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How to Core Sample a Roof

Currently published industry standards require that core samples be obtained when performing infrared roof moisture surveys. Properly procuring and patching core sample sites can help to maintain watertight integrity of sample sites.

Core sampling a roof involves physically removing a portion of the roof membrane and insulation layers to ascertain the composition and condition of roofing system components. Core samples may be square or round and range from a couple of inches in diameter to several square feet in size.

The following procedure outlines the steps in sampling and patching 2” diameter core samples on gravel-surfaced, built-up roofing systems.

• Locate sample site on flat portion of roof not subject to ponding
• Spud gravel off membrane for 12” diameter area. Use wire brush to remove dust
• Use core cutter to sample through membrane down to deck. Do not cut through roof deck
• Fill sample hole approximately ¾ full with cold roof mastic compatible with existing roof bitumen
• Install plug made from perlite insulation. Cold mastic should flow up and around plug once it has been seated firmly on roof deck at bottom of hole. Top of plug should be within 1/8” of top of sample hole when plug has been pushed to bottom
• Coat cleared area with roof mastic
• Center 6” diameter disk of 15 lb roofing felt over plug. Firmly press felt down to remove air pockets and fish mouths
• Apply thin layer of roof mastic over 6” felt
• Center 12” diameter disk of 15 lb roofing felt over plug. Firmly press felt down to remove air pockets and fish mouths
• Apply generous layer of roof mastic over 12” felt. Replace gravel and outline area with spray paint

Prior to sampling, determine if roof is under any warranty that could be voided by sampling. Always obtain permission to perform any invasive testing before you begin.

Infrared inspection of flat roofs is one of the many topics covered in the Infraspection Institute Level I Certified Infrared Thermographer® training course. For more information or to obtain a copy of the Standard for Infrared Inspection of Insulated Roofs, visit Infraspection Institute online or call us at 609-239-4788.