Girder spans for open porches

[Mr. Inspector]

To use 2018 Table R602.7(3) Girder and Header Spans for Open Porches acording to footnote c you need to use the measurement of the porch depth measured horizontally from the building face to the centerline of the header. I am not sure that you can only use this table when the header is parallel with the building exterior wall. I can't figure out why the spans would need to be different if the I used width of the porch roof when the headers were perpendicular to the exterior wall. Also it doesn't say if it is to be a shed, peaked or flat roof.
Can you use this table if the porch headers are not parallel with the building or when not attached to a building and a porch with a shed, peaked or flat roof?

 

[SDS]

I found this very interesting on the subject of R602.7(3)
Thank you Glenn

 

[Glenn]

Thanks for sharing my video, SDS. Since making that video, I discovered the AWC Wood Frame Construction Manual (A direct reference from the IRC) provides additional beam sizing tables, including glu-lams and an awesome table for sizing ridge beams. It will definitely be included when I update this class.

Page 330 for ridge beams spans: https://awc.org/pdf-viewer/?idp=4075&idf=3