Commercial Roof Installation and Replacement
Full tear-off and recover roofing for occupied commercial and industrial buildings across Toronto, the GTA and southwestern Ontario.
A commercial roof replacement in Toronto is either a full tear-off back to the deck or a recover over the existing membrane. The choice depends on how many roof layers are already in place, whether the insulation is wet, and the condition of the deck. NorthCan Roofing assesses all three before quoting. Call 416-456-0777.
Tear-off or recover: which does your building need?
This is the first decision in every replacement, and it changes the cost, the schedule and the disposal volume more than the membrane choice does.
Full tear-off
Everything above the deck is removed: membrane, cover board, insulation and vapour barrier. The deck is exposed, inspected and repaired, then a new assembly is built up from scratch. A tear-off is required when the insulation holds moisture, when the existing layers have reached the permitted limit, when the deck is suspect, or when the drainage has to be rebuilt with tapered insulation. It is the only approach that lets anyone actually see the structural deck.
Recover or overlay
A recover leaves the existing membrane in place and installs new insulation and a new membrane over it. It removes the disposal cost and the exposure risk of an open deck, and it is faster on a live building. It is only appropriate where the existing assembly is dry, the deck is sound and the number of existing membrane layers permits an additional one. A recover over wet insulation traps the moisture permanently and shortens the life of the new roof.
We settle this question with a moisture survey and test cuts, not with a look from the parapet. If you want that assessment as a standalone document first, order a commercial roof condition report.
What happens during the deck assessment?
The deck is the part nobody sees until the membrane is off, and it is the part most likely to change the scope mid-project. We assess it before quoting wherever the assembly allows, and we assess it again the moment it is exposed.
- Steel deck. We look for corrosion at the flutes, especially under long-standing wet insulation and under leaking rooftop units, and for fastener pull-through and elongated flute holes that will not hold new fasteners.
- Concrete deck. Spalling, delamination, previous patching and residual moisture, which matters because a fresh or damp concrete deck affects the vapour barrier and adhesive selection.
- Wood deck. Common on older Toronto commercial buildings. We check for rot at the perimeter and at drains, board gaps and deflection between joists.
- Structural concerns. Deflection, ponding that gets worse rather than better, and any doubt about capacity goes to a professional engineer. We are roofers, not the designer of record for the structure.
Deck repair is carried on the quote as a defined unit rate for the area actually found, so the price does not move on assumption. Where the deck is intact, that allowance simply is not used.
How is insulation brought up to current code?
When an assembly is torn off and rebuilt, the new assembly is designed to meet the Ontario Building Code requirements that apply to the building. In practice that usually means more insulation than the roof carried before, which has three consequences on your project.
- Height. A thicker assembly raises the roof surface. Base flashings, curb heights, door sills, mechanical unit curbs and parapet cap heights all have to be re-detailed so the membrane still terminates at an adequate height above the finished roof.
- Layering. Insulation is installed in two or more staggered layers with offset joints, so there is no continuous straight thermal and air path from the deck to the membrane.
- Drainage. Tapered insulation is designed to move water positively to the drains and away from the flat spots that caused the ponding in the first place. Crickets are built behind curbs and between drains. This is the single most valuable upgrade in most replacements, and it is easiest to do during a tear-off.
A cover board over the insulation protects the membrane from foot traffic, hail and fastener back-out, and gives the membrane a stable substrate. Below the insulation, a vapour barrier is selected to suit the interior humidity load, which matters a great deal on industrial buildings with wet processes. Those buildings are covered on our industrial roofing page.
How is a replacement phased over a working building?
We assume the building stays open. The phasing plan is part of the quote, not an afterthought.
- Sectioning. The roof is divided into areas that a crew can strip, insulate, membrane and terminate within a single working day. Nothing is opened that cannot be closed in.
- Daily water cut-offs. At every stopping point, the new membrane is tied into the existing roof with a temporary water cut-off so an overnight storm does not enter the building.
- Weather calls. Work stops before rain reaches the site, not after. Ontario shoulder seasons make this a daily judgement, and it is the foreman's call.
- Access and logistics. Crane or hoist placement, lane occupancy permits where required, staging areas, dumpster location and delivery timing are arranged with the property manager and communicated to tenants in advance.
- Interior protection. Where the deck is exposed above occupied space, we protect below and coordinate with your team about dust, noise and odour, particularly around fresh-air intakes, which are shut down or filtered during hot work.
- Safety. Guardrails or travel restraint at every open edge, controlled access zones and anchor points sized to the deck, in line with the Occupational Health and Safety Act and Ministry of Labour, Immigration, Training and Skills Development working-at-heights requirements. Fire watch is maintained after torch work stops.
WSIB coverage and certificates of insurance are provided on request.
Which system goes on the new roof?
System selection follows the building, not a preference. SBS modified bitumen gives a redundant two-ply assembly that tolerates heavy foot traffic and dense rooftop equipment. TPO and PVC are heat-welded single plies that cover large open fields quickly, with PVC chosen where grease or chemical exhaust lands on the roof. EPDM stays flexible in cold weather. Standing-seam and low-slope metal are covered under commercial metal roofing, and the full comparison of composition, seaming, cold-weather behaviour and failure modes is on flat roof types.
Whichever system is specified, the details are where roofs succeed or fail: cant strips at wall junctions, base flashing carried to an adequate height, cap flashing over the parapet, properly clamped roof drains with new lead or membrane flashings, scupper linings, pitch pockets replaced rather than re-caulked, and expansion joints that are allowed to move. Flashing work is described in detail on roof flashing and siding.
When is replacement the wrong answer?
Often enough that we say so. If the field of the roof is dry and intact and the problems are concentrated at a handful of details, a targeted repair programme buys real service life at a fraction of the disruption. See flat roof repairs. If the roof is sound but neglected, a maintenance agreement with scheduled spring and fall visits will do more for it than a capital project.
Replacement earns its place when moisture is in the assembly across the field, when the same areas are being repaired repeatedly, when the deck is deteriorating, or when a building change such as new rooftop equipment or a change of use makes the existing assembly unsuitable. For low-slope specifics, see flat roof replacement.
To budget before you commit, the roof cost calculator shows how the main variables shift the range. Then call 416-456-0777 for a free roof assessment and a written quote.
Frequently asked questions
How long does a commercial roof replacement take?
It depends on the area, the access and the weather. A single-section retail or office roof can be completed within a week; a large warehouse field runs in phases over several weeks. Ontario weather is the biggest variable, so we build the phasing plan around watertight daily stopping points rather than promising a fixed finish date.
Will tenants be able to work during the replacement?
In almost all cases yes. Noise is heaviest during tear-off and fastening, so we agree hours in advance with the property manager. Where torch-applied work is used near fresh-air intakes, those intakes are shut down or filtered for the duration and restored the same day.
Do you need a building permit to replace a commercial roof?
Sometimes. Permit requirements depend on the municipality and on whether the work affects the structure, the assembly type or the building envelope beyond a like-for-like replacement. We confirm the requirement with the local building department before starting and tell you what is needed on the quote.
What warranty comes with a new roof?
Two documents. A workmanship warranty from us covering our installation, and a manufacturer system warranty covering the materials as an assembly. The manufacturer warranty requires the specified components to be used together and usually requires documented maintenance. Both are set out in writing with the job.
Can you replace only part of a roof?
Yes, and it is common on large buildings that were built or re-roofed in stages. Sectional replacement works well when the sections are separated by an expansion joint, a wall or a level change. Where two areas drain into each other, we look closely at how the new and old membranes will be tied together.
What happens if you find a rotten deck once the roof is open?
It is measured, photographed and repaired at the unit rate already on the quote, so there is no renegotiation mid-job. Small areas are replaced in kind. Where corrosion or deflection suggests a structural issue rather than a local one, we stop and bring in a professional engineer before rebuilding over it.
Ready for your free roof assessment?
Tell us the address, the roof size and what you are seeing. We will book a time to get up there and put it in writing.
Call 416-456-0777 for anything urgent. Our emergency line is answered around the clock.
Call 416-456-0777