Hailstorms And Commercial Roofing Damage Analyses

Colorado’s metro area, rural areas, and regions extending northward into Cheyenne have been pelted with afternoon thunder and rainstorms over the past week.  Last night’s storm produced golfball-sized hail in Cheyenne, flooded homes and streets in Denver, and blew over trees in Elbert County, Colorado.  Following storms like this, it is very common to receive an influx of commercial hail claims.  This brought to mind an article written by Pie Minnesota engineer Brian Erickson regarding how our experts test for roof impact damage using desaturation and other methods.

Photo taken by Pie expert
{Photo taken by Pie staff in Cheyenne, WY, on July 13, 2011}

Commercial Roofing Damage Analysis via Solvent Extraction of Reinforcements

By Brian D. Erickson, M.S., P.E.. RRC

Commercial roof impact damage can be difficult to assess without solvent extraction and analysis of the reinforcements, commonly referred to as desaturation.  The presence of damage to the reinforcements will directly affect the repairs, which have a significant impact on the amount of the loss.  This brief article will summarize the process in which low slope commercial roofs, including built-up roof (BUR) and modified-bitumen (MB) systems, are analyzed using solvent extraction of the bitumen to expose the reinforcements.

Visual Inspection

The alleged impact damage is first documented by simple visual observation of the roof system and associated components and claddings to assess the presence, magnitude, direction, and extent of impact damage present on the building.  Also, the roof system and wearing surface is identified and classified as best as possible.  Single-ply systems such as EPDM, TPO, and PVC are easily distinguished from BUR and MB systems, but classifying BUR and MB systems can be challenging.  For example, a 3-ply and 4-ply BUR with a fluid-applied coating and a smooth surface MB cap sheet can appear similar, but a closer evaluation of the surface thickness and lap width can distinguish the two.  Roof cores are often necessary to identify the number of reinforcing plies, coverboard, insulation, and deck type.  Impact damage to the wearing surface can affect the ultraviolet resistance of the roof system only or it can affect the integrity of the strength of the plies and sheets via reinforcement damage.  The latter could be visually observed by punctures or fractures at unsupported areas such as base flashings, laps, and blisters, but the lack of this visual evidence requires laboratory analysis to closely examine the reinforcements for damage that may not otherwise be seen.  The presence of damage to reinforcements directly affects the repair options available, which must be determined based on an evaluation of the extent of damage observed, type and condition of the roof system, and climate.  Occasionally, a fully system replacement is warranted, but only after all other repair options have been assessed and deemed unsuitable, such as coating or re-coating, flood coating with aggregate, overlay, peeling the system but leaving the underlying components in tact, and others.

Solvent Extraction of Reinforcements

Core samples of the wearing surface can be obtained and analyzed via solvent extraction of the reinforcements, a process commonly referred to as desaturation.  The process utilizes specialized solvents that are able to remove the bitumen saturating the reinforcements, either fiberglass, polyester, or a combination, without actually damaging the reinforcements.  The solvent must be carefully selected and tested to ensure it does not cause damage to the specimen.  A vapor degreaser machine contains the solvent and utilizes a boiler sump, condensing coils, and a spray wand to carefully remove the bitumen from the roof samples.

Additional Roof System Analysis

In addition to solvent extraction analysis, commercial roof system damage should also be assessed via non-destructive means such as infrared thermography scanning, nuclear survey, or simple moisture scanning, in order to evaluate the presence of moisture within the system when the integrity of the wearing surface is suspected to have been breached.  Gravimetric analysis is possible to accurately quantify the extent of moisture within insulation systems as different insulations have different sensitivities to moisture.  Some insulation can tolerate greater moisture content without significantly affecting the insulating characteristics or compressive strength so it can remain in-place.  Gravimetric analysis requires roof cores to be taken from the roof system and patched with like material, from the insulation to the roof surface, by a qualified roofing professional.  The building owner and all parties involved should understand the process of obtaining roof cores and the fact that “patches” will be present on the roof surface, which may affect new roof system warranties.  However, the benefits of such analysis of roof cores and wearing surfaces should not be lost due to apprehension regarding obtaining cores or patches, as the repair extent and methodology could well depend on the results of the analysis.


Solvent extraction of commercial roof systems is a valuable tool to verify the presence and extent of impact damage that is not readily observable from the roof surface.  The results of the extraction are used when discussing and recommending repair options, especially if the results do not show damage to the reinforcements and repairs other than full system replacement or peeling can be viable and cost effective.

Pie has roofing experts and lab technicians available to assist on large commercial and residential roofs.   Please contact Pie Forensic Consultants at 1-866-552-5246 or at www.pieforensic.com for additional information or to schedule a roof analysis.

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