30' Gothic Arch house

What are the limits of 1-3/8" top rail?

Drawing up plans to DIY a 30' x 60' house.  Where we live rarely sees anything over 6" of snow at one time on the ground and it melts within a few days, should I be more concerned about ice accumulating? Wind is of some concern, we just had 90mph winds come through a few months back with a thunderstorm. Structure will be permanently installed.

Attached is a diagram of the hoops, 30' wide, 14' high, 6' walls. 3 purlins (top and midway down on the slope). The slope run is 17'.  Am I beyond a safe structure? What needs to change?

Are you doing this in wood and glass (or plexiglass/polycarbonate)? I'm asking because the materials you use will have a bearing on how much snow, ice, wind, etc. it can take. Also, have you ruled out a more conventional (these days anyway) pipe and plastic hoop-house in a Quonset hut shape? For wind and snow, rounded structures fare much better.

Deb Stephens wrote:Are you doing this in wood and glass (or plexiglass/polycarbonate)? I'm asking because the materials you use will have a bearing on how much snow, ice, wind, etc. it can take. Also, have you ruled out a more conventional (these days anyway) pipe and plastic hoop-house in a Quonset hut shape? For wind and snow, rounded structures fare much better.

Plan is to use galvanized pipe and sheet greenhouse plastic this is going to be for mainly season extension for our veggies.  Most of what i've read is telling me not to use 1-3/8" for more than 24' hoops for the hoop house.  I haven't ruled the Quonset shape out, just most of the 30' width hoop houses i've seen are gothic styled.

Gothic design are better suited in climates that have snow and ice. The gothic design sheds the snow and ice a bit better.

You may want to consider how you'll deal with the shedded water that runs off these structures.

The cross members of the bottom cords are ending almost in the middle of the top chord in the diagram. This would strengthen the top section and put excess load in the middle, which is already the weakest point. Extending them to the bottom like a scissor truss would fix that problem:

Scissor Truss on Wikipedia

By tying the bottom chords together where they cross it will help transfer some load on one side to members on the other side. Given the 30' span, it might need additional cross members or uprights between the top and bottom chords. Some pics to give you an idea:

Scissor Truss Images on Qwant

Alternatively, you could check other search engines for images. My experience has been with some conventional framed scissor trusses as well as countless prefabricated ones. It might be a really good idea to build one on the ground and stress it to find weak points. Once it is sufficiently reinforced to your satisfaction then you can copy it. It would be a shame to invest the time, effort, and money building them all and have it fold in on itself. I have seen some tricks where people fill pipes with something to keep them from kinking while trying to bend them by hand, perhaps finding something lightweight that can strengthen the pipes would add additional resistance to catastrophic failure under extreme conditions.

Dan Grubbs wrote:Gothic design are better suited in climates that have snow and ice. The gothic design sheds the snow and ice a bit better.

You may want to consider how you'll deal with the shedded water that runs off these structures.

True, but he is not in a high snow area in North Carolina. If necessary, placing posts at intervals of 8' to 10' apart (supporting a ridge beam the length of the greenhouse) under the center of the arch will help to ensure that no flat area develops -- in the rare event that there is enough snow to be a problem. Quonsets are much more wind resistant and considerably cheaper to build.