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Home / Why Skylights / Roof Types & Slopes


Columbia manufactures residential and commercial skylights for sloped and flat roofs. Please consider the following before you purchase the skylight.
  • The roof is critical to the integrity of your home or building, protecting the building from the weather and draining away water and snow without damaging the lower structure. A roof also ties together the entire building, providing strength and stability.
  • Roofing technology (sloped and flat) has advanced significantly over the last decade with the introduction of new roofing materials and construction techniques. It is important to understand how these will impact the skylight installation.
  • A sloped roof is built at different pitches (the angle of the slope) based on the requirements and design of the building and the architectural style. A flat roof has no slope, and water drainage needs to be sloped toward the drainage system.
  • Both sloped and flat roofs have elements that need to be taken into account, such as vents, heating systems, etc.
Sloped Roof
Sloped Roof Venting Skylight
  • Sloped roofs are typically found on residential dwellings, and specific commercial buildings.
  • The slope allows water to run off the building into the building drainage system.
  • The inside of a sloped roof is finished in a cathedral or vaulted ceiling, or an attic space with a floor of ceiling joists.
  • A sloped roof can be clad in a variety of roofing materials, including asphalt shingles, cedar wood shingles, high or low profile tiles, and metal.

The Two Typical Roof Structures

Rafters Roof Type
  • Sloped roofs are constructed using two techniques, Rafters and Trusses. Rafters are built on site and allow for an attic space, Trusses are manufactured off site.
  • With rafters, a section can be cut out to accommodate a wider skylight, with additional supportive framing. Please consult an experienced contractor or engineer.
  • A rafter style roof provides an attic space, or can be modified to form a dramatic cathedral ceiling.
  • Rafters are the preferred approach for remote location that is not accessible by a large truck and crane.
Trusses Roof Type
  • Trusses are built off site, they have additional supportive framing (triangular webbing) anchored to the bottom chord (beam). They are built in a factory to save time on site.
  • A truss roof is stronger than a rafter roof, able to span greater distances and support more weight.
  • The installation of trusses requires access for a large truck and crane.
Anatomy of a Sloped Roof
Sloped Roof Anatomy
  1. Decking
  2. Underlayment
  3. Attic
  4. Vents
  5. Rafter
  6. Ridge
  7. Collar Beam
  8. Battens
  9. Joists
  10. Soffits
  11. Fascia
  12. Rake
  13. Hip
  14. Eaves
  15. Valley
  16. Dormer
  17. Chimney
  18. Flashing
  19. Drip Edge
  20. Gutters & Downspouts
  21. Covering
How SlopeD Roof Pitch Is Determined
Roof And Pitch Diagram

Typical North American Pitches – Ratio of Rise versus Span

Different Types of Sloped Roof

Columbia’s skylights can be installed on all types of roofs.

Roof Types

Interior Finish

Another attribute of a sloped roof to consider is the interior structure and finish. There are three typical choices skylights can be installed in – Cathedral or Vaulted ceiling, finished or unfinished attic space. Check for obstacles that might impede the installation and require you to order a smaller skylight, such as ducting, wires, heat exchangers.
Cathedral or Vaulted Ceiling
Vaulted Ceiling Skylights

Typical framing for a Cathedral Ceiling follows the slope of the roof. A Vaulted Veiling does not follow the pitch of the roof or is the shape of an arch.

Attic Space Ceiling
Attic Space Ceiling

Attic space usually holds all of the homes mechanical systems, venting, ducting, electrical, etc. The photograph shows a framed lightwell directing light from the skylight to a custom lightwell.

Sloped Roof is Suitable for both COLUMBIA mounting types – Curb Mount and Self Flashing

Skylights are designed to work with the pitch of a roof, different types of skylights require different pitches. Columbia Skylights come in Curb Mount and Self Flashing, glass or acrylic, fixed and venting.
Curb Mount Glass

Min 2 12 Roof Pitch Lg

Curb Mount Fixed & Venting Skylight (Manual & Electric)
  • Sits on site built 2 x 4, 2 x 6, or 2 x 8 curb with flashing.
  • Minimum 2:12 roof pitch for glass.
Self Flashing Glass

Min 3 12 Roof Pitch Lg

Self Flashing Fixed & Venting Skylight (Manual & Electric)
  • Installed on roof surface and includes a built in curb.
  • Both acrylic and glass models must be installed on a minimum 3:12 pitch roof.
  • Does not require metal flashings.
Curb Mount Acrylic Dome Or Pyramid

Min 0 12 Roof Pitch Lg

Curb Mount Fixed & Venting Skylight (Manual & Electric)
  • Sits on site built 2 x 4, 2 x 6, or 2 x 8 curb.
  • Minimum 0:12 roof pitch for acrylic.
  • Can be installed on a flat roof.


Self Flashing Acrylic Dome Or Pyramid

Min 3 12 Roof Pitch Lg

Self Flashing Fixed & Venting Skylight (Manual and Electric)
  • Installed on roof surface and includes a built in curb.
  • Both acrylic and glass models must be installed on a minimum 3:12 pitch roof.
  • Does not require metal flashings.
For sloped roof applications Columbia recommends the installation of glass skylights due to superior energy efficiency and UV protection.

Fakro Logo FeatureConsider FAKRO’s Premium European fixed and venting skylights and roof windows.

Columbia manufactures a variety of residential skylights, commercial skylights, and sun tubes that can be used on a flat roof, bringing natural light into the structure below. Skylights can be specified with acrylic or glass, each glazing material has specific requirements for installation on a flat roof. The skylight needs to work with the roof’s drainage system to drain rain, and melting snow and ice.
  • Flat roofs are used on residential applications, factories, warehouses, sports facilities, government buildings, etc.
  • Flat roofs can be framed in wood, steel beams, concrete slab, or corrugated structural steel. A flat roof usually includes a layer of insulation and structural skin like plywood or weather proof sub-membrane.
  • The outer surface of a flat roof can be skinned using a waterproof roofing material, typically torch-heated asphalt or glued on. Gravel can be applied using hot asphalt to the roofing material, to weigh down the roof and protect it.
  • Green (or living) roofs are a type of flat roof that is becoming more popular because of sustainability and as an aesthetic choice. Green roofs have a strong underlying structure, and a tough waterproof membrane that holds the soil, typically incorporating a drainage and watering system.
  • Columbia Skylights can be used on flat roofs – an acrylic dome or pyramid skylight can be installed on a typical flat curb as the slope of the glazing drains the water away. Glass skylights installed on a flat roof require a sloped curb to create pitch and allow for water drainage off the flat glass surface. This provides an opportunity for the use of ENERGY STAR® certified glass skylights.

Review Our Extensive Range of Flat Roof Skylights

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Columbia Skylight Thumbnails

Columbia produces a wide selection of Canadian made skylights for flat roof applications – curb mount, fixed and venting, glass or acrylic skylights, sun tubes, a roof access door, and specialty skylights.

Bringing natural light into areas such as a kitchen or bathroom. Talk to your architect or contractor about installing a skylight on a flat roof.

Columbia has over 5 decades of experience manufacturing skylights that can handle the extremes of our northern climate.

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Fakro Skylight Thumbnails

FAKRO has superior design features and produces a premium range of flat roof skylights, featuring a strong durable built in curb. Available fixed or venting, with electric and solar powered operation, and Z-Wave Smart Home technology.

These products are of exceptional quality and incorporate state of the art materials and parts.

The new FVC-S Curb Mount Solar Venting skylights (with infinity glass) can be mounted on a flat roof.

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Slimlite Skylight Thumbnails

Slimlite specializes in commercial and residential flat roof skylights. Producing a range of exceptionally durable products in acrylic and glass.

Slimlite became part of the Columbia Group of Companies in 2017. Renowned throughout Canada for more than 50 years for exceptional manufacturing quality.

Review Slimlite’s extensive range of industrial grade skylights, with acrylic and glass options.

IMPORTANT NOTE: Columbia recommends you consult with your architect, contractor and roofing installer about the specific requirements of your skylight installation.

The information provided by COLUMBIA MANUFACTURING CO. Ltd. is for general informational purposes only. All information on the Site is provided in good faith, however, we make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability, or completeness of any information on the Site.