Floor Joist Spacing

by MacCookie
(Berks County, PA)

I have 16' x 16' footer in my back yard with 6" block walls on it. The northern wall is 16' outside measure long. The eastern/western walls are only 7' long with an 8 ft wide single pitch roof. The previous owner had run plywood for the southern wall and enclosed the remainder of the footer with fencing and used the structure for a kennel. My wife and I have used it for a shed since we moved in.

Now we are going to finish the block walls and put a gambrel roof on it. I want to reframe what had been the roof to be joists for 2nd story decking, full width. Since the 6" block walls are 16' x 16' on the outside, my joists are going to run 15' long on the inside. I then have to position the joists to cover a 15' width.

My question is: In doing the layout, do I position the center joist first and space centers going left and right so the ones against the outside walls have the shortened spacing, or do I start from one side and center space the joists so only the joist of the far side has odd spacing?

Thank you for considering this question. Very little seems to be out there on walls or decks that are irregular measures.