Apartment Building Roof Replacement: A Guide for Owners
How re-roofing a low-slope apartment building works in Ontario: when it is time, how the job runs with tenants at home, and which flat roof system fits.
Call 1-833-775-7663 Oakville head office · Flat roofs for residential, commercial, industrial and institutional buildings across Ontario
Karol Rajkowski
Vice President, OYH Roofing
Published October 1, 2026 · 7 min read
Short answer
An apartment building roof replacement in Ontario usually means removing the old low-slope roof in sections and installing a new membrane system while residents stay at home. Owners should plan it when leaks keep moving or a moisture survey finds wet insulation, not by age alone, and pick a roofer who plans safety, noise and access around tenants.
When does an apartment building need a new roof?
An apartment building roof replacement is due when the membrane itself has worn out, not just one flashing or one drain. The usual signs are leaks that show up in new places after each repair, wet insulation found in a moisture survey, and seams failing across the roof.
Age is a clue, not a verdict. Two roofs of the same age can be in very different shape, depending on drainage, foot traffic from service crews and how often the roof was inspected. The table shows what owners and property managers usually notice first, and what it tends to mean.
| What you notice | What it usually means | Usual next step |
|---|---|---|
| Stains or drips in top-floor units after heavy rain | Water is getting past the membrane at a seam, flashing or drain | Trace the leak; repair it if the rest of the roof is sound |
| Leaks come back in new places after each repair | The membrane is wearing out across the whole roof | Plan a replacement |
| Soft areas the roofer finds during an inspection | Wet insulation or a damaged deck under the membrane | Moisture survey, then replace the wet areas or the roof |
| Blisters, cracks or open seams in many places | The system is near the end of its service life | Budget for a replacement |
| Water still sitting on the roof two days after rain | Blocked drains, poor slope or sagging insulation | Fix the drainage; a re-roof can add tapered insulation |
If the problem is a single leak rather than a worn-out roof, start with a repair. Our guide to commercial roof leak repair in Toronto explains how leaks are traced and when repair stops making sense.
How does an apartment building roof replacement work with tenants at home?
An apartment building roof replacement is done in sections, so most of the roof stays covered at all times and every section is watertight before the crew leaves for the day. Residents usually stay in their units throughout.
Here is the usual order of work, in 7 steps:
- Inspect and test. The roofer checks the membrane, drains and flashings, and runs a moisture survey or core cuts to find wet insulation.
- Choose the system and scope. The owner decides on the membrane, the insulation and any drainage fixes, based on what the inspection found.
- Confirm permits and tell residents. The owner or roofer checks with the municipality whether a permit is needed (see our roof replacement permit guide), and residents get a written schedule.
- Set up safely. The crew sets up hoisting, a fenced work zone, protected entrances and fall protection that meets Ontario's construction safety regulation.
- Tear off and dry in, one section at a time. Old layers and wet insulation come off one area at a time, and each area is sealed the same day.
- Install the new roof and the details. New insulation and membrane go down, then flashings at parapets, curbs, vents and every drain.
- Inspect and hand over. A final walk-through with photos, a clean site, and the warranty documents for the owner's records.
| Concern | Why it happens | How it is usually handled |
|---|---|---|
| Noise | Tear-off and hoisting are loud | Work during set daytime hours, posted in advance |
| Odour | Torch-applied membranes, hot asphalt and some adhesives smell | Ask about low-odour options and plan around rooftop fresh-air intakes |
| Entrances and parking | Hoists and bins need space next to the building | Fence the work zone, keep one entrance clear, post notices |
| Rooftop units | Heating, ventilation and exhaust units sit on the roof | Plan shutdowns with the owner and the HVAC contractor |
| Rain during the job | Open roof areas can let water in | Open only what can be closed again the same day |
During an apartment building roof replacement, residents and building staff should never go up to look at the work. Roof access belongs to the crew, with proper fall protection.
Which flat roof system suits an apartment building?
Modified bitumen, TPO and PVC are the most common choices for an apartment building roof replacement in Ontario, and each one wins somewhere different. The right system depends on foot traffic, odour limits during the job, rooftop equipment and how much summer heat reaches the top floor.
| System | Where it wins on an apartment roof | Where another system wins |
|---|---|---|
| 2-ply modified bitumen | Two layers of protection; tough under foot traffic from service crews | Torch-applied versions need strict fire safety on an occupied building; a dark cap sheet takes in more summer heat |
| TPO | Hot-air welded seams and a white surface that reflects summer heat | A single layer; thicker 60 mil sheets suit busy roofs better |
| PVC | Welded seams; does not absorb ponding water | Usually costs more than TPO |
| EPDM | Stays flexible in cold weather; long track record | Seams are taped or glued, not welded |
On the residential building in Sault Ste. Marie shown here, OYH Roofing installed PVC with a 30-year warranty on labour and materials. On the City of Mississauga building at 3185 Mavis Rd, the crew installed IKO 2-ply modified bitumen with a 20-year system warranty.
Planning an apartment building roof replacement?
Tell us about the building and we will set up a free roof assessment and a written quote.
Call 1-833-775-7663Request an assessmentHow should owners plan the budget and timing?
Plan an apartment building roof replacement a season ahead, and get the inspection done before the quote, so the price reflects what is actually under the membrane.
| Factor | Why it changes the price |
|---|---|
| Roof size and shape | More levels, corners and parapets mean more detail work |
| Wet insulation | Every wet board found during tear-off has to be replaced |
| Layers to remove | Two or more old roofs mean more tear-off and disposal |
| Drains and slope | New drains or tapered insulation add material and labour |
| Rooftop equipment | Units may need lifting, new curbs or another contractor on site |
| Access and height | Crane or hoist time, street permits and protected entrances |
| System and warranty | Membrane type, thickness and the manufacturer's warranty terms |
Spring to fall is the usual season for an apartment building roof replacement in Ontario, when membranes and adhesives install best. Repairs and emergency work still happen in winter, with methods adjusted for the cold.
What residential roofing has OYH Roofing done?
OYH Roofing installed the roof on a new residential building in Sault Ste. Marie: 17,500 square feet of PVC with a 30-year warranty on labour and materials, the maximum warranty the company offers on any system.
The same crews work on commercial, industrial and institutional flat roofs across Ontario. One example is the 53,000 square foot recover in Mississauga, where the old roofing system was removed and a new 2-ply modified bitumen system went on. See the rest on the completed projects page, or read about our roofing services.
Frequently asked questions
My roof is 20 years old. Should I replace it?
Not on age alone. A 20-year-old low-slope roof that is dry and sound can keep going with repairs and twice-yearly inspections. One with wet insulation, failing seams or leaks that keep moving is usually due for replacement. A moisture survey and a few core cuts by a commercial roofer settle the question.
Is it more expensive to replace a flat roof?
Replacing a flat roof costs more up front than repairing one, because the old layers come off, wet insulation is replaced and every drain, curb and parapet is flashed again. Whether it costs more than a sloped roof of the same size depends on the system and access, so rely on a written quote after an inspection.
Who is responsible for the roof in a block of flats?
In Ontario it depends on how the building is owned. In a rental apartment building, section 20 of the Residential Tenancies Act, 2006 makes the landlord keep the building in a good state of repair. In a condominium, section 90 of the Condominium Act, 1998 makes the corporation maintain the common elements, which usually include the roof, unless the declaration says otherwise.
What are the building regulations for new roofs?
In Ontario, new roofs and re-roofing work must meet the Ontario Building Code, and the municipal building department decides whether a permit is needed for a given job. Changes to the structure, insulation or drainage can affect that answer, so check with your city before work starts. Roofers must also follow the province's construction safety rules.
Can tenants stay in the building during a roof replacement?
Tenants usually stay home during an apartment building roof replacement. The roof is replaced in sections and closed up at the end of each day, so units stay dry. Expect noise during tear-off, hoisting days, and limits on parking or entrances near the work zone, and give residents a written schedule.
Karol Rajkowski
Vice President · OYH Roofing
Karol Rajkowski is Vice President of OYH Roofing, an Oakville-based ICI flat-roofing contractor whose projects include the City of Mississauga building at 3185 Mavis Rd and the Marriott Hotel in Vaughan. Learn more about the OYH team.
Sources
- Residential Tenancies Act, 2006, section 20 (landlord's duty to repair), Government of Ontario.
- Condominium Act, 1998, section 90 (maintenance of common elements), Government of Ontario.
- Ontario's Building Code, Government of Ontario.
- O. Reg. 213/91, Construction Projects, under the Occupational Health and Safety Act.
- National Roofing Contractors Association (NRCA), guidance on low-slope roof inspection and maintenance.
- OYH Roofing project records: residential building, Sault Ste. Marie; City of Mississauga, 3185 Mavis Rd; Mississauga industrial recover (October 2026).
OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca