roof shed design strategy

Question

I am building a shed and just finished putting on rafter trusses. Now I have to decide where to take this roof. The plans I was following suggest using 2 x 4 purlins that extend 10” overhang, Followed by plywood sheathing on top. I would then nail the trim to the end of the purlins. However, I realize this is not a common design, It seems like it is more common to build ladders, and attached the plywood directly to the rafters. Which route should I go? Below is my current shed status.

Answer 1

I am going to just give you my opinion here because you are off to almost a perfect start for a shed. Seeing you flattened the area with a rock bed makes me misty and thinking maybe I need to step up my game on my projects. So let me just give you a couple of notes and you can take it or leave it because you are off to a great start and shed will be nice no matter what.

• I first learned about purlins as a kid going around southern Missouri with a grandpa who would buy out farms. We saw barns 100+ years old and incredible that everything looked like it was falling down but the roofs never collapsed... they all had purlins. The amount of structural integrity purlins add is incredible. The fact that you have trees overhead... branch falls... whatever... Do you want a piece of plywood getting dented and causing issues with your roof because you couldn't do a minor extra step?
• I am going on a tangent here but I have a medium (3x your size) premanufactured barn in my backyard and it is 30 years old. Roof is sagging in parts and I will be fixing it this summer. Big surprise no purlins.
• You can install the purlins as suggested (flipped) or the easy way (flat) because your structure isn't that big. Installing them flat would take you 1-2 hours.
• I would also suggest installing some joists across the shed. I would personally suggest a half-loft and T bar it. It will give you so much most stability. You could also do a 3/4 loft if you feel like crawling around and have stuff to store.