When Should a Commercial Flat Roof be Repaired or Replaced? – Video

This video shows how to know when a roof is not repairable.

Replacing a Commercial Flat Roof

The replacement of a commercial flat roof is inevitable. When the decision has been made to replace a commercial rubber roof, the following list is factors that will determine the overall cost.

  • The height of the building and size of the flat roof
  • Type of roof and number of existing layers
  • The type of roof system needed/wanted
  • Whether flashing is reusable on walls and rooftop structures
  • Roof accessibility
  • Size of parapet walls and caps
  • The number and sizes of a/c units, vents, drains, antennas, skylightsscuppers, etc

This video shows what signs to look for on a Hot Tar and Gravel roof if it needs to be replaced

Hot-Tar-and-Gravel Commercial Roofs

Hot-Tar-and-Gravel Roofs have been around for about 100 years. If your commercial roof is a Hot-Tar-and-Gravel roof, it is likely that it is between 25-40 years old and we would advise against making repairs to it. Chances are, that the asphalt layers are degrading and the tar is cracking, which will make repairs costly.

Modified Bitumen Membrane Commercial Flat Roofs

Another type of membrane commonly found on commercial flat roofs is the Single Ply Modified Bitumen Torch Down Rubber Roof (MB), which has been used since the 1960s. It is still a common practice to install MB roofs, over existing hot tar roofs. If an MB roof leaks, it is very likely that it is repairable. If it was never protected against harmful UV rays, with an aluminum asphalt coating, another MB membrane, with ceramic granules embedded for UV protection, should be installed over it.

An additional MB membrane fused to the existing one creates a 2 ply roofing system, which will provide a life expectancy beyond 40 years.

Important!  – Fuse the Old with the New 

Note – a Modified Bitumen Torch Down Rubber Membrane never has to be removed before a new Torch Down membrane can be installed. It is best to use the existing membrane as a base, and install another Modified Bitumen Membrane over it, fusing them together. This will double the thickness (it becomes a 2 ply membrane) of the roof, and will easily last 40 years and beyond.

Inspection of a Hot-Tar-and-Gravel Roof

  • Thickness Test – Buy a gallon of cold tar, a utility knife, and a small trowel. Cut a small square of the roof’s membrane; about 6″ x 6″ to determine the thickness of the material. If the membrane is at least 1/2″ thick, repairs are probable. Replace the patch with cold tar.
  • Roofing Blisters –  Blisters are a sign that the layers of the membrane are separating due to a moisture build-up between the layers of asphalt paper; a roof replacement is needed.
  • Stress Cracks – Cracks that are about 8-20 feet long is a sign that the roof needs to be replaced.
  • The disintegration of Asphalt Surface – When the entire roof looks like scattered puzzle pieces; replacement is recommended.
  • Multiple Repairs – When patches upon patches and tar build up is evident; replacement is necessary.
  • Interior  Leaks – When there are signs of many leaks on the interior ceilings; replacement is necessary.

Inspection of a Modified Bitumen (MB) Roof

  • Age – If the roof is over 30 years old, and numerous repairs have been made, replacement is recommended.
  • Loose Seams – This can be due to UV degradation, pooling water, or faulty installation; we recommend replacement.
  • UV Degradation – When there has been prolonged exposure to harmful UV rays without protection; replacement is recommended.
  • Metal Flashing – In many instances the MB membrane has become detached from the metal edgings and flashing; repairs are recommended.
  • Tar on Seams – If many of the seams appear to have been smeared with tar, as an attempt to fix leaks; replacement is recommended.
  • Roof Maintenance – If there is any damage done due to snow shoveling, or other maintenance activities; repair is recommended.

This video explains why it is better to keep an existing Modified Bitumen Torch Down membrane.

Important! – Do Not Repair a Roof with Tar

The most expensive mistake when making a repair to Modified Bitumen, is doing so using tar. It becomes labor intensive to remove multiple applications of tar and silicone caulking, prior to a proper repair. When proper repair can’t be done immediately, tar can be used as a temporary remedy only.

EPDM Rubber Roofs 

The EPDM single-ply rubber membrane is a popular roofing system. It is about 1/16″ thick, and the all-black, unprotected rubber absorbs harmful UV rays, which accelerates the degradation of the rubber and the adhesives used to glue the seams. This causes the roof to fail prematurely. From the onset of a newly installed EPDM single ply rubber roof, there will be leaks and repairs needed, which will continue throughout the life of the roof. If this is the situation with your current roofing, we advise a replacement with a 2 Ply Modified Bitumen Torch Down Rubber Roof System.

The video below shares tips about where to look for leaks on an EPDM rubber roof.

TPO Roofing Systems

Like EPDM roof systems, the TPO system is also a single-ply vinyl membrane that is about 1/16″ thick. This system is popular because the manufacturer guarantees the roof for 10-15 years. The roofing contractor must be certified by the manufacturer and an inspection of the installation is performed by them, as well.

If you want to replace your roof with TPO, the process is costly and takes time. The roof is installed by adhering the entire membrane, with a glue adhesive, to the substrate. The seams are fused together with heat guns.  A special flashing has to be pre-made, in the factory and installed on a roof that must first be properly prepared. This means the existing roof must be removed so that the new, special flashing, can be installed. We do not advise installing a TPO roof system.


Single ply roofing systems, as in EPDM and TPO, will always have leaks from the time they are installed to the time they need a total replacement. When the repairs become a regular routine, then the time has come to replace it with a different roofing system. A 2 Ply Modified Bitumen Torch Down Rubber Roofing System, can always be repaired and will last indefinitely.


When it’s time to replace a roof, it is far better to invest in the quality of a 2 ply rubber roofing system, that will last beyond 40 years with fewer maintenance issues than to commit to another single-ply roofing system like EPDM or TPO?

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