A skylight, roof window or daylight tube changes the roof as well as the light in the room. Product choice must match roof pitch, roof covering, structural opening and water-management detail. Include the curb or deck connection, shaft, air seal, insulation, shading and future service. A stain beneath roof glazing is a symptom to investigate, not automatic proof of a leaking glass seal.
Canadian planning context. Technical examples from other regions are identified in the guide; approval and performance requirements must be checked for the actual building and jurisdiction. Original explanatory diagrams are not construction details.
- Match the exact product and flashing kit to the roof and permitted pitch.
- A skylight, an operable roof window and a tubular daylight device offer different access and light paths.
- The shaft’s insulation and air barrier matter alongside the glazing.
- Overhead glazing, snow, access and structural alterations require project-specific review.
- Coordinate replacement with roofing condition rather than comparing only the glazing price.
01 /Choose the light path before choosing the product
A skylight brings light through the roof into a room, sometimes through a shaft. A roof window may be designed for reachable operation in an occupied sloping-roof space. A tubular daylight device collects roof-level light and redirects it through a tube to a ceiling diffuser. Products and naming vary, so ask what the selected unit actually does rather than relying on the category name.
| System | Typical planning advantage | Question to resolve |
|---|---|---|
| Fixed skylight | Daylight without an opening sash | How will heat, glare, cleaning and water be managed? |
| Venting skylight | Daylight with a controlled opening | Who can operate it and what happens in rain or power loss? |
| Roof window | Reachable glazing in some roof-room arrangements | What pitch, clearance and access does the product require? |
| Tubular daylight | Light routed to a smaller interior ceiling opening | What tube route, length, bends and diffuser are proposed? |
Decide whether the room needs view, ventilation, task light, diffuse light or all of them. A daylight tube supplies a different experience from a large view of the sky. A bigger opening is not automatically better: direct sun can create glare on a screen or excessive heat at a particular time of day. Draw the occupied room and its uses before selecting the glazing area.
02 /Match roof pitch, covering and flashing as one package
Roof pitch affects drainage and product suitability. The VELUX roof-pitch guidance explains that its skylights and flashing kits have specific pitch requirements. Do not apply one manufacturer’s minimum or maximum pitch to a different product or infer compatibility because a skylight physically sits on the roof.
The roof covering matters as well. Asphalt shingles, standing-seam metal, tile and low-slope membrane roofs have different interfaces. A flashing kit must match the specified product and roof arrangement. Draw the head, side and sill water path, including underlayment or membrane transitions. Surface sealant should not be treated as the entire roof-water detail.
Use the manufacturer’s installation library to identify the exact model and instructions. This American library is a technical reference; verify the Canadian product, local requirements and supplier’s current manual. A replacement offered as “same size” may use a different curb or flashing connection from the old unit.
03 /A curb and a deck connection are different scopes
A curb-mounted unit attaches to a raised curb; a deck-mounted arrangement connects differently to the roof. The existing curb may have hidden deterioration, unsuitable dimensions or inadequate insulation. Retaining it should be a reviewed decision rather than an automatic saving. Measure and inspect the supporting construction before placing the glazing order.
Ask who builds or repairs the curb, how it is flashed, how its exterior and interior connect and how the glazing is supported. The quote should distinguish the product, structural work, curb, roofing, membrane, shaft and finishes. Otherwise a low replacement price may exclude the work needed to make the assembly durable.
Roofing access and temporary weather protection are part of this scope. Agree on how an open roof will be protected if the replacement cannot be completed immediately. The safe work plan, fall protection and lifting arrangement belong with the contractor; an owner’s photograph from below is not a substitute for a roof-level assessment.
04 /Coordinate the structural opening and loads
Creating or enlarging roof glazing can affect rafters, trusses and other structural elements. Do not cut a member because the proposed product fits between the visible interior finishes. Obtain the necessary design and approval for changes to the roof structure. Snow, wind, the unit’s own weight and applicable loads belong in that assessment.
Overhead glazing has different consequences from a vertical window when glass breaks. Ask the designer and supplier which glass construction is required for the specific location and why. A generic “safety glass” description should be replaced by the actual pane make-up, applicable evidence and support detail. Tempered and laminated glass are different constructions, not interchangeable marketing terms.
Include rooftop obstructions, drainage paths, snow accumulation and nearby equipment in the survey. A unit that works on a clear roof slope may face a different exposure below a higher roof or near a snow-catching obstruction. Site-specific design matters more than a universal online rule about where a skylight should go.
05 /The shaft is part of the thermal and air enclosure
When the roof and ceiling are separated, the light shaft passes through a space that may be outside the conditioned enclosure. Its walls need a coordinated insulation and air-control detail. A warm-looking ceiling finish does not show whether the shaft behind it is continuous or whether moist indoor air can reach cold materials.
Review the shaft’s geometry with the room’s daylight and finishes. A deep narrow shaft may distribute light differently from a splayed one. Insulation and required clearances can reduce the space available. The designer should resolve those constraints before the roofer opens the roof, rather than leaving the interior contractor to improvise the enclosure.
For a daylight tube, identify the attic or roof route, joints, supports and the ceiling-level seal. Do not assume that a compact diffuser eliminates the need for air sealing. Ask for the approved tube materials and connections, and confirm access for later cleaning or component replacement. Avoid substituting an unrelated flexible duct or foil product.
06 /Separate rain entry, condensation and roof problems
A stain or drip can involve flashing, roofing, a glazing or frame defect, interior condensation or moisture in the surrounding roof assembly. Record when it happens: during rain, snowmelt, a cold clear morning or a period of high indoor moisture. Note whether the water appears on the room-side glass, frame, shaft finish or ceiling outside the opening.
A service inspection should follow the water path rather than resealing the nearest visible joint automatically. An exterior patch may conceal a defect while making later inspection harder. If the symptom occurs without precipitation, include condensation and interior moisture in the investigation; that pattern is useful but does not by itself prove the cause.
Keep people clear of damaged overhead glazing and arrange professional make-safe work. Persistent wet finishes or concealed moisture need a roof and enclosure assessment. Do not climb onto the roof to reproduce a leak. Photographs from a safe position and a weather log give the technician a useful starting point without exposing the owner to falls.
07 /Control heat, glare and operation
Roof glazing receives sunlight differently from a vertical opening, and the room’s experience changes with season, orientation and roof slope. Compare whole-product thermal and solar properties, shade options and light distribution. A dark tint can reduce light as well as solar gain; an internal shade and an external shading arrangement do not affect the assembly identically.
For venting units, decide whether operation is manual, electric or solar-powered and where the controls sit. Ask what rain sensing actually does, what maintenance it needs and how the opening behaves after a power or control failure. A rain sensor is a product feature, not a promise that no water can enter under every condition.
Plan cleaning and blind access. A tall ceiling can make an otherwise useful manual handle unreachable. A powered opener can solve reach but introduce batteries, controls or motor service. Include a practical handover demonstration and retain the pairing and reset instructions with the product identifiers.
08 /Make replacement a coordinated roof project
Review the roof covering’s condition when replacing an old skylight. A new glazing unit on an ageing roof may need another disturbance when the roof is renewed. Conversely, replacing a sound skylight during roofing should still be justified by its condition, compatibility and future service, not by an automatic rule that every unit must be new.
- Identify the existing product, curb or deck connection and roof covering.
- Inspect structure, curb, shaft and nearby roof materials.
- Confirm the selected product’s pitch and flashing requirements.
- Define structural, roofing, insulation, air-seal and finish responsibilities.
- Record glass construction, performance documents, shades and controls.
- Agree on weather protection, commissioning and future service access.
At handover, check the interior finish, operation and documentation as well as the exterior roofing detail. Save photographs taken before concealed transitions were covered. A homeowner should leave the project with a clear product identity, service route and care instructions, not merely a brighter room and an unexplained tube of sealant left behind.
FAQQuestions people ask
Can any skylight be installed on a flat roof?
No. Use a product and curb or flashing arrangement explicitly suitable for the roof’s pitch and construction. Verify the exact manufacturer’s requirements and local design.
Does a drip below a skylight always mean the flashing leaks?
No. Rain entry, glazing defects, condensation and surrounding roof problems can produce similar symptoms. Record the location and weather and have the complete assembly investigated.
Is a daylight tube the same as a roof window?
No. A daylight tube redirects light to a diffuser. A roof window is a glazed opening with its own view, operation and installation requirements. Choose by the room’s intended use.
