Joist size please??

[Casterbridge]

I have an arium (or lean-to), which contains glass, and I want to replace with slates and a velux (0.55m x.78m). Essentially I have a triangle, the horizontal bit is 1.25m, the upright bit is 0.8m, and the longest diagonal is 1.5m. So the joist lengths will be 1.25m and the "rafters" will be 1.5m long. I plan to insulate between the rafters and then board the rafters (not the horizontal joists).

Question, what size joists should I use.

 

[tony1851]

5x2 @16" c/s would be fine.

 

[limerockconstruction]

Or if you were born post 1851 125mmx50mm @ 400mm c/c

 

[tony1851]

Or if you were born post 1851 125mmx50mm @ 400mm c/c

You kill me.