Installing a new flat roof on a commercial building isn’t just about materials or price tags – it’s about everything that leads up to that decision. And honestly, the success of the roof has more to do with what happens before installation day than during it. A rushed plan, skipped prep steps, or unclear long-term goals? That’s where most failures start. In this post, I’ll break down five key things to think through before the first roll of membrane touches your rooftop. Whether you’re replacing a failing system or starting from scratch, these considerations can mean the difference between a roof that performs for 25 years – or one that causes headaches after year two. Planning matters more than most realize, especially in Ontario’s climate.
Understand the Purpose of the Building
This sounds basic, but it’s huge. Not every commercial roof needs the same thing. A grocery store with HVAC units and foot traffic needs a different system than a low-use warehouse. A factory pushing out heat and vibration needs something sturdier than a daycare center. The roofing material should match the activity happening underneath it.
For example, if your building generates heat (from ovens, exhaust, or heavy machinery), you’ll need a membrane that can handle thermal movement without shrinking or cracking. If foot traffic is expected – say for servicing rooftop equipment – walk pads and reinforced sections should be part of the plan. During our flat roof inspections, we often find mismatched materials because someone chose based on price – not function. That almost always backfires.
Start by listing out what the building is used for, what’s mounted on the roof, and whether tenants or staff ever need to be up there. It’ll shape every decision that follows.
Drainage Strategy Can’t Be an Afterthought
Flat roofs don’t drain by default – they require design. And if you don’t factor that in before installation? You’ll be living with ponding water, frozen drains, and structural load problems for years. We’ve seen buildings that installed new membranes beautifully… but left old, poorly-placed drains in place. It never ends well.
Before installation, we evaluate the slope. Some roofs may need tapered insulation added to improve flow toward scuppers or drains. Others might require new drain placements entirely. Ontario’s freeze-thaw cycles are brutal on standing water. What seems like a minor puddle in September becomes a solid ice patch in February – which expands, contracts, and starts opening seams.
Our flat roof replacement projects always include drainage assessment as a required step – not an optional add-on. It’s one of the few things that, if ignored, can ruin an otherwise solid install.
Choose Materials Based on Lifecycle – Not Just Price
It’s tempting to go with the cheapest material on the quote. We get it – commercial roofs are a major cost. But cheaper up front often means higher costs later. The goal isn’t the lowest bid. It’s lowest cost over the entire life of the roof.
TPO, EPDM, modified bitumen, PVC – they all have different lifespans, maintenance needs, and strengths. A white TPO roof might help with cooling loads in the summer, but might not perform well if exposed to sharp temperature swings and mechanical stress. Modified bitumen? Great for durability and repairs, but a bit heavier and needs experienced installers.
If your building is in a high-traffic zone or will have solar installed later, you need to choose with those future plans in mind. We walk clients through material pros and cons during every commercial roofing installation job. It’s not about pushing a product – it’s about making sure you know what’s actually going to work for your roof over the long haul.
Plan Around Access, Equipment, and Installation Conditions
Every building is different – and so is every rooftop. Before a single roll of membrane gets installed, you need to think about logistics. Can installers access the roof easily? Will lifts or cranes be needed to get materials up? Are there safety railings, or do they need to be added first? These factors can all affect install timelines and costs.
We’ve had projects in tight downtown areas where staging had to happen in shifts. Others where power lines or rooftop equipment had to be temporarily rerouted. These things need to be known in advance – not discovered halfway through the job. If your rooftop has outdated or abandoned units sitting there, decide whether they’re being removed or worked around. We cover all this in our maintenance and pre-project inspections so there are no surprises once install begins.
Also – look at the weather. Installing during the wrong season can delay timelines, mess with adhesives, or reduce membrane bonding. Spring and fall are ideal in most cases, but every roof and every year is a little different.
Think About Long-Term Maintenance Before Day One
This is where a lot of projects fall apart. Everyone focuses on getting the roof installed – but no one thinks about maintaining it. A flat roof should come with a plan, not just a warranty. What’s your inspection schedule? Who checks the drains? Are tenants allowed to access the roof? If not – who’s responsible for reporting damage?
We offer scheduled flat roof maintenance plans that kick in right after install. It’s not an upsell – it’s basic common sense. Most warranties require proof of maintenance to stay valid anyway. If no one’s watching the roof, little problems go unnoticed – and turn into big ones.
One office building we worked with in Richmond Hill had a new TPO roof installed… but skipped maintenance for three years. A simple clogged drain cracked the membrane during a deep freeze. Insurance denied the claim due to lack of upkeep. A $9,000 repair could’ve been avoided with one spring visit.
Final Thoughts – Don’t Let Planning Be the Weak Link
Flat roofs work. They perform well when designed properly, installed carefully, and maintained consistently. But they fail when any one of those steps is rushed or skipped. If you’re thinking about a new flat roof, take time on the front end. It’s the boring prep that saves you from expensive surprises later.
Need help sorting through materials, specs, or what your building really needs? Our team handles flat roofing across Toronto, Vaughan, Mississauga – and beyond. We’ll walk the roof with you, ask the right questions, and help you plan for success.
Start with a proper inspection and consultation. It’s the smartest step you can take – before a single tool hits the roof.