Why Flat Roofs Need a Different Kind of Skylight Install
A pitched roof sheds water in seconds. A flat roof holds it, sometimes for days. Snow drifts against anything sticking up, meltwater refreezes overnight and Toronto’s freeze-thaw cycles work every seam. A skylight on a flat roof has to sit above all of that.
So we never set a flat roof skylight on a low wooden frame and caulk the membrane to it. We build a raised, insulated curb, flash the membrane up its full height, add cant strips at the base and a cricket where water needs to be pushed around, and only then set the unit.
The 7 Flat Roof Skylight Challenges Toronto Installers Must Solve
- Ponding water sits at the base of short curbs and finds pinholes.
- Snow drift buries low curbs and holds meltwater against the seal.
- Freeze-thaw opens caulked joints within a couple of winters.
- Membrane compatibility means TPO, EPDM and SBS each need their own tie-in method.
- Roof warranties can be voided by improvised tie-ins.
- Condensation forms on cold curbs that are not insulated.
- Foot traffic on terraces means some units must be walkable and others screened.
Every flat roof install we do answers all seven.
Residential Flat Roof Skylight Installation
Rear Additions
The most common job. Toronto rear additions often have flat roofs and deep kitchens or family rooms that need light from above. A Velux CFP fixed flat glass runs $3,500 to $5,500 CAD installed, raised on a curb above the snow line and flashed into the existing TPO or EPDM so ponding water never sits against the seal.
Laneway Suites
Compact footprints and flat roofs make a skylight the best way to get daylight into the middle of the unit. We coordinate with your builder so the curb is framed before the membrane goes down, and the unit is sized to the city of Toronto laneway suite guidelines. Most installs run one day on site with a Velux CFP at the lower end of our pricing.
Condo Townhouses and Roof Terraces
Fakro DXW walkable glass lets light into the floor below a terrace while staying usable as deck. The DXW is load-rated for foot traffic and is the only flat roof unit we will install on a terrace where people walk or set furniture. Pricing runs $6,000 to $9,000 CAD and board approval paperwork is handled on our side.
Dormers and Low-Slope Sections
Low-slope dormers under 3:12 cannot take deck-mount units. A curb-mount or flat-roof unit is the fix. We match the curb to your membrane and lap the tie-in high enough that spring snowmelt cannot wick under it. Most dormer installs are a single-day job for a Velux CFP or CVP.
Garages and Sunrooms
Flat garage roofs and old sunroom roofs are quick installs with big payoffs. A single Velux CFP over a detached garage workshop turns a dark cave into a usable room in one day of work, and old sunroom glass-roof panels can be replaced with a curb-mount unit on the same opening. Honestly, these are some of the most satisfying jobs we do.
Mid-Century Bungalows
Scarborough and Etobicoke bungalows sometimes have flat sections over additions. We check the joist depth first so the opening can be framed without compromising the structure, and we match curb height to the roof so the line stays clean against the original mid-century lines. Most of these jobs fall in the middle of our CFP price band.
Commercial Flat Roof Skylight Installation
Retail and Office Roofs
Curb-mount glass and domes with screens, tied into the existing membrane. See commercial skylight installation. We stage the work around business hours so the store or office stays open, and our WSIB-covered in-house crews carry their own fall arrest and not the building’s.
Warehouses
Large flat roofs with per-bay units, phased around operations. We work bay by bay so the rest of the building keeps shipping, and we detail each curb to OBC 9.7 for the framing and OBC 9.26 for the membrane tie-in. Most warehouses need Velux CFP or domes with safety screens on top.
Restaurants
Flat-roofed dining rooms brightened without closing the business. We usually schedule the install for a Monday or Tuesday closed day, or work above a drop ceiling so the dining room never sees a panel come out. A Velux CFP at $3,500 to $5,500 CAD installed is the most common pick.
Multi-Residential Buildings
Podium and penthouse roofs where board approval and COI are part of the job. We supply the certificate of insurance before the first site visit and handle the status certificate form the corporation requires. Fakro DXW walkable glass is the usual pick on amenity decks where the surface has to stay usable.
Specialty Flat Roof Options
Velux CFP Fixed Flat Glass
Clean interior look with a hidden internal pitch to shed water. Our most-requested flat roof model at $3,500 to $5,500 CAD installed, with Low-E 272 glass and a laminated interior pane for the same energy numbers as a wall window. Pairs with our flashing kits for TPO, EPDM or SBS without improvising the tie-in.
Velux CVP Venting Flat Glass
Electric opening with a rain sensor. Perfect for additions that get hot under the ceiling, where a manual rod is not practical and a wall switch would need wiring through finished space. The CVP runs $4,800 to $7,500 CAD installed and is paired and tested against our founder’s checklist before we leave.
Fakro DXW Walkable
Load-rated glass for terraces and roof decks, the only unit we will install where people walk or set a chair. $6,000 to $9,000 CAD installed, with laminated glass under the top ply and a non-slip surface that holds up to Toronto winters. We have used it on Toronto rooftop deck and private terrace projects from Corktown to Port Credit.
Domes and Dynamic Domes
Lower cost, fast fit and good drainage. The classic choice on commercial flat roofs where light matters more than view, and the right pick when the budget is tight. We tie them in to the membrane the same way we tie in flat glass, so the cost saving is in the unit, not in the flashing.
Materials for Flat Roof Installs
| Item | What we use |
|---|---|
| Curb | Insulated wood curb, set above expected snow line |
| Membrane tie-in | Heat-welded TPO, adhered EPDM, torched SBS |
| Base detail | Cant strips, cricket where needed |
| Units | Velux CFP, CVP, Fakro DXW, unit domes |
| Glass | Low-E 272, laminated interior pane |
Our Flat Roof Expertise
We have replaced a lot of flat roof skylights installed by someone else. Almost every failure traces back to a short curb or a sealant-only tie-in. We would rather spend an extra hour on the curb than come back in March. Honestly, flat roofs are where a skylight installer’s habits show.
What Actually Stops Owners From Adding a Flat Roof Skylight
“Flat roof skylights always leak.”
In our opinion, they leak when the curb is short and the membrane is caulked. A raised curb with a proper tie-in is as dry as any pitched install.
“It’ll void my roof warranty.”
We tie in to the membrane maker’s details and coordinate with your roofer when needed. Most major TPO and EPDM makers publish approved curb and tie-in sheets, and we follow those by name on every job. If your roofer’s warranty requires we go through them, we will.
“Snow will bury it.”
We set the curb height above the expected drift line for your roof. On Toronto flat roofs that usually means 8 to 12 inches of curb above the membrane, which keeps the flashing above snowpack and out of standing meltwater. A cricket on the uphill side pushes drifts around the unit instead of into it.
“Walkable glass sounds fragile.”
The Fakro DXW is load-rated for foot traffic, with laminated glass under it. It looks like a regular glass floor panel from above but is engineered for regular use, which is why we put it on condo amenity decks where chairs and planters move around all summer. It is the only flat roof unit we recommend underfoot.
Flat Roof Skylight Timeline
Assessment
Roof survey, drainage check, membrane ID. Quote in two business days.
Approvals
Permit and condo board approval where needed, usually two to six weeks. We file the permit at cost as a separate line on the quote, and supply the status certificate paperwork for condo boards so the review does not stall. Honestly, condo timelines are the part we cannot speed up.
Install
One to two days per unit, weather permitting for torch-down. Our WSIB-covered in-house crews set the curb, weld or torch the membrane, install cant strips and a cricket where needed, then set the unit and check the flashing against our founder’s checklist. SBS work waits for a dry day above freezing.
Finish
Interior shaft, warranty registration, roof walk. Most finishes are done the same week as the install, with the Velux or Fakro warranty registered in your name and the roof swept for stray fasteners. We do a final walk with you so you see the curb, the tie-in and the interior shaft before we pack up.
Flat Roof Skylight Cost in Toronto: What You Are Paying For
The Unit
Domes cost least, walkable glass most. A standard Velux CFP sits at the lower end, the CVP venting flat glass adds a motor and rain sensor, and the Fakro DXW walkable is at the top of our published $3,500 to $9,000 range. Each unit ships with the matching flashing kit and a Velux or Fakro product warranty.
Curb Construction
Taller, insulated curbs use more material but prevent most flat roof failures. In our opinion, this is the line item that separates a flat roof skylight that lasts from one that leaks by the second winter. We build to OBC 9.7 for framing and insulate the cavity so cold corners do not sweat.
Membrane Tie-In
SBS torch work and older built-up roofs take more time than TPO. TPO is heat-welded up the curb in clean strips, EPDM is adhered or taped, and SBS needs a torch and dry weather. Each method has its own labour time and material cost, which is why we list it on the quote.
Crickets and Drainage Details
Small cost, big difference on slow-draining roofs. A cricket on the uphill side of the curb is a few sheets of metal and an hour of work, and it is what keeps meltwater from ponding against the flashing on wider units. We add one by default on curbs over 30 inches and on any roof with documented slow drainage.
Interior Shaft
Flat roofs usually mean shallow shafts, which keeps finishing cost down. There is rarely a deep attic cavity to frame through, so drywall work is minimal and the diffuser sits close to the ceiling. Where insulation depth is tight, we use a Velux pre-finished shaft kit to keep the build clean.
Access
Third-floor roofs and terraces with no direct access need hoisting. We bring our own rigging for low-rise buildings, and for taller ones we coordinate with a hoisting company we have used on past condo jobs. Either way, the cost shows up as its own line on the quote so there are no surprises.
Flat Roof Skylight Installation vs Replacement vs Repair: Which Service You Need
New opening? Installation. Old dome on a short curb? Replacement with a new raised curb is usually smarter than repair. Unit sound but the tie-in failed? A membrane re-flash may be enough.
Fixed, Venting or Solar: Choosing Your Skylight Type
Fixed flat glass (Velux CFP) for light only. Venting (Velux CVP) to clear heat from additions. Solar and smart controls suit high or hard-to-reach roofs. Walkable (Fakro DXW) for terraces.
Flat Roof Skylight Timeline in Toronto: What to Expect Week-by-Week
Week one assessment and quote, two to six weeks for approvals, one to two days on site, finishing the following week. Torch-down work waits for dry weather above freezing.
Why Flat Roof Owners Trust Our Crew
Certified for both Velux and Fakro since 2004, with WSIB-covered in-house crews who do the tie-in themselves instead of handing it to a roofer they cannot vouch for. Every flat roof unit we set is detailed to OBC 9.7 for the curb framing and OBC 9.26 for the membrane tie-in, and we list the building permit as its own line at cost on every itemized quote. Raised curbs, correct tie-ins, real warranties. We specd every detail in this page because they all matter.
