The spring of 2001 has been a particularly active one, weather wise. High winds, tornados and hail storms have occurred with frequency, especially across the Midwest.

Recently, a large Midwestern metropolitan area experienced a severe storm including damaging hail. Several suburban communities in the area reported hail from 1 inch to 2 3/4 inches in diameter.

Following the storm, Benchmark was asked to inventory hail damage and assign costs for repair of the damage. The property examined had multiple buildings with a variety of roof construction.

The following are descriptions of damage trends observed during the survey on the most common roof systems.

Punctures through the field membrane were only observed where the top membrane was blistered up as a single unsupported sheet. On well-adhered roofs, the only visual indication of hail impact was small dark round "blemishes" where surface granules had been scuffed or displaced.

On older membranes, where loss of granules was already pronounced, the impact sites appeared nearly black, with an almost total loss of granules at some of the impact sites.

The APP membranes were over firm substrate material and exhibited little outwardly visible damage.

(PVC, CSPE, EIP, CPE)

Damage to thermoplastic single-ply membranes varied based on age and type of reinforcing scrim. For instance, the hail easily punctured a 10-year-old PVC membrane with a non-woven fiberglass mat reinforcement. Adjacent to it, a 16-year old CSPE membrane, with a woven polyester scrim reinforcing, showed no signs of damage.

A 16-year-old, brittle CPE membrane with woven polyester reinforcing, did not puncture but was shattered at hail impact sites. This allowed water to filter through thousands of small fractures in the membrane.

In general, the more pliable membranes with polyester reinforcing fabric, installed over a firmer substrate material, incurred less damage.

The ballasted membrane roofs, covered with 1 1/2" to 2" diameter stone, were well protected from hail damage. On exposed fully adhered or mechanically attached membranes, the flexible nature of the material, when installed over a relatively forgiving insulation board substrate, allowed these roofs to withstand the hail without visible damage.

The only signs of hail impact were clean scuff marks on the membrane surface. Even where the EPDM flashing membrane was poorly adhered and bridged, the elasticity of the material kept it from being punctured.

The only signs of hail impact were clean scuff marks on the membrane surface. Even where the EPDM flashing membrane was poorly adhered and bridged, the elasticity of the material kept it from being punctured.

The cost of resolving obvious damage such as this, may only be a part of the total picture. Industry studies concerning the affects of hail damage on commercial roof systems suggest that often a portion of the damage done by hail impact is not readily apparent during initial visual inspection.

To obtain some perspective as to the potential for latent damage, it may be prudent to perform lab tests on a sampling of various roofing products, of different ages and construction, that are represented throughout the subject facility.