Flat Roof Repair Ontario | Commercial & Residential Flat Roofing

Professional flat roof repair across Ontario

Your flat roof isn't actually flat. It has a slight slope, usually a quarter inch per foot, just enough to move water toward drains. That minimal slope creates problems you don't see with pitched roofs.

Water sits longer on flat surfaces. Which means more time for it to find weak spots in seams, more opportunities to pool in low areas, and more weight on your structure when it doesn't drain properly.

Ontario winters make things worse. Water ponds during the day, freezes overnight, expands and cracks your membrane. Thaws the next day and seeps into those cracks. This cycle repeats from late fall through early spring, breaking down membranes that would otherwise last decades.

Here's the good news: most flat roof issues don't need full replacement. A commercial building leak doesn't automatically mean tearing off the entire roof. Ponding water on your garage usually gets fixed without structural work. Even widespread blistering can be addressed with coating systems at a fraction of replacement cost.

You just need contractors who specialize in membrane systems. Different materials need different repair methods. EPDM rubber patches one way, TPO heat-welds differently, modified bitumen requires torch work. Not every roofing contractor handles flat roofs properly.

Our network connects you with flat roof specialists across Ontario. They know membrane systems, drainage design, and how our climate affects these roofs.

Common flat roof problems in Ontario

Flat roofs fail in predictable ways. Catch problems early and you avoid expensive interior damage and structural issues.

Ponding water destroys flat roofs

Ponding water kills more flat roofs in Ontario than anything else. Water sits on your roof 48 hours or more after rain. Most people ignore it, thinking its just cosmetic. But its not.

Standing water breaks down your membrane every day it sits there. UV rays penetrate the water and attack the roof material. Algae grows. Plant matter accumulates. The membrane softens and weakens over time.

Winter makes it worse. Ponded water freezes solid. Water expands about 9% when it freezes. That expansion force splits membranes wide open. Spring arrives and you have leaks that weren't there before winter.

The weight alone damages your structure. Water weighs over 60 pounds per cubic foot. A 10-foot by 10-foot pond just 2 inches deep? That's over 1,000 pounds sitting on your roof deck constantly. Your structure wasn't designed for that kind of sustained water weight.

Ponding happens for several reasons. Insufficient slope during construction means water can't drain. Deck sagging under HVAC equipment weight creates low spots. Clogged drains can't handle water flow. Building settlement creates new depressions over time. Usually its a combination of these factors.

Ponding water cuts roof lifespan by 30% to 50%. A roof rated for 25 years might fail in 12 years if ponding isn't fixed.

Membrane damage from traffic and debris

Foot traffic damages flat roof membranes faster than most people realize. Every time an HVAC technician walks across your roof to service equipment, they're grinding dirt and debris into the surface. Winter cold makes membranes brittle. Walking on frozen membranes cracks them. You'll see visible wear paths on commercial roofs where people regularly access rooftop equipment.

Then there's falling debris. Tree branches that would bounce off a sloped roof pierce flat membranes. Hail creates tiny divots that collect water. Metal screws from toolbelts punch straight through. Wind-blown objects strike flat surfaces with full force.

Animal damage adds up. Raccoons scratch through membranes trying to access attics. Squirrels do the same. Once they create a small opening, water enters and damage spreads.

UV degradation breaks down membrane materials over time. White TPO reflects UV rays. Black EPDM absorbs them, taking continuous damage from sun exposure.

Seams and flashing fail first

Most flat roof leaks start at seams or flashing points. Not the main field, the connections between materials.

Seams separate over time. Heat-welded TPO seams fail if welding wasn't done properly. EPDM adhesive seams peel apart as adhesive ages. The main membrane might be fine, but open seams let water through.

Drain flashing deteriorates from constant water exposure. Rubber boots around drains dry out and crack. Water enters during every rain, rotting the deck underneath slowly.

Parapet wall transitions fail frequently. Where flat roofs meet vertical walls, the seal must be perfect. Caulk dries out. Metal flashing expands and contracts with temperature. Separation becomes inevitable.

Blistering and drainage issues

Blistering occurs when moisture or air gets trapped between membrane and deck. Bubbles form on the surface. They don't leak initially, but stepping on blisters creates punctures.

Drainage problems go unnoticed until serious damage occurs. Leaves and debris clog drains. Freeze-thaw cycles crack drain components. Some roofs have too few drains for their size, a design flaw from construction.

Older roofs shrink with age. Modified bitumen contracts. EPDM pulls away from edges when improperly fastened. Shrinkage creates stress at seams and penetrations, causing splits and tears.

Types of flat roofing systems

Before you can fix your flat roof, you need to know what type you have. Each system uses different materials and repair methods.

EPDM rubber roofing

EPDM is the black rubber membrane you see on most residential flat roofs and garages. Its been the standard for decades because it works reliably.

EPDM sheets come 45 to 60 mil thick, about the thickness of a nickel. You can get it fully adhered, mechanically fastened with plates and screws, or ballasted with rocks or pavers. Each method affects how repairs get done.

You'll get 20 to 30 years with regular maintenance. Ontario installation costs run $7 to $12 per square foot based on 2025 market rates.

EPDM typically fails at seams. Older systems used tape between sheets that eventually fails. Newer installations use liquid adhesives that last longer. Punctures from foot traffic or debris are common. Improper fastening causes shrinkage, pulling the membrane away from edges.

The good news? EPDM repairs are straightforward. Contractors patch holes with EPDM-specific adhesive, re-adhere separated seams, and replace failed flashing. EPDM repairs cost less than other membrane types.

TPO roofing

TPO is the white membrane you see on most commercial flat roofs. Its gaining popularity fast because those white surfaces reflect 85% to 90% of solar heat. Your cooling costs go down.

TPO thickness ranges from 45 to 80 mil. Unlike EPDM, TPO seams get heat-welded instead of glued. Technicians use hot air tools to melt and fuse the material together. When done right, those seams are stronger than the membrane itself.

Installation costs match EPDM at $7 to $12 per square foot in Ontario. You'll get the same 20 to 30 year lifespan too.

Where TPO fails: improperly welded seams. Wrong temperature or insufficient pressure during installation causes seam separation. Some older TPO formulations shrank, though modern versions fixed this issue.

TPO repairs require specialized heat-welding equipment. You can't just glue patches on. Repairs cost slightly more than EPDM but last longer when done properly.

Modified bitumen

This is an upgraded version of old tar roofs. You'll find it on commercial buildings and older flat roofs. It looks like flat asphalt shingles, either with a granulated surface or smooth black.

Modified bitumen goes down in layers, usually 2 or 3 plies. It can be torch-applied (where they use a propane torch to melt the bottom and stick it down), hot-mopped, or cold-adhered with adhesive. Lifespan is shorter than EPDM or TPO at 15 to 20 years.

These roofs typically fail at the seams between layers. Surface granules wear off where people walk a lot. Cold weather causes cracking. Flashing deteriorates faster than rubber membranes.

Repairs involve patching with matching modified bitumen, usually torch-applied. For roofs that are aging but not failing yet, you can apply a reflective coating to extend the life another 5 to 10 years.

Built-up roofing

This is the old-school "tar and gravel" roof. Multiple layers of asphalt and reinforcing fabric, topped with gravel or a flood coat of asphalt. You'll find these on older buildings, less common on new construction.

The lifespan varies wildly, 15 to 30 years depending on how many plies were installed. More layers means longer life.

These roofs are tough to repair properly. When they fail, its usually cracking and splitting throughout the surface, blistering between layers, or widespread gravel displacement exposing the asphalt underneath. Patching one spot doesn't solve the underlying aging problem.

Most contractors recommend replacing built-up roofs with modern EPDM or TPO systems rather than trying to repair them. It costs more upfront but you get a roof thatll last another 25 years.

Flat roof repair methods and solutions

The repair approach depends entirely on what's wrong and what type of roof you have. Here's how professionals fix the most common issues.

Patching punctures and tears

Got a hole in your membrane? A patch is usually the answer.

For EPDM roofs, the contractor cleans the damaged area thoroughly. Any dirt or moisture under a patch will cause it to fail. They apply EPDM primer, then install a patch using lap sealant or adhesive. They roll it down hard to make sure there are no air bubbles or gaps. The patch needs to extend at least 6 inches beyond the damage in all directions.

TPO repairs are more involved. The area gets cleaned with TPO-specific cleaner. Then the contractor cuts a patch and heat-welds it to the membrane using a hot air tool. After welding, they test the seams with a probe to make sure the weld is solid all the way around. If the probe can lift the edge, it wasn't welded properly and needs to be redone.

Patches installed correctly can last the entire remaining life of your roof. A patch on a 10-year-old roof that should last another 15 years? That patch should make it those 15 years.

Fixing separated seams

Seam repairs are some of the most common flat roof fixes. The technique depends on your roof type.

EPDM seams get re-cleaned and re-adhered with cover strips. The old adhesive or tape is scraped away, the surfaces are prepped, and new adhesive and a cover strip seal it back together.

TPO seams get re-welded. The contractor uses a heat gun to melt the separated seam back together. This actually fuses the material at a molecular level. When done right, you can't pull it apart.

Modified bitumen seams need torch work. The contractor torch-applies additional material over the failing seam.

Every seam repair gets tested. The contractor tries to separate it by hand. If it lifts, they redo it.

Flashing repairs at walls and penetrations

Most flat roof leaks happen where your roof meets something else. A wall, a drain, a pipe. These transition points are where problems show up first.

Parapet wall flashing fails because caulk dries out or the metal flashing pulls away. The fix involves removing the old flashing and installing new membrane flashing that extends 8 to 12 inches up the wall. Its then sealed and protected with metal counterflashing.

Pipe boots deteriorate from UV exposure. They crack and split, letting water pour in around the pipe. These get completely replaced. There's no fixing a cracked boot.

Drain flanges separate from the membrane over time. They can sometimes be re-sealed, but usually they need replacement. This is one repair you don't want to skip. A leaking drain can dump gallons of water into your building during every storm.

Coating systems that extend roof life

Your roof isn't failing yet but its showing age. Surface looks weathered, maybe some minor cracks. This is where coatings make sense.

A coating system is like giving your roof a new protective skin. Applied as a liquid, it forms a seamless waterproof barrier over your existing membrane. Done right, it can add 5 to 15 years to your roofs life at a fraction of replacement cost.

There are several coating types. Acrylic coatings are budget-friendly and easy to apply, lasting 5 to 7 years. Silicone coatings handle ponding water better than any other type and last 10 to 15 years. Urethane coatings are incredibly durable, perfect for high-traffic roofs. Aluminum coatings work specifically on modified bitumen, providing UV reflection.

Coating application isn't simple. The roof gets power washed first. Every repair gets done before coating. You're sealing the roof as-is, so any existing damage stays damaged. Some surfaces need primer for proper adhesion. The coating goes on at 10 to 20 mils thickness per coat, often requiring multiple coats. Temperature and humidity matter during application.

According to Ontario market rates for 2025, coating systems run $2 to $5 per square foot. For a typical 1,000 square foot flat roof, that's $2,000 to $5,000 versus $7,000 to $12,000 for a full replacement.

Roof restoration as an alternative to replacement

Got a roof with lots of small problems? Widespread minor membrane damage, failing flashings in multiple spots, some drainage issues? A comprehensive restoration might be your answer.

Restoration means fixing everything that's wrong, then coating the entire roof. All membrane damage gets patched. All flashings get replaced or re-sealed. Drainage problems get addressed. Then reinforcing fabric goes down in critical areas, followed by a complete coating system.

The cost is typically 40% to 60% less than full replacement. Instead of $15,000 to replace your roof, you might spend $7,000 to $10,000 to restore it. And you get another 10 to 15 years of life out of it.

Solving ponding water problems

Ponding water is the number one reason flat roofs fail early. You can't just ignore it and hope it goes away. It won't. You need to fix the underlying cause.

First step is figuring out why water ponds

A good contractor doesn't just patch the membrane under the pond and call it done. They diagnose why the water is ponding in the first place.

They'll measure the slope with a level. Flat roofs need at least a quarter inch of slope per foot. Less than that and water won't drain. They map out where water collects and how deep it gets. They check if you have enough drains and if they're working properly. They inspect the structure underneath for sagging or deflection. And they ask when the ponding started. What changed? New HVAC equipment added weight? Building settlement over time?

Without proper diagnosis, you're just treating symptoms.

Tapered insulation solves it permanently

This is the most common professional fix for ponding water, and it works.

Here's how it works. A contractor installs rigid insulation boards that get progressively thicker, creating a slope where one didn't exist before. These boards direct water toward the drains. Then a new membrane goes over the tapered insulation. You've eliminated the ponding without touching the structure underneath.

Cost for tapered insulation runs $6 to $12 per square foot installed in Ontario, depending on project size. For a 1,000 square foot roof with ponding issues, you're looking at $6,000 to $12,000.

The benefits are real. You permanently solve the problem. You add R-value to your roof, cutting heating and cooling costs. No structural work needed. And if your membrane was already near the end of its life, this incorporates a complete roof replacement with proper drainage from day one.

Adding more drains

Sometimes the problem is simple. You don't have enough drains, or the ones you have are too small for the water volume.

Adding drains in the ponding areas solves this. Install scuppers, those overflow drains that go through parapet walls, as backup. Upgrade undersized drains to handle more water. Cost runs $400 to $1,200 per drain installed, which is way cheaper than re-sloping the entire roof.

Structural reinforcement for sagging

If your deck is sagging under load, creating low spots where water collects, you've got a structural problem. This needs an engineer.

The fix involves adding support below the deck. Sister joists to the existing ones. Add beams. Shore up the structure so it doesn't deflect. This is the most expensive option, but sometimes its the only real solution. The roof surface might be fine, its the structure underneath that's failing.

Ponding water coating as a temporary fix

Got minor ponding and a tight budget? Silicone coating can buy you time.

Silicone coatings are specifically designed to sit in ponding water without degrading. Unlike other coatings, they don't break down when submerged. This extends your roof life 5 to 10 years at $2 to $4 per square foot.

Just understand this isn't fixing the ponding. The water still sits there. You're just protecting the membrane from the damage that ponding causes. Its a band-aid, not a cure.

The cost of waiting

Here's what happens if you ignore ponding water:

Year 1 or 2: A simple coating solution might work for $2,000 to $5,000. The membrane is still intact, just starting to show stress.

Year 3 to 5: Now you've got membrane damage. Patching plus coating runs $5,000 to $12,000. The ponding has done real harm.

Year 6 to 8: Serious deterioration. You need tapered insulation now. Cost: $12,000 to $25,000. What could have been fixed cheaply is now a major project.

Year 9+: Complete replacement required. $15,000 to $40,000 or more, depending on roof size. The ponding has destroyed your roof.

Act early. Its always cheaper.

Emergency flat roof repairs

Water pouring through your ceiling? That's an emergency. Flat roofs leak fast when they fail, and interior damage adds up quick.

When you need emergency service

Some situations can't wait until Monday morning.

Active leaks during rain are obvious emergencies. Water is coming in right now, damaging whatever's underneath. Large punctures that expose the interior need immediate attention. Every hour of exposure risks more water damage. Storm damage from wind or hail that compromises the roofs integrity. Clogged drains causing water to back up and overflow. HVAC service that accidentally punctured the membrane.

These aren't situations where you schedule an appointment for next week. You call for same-day service.

What emergency repairs look like

Emergency contractors focus on one thing: stopping water from getting in. Permanent repairs come later.

They might tarp the damaged area with heavy-duty material, secured so it doesn't blow off in wind. They'll apply quick patches to stop active leaks. These aren't pretty, but they work. Clogged drains get cleared immediately to stop water backup. Fast-curing sealants go on failing flashings to stop the immediate leak.

Based on 2025 Ontario rates, emergency service typically runs $500 to $3,500 depending on the severity and urgency. Some contractors add after-hours surcharges of 20% to 50% for night and weekend calls. Then you pay for the permanent repair after they assess the full damage.

How to avoid flat roof emergencies

Most emergencies are preventable with basic maintenance.

Get your roof inspected twice a year, spring and fall. A professional inspection costs $150 to $400 but catches problems before they become leaks. Clear your drains after storms. Leaves and debris clog them up fast. Fix minor issues immediately instead of letting them sit. A $300 patch today prevents a $3,000 emergency next month. Install protective walkway pads where people regularly walk to access equipment. They cost almost nothing and prevent most foot traffic damage.

Flat roof repair costs in Ontario (2025)

Flat roof repair costs vary wildly based on what's wrong, your membrane type, and how big your roof is.

Prices reflect 2025 Ontario market rates for typical residential flat roofs (500-1,500 sq ft). Commercial projects often get better per-square-foot rates.

Cost factors affecting final price

TPO repairs cost more than EPDM because they require heat-welding equipment. Not every contractor has it. Accessibility matters too. A high roof or one that's hard to reach adds to labor costs. Winter repairs in Ontario run 10% to 20% more because materials don't work as well in cold and conditions are harder. Emergency service adds 20% to 50% depending on urgency and timing.

The biggest cost variable? Whether there's underlying structural problems. A membrane patch might be $400. But if your deck underneath is rotted and needs replacement, you're suddenly looking at thousands more.

Repair vs replacement decision

Sometimes fixing your flat roof doesn't make sense. Here's how to know which way to go.

When repair is the right call

Your roof has plenty of life left. You're less than halfway through its expected lifespan. The damage is localized, maybe a puncture here, a failed seam there, but less than 25% of the total roof surface. The membrane itself is still in good shape, not brittle or cracking all over. You don't have major ponding water issues. Your budget is tight and you need to defer a bigger project for a few years. Or your roof is under 10 years old and still under warranty.

In these situations, repair makes total sense. You get more years out of an otherwise sound roof without the big expense of replacement.

When replacement is actually cheaper long-term

Your roof is 15 to 30 years old, approaching or past its expected lifespan. Damage is widespread, 30% or more of the surface has problems. You're looking at multiple repairs across the entire roof. There's significant ponding water that requires re-sloping. The membrane is brittle, cracking, or severely degraded everywhere you look. The cost of repairs is approaching 50% of what replacement would cost. And you plan to own the building for another 10+ years.

In these cases, replacement is the smarter financial move. You're throwing good money after bad trying to keep a failing roof alive.

Real numbers example

Let's say you've got a 1,200 square foot EPDM flat roof that's 18 years old with ponding water problems.

Repair option: Patch the damaged areas for $800. Apply silicone coating to handle the ponding for $4,000. Fix the failing flashings for $1,200. Total cost: $6,000. You'll get maybe 5 to 7 more years out of it. That's $860 to $1,200 per year.

Replacement option: Complete EPDM replacement with tapered insulation to fix the ponding permanently: $15,000. Expected lifespan: 25 to 30 years. That works out to $500 to $600 per year.

Replacement costs more than twice as much upfront. But its actually cheaper annually and you never have to deal with that ponding water again. Plus you get a roof thatll outlast your ownership of the building.

Frequently Asked Questions