What size

It is recommended that a skylight be 5 – 10% of the floor area of the room. If the room is an odd configuration, it may be more efficient
to install two well placed smaller skylights instead of one larger unit.

If one truss is cut on a roof built on 24” centres, then the new opening has an inside rough opening of 46.5”. If one truss is cut on a roof with 16” centres, then the new opening has an inside rough opening of 30.5”; or 46.5” if two trusses are cut.

Skylight sizes are based on roof truss spacing. The majority of homes have trusses installed on 24” centres. Thus, the inside rough opening of a skylight that would fit between your trusses, and not require removing a part of the truss, would be 22.5”. You then must decide on the length of your skylight.   Many older homes are built with trusses on 16” centres and the inside rough opening for a skylight to fit in this situation is 14.5”. As above, you can choose from a number of standard lengths. Other leading skylight companies have a very limited selection of sizes for this truss spacing. Columbia offers, as standard lengths; 14.5”, 22.5”, 30.5”, 46.5”, and 70.5” as well as any custom size you may require.

As per the Residential Products section, and different model type, glass skylights are available from an inside rough opening of
14.5” x 14.5” to 46.5” x 46.5”, or 2.75 sq. ft. to 18.75 sq. ft. Any larger unit skylight must be acrylic dome or pyramid. Acrylic skylights are available from an inside rough opening of 14.5” x 14.5” to 94.5” x 94.5”, or 2.75 sq. ft. to 69.5 sq. ft.