Gutters, Scuppers and Drains

  1. Check all gutters, scuppers, and drains for leaves, dirt, etc., that can restrict drainage.
  2. Check for cracks in the coating and SPF at these areas.
  3. Verify that screens and strainers are in place and properly secured.  

Rooftop HVAC Units and Penetrations

  1. Flashings at roof penetrations, such as vents, hatches, stacks, skylights, and HVAC equipment, should be sealed against the weather.
  2. Condensation from HVAC units should be piped to drains. Ensure that heater stacks have rain caps, seams in units are sealed with caulk, skylights are properly sealed, and there has been no damage to the surrounding roof system.  

Flashings, Roof Edges, Expansion  and Control Joints, and other Terminations:

  1. Look for cracks or splits in the system at roof terminations, such as edge flashings and expansion joints. 
  2. Ensure that coping joints and metal counter flashings are sealed. 
  3. Check masonry walls for moisture penetration and/or deterioration. 

Checking the Field

  1. Check for mechanical or physical damage caused by tools or heavy objects, hail, vandalism, excessive foot traffic, etc. 
  2. Inspect for blisters or areas of inner layer separation in the roof system.

Defects in the Roof Surface

  1. Check for blisters, pinholes, erosion of the coatings or polyurethane foam, cracks, and moisture penetration into the polyurethane foam insulation. A small “slit” sample may be taken to determine if there is any moisture present. A nondestructive moisture detection device may also be used. 
    Long cracks or splits in the SPF roof system may be due to structural movement below the SPF. These should be investigated by a qualified contractor or structural engineer.  


Sprayed polyurethane foam (SPF) is applied to a substrate as a liquid that turns to closed-cell foam, expanding almost immediately to 20 to 30 times its original volume. It's ultra-lightweight, with less than 5% of the density of water. Properly applied at 2.8 pcf, it develops a compressive strength of 40-50 psi.

SPF is spray-applied as a two-part mixture that's mixed at the hose nozzle as spraying takes place. In addition to the two basic ingredients, the field mixture also contains:

  • A blowing agent that helps expand the foam;
  • A surfactant (cell stabilizer) that controls cell size and cell wall rigidity;
  • A catalyst that controls the reaction rate between the two main ingredients; and
  • Fire retardants, that increase safety and help meet building code requirements.

It's resistant to the passage of moisture in liquid or gas form, but highly vulnerable to degradation from UV-caused oxidation and damage from abrasion or impact. For this reason, it's protected by installation of a liquid-applied elastomeric coating and/or aggregate.

Application: Installed in Multiple Lifts

To build thickness for insulation purposes, foam is typically applied in layers called "lifts". Although it varies with manufacturer's recommendations, lifts are typically limited to a maximum thickness of around 2". Blowholes, voids, fissures, or gaps may develop if foam is applied too thick.

Coating Requirements

Membrane coatings require the following properties:

  • Good adhesion to the foam;
  • Impact and abrasion resistance;
  • Thermal stability (flexible at low temps. and stable at high temps.);
  • Resistance to degradation from moisture and chemicals;
  • Weather durability;
  • Easily maintained;
  • Tensile strength and elasticity (to accommodate substrate movement); and
  • Fire resistance.

Coating Types

Although identification of a specific coating will typically require current documentation, the best coatings are:

  • Polyurethane elastomers;
  • Acrylics (poor choice where ponding or freezing temperatures are possible); and
  • Silicones (same as acrylics, but resistance to bird pecking and dirt retention mean they should be granule-coated).
  • Butyl is good when humid environments promote moisture migration toward the building interior

Surfacing Aggregate

Aggregate should be minimum 1/2" diameter with flat preferred over round. It may or may not be applied over a coating (may be applied directly over the foam) and may or may not be embedded in a coating.

Mineral granules like those used with asphalt shingles can be cast into a topcoat of  liquid-applied elastomeric coating as an alternative to gravel aggregate.


Asphalt plank or rubber walkpads embedded in the topcoat can cause problems related to water entrapment, heat retention, and differential expansion and contraction rates. Water entrapment can cause blisters and foam damage to develop beneath these walkways. Open pads embedded in a compatible caulk allow water and vapor to evaporate.

Roof to Wall Joints

  • Cant strip should be installed
  • Elastomeric coating should extend 2" minimum up the wall above the foam termination.
  • Where the roof deck is supported by the wall, the roof system can terminate against the wall.
  • Where the roof deck is supported by structural framing that can move independently of the wall, the roof system must be isolated from the wall by an expansion joint.

Blister Types

Interlaminar: Top Lift: These fragile blisters develop between the upper lifts or between the surface coating and the SPF, typically 2" to 12 (50 mm-300 mm)".

Interlaminar: Intermediate lift: These blisters are less fragile and develop between the lifts lower in the body of the foam. Typically 6" to several feet (150 mm - 1,000 mm) in diameter, they may grow as large as an entire roofing square (10'x10') (9 square meters). These blisters may vary in thickness from 1" to 3" (25 mm to 75 mm).

Substrate Bond Line: These blisters are the result of a loss of bond between the foam and the substrate and are readily visible. They're typically several feet in diameter or larger, fairly rigid and detectable while walking across the roof.

Intra-substrate: These blisters are located between felts or between components of a recovered roof. They may be large and difficult to detect.