What Commercial Reroofing Involves and How Long It Takes

Commercial reroofing usually starts with an inspection of the existing roof deck to decide whether the old system can stay in place under a new layer or needs to come off entirely, followed by choosing a system, such as built-up roofing, modified bitumen, single-ply, or metal, that matches the building. From there, it moves through prep, installation, and a final quality check. How long that process takes depends more on the building's specifics than on the calendar.

King Koating has been providing reroofing services across Ontario since 1988, holding COR certification and membership with the Ontario Industrial Roofing Contractors Association, the Canadian Roofing Contractors' Association, and the National Roofing Contractors Association. Here's what a commercial reroof typically involves, and what determines the timeline.

What Commercial Reroofing Involves

A commercial reroof starts with an inspection of the roof deck to check for moisture, structural damage, or drainage issues that need to be addressed before any new material goes down. From there, a contractor determines whether the project is a full tear-off, removing the existing roof down to the deck, or a recover, where a new system is installed over sound existing material.

Once that decision is made, installation follows a set sequence: preparing the deck or existing surface, applying the chosen system in layers or panels depending on the material, then a final inspection to confirm seams, flashing, and drainage are performing correctly before sign-off.

Reroofing Services: Choosing the Right System

Not every commercial building calls for the same roofing system. Reroofing services typically cover a handful of options, including built-up roofing, modified bitumen, single-ply systems like TPO and EPDM, liquid applied systems, and metal roofing, each with different lifespans and maintenance needs.

Metal roofing, for example, is often chosen for its longevity, with a service life that can run 40 to 70 years, while built-up systems are valued for their durability on low-slope commercial roofs. Our article on the difference between modified bitumen and built-up roofing breaks down how to weigh these two options against each other.

What Affects How Long a Commercial Reroof Takes

There's no single timeline that applies to every commercial reroofing project, since duration depends on the size of the roof, the system being installed, whether it's a tear-off or a recover, and how easily crews can access the site. A small recover on a straightforward low-slope roof moves faster than a full tear-off on a large building with multiple drains or rooftop equipment to work around.

Weather and scheduling matter too. Reroofing generally needs a run of dry conditions to install properly, and projects on occupied buildings are often phased around business hours. The most reliable way to get an accurate timeline is a site-specific estimate, since a roof's actual condition drives the schedule more than any general rule of thumb.

Where Waterproofing Fits Into a Reroofing Project

On some commercial roofs, roof waterproofing in Ontario is part of the reroofing scope rather than a separate project, particularly on flat roofs where standing water and seam integrity are ongoing concerns. King Koating's Natural Seal system is a cold-adhesive, multi-layer application that's 100% VOC-free and odourless, making it practical on occupied buildings where a strong-smelling application isn't an option.

Deciding whether waterproofing should be bundled into a reroofing project usually comes down to the inspection findings, since a roof with a history of ponding water or leaks benefits from that extra protection being addressed at the same time as the rest of the system.

Commercial reroofing involves more moving parts than most building owners expect, from the initial deck inspection through system selection, installation, and final quality checks, with the actual timeline shaped by the roof's size, condition, and the system chosen. King Koating has been providing commercial reroofing and roof waterproofing in Ontario for over 35 years, backed by COR certification and membership in the province's leading roofing associations. If you're planning a reroof and want a timeline specific to your building, we can walk you through what to expect.