Courtesy of James K., Virtually Green, San Francisco, CA
A good source of practical ag info about high tunnels is the organic.kysu website page: http://organic.kysu.edu/CurrentProjects.shtml
It covers a lot of things of interest to SPIN farmers, including info about high tunnel construction, operation, energy efficiency, pest control, etc.
By the way, their peaked high tunnel design helps reduce problems with snow loading, as well as with condensation drip from the interior apex curve of half-hemisphere shaped high tunnels.
Their high tunnel design is 30′ x 40′ but can scale.
My friend Mike Bomford leads much of the research and field extension work of the KYSU sustainable ag program.
For those of you considering building high tunnels that are large and to last for a good number of seasons you should consider making your high tunnel out of steel pipe. There are a number of good steel pipe hoop bending tools out there that make the job easy and quick. You end up with a strong greenhouse that has the structural strength to handle attachment of interior fans, shades and lights (within reason).
You might modify any high tunnel design to bend half hoops instead of full hoops, with the last couple feet of each half hoop being straight to attach to a ridge beam and create a peaked roof. A peaked roof also makes it easier to build in ceiling vents if you need the ventilation in hot weather.
You might also consider straight sides and straight roof, using the pipe bender just to bend the wall- roof elbow (at the top of the sides and bottom of the roof): this increases the interior greenhouse air volume a bit and makes the interior edges of your planting area a bit easier to work. Here’s a couple high tunnel hoop bending tool sites:
http://www.lostcreek.net/cseriesbender12999.html
http://hoopbenders.net/