I'll look in my Engineer's Desktop Reference to see if there is any data on strength of pipe structures mounted horizontally. Try not to lock yourself into buying it (as in, laying out your hard-earned money for it) but rather see what you can find at salvage yards or various "throw-out" places. Rule of thumb::::: Rigid electrical conduit is approximately equal in strength to ordinary schedule #40 black water pipe. The most salient feature of elec. conduit is the hot-dip galvanizing. It will not rust or corrode in the outdoor weather. For a six-foot span you could get 2" pipe for very little cost and it will be incredibly strong. It will hold just about anything you put on it. If it is rusty when you get it then sand it down lightly and coat it with Rustoleum "Rustformer". It creates a polymerizing finish on tight rust and becomes the primer coating for a top coat. Medium green is good. I apply "Moore's Law" to structures like this. Moore's Law::::::::::::::: If a little is good, then more is better and WAY, WAY TOO MUCH IS JUST RIGHT!!!!! LOL

How it all turned out, in case someone else wants to do the same project: This project started by planning to take electricity (a 20amp circuit) from my house to my barn. Then I said: "Since Im going through the trouble of digging the trench, why not also run a phone/network cable then why not water for a sink someday then why not warm water for the future and so. I ended up running four 1 1/4" conduits to my barn. One for electric, one for phone/cable/network and two for water (cold/hot) I ran two 3/4" PEX water lines inside two of the conduits. The ½ PEX line would have gone in easily but the ¾" was a different story. I had to both push on one end and pull from the other. I suspect that the only reason I was able to finally do it is because I only used 45degree elbows (5 elbows on each conduit run). Had I used 90 degree elbows, ½" PEX may have been the only realistic option. I did use electric PVC because of the gentler elbows. Regular white PVC elbows are too sharp to pull PEX through. Could have used ABS, I suppose, but decided on electric PVC. The run is short (50ft) so the use is obvious looking at the two ends where the electric cables and water lines come out. In retrospect, I should have marked (written on) the entire conduit length to indicate use, since how the 4 pipes are routed may not be obvious to someone digging just a hole. But in any case, the water lines are at the bottom 24" under, the electric line is just above at 21" and the data/network lines are at about 14" (I separated data from electric lines to prevent possible interference). No frost issues even at 14" here in central California (we have many problems but frost is not one of them). I also had to construct an insert to put in front of the PEX in order to push/pull it, to prevent the PEX edges from catching at the PVC conduit joints. It was a rather fallic looking insert made from a wooden dowel, shaped on a grinding wheel and a metal edge to reduce friction. I do not know if they make something commercially for this purpose. I immagine its a common problem. Also, I dont know if there is something to lubricate the PEX to help out, but I did not use anything and certainly stayed away from oils as they do degrade most plastics (including PEX?). If I had to do it again, I would have taken lazypups advice, skipped the conduit and burried the PEX water lines directly, in spite of the PEX manufacturers advice to avoid burying the PEX in clay soils (my type of soil). I had to tunell under concrete for 3 ft so opening a small hole for the ¾ PEX would have been much easier than opening a 1 ½" hole in the dirt for the 1 ¼" conduit. The cost of the conduit is not much (around $30 for 50ft run) but it does take considerable amount of time to assemble it correctly in the trench and tunel it under the concrete. I would have still had to deal with the two conduits for electric and data though. If the PEX water line ever goes bad, I may be glad I did it, especially if Im 70 by then, Ill appreciate not having to redig the trench. Actually, after reading the comments, I would have run the PEX in 1 or 1¼" poly, but I could not find any at the usual stores (HD/Lowes). I ran PEX because I wanted to keep the water potable. I call it barn but use it mostly as a shop. No animals, it is only 250 sqf. PEX has been used for over 20 years in quality an regulation obsessed places like Germany. Id say it is a safe and reliable option. I have anecdotally heard of mice chewing through exposed poly in rural settings, especially if they can hear the water running in it. Perhaps theyve figured it out in dry climates. I have put a poly string in all the currently unused conduits. Took me 2 days to dig the 50ft, 24" ditch alone by hand, including tunneling under concrete for 3ft, and one day to buy the materials and assemble the PVC in the trench. Then a couple of hours to fill back the trench. I am not sure how I will handle the hot water if I ever hook up this water supply. I may try out to see how hot remains the water once it reaches the barn and if the results are not satisfactory I may install a small electric water heater now that I have also run conduit for electric. I guess, if I end up not using the second PEX line for hot water, I could then turn it into a second cold water line to increase my max water flow. Running the actual electrical cables to the barn is still pending, subject to resolution of some grounding issues (I have an active post in the electrical forum). Thanks for the advice.

Thanks for the input, but now I'm confused. The schedule 40 PVC pipe I'm using is stamped DWV. But it's pressure rated to 280 psi, and its NSF pw certified (potable water). It's also ASTM D1785, which is the standard for pressure rated PVC pipe. I'm not clear on what is wrong with this. Is it just that I didn't buy it from a pool place? I know the there is a big difference with the fittings, DWV vs. pressure. I have the pressure fittings. Spa flex is rated at 55 psi. Obviously easier, but junk by my standards. I can't get myself to use that, I want to use rigid pipe.

Lots of cheap, quick "structures" have been jury-rigged with all sorts of non-listed materials. Being in a Level 1 HVHZ, this is NOT a luxury I have, legally, practically, or ethically. Excuse my bias, but at least it's in the direction of "overdoing" it. >>>I'll give the OP credit for at least specifying beefy, OUTdoor-listed RIGID, because over in the sister greenhouse forum he cites, there's peeps using--I am NOT MAKING THIS UP--EMT (thin-wall) conduit for OUTDOOR PRIMARY STRUCTURAL SUPPORTS! HMOG, this stuff's not even listed for merely protecting wires outdoors, let alone for holding up a roof!... but hey, it's galvanized... lol. Cost is always a valid factor, and no sense building to hurricane codes if not necessary. But if you live in an area where such ad-hoc conduit "structures" are common, well then, I guess join the "guild" and have at it, lol. Regardless of your locale, and lot size, you should at the very least consider what your AHJ, an insurance adjuster, and/or a court of law would say should a blustery thunderstorm or blizzard cause your high sail-area "structure" to topple into, or missile-impact, your residence, or--much worse--SOMEONE ELSE'S. =:O Bottom line: since the LOAD ("strength") data you're seeking does NOT exist for electrical conduit, you'd always be GUESSING at whether your spans, angles, connections, etc. had adequate SAFETY MARGINS for the task. OTOH there's a plethora of I-beams, T-beams, C-channel, U-channel, square, round, and triangular tubing LISTED for structural use, and a plethora of load tables (and application examples) to go with them. ;') OK, look... when you're done with this thing... add a (LISTED) steel cable GUY WIRE to each corner!