Foam Roofing vs Hurricane Andrew

I. Introduction
II. Very High Winds: Buildings 1-4
III. High Winds: Building 5
IV. Moderately High Winds: Buildings 6-13
V. Discussion
VI. Conclusions
VII. Recommendations

I. Introduction

Anyone with a lot of experience dealing with Foam Roof Systems knows they are actually more durable than a standard roof. The closed cell, high density foam used on roofs is specially formulated, and is nothing like the open cell foam you might find in a couch or a pillow. Closed cell foam is water repellant, while open cell foam is water absorbent. Walking on a foam roof is somewhat like walking on a concrete sidewalk. After the foam is sprayed, it only needs about 1 minute to cure before it can be walked on. Sprayed Foam Roofing, when properly applied, is a durable, lightweight, self-adhering, and surprisingly strong material.

But just HOW durable is a foam roof verse a traditional roofing material? In 1992 Hurricane Andrew struck Florida, and in the wake of the damage, we were left with the answer: Foam roofing is amazingly durable. Due to the light weight, high tensile strength, and excellent adhering nature of foam roofing, this type of roof has been proven to often withstand even hurricanes.

Here is a summary of eleven different Florida PUF systems, inspected after Hurricane Andrew struck in 1992.

II. Very High Winds

II. a. Building 1

This roof is about 8 miles from the coast. This Polyurethane Foam (PUF) Roof was installed over a BUR mineral cap sheet, a ply sheet and a nailed base sheet over wood panels. The two story residence was built near Naranja, and has roofing surfaces at both level one and two.

Portions of the PUF roof were blown off on both the upper and lower levels. Half of the main roof is on a canopy area which was open on three sides. The BUR / PUF / Composite roof was blown away by the hurricane winds, but it did not fail beyond the canopy area. There were other smaller roofs of 100 square feet each that were not damaged beyond some minor missile damage. On one part of the roof there was a 4 foot overhang, where the PUF blew off, but it appears the PUF did not fail beyond the overhang.

II. b. Building 2

Building 2 had a low slope BUR roof, which was completely blown off by the hurricane winds.

II. c. Building 3

This commercial building, set 3 miles of the coast near Cutler ridge consists of two intersecting domes. The roof is polyurethane foam (PUF) over thin shell concrete, self flashed at the edge. Notably, this PUF roof had no peeling; (the PUF surface was intact. Little or no missile damage is apparent on this roof, possibly because of the lack of other buildings within 110 feet. The only damage on this roof consisted of some things such as antennas or other roof attachments that were completely blown way by the gale force winds.

II. d. Building 4

This house located 2.5 miles from the coast near Howard, has a 10 year old, two inch thick PUF roof over a BUR substrate. The only visible damage to the PUF roof consists of scattered minor missile damage. An electrical conduit penetration was moved back & forth causing a hole. The owner of this home reported no leaks, and the roof inspection revealed this roof only required very minor repairs. All of the other roofs in the surrounding area were asphalt shingle, tile, and bur. These roofs all lost shingles, tiles, and the bur roofs had roof surface peel back.

III. High Winds

III. Building 5

The next roof is located 10 miles from the coast, near Kendale Lakes. The one year old roof is coated PUF, with a loose gravel aggregate on the surface. The underlying substrate is BUR, and the roof is self-flashed by PUF at the edges. A large area of the loose aggregate is blown aside, although a parapet prevented the gravel from completely blowing off the roof. The only apparent damage to the roof was caused by minor missile damage, which appears easily repairable (mostly just reallocation of the loose aggregate).

IV. Moderately High Winds

IV. a. Building 6

This building is a two story hotel on the east side of Miami Beach, across the street from the beach (and hence, very near the ocean). This five year old roof is a PUF system, self flashed, over a BUR substrate with a 32 inch tall parapet. The only visible damage on this roof is due to missile damage, and the roof is otherwise intact. There is one small area of 17 x 22 inches where the acrylic coating peeled back. Only minor repairs will be required and the owner confirmed the roof had no leaks, despite the missile damage.

IV. b. Building 7

This vault shaped church near West Miami is three stories at its maximum height, set 6 or 9 miles from the coast (at the respective East and West ends). This one year old PUF roof is self flashed at the edges, over a concrete substrate. Some membrane damage is apparent where a gutter lifted (peeling the membrane back in a 6x 10 area) and where tree limbs caused some light missile damage.

IV. c. Building 8

The next roof is located 8.5 miles from the east coast of Miami Beach. This eight year old one story roof is PUF over a BUR substrate. There is no visible damage to the PUF, possibly because this one story roof is taller than a normal one story building. The surrounding lower one story roofs display normal missile damage, and one nearby BUR roof suffered extensive damage. Building 9 is only two buildings away from this building.

IV. d. Building 9

This warehouse is about the same height as building 8, and consists of a ten year old PUF 3/4 inch thick surface over a BUR (built up roof) substrate. At one corner the metal flashing, nailer and PUF/BUR lifted over a 20 x 45 foot area of the coating membrane (on top of the PUF). A few areas displayed minor missile damage. Thin uncoated PUF covered the peel back area and the inspection revealed only a few additional minor repairs were required to completely restore the roof. Building 10 is also adjacent to this building.

IV. e. Building 10

This aggregate surfaced BUR, is nailed to a lightweight concrete deck, which is surfaced by perlite aggregate. This building had peel back of 20x 40 feet, near the same area of building 9 which peeled back. The peel continued 25 feet further, in a strip varying between two to eight feet. It appears the damage was caused by the uplift of a gutter and attached flashing where the nailer failed.

At another corner of the PUF roof, both the membrane and roof deck were missing creating a 5 foot long hole between bulb tees. The damage was caused by debris from an adjacent roof composed of PUF/ BUR. Other than the area where a portion of the roof was completely missing, only minor repairs were required. This indicates the roof could be repaired, instead of completely replaced. However, near the area with the 5 foot hole in the roof, some deck was exposed to weather and rain for over 30 days. Mostly likely, the rotten wood in this area would have to be replaced completely.

Near buildings 8, 9, and 10, there were several other warehouses all with BUR or composite roofs. All of these roofs had minor membrane peels near the edges where the metal flashing was unable to withstand the force of the hurricane winds (this flashing was not cleated or face-fastened).

IV. f. Building 11

This tall one story warehouse consists of Polyurethane Foam (PUF) over a built up roof (BUR) substrate, and is located about a 1/2 mile from buildings 8, 9, and 10. The one year old foam is covered by a loose aggregate (gravel). There was no apparent damage to this roof, nor did the aggregate require any redistribution.

The two buildings behind this building were aggregate surfaced BUR roofs, which both had flashing damage, minor peel back, and minor missile damage. Three different roofs across the street had minor BUR membrane peeling as well.

IV. g. Building 12

This tall one-story warehouse roof is another PUF system over a BUR substrate located near Hialeah, only a few miles from building 11, and about 11 miles from the east coast of Miami Beach. There is no apparent damage to the polyurethane foam. An aggregate covered PUF roof behind this building had visible scour at two corners (places where the wind blew the aggregate out of place). Building 13, which will be described next, is next to building 12.

IV. h. Building 13

This eleven year old warehouse roof consists of 1.25 inch thick polyurethane foam (PUF) over built up roof (BUR), with a nailed base sheet over a perlite aggregate thin insulating concrete deck. At one corner where the metal flashing lifted, the PUF and BUR composite lifted and peeled creating a 20 x 30 foot area of damage. This roof also had other damage, however, none of it was hurricane related. Across the street, a BUR roof with a nailed base sheet displayed extensive peeling.

V. Discussion

1. Based on the observations made, if the substrate peels, the polyurethane foam can play a role in limiting the size of the peel. For example, on Building 1, the PUF limited the size of the peel, and prevented progressive peeling failure. In contrast, the peel back on the roof of Building 9 was not significantly less than that of Building 10. It appears the thickness of the PUF is negatively correlated to the size of the peelbacks. In other words, the thicker the polyurethane foam, the more peelback is prevented. The increased thickness causes the BUR/PUF to snap off closer to the edge which limits the size of the peelback. And this also prevents progressive damage (thinner PUF roofs which had more peelback experienced additional damage when sections of the roof snapped off, impacting futher sections of the roof, in other words, snowballing the damage.

2. PUF is more susceptible to missile damage than BUR, modified bitumen or metal, however, the damage is easier to visually find and repair as well. One great benefit of PUF is also, that as long as a missile does not completely penetrate the closed cell foam, the surface remains watertight. The allegorical data collected implies that a thickness of 2 inches prevents penetration of most missiles. Furthermore, PUF is not susceptible to progressive peeling after the impact of big missiles (in contrast to BUR, metal, modified bitumen, etc).

3. Scour of aggregate on PUF roof surfaces causes no damage as long as it does not completely blow off the roof and as long as it is properly redistributed within a few months. In the case that loose aggregate does blow off the roof, substantial damage can be inflicted on people, buildings, and vehicles. In any environment where high winds are expected, parapets can prevent winds from blowing off aggregate.

4. Much of the damage to the warehouse roofs were due to building age and poor construction methods, such as use of cut nails to attach nailers to concrete and the use of uncleated metal flashing edges. Nailer deterioration also caused great damage, hence, we recommend the use of treated nailers in high wind environments, where deterioration could cause great damage.

VI. Conclusions

Based on this study, Polyurethane Foam Roofing Systems have the potential to withstand most damage during high wind events such as Hurricane Andrew and Hurricane Hugo. Aside from resistance to wind loading, polyurethane foam resists multiple types of potential causes of roof failing including: progressive peeling, missile impact damage, deck failure, and lifting at the roof edge. And, the fact that a PUF roof will remain watertight, unless a missile completely penetrates it, is a great benefit, considering the length of time emergency repairs may take in a disaster area.

VII. Recommendations

Here are a few guidelines, or take away concepts we can benefit from with this observational study.

1. When a PUF roof is installed in a potentially high wind environment, it is best to avoid the use of an aggregate surface, unless the designer specifies it is ideal. In that circumstance, parapets can be installed to prevent blow off, and risks can be further determined using the 1976 Kind and Wardlaw guide.

2. When determining which metal-edge flashings to use, and what to attach them with, follow the recommendations of the 1990 IJORT.*6 guide.

3. If a contractor recommends a polyurethane foam roof over an existing membrane substrate, an engineer should still evaluate the deck if deterioration is in any way evident. To some extent, a roof is only as reliable as the substrate it is installed on. Especially in the case of a disaster.

4. When installing a PUF roof in a high wind environment, a minimum thickness of 1.5 to 2 inches can limit the potential peeling failure of the membrane in a disaster.

5. When a PUF roof is installed over an existing substrate, and if the existing flashing is used, the metal face should be evaluated by a designer. In the case that the flashing is uncleated, or has poor interlock, that additional measures should be taken to attach the metal along its face or to replace it completely. In the case that the flashing is not replaced, it is difficult to determine the condition of the underlying nailers and whether they are securely attached.

Foam Roofing vs Hurricane Force Winds

Although the observations of this article may be a bit dry, there's a great take away from all this we can benefit from. A foam roofing surface at a depth of 1.5 to 2 inches is ideal for withstanding hurricane force winds, as long as the underlying nailers, deck and flashing are all in good condition. And often, foam is easily repaired. The only exception may be a foam roof with an aggregate (loose gravel) surface. If possible, it is probably best to just surface the roof with an acrylic coating. However, if aggregate absolutely must be used, it's best to have a parapet to block the aggregate from completely blowing off the roof (a liability indeed), and damaging nearby homes, vehicles, and possibly even people.

While roof surfaces such as BUR, metal, and modified bitumen invariably displayed uplift and other damage, many foam roofs endured the hurricane and were leak free, even despite substantial missile damage in many cases. When a PUF roof was at least 2 inches thick, it appeared most missile damage was unable to penetrate, and the roof remained watertight.

Find a local Foam Roofing contractor.