What You Need to Know About a Commercial Roof Installation

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Author: Dan Stout | February 27, 2024

If you have experience as a residential roofer and are looking at moving into commercial roofing, the change can be daunting. Luckily, it's not impossible — you simply need a little training and assistance to do it right.

We spoke with Jason McDougal, a Beacon branch manager with decades of experience in the roofing industry, about why it can be difficult to get into commercial roofing, even from residential roofing. Too often, he says, roofers simply don't take into account that a commercial roof installation takes a different set of skills.

Here's what you need to know as an aspiring commercial roofer to understand the commercial roofing process, from initial training to final inspection.

Beacon delivering commercial building products

Licensing and Certifications

There are two types of qualifications that commercial roofers have to consider: licenses and certifications.

  • Licenses are issued by your state or local municipality. Some areas require licenses for commercial roof work; others do not. Check with your local building department for the requirements before beginning any work.
  • Certifications are issued by roofing manufacturers. While not required to perform commercial roofing, they determine the training and support you'll receive from the manufacturer and the types of warranty you can offer your clients.

McDougal suggests beginning by talking with your local distributor. Find out what manufacturers they work with, then reach out to those manufacturers to get certified.

For example, a manufacturer may offer commercial roofing certifications at multiple levels, with each certification providing a different level of warranty coverage.

Project Estimation

When preparing a bid, you must understand the existing roof structure. Is this a replacement roof or a new build? If there's an existing roof, does it need to be removed or can it be roofed over? While it's relatively easy to determine if shingles have been roofed over once before, a flat roof requires a more invasive method: the core cutter.

"A good commercial contractor always will do a core cut to see what's under the membrane," says McDougal. A core sample will reveal everything from how thick the insulation is to whether there are one or two existing roofs on the building.

As McDougal points out, finding two roofs can double your tear-off labor. "You can be a quarter of the way into a job and have already exceeded your budget." Knowing what you're working with upfront can help prevent going over budget from the outset.

Material Selection

Once you understand the existing roof structure, you can select a type and brand of materials that are a good fit. There are several materials available for low-slope roofs, including TPO, EPDM, modified asphalt, metal, and PVC.

The first step is to see if there's a system specified in the job documentation. If there is, make sure that it matches the needs you observed. If there's no specification, it'll fall to you to recommend a system to the customer.

Here the issue of certification comes back into play because the options you provide the client will depend on which manufacturers you're certified with. For example, if you're presenting a choice between two brands of EPDM, but you're only certified with one manufacturer, the warranty coverage you can offer on one brand versus the other will be dramatically different.


While there are too many variables in commercial roofing to give a universal set of instructions, it can be valuable to get a general feel for what a commercial roof installation might entail. Here are two different example roofs, and the basic steps in each installation.

EPDM Membrane Installation

First, we'll focus on installing a fully adhered EPDM membrane on a new-build roof with a plywood substrate and no insulation. (We're also not addressing gutters, penetrations or trim.)

  1. Clear off the workspace. Use a leaf blower or push broom to clear any debris. If there are puddles or wet areas, allow the surface to dry.
  2. Roll out the membrane and let it relax. "Relaxing" a membrane simply means that creases or folds will fall out. This usually takes about 30 minutes but may take longer on chilly days. This is also the time to double-check that any overhangs are lined up correctly and blend the adhesive.
  3. Apply the adhesive. Draw one edge of the membrane to the center. Apply the adhesive to the exposed plywood using a paint roller. Leave a ring around the edge as a walkway, and don't place adhesive in areas where seams will fall. Be aware that some adhesives respond to the climate, affecting working time.
  4. Lay the membrane back into place. Be careful to avoid creases or bubbles.
  5. Apply the next section of adhesive. Pull back the opposite side of the membrane and repeat the adhesive application process.
  6. Sweep the membrane with a broom. This helps remove air bubbles and encourages a strong adhesive connection.
  7. Set in seams. This will vary by product but often requires seam tape and adhesive.

TPO Membrane Installation

Now let's look at the installation of a mechanically attached TPO membrane. Again, we'll assume a substrate that's in good shape.

  1. Clear off the workspace. Just like EPDM, the first step is to begin with a clean surface.
  2. Install insulation. The TPO membrane will sit on top of an insulation layer. Use the fastener pattern recommended by the manufacturer to secure the insulation.
  3. Lay in the membrane. Rolling it into position, allow the membrane to relax for 15 minutes (longer if it's below 60°F ).
  4. Secure the membrane. The membrane is held down at the seams with a series of disk-shaped plates, typically 12 inches on-center. The next membrane is rolled out to overlap the secured plates.
  5. Weld the seams. The overlapping material will be welded together with hot air, either from a hand-held unit or an automatic welder. Start by cleaning the membrane overlap with the manufacturer-approved cleaner—you'll mostly be cleaning away boot prints. Apply heat with the hand-held unit, using a roller to secure the two overlapping membranes.
  6. Test the seam. Once the welds have cooled, use a probe to test for a solid weld. The best practice is to test all welded seams before the end of the work day. Correct any loose seams.
  7. Trim the edges. Trim the edges and seal them to edge strips.


To offer the best possible warranty, expect to have the manufacturer inspect your installation to confirm that it conforms to their best practices.

"On the commercial side," says McDougal, "if the building owner wants a warranty, the manufacturer sends their inspector to the site." That inspector will double-check everything before the manufacturer issues the warranty.

Getting Started on Your Roofing Journey

Moving into commercial roofing takes hard work, but with preparation and commitment, it absolutely can be done.

"Commercial roofing is a specialty," says McDougal. "Reach out to the local distribution and find out which manufacturers they work with, so you can get set up properly and trained."