Sounds like you've really thought this project out thoroughly! I think I follow what you have planned. The main criticism I have is with the 6-mil film you plan to use. Having used 6-mil myself for several years before arriving at the product I use now, I can say that it's flimsy and easily prone to tearing. Commercial gh's that use inflated film covering will use 11-mil on the exterior, and, if they're trying to cut costs, will use the 6-mil on the inside because it doesn't require as much durability. By attaching your film just on the edges of the structure, you'll be asking for trouble. 6-mil stretches, and no matter how tight you pull it, it'll still flap in the wind. Also, with so much potential force focused on a single attachment point along the edge, it'll be prone to pulling free...unless you somehow roll it a couple times around something to evenly-distribute the force. The problem with the wind blowing over it is the element of "lift." Depending upon the wind direction, even with the ends open, the covering will alternately want to rise, then snap back down against the frame. A few hours of windy conditions is all you could ask of 6-mil. Even though the cost is higher, I'd highly recommend the 5.2-ounce translucent tarp linked below. It's 12-mil, and has a woven fabric of fibreglas "tapes" inside the plastic for strength. It's like iron, doesn't stretch, and can withstand just about anything you throw at it. Since it's stronger, and heavier, you'll have less of an issue with it tearing free from attachment points. You also may be able to get away with wider spans, saving you on some rebar. Another plus is the light diffusion through it -- no possibility of burning tender plants/seedlings. I'd have much greater confidence in this material meeting your needs, only attaching it along the edges. The one weakness as I see it for your application is that the largest width available is twelve feet. FarmTek has two products that would be suitable for this purpose. The first one is their Super Tape Seaming & Repair Tape, which is $22.95 for a 3"x60' roll, or $32.95 for a 6"x60' roll. The second is the Premium Repair Tape (product #105383), which is $71.95 for a 4"x100' roll. I'd feel safest sealing both the outside and inside edge, with a 6" overlap of the tarp. Hope your idea for securing the framing against possible racking works OK. If it didn't for some reason, you could retrofit easily with a support line and stake on either end. If you can find a good source for purchasing the wrapping material (to cover the rebar) you described in bulk, that's probably a good bet. I know FarmTek sells something for this purpose, but I'll be darned if I can find it now. The only thing I'd suggest is to use a good-quality tape. I know duct tape is a popular do-all, fix-all, but it performs miserably whenever moisture and heat are present! For this reason, you may want to consider a wire-wrap over the packing material, as an inexpensive material to tightly secure it. Removing the covering in the summer will expose all your handiwork to the elements, so that's another thing to consider. All that work to wrap your rebar may not survive unprotected. Hope there was something helpful here. -Bruce Here is a link that might be useful: 5.2-ounce fabric at FarmTek

A couple of thought: First, having just gone thru designing and building an engineered GH, I doubt your conduit on 4' centers will hold 52#/sqft load. My place is also 15' wide. I use 14ga 2" sq steel tubing on 4' centers, and that would not meet our 48# load. I ended up needing a center support (a small I beam) running the length at the midpoint of the span, with posts to ground to take the extra load. So I doubt the smaller, thinner conduit will be able to do it without some mid span supports. The steep slope of your roof might help (I don't recall the amount of load shedding that gives), but if you really want the structure to be able to hold 52# per sq ft, I don't think this will do it. You could look into building the "arches" into trusses (more so than you are already doing), by adding strategic cross members. That would certainly up the load they can handle but I can't say that alone would get you to 52#. Of course, if you are willing to go out there and brush the snow off after every big storm, it may not matter. BTW, does your 52# load include wind loading? I am curious why you plan to run the length of the GH N-S vs E-W. Typically for maximum solar gain in fal/spring/winter one aligns them E-W. I'd agree with the other comments about vent size. You might consider vents on the ends close to the peaks. Not entirely as good as peak roof venting, but much easier to build, and if the building is aligned with the prevailing breezes, can work OK. You might even consider removing the ends for the summer.

I have a very similar design happening, large format tiles, curbless with trench drain, floating vanity etc. I am very close to the glass install. Curious about your glass install. How is it secured so that it does not wobble? Floor to ceiling, wall brace, or? I am considering a panel about 72" high by 54" long, the length of the shower, fixed to the wall and secured to the floor without screws because of danger of puncturing membrane. Panel would be stabilized by a return panel 8-12" across the shower opening. We were going to try it first without a door. Thanks.

Excellent question!... wish I knew the answer. I see no mention of it in Ray Mullin's classic 'Electrical Wiring, Residential', or anywhere else, so I agree with you, i.e. assume it's NOT allowed. OTOH it costs nothing (but a little time and aggravation) to call your AHJ. Try using the term "chemical anchor" vs. "epoxy"... sounds better, lol. I understand your reluctance to drill into a structural steel column, esp. if there's environmental exposure (rust). And welding on a backing plate is a bit over the top. Will the entire perimeter of column be visible, as in an industrial setting or unfinished basement? Maybe there's a hose-clamp type solution? Perhaps your "loophole" around the code/AHJ is to epoxy your wood/metal/PVC "backer" to the column, and then screw into that... if you can live with the extra standoff. Totally speculating here. In non-electrical apps, I've used chemically related anchoring epoxies (Simpson Strong-Tie ET/SET, PC-Concrete, etc.), and been very impressed with their strength, but they all have "deflection" temps only in the 150degF range, i.e. the point they start losing significant strength. That's amazing that JB has a product (which one?) that's good up to 600F!! Need to keep some on hand for radiator leaks. That represents quite an advance in civilian copolymers. PS: How are you planning on "strapping" the conduit to this column? Please follow up and let us know how you made out.