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  • Writer's pictureElite Roofing

What is a Core Sample?

Updated: May 23, 2023

Core Samples are necessary in most cases as they inform a roofer of how many layers you have on your roof, and what materials have been used. Core Sampling is a constructive test that involves cutting and removing a small sample of the roof layers until the structural deck is reached. There are many reasons as to why a roofer will request a core sample to be taken; read on to learn why!

Core Sample conducted by Elite Roofing of Jersey City

(Check out this example of a core sample taken from a roof in Union City, New Jersey!)

First, let’s look at the different options/methods roofers have when taking a core sample from your roof! “One method of taking a core sample is with a special tool developed by the Cold Regions Research Engineering Laboratory, called a CRREL cutter. This tool consists of a 12” long, 2” diameter pipe. One end has saw teeth cut into the pipe, the other has a place to insert a steel rod. The CRREL cutter saws a 2” diameter hole in the roof. The “core” can be pushed out of the pipe and its components examined. The CRREL cutter is fairly efficient, cuts a nice, neat hole (that is easy to patch), and the time involved in cutting is fairly short. The negatives to this method of cutting are that sometimes the 2” diameter hole is not large enough to allow for specific observations and the CRREL cutter tends to compress the insulation (particularly plastic foam) layers. It is also limited to a depth of about 8”, which is normally sufficient, but can leave you short on roofs with deep tapered insulation systems, for example.”

Another method of collecting a core sample can be with the use of an ax, knife, and/or insulations saw or reciprocating saw. When cutting with a knife, your roofer can get a clean sample of the top layer, but this limits the roofer to how deep they can get with this tool. An ax could also be used for collecting core samples, but we do not recommend this as it can cause damage to the roof and give an inaccurate sample as the layers can become crushed/mashed up. For roofs that require larger samples, we would recommend the use of a reciprocating saw as it allows a roofer to take a large-scale sample without disturbing the integrity of the roof itself. In all, the CRREL cutter is the best option for the roofs here in Hudson County, New Jersey!

(Check out this video that estimators took while performing a core sample on a roof in Jersey City, New Jersey!)

Now, let's move on to the legal obligations a homeowner has when looking to replace or repair their roof. In New Jersey specifically, homeowners are legally limited to two layers of roof shingles. There are a few reasons as to why the maximum amount of layers allowed on a shingle roof is two; one of which is because two layers of shingles trap more heat, which in turn damages the shingles and shortens the life span of the roof. Another reason is that multiple layers can add a tremendous amount of weight to your house which can risk your structural integrity and even cause costly damage to the structure itself. In the event that you need a new roof but already have the maxim amount of layers allowed, you’ll need a full roof tear-off. Additionally, if your roof is severely damaged, it likely won't be able to support the weight of a reroof and will need to be torn off.

Although asphalt shingles are only legally allowed to be two layers, flat roofs on the other hand can contain multiple layers if necessary. Materials such as EPDM and TPO are usually approved for use up to two layers, but Modified Bitumen (Mod-Bit) can be up to six layers, depending on your roofing needs: deck, insulation, plies, membranes, adhesives, and surfacing. Cap Sheet roofing is either two or three layers applied over your low-slope roof's insulation and deck.

Hole in roof created from Core Sampling

(On this roof, you'll be able to see a thin metal layer by examining the core sample!)

Another reason roofers collect core samples, besides looking for what type of materials have been previously used, is to identify what materials are used when creating slopes in your roof. “Generally in newer buildings, the roof structure is sloped to drains or scuppers, which are placed at low points in the structural deck. Poured-in-place deck materials, such as lightweight insulating concrete, are sometimes used to provide slope on a flat structural deck. Finally, tapered insulation may have been used to create a slope on top of a flat structural deck. Particularly with reroofing design, it is imperative to understand what element provides slope, structure, topping layer or tapered insulation.”

Diagnostic core sampling is another way to check the overall condition of your roof. “Core sampling is a very useful tool to help diagnose whether or why a particular roof defect may exist, such as blistering in a multi-ply asphalt roof, loss of roof adhesion (blow-off), hail damage, or suspected wet insulation. Core sampling is the surest method of verifying the presence and location of wet roofing components when conducted at the conclusion of an infrared or nuclear moisture detection scan.” Diagnostic core sampling overall allows your roofer to understand exactly why your roof is having certain issues and informs the roofer of what they need to correct.

Another common type of core sampling is a Hazardous Materials Identification core sample. Although not as common, Hazardous Materials Identification core samples are useful when conducting testing for asbestos content in roofing materials in older homes. “Identifying the existence of phenolic foam insulation during core sampling is very important information as this material can cause greatly accelerated corrosion on ferrous materials, such as steel roof decking.” For your roofer, understanding what materials have been used prior not only helps the roofer decide what materials to use, but helps the roofer pick the best materials for the safety of you and your home.

Overall, core samples aren’t always needed when looking to repair or replace your roof, but in most circumstances, your roofer may request to take a sample to ensure the quality of your roof is in its best condition. Want to learn more? Be sure to head on over to and check out Vlog#11- How Many Layers Is On This Roof!? for behind-the-scenes footage of why collecting core samples are necessary to avoid problems like this!

If you’re interested in getting a roof repair or replacement, be sure to contact us here at Elite for a F R E E estimate! Contact us today at (201)436-1011, or email us at for more information!

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