Another shelter question: PVC vs. EMT for custom canopy

Nomenature · Post by **Nomenature** » Tue Mar 13, 2007 8:30 pm

Hi folks,

Our main shelter is beginning to hatch from plans. First off, I found this really awesome site that allows you to configure your own custom canopy, shows you the plans, and gives you instructions as to what parts you need to buy etc. Not that we know anything about their products, but the planning aspect of this site is really cool:

http://www.creativeshelters.com/Design- ... -Tool.aspx

So we have designed our own canopy. Most of these online sites do not sell the tubing for the legs, side struts, etc. They suggest that you go to a local source as the shipping on 10 ft lengths of pipe is pretty high. So here's the question: (finally!)

In lengths of 7' and 10', could 1" PVC pipe work as well as 1" EMT tubing?

We plan to cover our (20' x 30') shelter with Aluminet, so we won't get as much lift as with a solid tarp cover. And yes: thank you, we know we have to really tie the thing down, use 18" rebar... etc.

What we really want to get some opinions on is whether (lighter, cheaper, easier to cut) PVC at those lengths would have too much 'give' under windy playa conditions or whether we should stick with the EMT or chain link fence tubing.

Also: any opinions on 1" vs 1 3/8" in any of the above materials?

What do you sage folks think?

Many thanks in advance for your weesdome and thyme.

Respectfully,

Momma Nomen.

Zhust · Post by **Zhust** » Wed Mar 14, 2007 7:15 am

Structurally, I think you should be okay to use either. I personally recommend against PVC because of environmental nastiness in its life-cycle.

When PVC -- polyvinyl-chloride -- is manufactured, careless practices can release chlorine into the environment which creates dioxin, a nasty chemical that's hostile to organic life. Further, the monomer vinyl-chloride causes liver cancer (my citation is derivative through a documentary called "Blue Vinyl").

During its useful life it is quite benign. It tends to outgas a little but chemically it's quite stable. For building structural elements, it does have a tendency to shatter when it fails so that's a vote against it.

When it needs to be disposed of, well, there is no way to dispose of it. If you burn it, it releases vinyl-chloride again (hint: don't breathe fumes from a vinyl-sided house on fire). If you bury it, it'll eventually decompose and ultimately release chlorine. As far as I know there is no way to recycle it.

That said, making use of scrap PVC is desirable because the only thing you can do with it is to reuse it. Buying new -- especially for a temporary installation -- is not such a good idea.

Thanks for listening!

dragonfly Jafe · Post by **dragonfly Jafe** » Wed Mar 14, 2007 8:52 am

Nomenature wrote:In lengths of 7' and 10', could 1" PVC pipe work as well as 1" EMT tubing?

in a word, No.

I use PVC for my structures, but I curve the pipes into arcs and interconnect them at the nodes (using tape). Even then some of the windstorms can get scary (almost lost my structure during wednesdays storm last year - had to add a bunch of lines and cut loose some tarps to save it).

You can make PVC work, but it will wiggle in the wind (if not break), and 1 year is all you will get out of it most likely.

If you can work the EMT, it will be stronger and last for years. And it will be the same every time you set it up.

robotland · Post by **robotland** » Wed Mar 14, 2007 9:01 am

Hopefully your intent is to create a structure that can be used throughout the year- So you may as well build it to last. If you look at those carport kits you'll see that they use a bare minimum of 1" tubing, and it's usually a little different from regular electrical-use EMT. At lengths of seven to ten feet a stick of 1'' EMT will bend under a windload and I wouldn't use it except for corner uprights. Perhaps a hybrid structure, with metal uprights and PVC crosspieces...Use more instead of bigger, and count on the roof flexing in the wind instead of bending and then NOT bending back. Another alternative would be to use wood- At week's end you have your choice of taking it back home, burning it or donating it. I've been making more and more "one way" structures, and enjoying the extra elbow room on the long drive home.
ULTIMATE SOLUTION: Build a dome. It's a great storage structure for the rest of the year, breaks down relatively small for transport, and will bear a PHENOMENAL load.

phil · Post by **phil** » Wed Mar 14, 2007 11:19 am

The easy, but expensive, answer is to try it at home. I recall that Louise and I tried PVC in sewer pipe size for a flat canopy shade structure and that even at that diameter and wall-thickness the PVC was too flexible for structural stability. I can't remember the diameter, I'm sorry to say, but it was way more than an inch. We ended up going with EMT, which worked fine. We've had it for years, but we've switched to a canopy with cyclone fence rail for pipes. We'll be using the EMT shade at Dark Skies this year, though, as it is an easier fit in our SUV than the fence railing.

The reason we quit using the EMT canopy is that it had a flat roof, which holds rainwater when it rains. The metal structure withstood the weight of a canopy full of rain, but the canopy was permanenty stretched and drooped in the middle, meaning you couldn't stand up under the canopy. We went with a peaked roof which used fence rail and was larger. (The EMT is 10x10 on top and 7 feet high on the legs. Flat roofs have their proponents, but every design has its bads and goods. Since we've had our peaked roof shade, we've had no rain at all, so I figure that's because we now have a peaked roof. :->

MikeVDS · Post by **MikeVDS** » Wed Mar 14, 2007 3:52 pm

I would not be confident in the PVC. Even the EMT is a little weak for my tastes though. My philosophy is, if I can't do a pull-up on it, then it's not sound.

Jordan 10-E · Post by **Jordan 10-E** » Thu Mar 15, 2007 8:04 pm

Hello. I can answer your question. I set up a 40' x 40 flat roofed structure each year with the very connectors your looking into. It works great. I use 1" EMT conduit. Anything less than 1" is no good even though they sell connectors for smaller size tubing. The wind and other forces will destroy anything less.

As for PVC, it will absolutely NOT work for this type of structure. First, it is in no way rigid enough to do the job. You must use EMT. There is a second reason PVC will not work. When referring to the size of EMT or PVC (say 1") it is the INSIDE diameter of the tube they are talking about, not the outside. The walls of PVC pipe are 2-3 times thicker than the walls of EMT. PVC will not fit into the connectors.

Last but not least, cost. I just finished responding to another related thread on Tribe concerning domes and EMT. One of their concerns was the same as yours, cost. It can be expensive to buy 1" EMT, no doubt. However, buying anything thinner (or different) will not work, or will result in failure when your poles bend. You need to look at this as a investment that will last for years if you take care of your conduit (don't throw it around). Just suck it up and buy the 1" EMT. It is a very convient and easy to set up system. I love my conduit and connectors.

Jordan 10-E · Post by **Jordan 10-E** » Thu Mar 15, 2007 8:08 pm

Unfortunately, though cheaper than EMT, chain link fence posts will not work either as they will not fit into the connectors. Their width is not the same as EMT.

diane o'thirst · Post by **diane o'thirst** » Thu Mar 15, 2007 8:33 pm

Consider bamboo as a third alternative. If you have a Craig's List or Freecycle in your community, you can probably get it for free.

Slightly different joinery technique. This site tells you how:

www.desertdomes.com

Nomenature · Post by **Nomenature** » Thu Mar 15, 2007 8:37 pm

Hey Jordan (any everyone):

Thanks for the replies!

This site I put a link to above has connectors to specifically work with 1 3/8" Chain link fence tubing. That's one of the possible configurations they allow on their site. I have to believe that thier connectors will work with that tubing, if they are specifically indicating that. But I will ask them that - for certain.

I have not been able to locate a good source locally for the 1" EMT pipe. I was floored that they did not have that at Home Depot. But what they DO have is 10' lengths of 1 3/8" chain link tubing. So we'll go for sturdier, stronger and go from there.

Jordan: I like your comment about it being an investment. That's exactly how we are looking at this. Our structure with Aluminet will cost out at around $850+, but we 'founders' are looking at this being an investment in a community, one that will have a life after this one year. BTW: we are / will be Camp Kismet: virgins all 'cept one :).

Peace :)

Jordan 10-E · Post by **Jordan 10-E** » Thu Mar 15, 2007 8:51 pm

I forgot that they make them for the fence tubing. You might want to do that because the poles are strong and it is cheaper than EMT.

gyre · Post by **gyre** » Thu Mar 15, 2007 10:45 pm

You can use rigid steel or aluminum conduit.
As mentioned you must size the pipe and fittings together.

robotland · Post by **robotland** » Fri Mar 16, 2007 6:49 am

Of course, you could always design your OWN fittings and couplers...Given the facility to do so, it can be quite satisfying. One of the great joys of EMT domes is that it doesn't matter what sizes you fasten together as long as there's a hole for a bolt. And you can combine either EMT or PVC with wood at strategic points , using two-hole conduit straps and drywall screws. I use this technique to reinforce high-traffic struts in my dome structures.

phil · Post by **phil** » Sat Mar 17, 2007 2:25 pm

For a photo of a PVC shade see this thread:
http://eplaya.burningman.org/viewtopic. ... c&start=60

Scroll down to the photos - the PVC tarp and lower down for our fence railing shade.

It may be that side panels are the real destroyer in winds.

phil · Post by **phil** » Fri Mar 23, 2007 4:36 pm

Okay, forget PVC and EMT, Amazon is offering this amazing 10x18 wedding chapel with wood roof:

for $21,000 - but GET THIS! It's delivered fully assembled. Includes screen windows! Shipping may cost an additional $1,700, but it's delivered fully assembled.

If that's too much, this very tiki hut

is only $14,000 and is rated to withstand gale force winds. I'm not sure it's delivered assembled, though.

BAS · Post by **BAS** » Fri Mar 23, 2007 6:25 pm

Cool! Do they promise delivery to ANYWHERE?!!

Let me check the sofa and see if I have enough in spare change to get them both...

(Since when did Amazon start selling buildings?! I suppose the logic is that you have to have somewhere to put your books....)

B.

Another shelter question: PVC vs. EMT for custom canopy

Another shelter question: PVC vs. EMT for custom canopy

Re: Another shelter question: PVC vs. EMT for custom canopy