Joist size calculation for attic loft conversion
I don’t know anything about metric, but I’ll try.
The “Tables” you refer to have footnotes that are not available. I’ll assume the footnotes qualify the loading, etc. Because the Tables indicate “Maximum Spans for Floor Joists” I’ll assume they’ve added a dead load factor and live load factor.
I don’t know why you’d want to use “Northern Species” or “Spruce”, when you live in the middle of Douglas Fir Larch country. However, I’ll try to answer your questions.
So, Douglas Fir Larch grade Select Structural 2x8’s at 16” on center spanning 12’ can support 40 lbs. per square foot (psf) live load plus 10 psf easily.
Likewise, your Table says Northern Species (whatever that is) 83x 400 can support a floor load spanning only 2.41 m. with a grade of Select Structural.
Likewise, your Table says Spruce can only span 2.85 m. with a grade of Select Structural.
So why not use Douglas Fir Larch. It’s probably what’s in your local lumber yard.