Rooftop Equipment on a Flat Roof: Protect the Roof Below
Curbs, clearances, walkways, weight and warranties for a commercial roof that carries HVAC units.
Call 1-833-775-7663 Oakville head office · Roofing, repairs and re-roofing around rooftop equipment across Ontario
Karol Rajkowski
Vice President, OYH Roofing
Published October 14, 2026 · 10 min read
Short answer
Rooftop equipment needs a roof built around it: units on curbs fixed to the deck, flashings at least 200 mm high, separate flashings for every pipe, enough clearance to reroof under stands, walkways on service routes, and an engineer's check before heavier equipment goes up. Penetrations are the most vulnerable spots on any flat roof.
What does a flat roof with rooftop equipment need?
A roof with rooftop equipment needs seven things that a bare roof does not: solid curbs, high flashings, clean penetrations, room to work under units, drainage around curbs, protected walking routes and a structure checked for the extra weight. Each one comes from Canadian roofing practice or the Building Code.
| Rule | What it means | Who says so |
|---|---|---|
| 1. Fix curbs to the structure | Curbs sit on the deck or on solid blocking, never on top of the insulation and membrane | CRCA, RCABC |
| 2. Keep curbs and flashings high | CRCA recommends curbs at least 300 mm high and flashings at least 200 mm above the finished roof | CRCA |
| 3. Flash every penetration on its own | Pipes kept apart and flashed one by one; sealant pockets only as a last resort | RCABC |
| 4. Leave room to reroof under stands | Curbs are preferred; units on stands need enough height to repair and replace the roof below | NRCA |
| 5. Drain water around curbs | Crickets on the high side of curbs, required on every replacement roof under RoofStar | RCABC |
| 6. Protect the service routes | Walkway pads or pavers around units and along access paths | CRCA, RCABC |
| 7. Check the structure first | Permanent equipment is part of the dead load, and tall equipment collects drifting snow | Building Code |
Why does rooftop equipment cause roof leaks?
Because every unit, pipe and cable is a hole in the roof, and every visit to service it is foot traffic on the membrane. The Canadian Roofing Contractors Association (CRCA) calls penetrations the most vulnerable locations on the roof and among the major causes of roofing problems.
The equipment itself can leak too. CRCA's bulletin on rooftop equipment warns that wind-driven rain gets into unit casings and drops through the curb opening, and that a unit that is not level can overflow its condensate pan inside the building. Neither leak comes through the membrane, so a roofer should rule them out before cutting the roof open; our flat roof leak detection guide explains how.
Heavy equipment raises the stakes. The Roofing Contractors Association of British Columbia (RCABC) notes that leaks beneath a heavy structure cannot be repaired without considerable expense to the owner, which is why the details under and around equipment matter more than anywhere else on the roof.
What is the recommended height for a roof curb?
At least 300 mm (12 in.), says CRCA, with the membrane flashing carried at least 200 mm (8 in.) above the finished roof. RCABC's RoofStar standard, used in British Columbia, sets 203 mm (8 in.) from the finished roof surface as the minimum for curbs, sleepers and equipment pads.
The height has to survive the roof that is built around it. CRCA's bulletin points out that a curb fastened directly to the deck can end up well below 300 mm once thick or tapered insulation goes in, so curbs belong on solid wood blocking cut flush with the top of the insulation. RCABC adds that curbs must be secured to the deck or to blocking and must not sit on top of the roof system.
| Detail | Minimum | Source |
|---|---|---|
| Curb height | 300 mm (12 in.) recommended | CRCA |
| Membrane flashing up a curb or wall | 200 mm (8 in.) above the finished roof | CRCA |
| Curbs, sleepers, equipment pads | 203 mm (8 in.) above the finished roof | RCABC |
| Fully wrapped curbs and sleepers with nothing through the top | 102 mm (4 in.), or 127 mm (5 in.) with a metal cap | RCABC |
| Sealant pockets around gas and electrical lines | 102 mm (4 in.) tall, and only where unavoidable | RCABC |
| Space between penetrations, curbs and walls | 305 mm (12 in.) on new roofs | RCABC |
Water also has to get past the curb. RCABC requires crickets, small sloped saddles on the high side of a curb, on all replacement roofs, and on new roofs for curbs and sleepers longer than 1,219 mm (48 in.). Our roof flashing repair guide covers how curb flashings fail and how they are fixed.
How should equipment on stands, pipes and cables be supported?
High enough that the roof under them can be repaired and replaced. The National Roofing Contractors Association (NRCA) prefers curbs to support stands for that reason, and says a unit on stands should sit high enough above the roof to allow roofing work and repairs beneath it.
Ontario's Building Code does not set a clearance. Florida's building code, as one example, ties it to the unit's width, from 14 in. under units narrower than 24 in. to 48 in. under units wider than 60 in. For a building in Ontario, the practical test is NRCA's: can a roofer reach the membrane under the unit without moving it?
Pipes and cables follow the same idea. RCABC asks for each penetration to be flashed on its own, rules out open-top flashings filled with sealant, and treats sealant pockets as a last resort. Electrical cables above the roof should be raised on supports so the roof can be maintained and replaced under them.
How much weight can a flat roof support?
As much as it was designed for, and only an engineer can say how much more it can take. Ontario's Building Code designs a roof for whichever is most critical: a uniform load of 1.0 kPa (about 21 lb per sq ft), a concentrated load of 1.3 kN on a 200 mm square, or the local snow and rain load.
In most of Ontario the snow load is the largest of the three; our flat roof snow load guide lists the values by city. Equipment adds to it in two ways. The code counts the weight of permanent equipment as dead load, and it requires the designer to allow for snow drifting against roof-mounted projections, except small ones less than 3 m long.
That is why a heavier replacement unit or a new solar array starts with the structure. Ontario's Ministry of Labour warns that solar panels on an existing flat roof may place considerable loads on a structure not designed for them, and Toronto requires structural calculations by an Ontario registered engineer for rooftop solar larger than 5 m².
What should you check before adding or replacing a rooftop unit?
Four things: the structure, the roof warranty, the permit and who does each part of the work. The warranty is the step owners miss: every commercial roof warranty we checked can be voided by equipment added without the maker's approval.
| Check | What to confirm | Source |
|---|---|---|
| Structure | An engineer confirms the roof can carry the new or heavier equipment and the snow that drifts against it | Building Code |
| Roof warranty | Written approval from the roof's maker before equipment, curbs or penetrations are added. IKO asks to be contacted before new curbs, penetrations, rooftop units or solar | Sika Canada, IKO, Carlisle, Elevate |
| Flashing | The maker's approved roofer cuts and flashes the roof, not the equipment installer | Sika Canada, Carlisle, Johns Manville |
| Permit | Toronto issues stand-alone mechanical (HVAC) permits that ask for the type, location and size of the equipment; new developments in Mississauga must screen rooftop units through site plan review | City of Toronto, City of Mississauga |
| Gas work | Only a certified gas technician may install, service or remove a gas appliance; a G.2 holder covers appliances up to 400,000 Btuh | O. Reg. 212/01, 215/01 |
Sika Canada's maintenance bulletin puts it plainly: do not let equipment servicemen penetrate the roof unless qualified personnel flash the penetrations, and tell Sika before the roof is cut. Our roof replacement permit guide covers when roofing work itself needs a permit, and the commercial roof warranty guide explains what each warranty type covers.
How is a roof replaced around rooftop equipment?
By planning the equipment work as part of the roofing job. Units are disconnected by licensed trades and lifted where needed, curbs are raised if the new roof is thicker, crickets go in on the high side of curbs, and walkways are replaced once the new membrane is down.
Curb height is easy to lose. Minimum curb and flashing heights are measured from the finished roof, so a new roof that is thicker than the old one, for example because insulation is added, can bury a curb that met the minimum before. The curb has to be raised with it.
Lifting equipment brings its own rules. Ontario's Ministry of Labour treats replacing a rooftop unit as construction work under the construction regulation, and a worker who signals a crane from the roof edge must be protected from falling. In Toronto, a mobile crane, boom truck or roof hoist that stands on the boulevard, sidewalk or road needs a street occupation permit. Solar arrays add a step of their own: CRCA notes that the entire PV system has to come off when the roof is replaced.
See our warehouse roof replacement guide for the rest of the replacement process.
Replacing a roof with units on it?
We can walk the roof with you and your mechanical contractor and list every curb, line and walkway that has to be dealt with.
Call 1-833-775-7663Request an assessmentHow do you protect the roof from trades and keep them safe?
With walkways on every route to the equipment, rules for what trades may do on the roof, and fall protection for everyone who goes up. Rooftop equipment brings regular visitors, and each visit is a chance to puncture the membrane or fall.
- Walkways. CRCA recommends walkway pads or pavers around units and along access paths. IKO says to put them at every roof access point and around every serviceable unit, and Carlisle requires them where equipment is serviced every 30 days or more often.
- Condensate and grease. Johns Manville says condensate lines should rest on wood blocks or rubber supports, never directly on the roof. IKO's BUR warranty excludes damage from greases and oils, and IKO asks for a sacrificial sheet wherever anything is vented onto the roof; see our restaurant roofing guide for grease.
- Fall protection. On construction work such as replacing a unit, the Ministry of Labour says workers must stay at least 2 metres from an unguarded edge or a guardrail must be installed. In industrial establishments, a worker who could fall more than 3 metres must wear a harness and lifeline.
- Skylights and hatches. The Ministry warns that a skylight that meets the building code may not carry the loads of construction work, and an open roof hatch should be guarded.
Our commercial roof maintenance guide covers roof access logs and rules for other trades.
How does OYH Roofing work around rooftop equipment?
OYH Roofing installs, replaces and repairs flat roofs on commercial, industrial and institutional buildings across Ontario, and many of them carry rooftop units, like the roofs we installed at the Millomat Stampings plant and the City of Mississauga building at 3185 Mavis Rd. Before a replacement or a new unit goes in, we can review the curbs, flashings, supports and walkways on your roof.
See the Millomat Stampings TPO project, the City of Mississauga roof and the rest of our completed projects. For leaks around units, see commercial roof leak repair in Toronto and in Mississauga.
Frequently asked questions
What are the HVAC units on roofs called?
Rooftop units, often shortened to RTUs. A rooftop unit is a packaged unit that heats, cools or ventilates the building from a single cabinet on the roof. It usually sits on a curb over an opening in the deck, with ducts running down into the building and gas and electrical lines running across the roof to it.
What is a curb for a rooftop unit?
A raised frame that lifts the unit and its opening above the roof, so the membrane can be flashed up its sides. The Canadian Roofing Contractors Association says curbs must be built for all roof openings, and that they should be fixed to solid wood blocking rather than directly to the deck under thick insulation.
What is the recommended height for a roof curb?
The Canadian Roofing Contractors Association recommends curbs at least 300 mm (12 in.) high, with membrane flashings at least 200 mm (8 in.) above the finished roof. British Columbia's RoofStar standard requires at least 203 mm (8 in.). Measure from the finished roof surface, because new insulation can bury a curb that once met the minimum.
How much weight can a flat roof support?
As much as it was designed for. Ontario's Building Code designs roofs for the most critical of a 1.0 kPa uniform load, a 1.3 kN concentrated load or the local snow and rain load, and snow usually governs. New equipment adds dead load and drifting snow, so have an engineer check the structure before anything heavier goes up.
What is the minimum height for a parapet on a flat roof?
There is no single minimum. Ontario's Building Code requires a guard at least 1,070 mm high around a roof used for other than maintenance, and a firewall that reaches the roof must usually rise above it as a parapet at least 150 mm high, or 900 mm for a 4-hour firewall. The membrane flashing should run at least 200 mm up the parapet.
Adding equipment to your roof?
Call before the unit goes up, and we will check the curb, the flashing and the warranty conditions with you.
Call 1-833-775-7663Request an assessment
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
- CRCA: Roof Top Equipment, Technical Bulletin Vol. 44, October 1995; Canadian Roofing Reference Manual, 3.1.4 Curbs, 4.1.3 Membrane flashings and 11.2 PV installation, 2020.
- RCABC: RoofStar SBS Roof Systems Standard, adopted January 20, 2026, and Notes to the SBS Standard (British Columbia).
- NRCA, Professional Roofing: Manual elements, November 2005. Florida Building Commission: Florida Building Code 1510.10 and Table 1510.10, as quoted in December 2022 (U.S.).
- 2024 Building Code Compendium, Volume 1 (3.1.10.4, 3.3.1.18, 4.1.4.1, 4.1.5.3, 4.1.5.5, 4.1.5.9, 4.1.6.7), January 16, 2025 edition, Publications Ontario.
- Ontario Ministry of Labour, Immigration, Training and Skills Development: Construction projects on flat roofs, March 1, 2023. Ontario regulations: O. Reg. 213/91, R.R.O. 1990, Reg. 851, s. 85, O. Reg. 212/01, s. 6, and O. Reg. 215/01, ss. 20 and 21.
- City of Toronto: Stand-alone Mechanical (HVAC), Solar Collectors and Street Occupation Permit (2026). City of Mississauga: Screening for Roof Top Mechanical Units, September 2014.
- Sika Canada: Sarnafil System Warranty, sample, March 2022, and Technical Bulletin 005, March 2020. IKO: Roofing System Building Owner's Guide, February 2026, and BUR Limited Labour and Material Warranty.
- Carlisle: Owner's Manual, March 2025 (U.S.). Johns Manville: Owner's Manual RS-1780, 2026 (U.S.). Elevate: Red Shield Limited Warranty (U.S.).
- OYH Roofing project records: Millomat Stampings, Mississauga; City of Mississauga, 3185 Mavis Rd (October 2026).
OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca