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Measuring for your Skylight

Size is typically the most important factor in purchasing and installing a skylight. While both size and position will determine how much extra light is admitted to the space below, size is the dominant factor. Use the following "rule of thumb" for sizing a skylight: the skylight size should never be more than 5% of the floor area in rooms with many windows and no more than 15% of the room's total floor area for spaces with few windows.

Keep in mind that the measure is absolutely critical! It must be accurate and needs to be based upon typical industry reference points as provided below. Nothing can be more frustrating than receiving the wrong sized material. Although it is nothing to be afraid of, we would encourage you to familiarize yourself so as to avoid a potentially costly mistake.

When ordering or describing a skylight, the measurements are always expressed as width (dimension horizontally across the roof) x length (dimension vertically up the roof).On venting skylights, the hinge will be on the width dimension.

Thermo-Lite series skylights are fitted into an opening in the roof. The 'rough opening' is the size of the hole built into or cut into the roof to accept the skylight. The actual size of the skylight will be 1/2" smaller in both width and length, allowing some ability to adjust the actual skylight position within that opening.

Metro-Lite series skylights are mounted onto curbs on the roof. Curb Mounted frame sizing is taken from the Outside Curb Dimension. The Outside Curb Dimension is the overall OD (outside dimension) size of the of the finished built up curb. Importantly, this also includes the applied roofing materials as taken from the top of the curb where the skylight is to fit. Skylights are sized slightly larger than the OD of the curb in order to fit over the top like a crown, and reference what is commonly referred to as  the Inside Flange Dimension, also known as the Inside Aluminum Dimension or the Inside Unit Dimension. The important issue here is that you provide us with the proper OD of the curb. We can assist you with the rest!

Should you need a skylight size that is not included in the size charts above, don't worry: both the Thermo-Lite and Metro-Lite series skylights can be ordered in custom sizes. Please use our Custom Sizes page to request a quote for your custom size skylight..