Flat Roof Repairs in Toronto: The Most Common Problems and How to Avoid (Or Fix) Them

Commercial flat roof repairs can be a significant concern for any Toronto landlord, property manager, contractor or tenant. No one wants to deal with the hassle and expense of membrane punctures, soiled insulation, abandoned HVAC equipment and other flat roofing issues.

Unfortunately, these are facts of life when you own, manage or rent a commercial property with a flat roof. Critical advice includes regular maintenance of flat roofs, prompt repairs and having the roof professionally inspected at least twice a year.

Here is our list of the most common flat roof repairs we see with our clients in the Greater Toronto Area. We’ve also included helpful tips on how to avoid them and address any necessary repairs.

Steps you should always take for flat roof repairs

Before moving on to the most common flat roof repairs we see with our Toronto clients, here are essential tips for protecting the roof and ensuring its performance. You should always: 

• Conduct periodic visual inspections of your commercial roof and schedule professional inspections twice a year.
• Perform ongoing commercial flat roof repairs promptly.
• Always make sure your flat roof remains clear of debris.
• Select high-quality materials and use them according to the manufacturer’s instructions.
• Plan for flat roof access and minimizing foot traffic.
• Ensure all repair materials are compatible with the current roof membrane and components of the existing assembly.
• Be transparent and do not hide or fail to repair active leaks or impact damage when they occur.

1. Damaged BUR membranes, including splits, ridges and blisters

Common damage to BUR (built up roofing) membranes includes splits, ridges and blisters. Some typical causes include normal wear and tear, aging, off gassing and poor installation. Risks include water infiltration, accelerated deterioration, reduced thermal efficiency and mould growth in insulation.

How to avoid flat roof damage:

• Ensure an even application of each layer of membrane, fully bond it to the layer below and distribute the weight properly.  Also, ensure that the roof membrane is not directly exposed to the sun’s ultraviolet rays.

Flat roof repair tips:

• Cut, dry and patch small splits, ridges and blisters with compatible BUR materials.
• Repair splits and ridges by removing, patching or re-fabricating the ply layers.  
• If there is wet insulation then, according to best trade practice, it should be cut out and replaced with new dry material.
• Re-instate stone ballast, if and as required.

2. Holes in TPO membranes

TPO membranes are vulnerable to a variety of issues, including punctures, thermal expansion, foot traffic and aging.

How to avoid flat roof damage:

• Install walkway pads at traffic routes, ladders (top and bottom), exit doors and around HVAC equipment, 
• Use protective mats on work areas and limit foot traffic.
• Ensure seams, corners and flashings are properly installed.

Flat roof repair tips:

• For small punctures, clean the membrane with a TPO cleaner or mild soap and water and repair them with hot air welded TPO membrane of sufficient size, which should extend a minimum distance beyond the hole(s) on all sides.
• Use a silicon roller for a tight bond.
• For larger holes, consider removing and replacing a larger section of membrane.
• If there is wet insulation then, according to best trade practice, it should be cut out and replaced with new dry material.

3. Improperly sized tall cones

Installing a new high-efficiency exhaust system creates risks related to sizing tall cones. A mismatch in size or configuration may result in poor sealing around the penetrations that cause water infiltration, membrane damage, condensation and code violations.

How to avoid flat roof damage:

• Always remove and replace the original chimney exhaust vent and tall cone and install all-new flashing and seals around it, accurately match the new exhaust dimensions and slope and measure for the proper height.  Do not run the newer smaller diameter (due to higher efficiency) chimney exhaust inside the original vent.
• Coordinate with the mechanical installer for installation of the proper chimney vent, cap and storm collar, as needed.

Flat roof repair tips:

• Carefully remove the old cone, install a correctly sized cone and flashing boot, and re-flash the penetration.
• It may be necessary to close a portion of the deck substrate opening and insert insulation at voids.
• Use a compatible roof membrane to ensure watertightness and proper bonding of new and original materials including proper surface preparation and an appropriate primer, where applicable.

4. Damaged membrane and soiled insulation on BUR roofs

Soiled insulation can cause leaks, accelerated deterioration, reduced energy efficiency, mould and mildew, rot or corrosion, accelerated deterioration, damage to the interior and possibly overloading the roof assembly or structure.

How to avoid flat roof damage:

• Hire a roofing contractor to identify the leak source and locate wet areas.
• Remove compromised areas of the roof membrane and replace the soiled insulation.
• Check the surrounding areas. 

 Flat roof repair tips:

• Identify the damage through visual inspection, core cut(s) and an infrared scan (if needed).
• Cut out and remove the damaged membrane and soiled insulation
• Insert new dry insulation to match the existing stock and thickness
• Rebuild the layers of the BUR membrane, reinforce seams and apply a flood coat of hot asphalt and install ballast (where applicable) .

5. HVAC unit(s) on sleepers with duct curbs

HVAC units may be installed on sleepers with duct curb(s) penetrating through a flat modified bitumen or BUR roof. Challenges may include limited access below the HVAC units and sleeper movement with thermal expansion and contraction. Over time, a breach in the roof membrane can lead to rotting of the wood sleepers.

How to avoid flat roof damage:

• Use metal sleeper copings to protect the membrane from damage, weathering and to improve longevity.
• Add new mechanical/electrical flashings, where appropriate, for cable or pipe penetrations.
• Coordinate with other trades, including HVAC and refrigeration contractors for connections and lifting of equipment.
• Install new membrane and seals around all penetrations, and terminations.
• Allow for thermal movement of the unit and sleepers when detailing the membrane.

 Flat roof repair tips:

• Coordinate with the HVAC team to handle all connections of duct work, gas piping and electrical wiring.
• Inspect the insulation and deck for damage or moisture, replacing it as needed.
• Temporarily seal exposed duct curbs and lines to prevent water intrusion during repairs.
• Repair damage around the sleepers.
• Seal sleeper ends and transitions.
• Ensure that all terminations are secure. Seal any edges, corners, or penetrations as needed.

6. Replacing a flat roof drain, including plumbing connections by others

Replacing a roof drain requires coordination between roofing and plumbing trades. If not organized properly, there is a risk of membrane damage, ponding or leaks.  

How to avoid flat roof damage:

• Ensure the drain bowl is secure and check watertight seals at pipe connections.
• Plan and coordinate with the plumber on drain location, size, and scheduling. Make sure the plumber doesn’t remove the old drain until the roofer temporarily seals the opening.
• Use drain inserts to temporarily cover during bad weather or plumbing delays. 
• Install a drain sump or tapered insulation if needed to prevent ponding.
• Properly clamp or bond the membrane into the drain.
• Ensure that there is no backfall on the rain water leader inside the premises

 Flat roof repair tips:

• Repair and protect the roof before and during work.
• Check and prepare the substrate, replace wet insulation, and repair any damaged roofing or deck substrate panels.
• It may be necessary to close a portion of the deck substrate opening and insert insulation at voids.
• Water test the drain, checking for leaks around the pipes, ponding, fast draining and tight seals to the edge of the membrane.
• Use copper/cast iron drains wherever possible, complete with cast aluminum or cast iron drain baskets instead of plastic drain baskets ones that don’t survive Canadian winters and the freeze/thaw cycle.

7. HSS steel post penetrations

HSS (hollow structural section) is steel tubing that penetrates the roof system to support items such as posts, railings, equipment frames or screens. Typical flashing methods include chem curbs, SBS modified bitumen and PMMA flashings such as ALSAN and PermaFlash. Challenges include the post being rigid, lacking the proper flashing boots or pre-installed curbs, and contraction and expansion from temperature changes.

How to avoid flat roof damage:

• Never leave the HSS tubing open at the top to prevent rust from the inside out.
• Use galvanized or stainless steel for long-term durability in exposed conditions.
• Provide at least 8″ of vertical clearance between membrane and termination if possible.
• Always check for movement potential and coordinate with a structural engineer as appropriate to securely anchor the post.
• Ensure that condensation holes are drilled into the HSS posts to prevent condensation problems in the winter months. 

 Flat roof repair tips:

• Use a professional roofer to identify problems like rust, dents and leaks at the penetration site(s), cracked welds at base plates or attachments, misalignment, and water intrusion inside the post(s).
• Choose an installation method that is compatible with the roof membrane. The main methods used on BUR flat roofs in Toronto are:
  • Chem curb type products: Use brands such as ChemCurb when traditional flashings aren’t feasible such are when the wire or pipe is already in place and cannot be disconnected..
  • Cold-applied systems: ALSAN’s Soprema and Johns Manville’s PermaFlash together with fleece are liquid applied membrane solutions.
  • SBS modified bitumen membrane: Membrane can be installed onto the HSS post after it is coated with an asphalt primer.

• Repair the membrane around the post.

8. Abandoned flat roof curb removal with substrate repair

A roof curb or tall cone from a removed HVAC unit, exhaust fan or skylight that is no longer in use must be completely removed to avoid water infiltration and damage to the roof system, damaged insulation, and roof deck, air and energy leaks, and structural risks.

How to avoid flat roof damage:

• Ensure that roof inspections are carried out when tenant’s vacate their premises to ensure that the base building condition is restored. TIP: if this is done prior to the tenant vacating the premises then the work might be done at the tenant’s cost or set off against the amount remaining as a security deposit, subject to the terms of the lease agreement.
• Coordinate with a structural engineer if large penetrations or curb removal may affect load distribution, as needed.

 Flat roof repair tips:

• Coordinate with the HVAC team to handle all connections of duct work, gas piping and electrical wiring, if needed.  Any duct penetrations below the roof line should be removed and disposed of by others prior to the roofing crew mobilizing on site.
• Repair the openings in the deck substrate in a professional manner.
• Rebuild the roof layers and perform a final sealing.
• Thoroughly inspect the areas to ensure that membrane laps are watertight, and reinforce or apply ballast/granule, if and as needed.   
• Coordinate with a structural engineer if large penetrations or curb removal may affect load distribution.

 9. High parapet wall upturns with metal termination into a reglet

• When working on a high parapet wall upturn, the roof membrane termination can’t be left exposed. 
• The upturn must run vertically up the parapet wall, terminated with a metal counterflashing and should be inserted into a reglet (this is best practice) —a groove that secures the flashing and waterproofing system.

How to avoid flat roof damage:

• Ensure the counterflashing is properly anchored and braced if needed.
• Leave an air gap or weep area if required by specifications.
• Watch for any reglet sealant degradation.

 Flat roof repair tips:

• Remove damaged components, clean out the reglet, remove old sealants, and chase or recut the reglet if it has deteriorated.
• Extend the new membrane upturn to the required height.
• Secure a compatible termination bar.
• Install metal counterflashing with a drip edge. Securely insert it into the reglet using appropriate wedges, fasteners and sealants.   
• Inspect the membrane for gaps or missed sealant areas.

10. Low parapet membrane repairs requiring the removal of metal copings

A low parapet wall typically has metal copings that cover the top of the wall to protect it from weather damage and water infiltration. Over time, these copings may need to be removed for repairs, maintenance, or replacement of the underlying membrane or structure. 

How to avoid flat roof damage:

• Use corrosion-resistant materials such as pre-painted 8000 Series steel with a gauge of 26 or lower.
• Check the flashing and coping alignment to prevent water infiltration.
• Provide adequate drainage along the parapet to avoid pooling/seepage at the locks in the metal coping.
• As a design consideration, ensure that the top of the parapet wall is sloped towards the roof.

 Flat roof repair tips:

• Inspect the parapet wall for structural integrity, cracks, loose masonry, or water damage.
• Repair or replace damaged sections.
• Carefully detach the metal copings, inspecting for rust or corrosion.
• Repair the parapet wall or membrane to ensure wall upturns are intact, sealed against the wall, and fully integrated with the membrane.
• Install new metal copings or re-install existing ones, carefully aligning and securing them, a proper overhang to shed water, continuous hook strip and fasteners that allow for some expansion and contraction.
• Apply a waterproof sealant around the edges of the coping, where required.

Call Elite Roofing for inspection and repair of your flat roof.

All commercial flat roofs will need repairs as they age, but there are steps you can take to avoid some of the most common problems. Always use an experienced, knowledgeable roofer who will provide sound advice that meets your objectives and criteria. Get the #EliteAdvantage by hiring our superior craftsmen, taking advantage of your emergency repairs, and acting fully transparently.  

Frequently Asked Questions about Flat Roof Repairs in Toronto

Q: How can I tell if my flat roof needs repairs?

A: There are a few signs to look for, such as active leaks, staining on exterior/interior walls, ponding water, damaged membrane, abandoned equipment and more.

Q: How long does a flat roof repair take?

A: The duration of a flat roof repair depends on the extent of the damage. Minor repairs could take at least a half day, whereas more extensive repairs or issues could take longer to address properly.

Q: Can I perform flat roof repairs myself?

A: We always recommend hiring a professional, licensed contractor for flat roof repairs to properly address any specific issues and ensure safety.

Q: What sets Elite Roofing apart in flat roof repairs?

A: Elite Roofing offers experienced craftsmanship alongside high-quality roofing materials tailored to your commercial flat roof building and the Greater Toronto Area’s unique climate. We don’t cut corners or take the easy way out. We work with you to ensure that you are fully satisfied with your new roof or flat roof repairs. That’s the #EliteAdvantage.

Q: Can I schedule a flat roof inspection with Elite Roofing before committing to repairs?

A: Yes. You can schedule your flat roof inspection with Elite Roofing by contacting us through our website or giving us a call at 888-710-3797. 

Q: What are the most common causes of flat roof damage?

A: Flat roof damage often results from poor drainage, UV exposure, membrane aging, harsh weather conditions, and improper installation. Regular inspections can help catch these issues early.

Q: Is it better to repair or replace my flat roof?

A: It depends on the age and condition of the roof. If the roof is nearing the end of its lifespan or has widespread issues, replacement might be more cost-effective. Elite Roofing can help assess your roof and recommend the best course of action.

Q: How often should I have my flat roof inspected?

A: At minimum, your flat roof should be inspected twice a year—typically in the spring and fall—and after major storms. Regular inspections help extend the life of your roof and prevent costly repairs.

Q: What types of flat roofing systems does Elite Roofing work with?

A: We work with a range of commercial flat roofing systems including TPO, EPDM, modified bitumen, and built-up roofing (BUR). Our team will recommend the best system for your building’s specific needs and climate conditions.

Q: Will flat roof repairs disrupt my business operations?

A: At Elite Roofing, we understand the importance of minimizing downtime. Our team works efficiently and can schedule repairs during off-hours or weekends when possible, ensuring minimal disruption to your daily operations.