Choosing the right skylight starts with understanding VELUX skylight sizes, and for Toronto and GTA homeowners the dimension question trips up more renovation budgets than almost any other detail. A skylight that looks perfect in a showroom can become a costly headache when it does not align with your rafter spacing, your flat roof membrane, or the ceiling shaft running through your attic. As a certified VELUX dealer serving the Greater Toronto Area, our team at Toronto Skylight Installers walks homeowners through standard dimensions, custom rough openings, and the practical realities of fitting natural light into a 1960s Scarborough bungalow or a new infill home in Leaside. This guide explains how the sizing system works, what each code means, and how to plan an opening that passes Ontario Building Code inspection the first time.
By summer 2026, daylighting has become one of the most requested upgrades in GTA homes, and homeowners want to make confident, informed decisions before a single shingle is lifted. Getting the size right the first time protects your roof, your budget, and the architectural balance of your room. Below, we break down everything from the famous VELUX size codes to rough opening tolerances and the real installed costs you can expect across Toronto this year.
Understanding VELUX Skylight Sizes and the Size Code System
VELUX uses a standardized alphanumeric code to identify each skylight footprint, and learning to read it removes most of the confusion around VELUX skylight sizes. Each model carries a two-character code, such as C04, M06, or S06. The letter indicates the width grouping, and the two digits indicate the height grouping. This system lets installers, suppliers, and inspectors reference an exact frame dimension without measuring every unit by hand, which is invaluable when ordering replacement glass or matching a new unit to an existing curb.
The width letter follows a consistent pattern. A “C” frame is roughly 550 mm wide, an “M” frame is roughly 780 mm wide, and an “S” frame is roughly 1,140 mm wide. The height numbers scale similarly, so an “04” is shorter than an “06,” which is shorter than an “08.” Because the codes are modular, a C04 and an M04 share the same height but differ in width, which helps designers create symmetrical groupings of two or three skylights across a single roof plane. For a deeper look at how these units perform once installed, our skylight installation team can match a code to your specific rafter layout.
One important note for Toronto homeowners: the frame dimension in the code is not the same as the rough opening you cut into your roof. The rough opening is always slightly larger to allow the frame to seat properly and to accommodate flashing. We cover that gap in detail further down, because misreading it is the single most common sizing mistake we correct on GTA jobs.
Standard VELUX Skylight Dimensions Chart for GTA Homes
The table below lists the most common VELUX size codes requested across Toronto, with their approximate frame dimensions and rough opening requirements. These are the units we install most frequently in GTA bungalows, two-storey homes, and finished attics. Always confirm the exact figures against the current VELUX specification sheet for your chosen model, as deck-mounted and curb-mounted versions differ slightly.
| Size Code | Frame Width | Frame Height | Typical Rough Opening (W x H) | Best Use in GTA Homes |
|---|---|---|---|---|
| C04 | 550 mm | 980 mm | 572 x 1,000 mm | Small bathrooms, hallways, narrow rafter bays |
| C06 | 550 mm | 1,180 mm | 572 x 1,200 mm | Stairwells, ensuite bathrooms |
| M04 | 780 mm | 980 mm | 802 x 1,000 mm | Kitchens, bedrooms, home offices |
| M06 | 780 mm | 1,180 mm | 802 x 1,200 mm | Living rooms, open-concept main floors |
| M08 | 780 mm | 1,400 mm | 802 x 1,420 mm | Great rooms, vaulted ceilings |
| S06 | 1,140 mm | 1,180 mm | 1,162 x 1,200 mm | Large feature installations, double-height spaces |
For most Toronto homes built on 16-inch or 24-inch rafter centres, the M-series strikes the best balance between daylight and structural simplicity. An M06 typically fits a single rafter bay on 24-inch centres with minimal framing, while wider S-series units usually require cutting a rafter and adding a header, which raises labour costs. If you are weighing a fixed unit against a venting model, our guide to a fixed skylight explains where each size shines.
Rough Openings, Tolerances, and Ontario Building Code Requirements
The rough opening is the framed hole in your roof deck that receives the skylight. For VELUX deck-mounted units, the rough opening is generally about 16 mm to 22 mm larger than the outside frame dimension in both width and height. This small gap is intentional, giving installers room to shim the unit square, seat the integrated flashing, and accommodate slight irregularities in your roof structure. Cutting the opening too tight forces the frame and risks cracking the seal; cutting it too loose leaves gaps that compromise weatherproofing.
Ontario Building Code treats skylights as part of the roof assembly, so any opening that cuts through a structural rafter requires proper headers to redistribute the load. In practice, an M-series unit on 24-inch centres often fits between rafters, while an S-series unit almost always needs an engineered header. Toronto’s permit requirements vary by the scope of structural work, and our installers coordinate the framing so your new skylight installation meets code without surprises during inspection.
| Specification | Deck-Mounted Requirement | Curb-Mounted Requirement | Notes for GTA Installs |
|---|---|---|---|
| Rough opening tolerance | +16 to +22 mm over frame | Match curb outside dimension | Confirm per model spec sheet |
| Minimum roof pitch | 14 degrees (deck-mounted) | 0 degrees with curb | Flat roofs require a curb |
| Header requirement | When cutting a rafter | When cutting a rafter | Engineered for S-series spans |
| Flashing type | Integrated step flashing | Curb-specific flashing kit | Match to roof covering |
| Ceiling shaft | Straight, splayed, or flared | Same options | Affects perceived light spread |
Flat-roof properties, common across Toronto’s downtown semis and many commercial conversions, almost always use a curb-mounted approach. The curb raises the unit above the membrane to shed summer rain and provides the slope a flat surface cannot. If your home has a low-slope or flat roof, review our flat roof skylights options, which are engineered specifically for these assemblies.
When You Need a Custom Rough Opening Instead of a Standard Size
Standard VELUX skylight sizes cover the vast majority of GTA homes, but certain situations call for a custom approach. Heritage homes in neighbourhoods like Cabbagetown and the Annex often have irregular rafter spacing, hand-cut framing, or existing openings from a previous skylight that do not match any modern code. In these cases, the goal is to adapt the opening to a standard VELUX unit wherever possible, because custom-glazed units carry longer lead times and higher costs.
The most common reason GTA homeowners think they need custom sizing is an existing skylight of an obsolete dimension. Rather than fabricate custom glass, our team frequently reframes the opening to accept the nearest standard size, which preserves the VELUX warranty and keeps replacement parts readily available for decades. When a like-for-like swap makes sense, our skylight replacement service handles the transition cleanly, including adjusting the ceiling shaft to align with the new frame.
Truly custom situations include double-height great rooms, commercial atriums, and architectural feature walls where designers want a specific proportion. For these, VELUX offers larger panels and modular skylight arrangements, and we coordinate the structural engineering. Businesses exploring larger daylighting projects can review our commercial skylights range, which scales well beyond standard residential codes.
Matching Skylight Size to Room Size and Daylight Goals
Bigger is not always better. A skylight that is too large for a room can create glare and overheating during Toronto’s bright summer months, while one that is too small leaves the space feeling under-lit. The widely used rule of thumb is that skylight glazing area should be roughly 5 percent of the room’s floor area for spaces with several windows, and up to 10 to 15 percent for rooms with few or no windows. Translating that into VELUX size codes helps homeowners pick confidently.
| Room Type | Approx. Floor Area | Suggested Glazing Target | Recommended VELUX Size |
|---|---|---|---|
| Powder room / ensuite | 4 to 6 m squared | 10 to 15 percent | One C04 or C06 |
| Bedroom / home office | 10 to 14 m squared | 5 to 10 percent | One M04 or M06 |
| Kitchen | 14 to 20 m squared | 7 to 12 percent | One or two M06 |
| Living / great room | 25 to 40 m squared | 5 to 10 percent | Two M08 or one S06 |
| Dark stairwell / hallway | 3 to 8 m squared | Variable | Sun tunnel or C06 |
For interior rooms with no roof access directly above, a rigid sun tunnel can deliver daylight through a compact tube, which avoids the structural cost of a full skylight opening. These are popular for Toronto closets, laundry rooms, and hallways where a standard rectangular unit will not fit. Explore how a sun tunnel skylight can brighten awkward spaces without major framing changes. For rooms where you want fresh-air ventilation alongside daylight, a solar-powered fresh air skylight in an M06 size is one of our most requested summer upgrades.
VELUX Skylight Size Costs in Toronto for 2026
Installed pricing in the GTA depends on the size code, mounting type, glazing options, and whether your opening requires structural framing. The figures below reflect typical fully installed ranges for summer 2026, including the unit, flashing kit, interior finishing, and labour. Solar-powered venting and electric models cost more than fixed units of the same size, and custom or oversized glazing sits at the top of the range.
| Size Code | Fixed Unit Installed | Venting Unit Installed | Notes |
|---|---|---|---|
| C04 / C06 | $2,400 to $3,400 | $3,200 to $4,400 | Fits most single rafter bays |
| M04 / M06 | $2,900 to $4,200 | $3,900 to $5,400 | Most popular GTA size |
| M08 | $3,400 to $4,900 | $4,400 to $6,000 | May need light framing |
| S06 | $4,200 to $6,200 | $5,400 to $7,800 | Usually needs a header |
| Sun tunnel | $1,400 to $2,400 | Not applicable | Compact, low structural cost |
Two factors push costs upward most often: cutting a rafter that requires an engineered header, and a deep ceiling shaft that needs extensive drywall and finishing. A straight shaft in a flat ceiling is the simplest, while a splayed shaft that flares the light across a room adds labour. Proper flashing is non-negotiable in our climate, and using the correct skylight flashing kit for your roof covering protects the entire investment. If your existing skylight is leaking rather than undersized, our skylight repairs service can often resolve the issue without a full replacement.
Frequently Asked Questions About VELUX Skylight Sizes
How do I read the VELUX skylight sizes code?
What is the most common VELUX skylight size in Toronto homes?
How much larger should my rough opening be than the skylight?
Do I need a custom size or will a standard size fit?
Can I replace an old skylight with the same size VELUX?
What size skylight is right for my room?
Get the Right VELUX Skylight Sizes for Your GTA Home Today
Choosing among the many VELUX skylight sizes does not have to be guesswork. The right code, mounting method, and rough opening depend on your roof structure, room dimensions, and daylight goals, and getting all three correct the first time protects both your budget and your roof. As a certified VELUX dealer, Toronto Skylight Installers measures your space, confirms code requirements, and recommends the exact unit that fits your home and your vision for natural light this summer.
Call us today at (416) 365-7557 or book a free skylight consultation to get an accurate sizing assessment and a clear, fixed quote before any work begins.
Toronto Skylight Installers proudly serves homeowners across Toronto and the GTA with expert skylight sizing, installation, and replacement backed by certified VELUX expertise.