Why Do Commercial Flat Roofers Take Core Samples?

by | Apr 4, 2023 | Flat Roof Inspections

​It is important for commercial and industrial flat roof property managers and building owners to let roofers take a core sample of their roof because it helps the roofer determine whether a repair, restoration, or replacement roofing system is needed.

A good roofer will be able to use the core sample to identify wear and damage you can’t see from the ground or roof surface. He or she will be able to accurately determine the exact nature and extent of roof damage and use that information to determine whether a roof repair or recovery is possible. Results can then be used to come up with an accurate price and timeline for work completion.

Four Questions 

There are four main questions a roofer is trying to answer when he or she cuts into your roof:
  • How many roof layers are present in the existing system?
  • How thick is the roof system?
  • What is the roof system composed of (insulation, stone, asbestos, tar, etc.)?
  • Does the roof system have moisture? (Is the core cut sample wet or dry?)

Answers to these questions will feed into the roofer’s recommendations and next steps.

Existing Roof System Layers

Most building codes let you have up to two layers of roofing on a building – for weight reasons. They don’t want to overburden the building with too much weight. If your roof already has two layers, then your options are limited to a roof restoration (coating) or a tear-off and replacement.

State building departments like to see you tear off down to the deck and rebuild everything (not just remove the top layer) so that you can upgrade the insulation to the current code requirement (2023 R30; 2024 R38). The core cut will tell if your building has one or more roofs. If you only have one roof and it is dry, then you have the most options. You can tear off and replace, do a recovery, or do a flat roof coating system.

Existing Roof System Thickness

If you have to do a tear-off, this will drive the price up as the thicker the roof is, the more materials there are to remove and dispose of in a dumpster. If you are doing a recovery, the roofer will know what size fasteners to use (the longer the fastener the more expensive it is).

Existing Roof System Composition

Insulation board and a single-ply membrane is very easy to remove as opposed to 3+ inches of hot tar, stone or asbestos. Hot tar and stone are hard to cut through and very heavy. It is slower to remove and requires many more dumpsters as they are limited by weight, not just volume.

In contrast, insulation board is very lightweight. Single-ply membranes are easy to cut and deposit in a dumpster.

Core Cut Moisture

Regardless of how many layers are present, if the existing roof is wet or saturated, then you must tear-off and replace. If the roof has one layer and is dry you can do a recover (add an additional layer) or a coating system.

Sometimes a core cut can be dry but, because of the age of the roof and chronic leaks, it is best to get an infrared (IR) scan. A core cut is only a 2-inch sample of the roof. It is therefore possible to core dry spots on a wet roof. An IR scan uses a special thermal camera that can detect moisture in the substrate. It scans the entire roof, not just a small section, so you can see definitively if and where moisture is present .

In The End

Core cuts are highly informative for flat roofing professionals and building owners alike.

Core samples help:

• uncover the health and makeup of the existing roof system; and
• expose options for remediating problems that might be occurring now or in the near future.

It is safe and informative to allow a roofer to take core samples. The samples ensure an accurate roof assessment and help formulate options for both the roofer and building owner.

Expert Advice

Whether you’re a beginner, need advanced information about flat roofing topics, or a refresher,  this is where you can learn everything you need to know about commercial and industrial flat roofing.

Contact us for more information or pricing.




Jared Van Vranken is Vice President and lead estimator at Flat Roof Solutions in Malvern, PA. Jared has directed the installation, repair, recovery, and replacement of commercial flat roofs for more than a decade at Flat Roof Solutions. He guides clients in selecting the best roofing materials for their needs and budget.

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