Research and field observations have shown that spray polyurethane foam roofing systems have exceptional characteristics. SPF offers great insulation, is resistant to high winds, protects the substrate against damage from hail and wind-driven debris, and can be recoated to extend its life. In more recent years, in the roofing industry, there are poor perceptions of how SPF roofing systems perform in hail events. For many years, the conventional roofing market perceived SPF roofing as soft and easily damaged.
A typical hail damage repair procedure for conventional roofing systems is tear-off and replacement. According to renowned roof expert Richard Fricklas, former director of the Roofing Industry’s Educational Institute (RIEI), “There seems to be a mindset among some roofing contractors as well as building owners and designers that foam roofs are not suitable for hail regions at all.” However, the National Roofing Foundation (NRF) report on SPF roofing systems confirmed where SPF roofs had experienced hail damage, the damage was localized to the upper surface of the foam and most roofs were repaired, rather than replaced. With continued trends towards “sustainable construction,” it is within the best interests of the roofing industry to repair rather than replace whenever possible and practical.
Research has indicated that damage caused by wind-driven debris typically does not cause a roof to leak. A unique aspect of SPF roofing systems is that with respect to mechanical damage, they are not in imminent danger of leaking, provided the penetration does not extend all the way through the foam.
Wind damage may be isolated to small areas of the roof or cover large areas. Substrate damage and structural damage may or may not occur. Research done by Thomas Smith, however, notes that a thickness of 2 inches (of foam) is sufficient to prevent penetration of most missiles. How many and type of repairs required will depend on the size and severity of the damage.
So, all of this begs the question, how does SPF minimize damage from hail and how can you design a SPF roofing system to specifically resist the damage?
First, you must consider the physical characteristics of the SPF roofing system. The most common system begins with a layer of at least 1 inch and more often 2-3 inches of a high-density spray polyurethane foam covered with a minimum of 25-30 mils of a protective coating, either acrylic, silicone, or polyurethane.
SPF used in roofing ranges in density from 2.5 to 3.2 pounds per cubic foot with compressive strength from 40 psi to over 60 psi. The compressive strength of the foam combined with the thousands of tiny cells tends to act as shock absorbers against impact. The top of the foam can get crushed, however, the foam below will remain intact. Any coating used over the foam adds additional strength to the system depending on their tensile strength, flexibility, and thickness. This basic system can usually withstand hail impact of a ½” to 1” size hail stone, leaving a small depression of up to ¼” deep in the foam and no cracks in the coating.
As hailstones increase in size, the depressions in the foam also get larger and cracks become more frequent. However, even in the event of more severe hail, damage can frequently be repaired. SPF roofing systems are typically repaired rather than removed and replaced, so long as repairs are performed in a reasonable time frame. This is an important factor since most other roofing systems require a tear off and replacement.
So why is it that we can repair and not replace SPF roof systems?
In most other roofing systems, the exterior membrane is the waterproofing or water shedding medium. When hail or other debris impacts, it cracks or bruises a roof system such as single ply, shingles, BUR, etc., and leaks will often follow. When it’s a SPF roof system we typically see a cracked coating and an indentation to the foam itself. Damage typically occurs in the top ⅛ inch to ¾ inches of the foam depending on the size of the hail and the physical properties of the SPF and coating. Since the foam below the dent is closed-cell, it continues to provide water resistance so that leaks do not occur. This allows a SPF roof to be repaired in the damaged areas rather than having to remove and replace the entire system.
Other Roofing Systems Hail Resistance:
How do other roof systems perform in hailstorms? Evaluating the results of the RICOWI’s (Roofing Industry Committee on Weather Issues) 2004 Oklahoma investigation and the subsequent investigation of the 2011 Dallas/Fort Worth, Texas hailstorm, it is apparent that some roofing systems perform better than others.
Asphalt Shingles: In the Dallas/Fort Worth storm, a total of 68 asphalt and modified bitumen shingle roofs were inspected. Forty roofs showed some form of damage (categories 2 or higher) and 28 having moderate (category 3 or higher) or greater damage reported. Maximum hail sizes on the asphalt shingle roofs inspected ranged from 0.25 inch to 3.25 inches in diameter…roofs with category 2 or higher damage had been struck with hailstones 1 inch or larger. Of the asphalt shingle roofs rated with category 3 or higher damage, 92% had been struck with hailstones 1.25 inch diameter or larger. Shingles that were 9 years old or newer had an average rating of 2.1 while shingles deemed older than 9 years had an average damage rating of 4.2.
Built-Up Roofing (BUR): Aggregate covered BUR roofing systems appeared to perform well in the Dallas/Fort Worth storm. Six roofs were inspected, to which 5 of the roofs were impacted by hail of 2.25 inches or larger in diameter while the last was impacted with 1.75 inch hail. All were rated with damage levels 1 or 2, which indicates little observable damage and general good performance. During the Oklahoma investigation, 13 BUR roofs were studied. Some of the aggregate covered BUR performed well endring hail impacts of 1.5 to 2.0 inches without apparent damage in the field of the roof. However, damage was found in the field (and flashings) of five roofs with hail size ranging from 1.0 to 2.5 inches in diameter.
Single Ply Membrane: Six single ply roofs were inspected in the Oklahoma study, three EPDM, two PCV, and one TPO. Both ballasted and fully adhered EPDM roofs sustained 2.0 inch hail impacts without apparent damage. However, insulation under the fully adhered membrane was dented. The PCV and TPO membranes showed hail impact marks but no visible fractures. In the Dallas/Fort Worth study, three low slope single ply membranes were inspected. One roof was rated to have damage level 5 that was impacted by 1.75 inch hail. Another roof was rated level 3 when exposed to 2.5 inch hail. One single ply roof did not have any visible damage when exposed to 2 inch hail. The Oklahoma study noted that “While performance was generally good on examined roofs with single ply sheet membranes, there were not sufficient sample sizes to identify conclusions regarding hail impact resistance.”
Metal Roof Systems: The Oklahoma investigation reported that “Hail effects on metal roof systems were seen largely as cosmetic, rather than functional…with the extremely large hail there were instances of distorted seams or spalled granule surface, but even this was rare.”
At the conclusion of the Dallas/Fort Worth, Texas investigation, almost no damage was found in areas where the maximum hailstone size was less than 1 inch in diameter with the exception of badly deteriorated and unsupported material. When maximum hailstone size was between 1 and 2 inches in diameter, the level of damage ranged from none to considerable depending on the material, age/condition, roof slope, and support conditions. When maximum hailstone size was greater than 2 inches in diameter, most roofing material sustained damage or denting of metal.
Regardless of the conclusions from the RICOWI’s hail investigations, with the exception of metal roofing, even light to moderate hail damage to roofing systems other than SPF, can lead to roof leaks. Consequently, removal and replacement is the most common recommendation by roof consultants for hail damaged roofs in category 2 and above.
Increasing the Hail Impact Resistance of the Typical SPF Roof
While the basic SPF roof system described above has good hail impact resistance, additional design elements can be used to significantly increase its hail resistance. The following design elements can be used to significantly increase its hail resistance. The following design elements can be used to develop a SPF roof that can resist cracks and dents from fairly large hail in the 1.5 inch to 2 inch category.
- Use a higher density foam. As reported above, SPF roofing foam ranges in density from 2.5 per cubic foot (pcf) to over 3 pcf. As the density increases, so does the compressive strength of the foam and its resistance to impact. In order to provide the best hail impact protections, use a SPF that has a density over 3.0 pcf (under 4 pcf) and a compressive strength of 60 psi or more.
- Add a 3rd layer of coating. Most SPF Roofing systems consist of 2 layers of 10-15 mils each of coating. Adding another layer of coating thereby increasing the thickness of the coating, which significantly increases its tensile strength providing greater hail and wind-driven debris impact resistance.
- Combine tensile strength with high flexibility. Impact resistance of a coating system is a combination of both tensile strength and flexibility. For example, a coating system with 400-psi tensile strength and 400% elongation is less likely to crack from hail impact than a coating system with 1500 tensile strength and 75% elongation. A combination of high tensile strength and high long-term flexibility provides the greatest protection.
- Top coating system with granules or crushed aggregate. Past field studies show that adding granules or crushed aggregate help reduce hail impact damage more than just coating alone.
- Check out the weathering characteristics and field history of the coating. It does little good to use a coating that starts with great tensile strength and flexibility, which after a few years loses its flexibility. It is important to use a coating that has demonstrated good impact resistance in the field over time, particularly against moderate to heavy hail.
Repairing SPF Roofing Damaged by Hail
When a roof sustains damage from wind-driven missiles or hail, how does one determine what procedures are required to maintain the roofs long-term performance? Under what conditions can the roof be renewed? When must it be scarified, recoated, or torn-off?
Now we will discuss what type of damage is likely to occur during windstorms and hail events, the effects on the SPF roofing system’s performance, and industry guidelines developed by the Spray Polyurethane Foam Alliance (SPFA) for inspecting, evaluating and recommending repairs.
Damage from Wind-Driven Missiles
Hailstorms are frequently accompanied with high winds that create airborne debris which can impact and damage a roofing system, specifically the SPF and coating. The type of repairs required from this damage depends on the size and severity of the damage sustained.
Missile damage refers to cuts, gouges, dents, and abrasions to the coating or SPF caused by materials such as tree branches, signs, parts of other buildings (shingles, metal panels, flashing, doors, windows, etc.), and many other unsecured items hitting the roof during a windstorm.
Small cuts, gouges, etc. (less than 3” in diameter) in the SPF can be repaired by caulking the holes after the damaged SPF is removed. Repair larger damaged areas by removing the damaged SPF and applying new SPF and coating to the void.
Hail Damage
The type of damage most likely to occur to SPF roofing systems during a hail event consists of cracks, punctures and dents to the surface of the roof. Both the protective coating and the SPF can be damaged.
The diameter of the cracks can be used to determine the hail stone size. The SPF, depending on the size, weight, and shape of the hail, may be dented as well. The depression typically ranges from ⅛” to ¾” in depth. Hail damage can be isolated to small areas or cover the whole roof. Determining short term and long-term repairs depends on identifying the severity of the damage. It is important to note both the size and quantity of hail dents and cracks.
Sometimes, mechanical damage is not discovered for months or even years after the damage occurred. In these circumstances, repair procedures differ depending on the extent of UV degradation of exposed foam and moisture absorption of the roof. Any UV-degraded or moisture-laden SPF in the cuts, cracks/dents should be removed and caulked. If the cuts, cracks/dents are too numerous to remove and caulk, the affected areas should be scarified, re-foamed and coated.
Inspection Procedures
The first step in making an evaluation and repair recommendation of a damaged SPF roofing system begins with an inspection that includes visual observations and destructive sampling and testing. The following inspection procedures can be helpful.
Visual Inspection:
- Look for blisters or delaminated areas
- Check the condition of the roofing system at all flashing and termination points
- Look for splits or cracks in the SPF
- Look for damage from impact
- Check for pinholes in the SPF or coating
- Check for exposed SPF and areas of eroded coating
- Check for areas of ponded water
- Check for obvious substrate or structural damage
Physical Inspection:
- Perform a non-destructive moisture survey. Follow-up suspected moisture laden areas with a moisture probe or core samples
- Probe to determine SPF thickness
- Take slit samples of the existing coating (at least 1 per 2500 square feet)
- Take SPF samples (at least 1 per 10,000 square feet)
- Take random slit samples of damaged areas
Analyze Inspection:
Core and slit samples should be examined for the following characteristics.
- UV degradation
- Presence of moisture saturation
- Adhesion of SPF to substrate
- Adhesion of base coat to SPF
- Adhesion of top coat to base coats
- Tye and condition of protective coating
- Condition of SPF
- Depth of damaged SPF
Indicate on a roof sketch the following:
- Location of core and slit sample
- Type and location of coating deficiencies
- SPF or coating blisters
- Poor drainage
- Repairs required for foamstops, parapet walls, gutters, flashing, scuppers, edge terminations, expansion joints, and other perimeter items.
- Repairs required to soil and vent pipes, drains, roof hatches, equipment curbs, or supports, guy wires, hot stacks, skylights, mechanical units, walkways, sleeper, pitch-pans, and other penetrations.
- Water-saturated sub-roofs, insulation of SPF
- Sub-roof damage or deterioration
- Areas of special consideration
Repair Recommendations
After you’ve obtained information from the roof inspection, repair recommendations can be developed specific to the damage sustained. As mentioned earlier, repairs will vary depending on the severity and the frequency of the damage.
The chart below was obtained from SPFA’s technical document AY 139 can help classify the mechanical damage and provide repair recommendations.
| Damage | Size & Severity | Extent per 100 ft^2 | Recommended Repair |
| Light | ½” diameter or less than ⅛” deep | Less than 10 cracks, cuts, and/or dents | Coat and/or caulk dent, cuts, & cracks Note: Re-coat should be considered based on remaining service life of coating |
| More than 20 cracks, cuts, or dents | Re-coat as required to fill in cracks Note: Some caulking may be required to seal deeper cracks | ||
| Moderate | ½’ – ¾” diameterless than ¼” deep | Less than 10 cracks/dents | Coat/caulk cracks |
| More than 20 cracks, cuts, or dents | Recoat as required to seal cracks Note: Some caulking may be required to seal deeper cracks | ||
| Heavy | ¾” to 1½”¼” to ½” deep | Less than 10 cracks/dents | Remove damaged SPF: Caulk holes and recoat as required |
| More than 20 cracks/dents | Scarf ½” of roof surface: Refoam & coat | ||
| Severe | 1-½” or larger | Less than 10 crack/dents | Remove damaged SPF: Caulk holes: Recoat as required |
| More than 20 cracks/dents | Scarf ¾” of roof surface: Refoam and coat |
Other Factors to Consider
The recommendations listed above are not specific to regions or varying climates. While the recommendations remain consistent in varying climates, consequences of untreated wind and hail damage to SPF roofs vary in different climates.
Hot Arid Climates:
Climates such as Phoenix or Las Vegas are more forgiving in regards to light to moderate hail damage. However, cracks in the coating can allow UV degradation over time. This degradation may take months to occur. However, this degradation typically does not affect the roof’s water resistant characteristics since the low humidity and exceptional drying characteristics of the climate does not allow the SPF to saturate over time. The main concern of light to moderate hail damage in this climate is to maintain the coating’s capacity for recoat/renewal. Eventually, UV degradation of the SPF under the coating will affect the adhesion of the coating to the foam. It is recommended that the damaged areas be removed and caulked or re-foamed.
Hot Humid Climates:
Climates such as South Texas and Florida have more complex factors affecting hail damaged SPF roofs. High temperatures tend to dry out the moisture that has seeped into the cracks and crushed foam cells very quickly. On the other hand, the high humidity creates a higher potential for SPF saturation particularly during cooler times of the year. Lower perm rated coatings/covering also increase the potential for moisture saturation of the hail damaged roofs because they do not allow drying to occur as efficiently as higher perm rated products. As in the hot arid climates, UV degradation that can affect coating adhesion typically occurs within a few months.
Cool Climates:
In cooler temperatures the greater concern of hail damaged roofs is moisture saturating into the SPF. There may be long periods of time where drying conditions do not occur. In many areas snow may stay on the roof for extended periods increasing the possibility of moisture saturation. It is important to repair crushed foam and coating cracks as soon as possible to prevent moisture saturation of the damaged areas.
Conclusions
SPF roofing systems have unique characteristics that allow the repair rather than the replacement of the system after hail and wind damage. Hail and wind damage repairs to SPF roofing systems vary according to size, severity of damage and the length of time after the damage. It is important to inspect and evaluate the damage in order to make the correct repair recommendations. However, with the correct repair. SPF roofing systems can perform for many years after a significant wind or hail event.
Closing Remarks
After Reading this post, we hope you have a much better understanding different types of roofing systems and how hail damage can cause different issues.
What types of roofing systems do you create? Have you had to repair a roof after hail damage? What testing was performed in order to assess the damage? We’d love to hear from you! Leave a comment below discussing your experience, thoughts, tips, or questions you have about roofing systems.