that West Roofing Systems installed in the 1980’s are currently on their 2nd and 3rd recoats.


A spray foam roof can be installed on a smooth or gravel-surfaced built-up roof since the roof is fully adhered to the underlying substrate.

For spray foam to be installed over a gravel built-up roof, a wet-vac process needs to remove the stones and gravel so there’s a clean surface left behind.

In both instances, the roof will need to be power washed clean before spray foam can be installed.

NOTE: if you have a gravel built-up roof and you have a roofing leak, it’s difficult to determine where on that roof the problem is.

Modified bitumen

A spray foam roof can be installed over an existing modified bitumen roof. Since “mod-bit” comes in a roll, whether they are torched or adhered down, it’s a fully-adhered system where a cover board isn’t needed.

If it’s a granulated mod-bit, those granules are fused into the top layer, which is still fully-adhered.

NOTE: since modified bitumen roofs come on a roll, they have the same issues with not fully encapsulating penetrations as single-ply and built-up roofs do. Having penetrations un-encapsulated can allow water to come in and HVAC energy to escape.