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Measuring
Your Skylight

Correctly measuring your skylight before
your order is essential.
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How To Measure Your Curb Mount, Deck Mount, Or Self Flashing Skylight

Columbia manufactures and distributes Curb Mount, Deck Mount and Self Flashing skylights. Each installation method requires specific measurements when ordering. Determining the correct size is critical for a successful skylight installation. Columbia and FAKRO sizes are specified Width x Height (W x H).

Standard or Custom Size?

  • Columbia manufactures standard and custom size skylights.
  • Standard size skylights are typically designed to work with roof trusses 16” or 24” on center apart.
  • Custom size skylights can be manufactured to the exact size of the skylight being replaced.
    NOTE: Ordering a standard size skylight will save you money and time.
  • Columbia manufactures custom size Curb Mount and Self Flashing fixed and venting skylights only.
  • Custom sizes are not available for FAKRO Deck Mount Skylights.

Standard Columbia Sizes       Custom Columbia Sizes

For FAKRO skylight sizes consult the individual product pages.

See below for measurement instructions for a new or replacement skylight.

How to measure the size of your skylight

  • There are three typical skylight installation types – Curb Mount, Deck Mount or Self Flashing.
  • Curb Mount Skylights are installed on a flashed/waterproofed site built wood curb. Available as Inside or Outside fastened, depending on the model. Most new skylights are Outside fastening. Inside fastening is typically specified for the replacement of an existing inside fastening skylight.
  • Outside fastening Curb Mount skylights require the outside finished flashed curb dimensions.
  • Inside fastening Curb Mount skylights require the inside curb and outside finished flashed curb dimensions.
  • Deck Mount and Self Flashing skylights require the roof opening measurement.
Curb Mount
Available in Inside & Outside Fastening
Measuring Inside Curb Skylight

For Curb Mount Skylights, measure the Inside curb and Outside finished flashed curb. DO NOT measure the outside of the existing skylight metal frame (not applicable). Exclude any interior/drywall finishing materials for the inside curb measurement. Measure Width x Height.

Curb Mount Installation Instructions

Deck Mount & Self Flashing
Installed with integrated curbs
(The curb is manufactured as part of the skylight)
Measuring Deck Mount Skylight

For Deck Mount & Self Flashing Skylights, measure the Inside of the roof opening. Both have integrated curbs that attach directly to the roof deck. Exclude any interior/drywall finishing materials. Measure Width x Height.


Self Flashing Installation Instruction

For FAKRO Deck Mount skylight sizes go to
the individual product pages.

Colby Measuring Skylights Tip

Columbia offers two Curb Mount fastening options – Inside Fastening & Outside Fastening. Each requires specific measurements.

OUTSIDE FASTENING
  • Outside fastening – the skylight is fixed/fastened to the outside finished flashed curb.
  • Measurements are always taken from the outside finished flashed curb (NOT the outside of the existing skylight metal frame).
  • Columbia recommends Outside fastening, as it allows for a cleaner application of drywall in the lightwell, with the PVC skylight frame of the skylight hardly visible.
Curb Mount Outside Fastening
Curb Mount Outside Fastening
  1. Aluminum Cap Finish
    Standard exterior extruded aluminum frame with baked enamel paint finish. Columbia offers 7 standard frame colours, and unlimited custom colour matching.
  2. Base Frame
    Maintenance free, white PVC, thermally broken vinyl base frame.
  3. Installation Method
    Outside Fastening – any curb width.Can be installed on a 2×4, or 2×6, or 2×8 site build curb.

    Outside Fastening skylights can be installed in either portrait (vertical) or landscape (horizontal) orientation.

    Columbia applies stickers to the frame indicating the correct mounting direction. Not following these instructions will result in a poor installation and void the warranty.

INSIDE FASTENING
  • Inside fastening – the skylight is fixed/fastened to the inside of the curb.
  • Measurements are always taken from the inside curb rough opening (not including drywall).
  • Inside fastening is a previous Columbia design. If you are replacing an inside fastening skylight, it is recommended to replace with inside fastening again, to avoid interior finishing work.
Curb Mount Inside Fastening
Curb Mount Inside Fastening
  1. Aluminum Cap Finish
    Standard exterior extruded aluminum frame with baked enamel paint finish. Columbia offers 7 standard frame colours, and unlimited custom colour matching.
  2. Base Frame
    Maintenance free, white PVC, thermally broken vinyl base frame.
  3. Installation Method
    Inside Fastening – maximum 2” curb width.Can be installed on a 2×4, or 2×6, or 2×8 site built curb.

    Fixed Skylights – Inside Fastening

    • Fixed inside fastening skylights can be installed in either portrait (vertical) or landscape (horizontal) orientation.

    Venting Skylights – Inside Fastening

    • Venting skylights can be manufactured in portrait (vertical – hinged on short side) or landscape (horizontal – hinged on long side). The hinged side must be noted when ordering.
    • All venting skylights are inside fastening and can only be installed with the hinge orientated to the roof peak. Never install with the hinge orientated downward or sideways.
Mounting Types Explained

New Skylight Installation

Before proceeding consult Columbia’s installation instructions.
Measuring Roof Rafters

For a new skylight installation always check if the distance between the roof rafters can accommodate the skylight width you want to install. As you determine the height, accommodate for obstacles like ducting or electrical. A site built roof and a factory built roof have different interior structures, inspect your attic space, consult an expert if necessary.

LEARN MORE

Rafters Structural Work

A wider skylight can be accommodated with additional structural framing. Anytime you are cutting trusses/rafters consult a structural engineer. As you determine the height, accommodate for obstacles like ducting or electrical. For this type of installation consult an expert.

LEARN MORE

Measuring to replace an Old skylight

It is essentially the same process, with one important difference. Always measure the existing curb or roof opening.
  • To ensure a perfect fit, Columbia advises that you measure the curb (or roof opening) that is remaining on the roof, not the old skylight that is being thrown away.
  • The old skylight may be damaged, or warped, during removal, and this might effect the measurement.
  • Outside fastening Curb Mount skylights require the outside finished flashed curb.
  • Inside fastening Curb Mount skylights require the inside curb and outside finished flashed curb.
  • Deck Mount and Self Flashing skylights require the roof opening measurement.
Curb Mount
Available in Inside & Outside Fastening
Measure Flashing Curb

Always measure the flashed curb, not the skylight. Columbia provides a ¼” tolerance on all models. This is your maximum skylight clearance. TIP: If the roof is too steep for safe access, use finished drywall dimensions as a guide.

Deck Mount & Self Flashing
Installed with integrated curbs
(The curb is manufactured as part of the skylight)
Measure Finished Interior

For Deck Mount and Self Flashing measure the finished interior lightwell W x H, and add +1” to account for drywall on all sides. This will be equal to your rough opening dimension.

AVOIDING OBSTACLES ON YOUR
ROOF: Minimum Clearance

It is recommended that you do not install a skylight close to an obstacle, such as a vent, slope changes, valleys, eaves, wall or dormer. The attic space can hold electrical wiring and venting.
Check the exterior and interior of your roof.

Avoid Obstacles For Skylight Install