I'm planning to build a 30x40 greenhouse. Effectively it will be a pole building that is covered in 5mm solexx. It will use 30' steel trusses for the roof. My plan would be to use metal siding with 2" XPS insulation on the north facing wall. I live in central PA (zone 6A)

My questions are:

1). Should I use gable or lean-to trusses? Lean-to would allow me to have the whole roof be south-facing. My concern is they are lower pitch, so snow would accumulate more. (Not worried from a structural perspective. More from a light blocking perspective)

2). If I use gable trusses, should I only put solexx on the south facing roof side and put metal roofing with some XPS insulation on the north facing side of the roof?

Thanks!

Welcome to NGA @bignateyk

That is quite a project that you're taking on, and I hope you will continue to post and let us know how it progresses!

Hopefully someone here will have some good advice for you - I'm afraid this one is a bit beyond my abilities.

I don't know much about steel construction, so I can't answer that. The heavy insulation ought to be on the side or sides of prevailing winter wind (which isn't always north: ours is W/NW) rather than in the roof. If you need extra ceiling insulation, go for bubble wrap or plastic sheeting with air space.
Questions:
How is that big space to be used - and for how much of the year?
Are you installing some heating system? And how will you regulate the heat?
(Hint: If you include your location and zone in your profile, whenever you have a question, people will know at a glance what your climate requirements are and find it easier to respond. )

Depending on the snowfall in your area, it might be good to consider how you plan to clear snow from the roof. A single span roof 30 ft. across will be hard to access. I use a painter's extension pole with a rubber blade intended for getting snow off truck windshields. It also works for solar PV panels and collectors.

Depending on the snowfall and temperatures, a steeper-pitched roof of polycarbonate with heat underneath might be self-clearing. But make sure there's enough overhang for snow to pile up without blocking or damaging vents or pressing on the outer wall.

If there are commercial greenhouse growers nearby, you might check with them. Good luck!