Conduit greenhouse, the frugal way (frame design help)

So i'm thinking of a design that would be very dog house looking with gutters on each side that feed to 2 55 gal water barrels inside. Im going to make a double layer, slightly into a hillside, and expiriment with what i can put in there. Im a zone 5 in south wisconsin us.

Heres the problem. Im cheap, and the tent fittings online are like 4 dollars or more. With the double layer, it gets pricey.

So i have some plumbing and electrical skills and conduit is limited in fitting options at menards, and copper pipe is crazy expensive. Pvc is obvious, but not long lasting.

Ive thought about using cheap copper fittings to fit onto cheap conduit. They are slightly different sizes and im hoping 3/8s copper female fitting fits as a male into 1/2in conduit. Normal menards and home depot do not have 3/8s size. Or maybe i should look harder. It exists though. I wont give away all my secrets (until i know they work) but is this too complex to consider, and theres some cheapo tent fittings i can use? I mean these will be 50 to 60 cents, strong and weather proof. Thats tough to beat.

The only thing im ignoring is that copper and galvanized are corrosive to eachother, but im not filling these things with water.

Try pricing electrical fittings for emt. They have 45s 90s etc. all pre bent with set screws.
Note.. You're looking for the fittings that look like pre bent conduit not the pull elbows with a door/cover for accessing the wires.
Also you could find a cheap used emt hand bender of ebay or such and bend all the conduit you want for the cost  of a few fittings.

I'm assuming your main challenge is the fittings at the ridge?  What about using a 2x4 as the ridge and drilling holes into it at the correct angle so you can just stick the conduit into the holes?

edited: (Mike J, I like that idea.  Simple, strong, economical, customizable.  Also you can make the ridge beam/pole as large as you like and make it part of a wood frame, post-and-beam type structure for added strength and stiffness.  Make the top as smooth and gently curved as possible, to make it easy to pull the plastic over without snagging or tearing, and since it will be the least accessible part. The wood can last longer than the plastic so likely the plastic will be changed out after awhile.)

Johnmark,

Why does PVC not last?  Does ultraviolet make it brittle?  That's the only reason that comes to mind.  If so, then dark paint should fix that.  They now sell paint that is supposedly better at adhering to PVC.  But whether you use that or not, a chemist would treat it to create (chemical) "functional groups" on the surface.  This is as simple as briefly passing a flame over it, or some other plasma, like a high-voltage electrical coronal discharge ("St. Elmo's fire").  Ironically this contains UV, ozone, high temperatures, all things that ironically destroy the outermost surface of the plastic; however, as long as the paint sticks to it, and is opaque, then it should protect the inner layer from UV.  

Also "zinc oxide" is a UV stabilizer that could be added to materials.  You could also wrap the plastic in aluminum foil, which is definitely opaque.  
(Side note: I wonder if someone should make "zinc foil", or zinc powder additive, since this is opaque, and is a sacrificial anode to reduce the corrosion of steel (galvanizing), and when it did corrode it would make zinc oxide which continues to inhibit UV.  Might be a useful material here somehow, depending on what you're doing.)

Anyway, I'd say be cautious about using dissimilar metals together because galvanic corrosion happens *way* too easily between certain metals (like copper and steel).  Even when we think there's no water, it shows up.  Outdoors, in a humid greenhouse environment, with condensation?  There's going to be water, and it doesn't take much.  However, any sort of electrical insulator you put between the metals will essentially prevent that type of corrosion.  Again you can use paint, adhesive, or plastic film, melted wax blended with oil...really anything durable that doesn't pass electricity.  

Use a material and a structure that will be "thick" in all dimensions for high-stiffness.  Stiffness goes as the thickness to the 3rd power.  So 50% thicker is over 3x stiffer.  You want to be able to pull the plastic tight and minimize the amount that anything will: bend, wobble, flex, or flap, in wind and snow.  

To get the most growing area for the least materials, physics suggests to skimp on height and make it low.  This also reduces wind loading.  If you're taller than the plants you're growing then you're building it tall for you to walk in.  Other ways to deal with that might be with a low tunnel where you access it from the outside by lifting the plastic.  If it's messy or a pain to lift the plastic then it might make sense to have some kind of a rigid structure that could be lifted for access.   Another way to use materials economically might be to dig down between the beds to give you more headroom.  Then it will feel like you're working on raised beds.  An economical way to make the wall for a raised-bed (or sunken walkway), might use "rammed earth", "earthbags", adobe, straw bale, or "stabilized earth"...pick your favorite.  This could even be terraced to the south.  You can also build up slightly to make a sort of foundation.  I think building into the hill makes sense.

Anyway, there's a balance between trying new things and using tried-and-true methods.  Definitely try to learn from the successes and failures of different designs.  

The grey PVC electrical conduit is UV stabilized and not subject to corrosion from condensation like the metal conduit. You could also go without many fittings if you use a larger diameter for the ridge and bottom plate and drill holes into it to receive the lengths of conduit.  

I'm an electrician,and thus kind of build has been in my mind.
PVC,lasts. I've used it out doors for years,structurally, with no problem.
Definitely use a bender , save money on fittings.
Galvanized electrical boxes are cheap,and offer many holes that can be knocked out.
These could make joints at right angles ,with or without the use of connectors.
Drill a proper sized hole in any hollow thing,a peice of 4" pvc for instance,and you can use them in the same way as an electrical box.
Geodesic dome builders flatten the ends of  conduit ,drilling holes through them and joining them with bolts and nuts.
Google "electrical condulet" and "1/2" emt jake" for more options.
Check 1/2"  black iron and galvanized  steel plumbing fittings  for compatibility.
Consider using flexible hose as a joint,choose one that just fits over the end of the conduit.
Use this to create joints with flexible angles, drill and bolt multiple hose joints together to bring 2,4, or 6 conduits together at one point.
What kind of joint are you trying to emulate?
Link to a picture,that would help us help you.

PVC is going to be the easiest and will last fine as others said.  It makes a great hoop-style greenhouse.  One of the problems with it is it can get a little too flimsy if your greenhouse is getting large or when you have snow loads.  One solution I saw once (haven't tried it myself) is putting rebar inside the pvc.  You can get 20' lengths of both PVC and rebar so you do one continuous piece for each hoop.  In the plans I saw (Richo Cech's book on growing herbs), he just pounded some 1" metal conduit into the ground and the 3/4" PVC with rebar slides into the conduit.  That makes it easier to take down and put up.  He was just draping the plastic down and holding it down with dirt or sand bags.  It is meant to be a cheap yet stable greenhouse but is not going to be quite as nice or permanent as one with nice built endcaps.  

Also, a conduit bender is awesome.  It allows you to build all sort of things from thin-walled metal conduit.  I've built a mobile chicken coop and a garden cart that are strong, light, and really durable.  I've replaced the wood slats on my garden cart twice and the metal frame looks like I built it yesterday.

Wood is as easy to work as plastic, the same price or less, and can last just as long.  You don't even need to paint it if you find a rot-resistant variety (for example: resin-filled pine/spruce, white oak, or locust, cedar, and many others).  Black locust can grow 3/4" in diameter per year.  It is cut-and-come-again.  The bark comes off easily, and even the bark fiber might help lash the poles together.  
It puts nitrogen into the soil.  Plastics can leach chemicals like plasticiser pthalates.  Locust provides food for animals and bees.  Wood is easily recyclable/compostable and makes great firewood as an energy source.  (PVC isn't recyclable.  At least polyethylene irrigation tubing is more recyclable/reusable, less toxic and could even be burned like a wax candle if you had to.  PVC releases toxic chlorine-compounds if it burns.  It might be better to just use that for plumbing.)  You might find locust seeds near you for free, if not a seed packet costs just a few dollars with shipping, and you can save seeds after that.  Plants grow materials locally on-site for free using solar energy.  PVC requires large amounts of petroleum oil to manufacture, ship and deliver.  Maybe petroleum products were okay when there was vast quantities of domestic oil, but when you have to import expensive foreign oil from leaky drilling rigs, tankers, and pipelines, maybe that isn't the best, or most sustainable idea compared to growing a plant like locust that grows poles like some kind of bamboo weed!   If you're like me, it probably grows near you but you wouldn't even recognize it or know how to use it until someone teaches you or you take the time to learn.  Well, isn't that what a forum like this is good for?  

videos:
http://www.youtube.com/watch?v=du9LeeYX1o8

http://www.youtube.com/watch?v=JUH0leNsP_4

Plastic or metal poles are ready to use off the shelf,they come in regular shape and sizes,there are lots of fittings available.
The journey from plant to useable poles is a lot of work. Access to the raw materials is not a given.
Time and personal energy are limited resources along with fossil fuels and clean air.
Maybe split the difference,use dimensional lumber  as efficiently as possible.
Reuse discarded  materials when possible.
I know I wouldnt be able get anything done if everything had to be done from scratch, and the wood equivalent of a 10' stick of  1/2" pvc  isnt easily availble.

I think this website was founded because the philosophy of buying a corporate petrochemical product for every need hasn't left the world or its residents with as good a quality of life as growing your own, at least some of the time.  I think we're here in large part to share information on how to "grow your own".  Are you sure you're at the right website?

If you watch Paul's video from 1:00 to 5:00 , the guy says that it's trivial to take the bark off of a Black Locust pole.
It's just as easy to cut 1-inch saplings as it is to drive several miles to a big box store, then have to pay for the items (if they have what you want.  Access to "shelf materials" is not a given.), and haul those long poles back.

PVC, petroleum, and dimensional lumber is more of a scarce resource and less-renewable than 1" saplings.
Anyway for these purposes, material like a 1" wood pole is substantially equivalent to a 1" plastic pipe.   They are both polymer material.  So a design that uses one is no more "from scratch" than the other.  A 10 foot stick of 1/2 inch wood is *totally* available, and probably closer to you, in greater quantity, with wider selection, provided more sustainably, with less toxicity and for a better price!  If going with the big-box store seems easier, it might be because you're relying on all the people running the store and the factories for their collaboration and for the specialization in the division of labor.  If a local community, or "permies.com" had a similar level of collaboration and specialization in the division of labor, then this aspect would work just as well as a big-box store model, if not better.  

Some designs might call for precision parts with tight tolerances but there are plenty of designs that don't require that, and having the flexibility to not need that is a good thing, because it allows one to use whatever is available.  If you simply lash poles together for example, then you can use any size materials.  In Asia they erect construction scaffolding out of bamboo and it is extremely strong.  It is probably more economical, more sustainable and probably has a better strength-to-weight ratio than steel, making it more efficient, easier to put up or take down, and easier to move around when needed.

Even if you use end-fittings, I don't recall you mentioning how you were going to fasten them.  PVC cement isn't ideal.  Using a set-screw is sort of convenient but rather weak.  That method often fails.  A clamping action is best because it grips the entire surface, is adjustable, reusable and is a custom fit every time.  Wrapping with fiber offers a similar method of clamping.  It might not be ideal in every way, but it is effective, tried and true, and can be used with any fiberous/twine/string/rope material available, which is often rather economical.   Again the sheathing material is conformally wrapped, so it does not require a precision structure.  It is generally a lot easier, faster and more forgiving to build something when it doesn't have to be precise (because the allowable tolerance is greater).

This is like the argument between building log homes using natural logs, versus building them from kits made of machined dowels.  If you really want everything to snap together like tinker-toys, you can probably put some sort of tool-die in a hand-drill chuck and quickly turn the end of a pole into a dowel.  This isn't necessarily strong or efficient though.  A clamping system is often preferred, even on tight-tolerance designs.  

Mike Phillipps wrote:I think this website was founded because the philosophy of buying a corporate petrochemical product for every need hasn't left the world or its residents with as good a quality of life as growing your own, at least some of the time.  I think we're here in large part to share information on how to "grow your own".  Are you sure you're at the right website?

Yeah,Im sure.
Most people here won't insist on their ideas as the one true way,while demonizing other, less sustainable methods.
Part of the "be nice" policy.

Mike Phillipps wrote:
If you watch Paul's video from 1:00 to 5:00 , the guy says that it's trivial to take the bark off of a Black Locust pole.

I'll check that out. Having stripped small logs before, I wouldn't call the processes trivial.

Mike Phillipps wrote:
It's just as easy to cut 1-inch saplings as it is to drive several miles to a big box store, then have to pay for the items (if they have what you want.  Access to "shelf materials" is not a given.), and haul those long poles back.

That depends. Where do you live? I live in a city. I dont own a stand of locust saplings.
I belive more people on Permies have access to money and/or vehicals,than to land and saplings.
I'm glad you suggested natural materials,as they will be an reasonable option for some people.

Mike Phillipps wrote:
PVC, petroleum, and dimensional lumber is more of a scarce resource and less-renewable than 1" saplings.
Anyway for these purposes, material like a 1" wood pole is substantially equivalent to a 1" plastic pipe.   They are both polymer material.  So a design that uses one is no more "from scratch" than the other.

If I pick corn, cut it off the cob,and cook with it,  that is "from scratch" .
If I pour it out of a plastic bag from the freezer section,  isnt.
Preparing saplings for use in building is more like former than the later.
My experiences with pvc suggests that it bends in a way that a wooden pole does not. Wooden hoophouses exist, made from furring strips. The furring strips are not as a flexible,and are assembled  into bows in pairs with wood glue ,two by four blocks,clamps,skills and screws.
Willow might work,but it isn't as easy to get while of for some people, including me.

Mike Phillipps wrote:A 10 foot stick of 1/2 inch wood is *totally* available, and probably closer to you, in greater quantity, with wider selection, provided more sustainably, with less toxicity and for a better price!  

Really? I would like to know more. I wouldnt know where to find such a thing. The woods nearby don't belong to me and are filled with short limbed honeysuckle,not willow or locusts saplings. The stores stock 1/2" inch dowels,too short,too expensive and too weak.
Available bamboo doesn't perform in the same way. It's free,but low strength and cannot survive being bent like pvc can.I can find 3 different kinds of 1/2" pvc,closer to me than the other  items,and what it does is not easily duplicated by any wood product similarly available.
Me personally,  I'm designing with Polypipe in mind.
It's about $4.00 for 10 feet of 1.25" locally.

Mike Phillipps wrote:If going with the big-box store seems easier, it might be because you're relying on all the people running the store and the factories for their collaboration and for the specialization in the division of labor.  If a local community, or "permies.com" had a similar level of collaboration and specialization in the division of labor, then this aspect would work just as well as a big-box store model, if not better.  

Such a community,with such collaboration and and specialization does not exist near me.
So buying stuff from the big box doesn't just seem easier, it IS easier.
I suspect more people on Permies are near a big box than they are such a community.
I have bought cedar slabs on Craig's List, for a great deal for both parties.
Since then I've needed more. No new ads, old phone number is dead. Who does have cedar fencing?
The big boxes, each and every one of them.

Mike Phillipps wrote:Some designs might call for precision parts with tight tolerances but there are plenty of designs that don't require that, and having the flexibility to not need that is a good thing, because it allows one to use whatever is available.  If you simply lash poles together for example, then you can use any size materials.  In Asia they erect construction scaffolding out of bamboo and it is extremely strong.  It is probably more economical, more sustainable and probably has a better strength-to-weight ratio than steel, making it more efficient, easier to put up or take down, and easier to move around when needed.

I've used staples,nails, screws, bolts and zip ties to secure things. I find that,while I can just drive a screw, and be certain of the soundness of the connection,lashing isn't as easy to do,requiring skill I do not have. No design of mine has ever survived contact with reality, precision is one thing, but reliability  is what I seek in a building material.
One can build rocket stoves from not much more than mud, and many do,but the reliability of store bought materials has lead most of the community to use them.
The big boxes here don't carry big bags of perlite or fireclay, and they won't ship them too the store either.
Kind of a bummer, but I'm working my way around it.

Mike Phillipps wrote:
Even if you use end-fittings, I don't recall you mentioning how you were going to fasten them.  PVC cement isn't ideal.  Using a set-screw is sort of convenient but rather weak.  That method often fails.  A clamping action is best because it grips the entire surface, is adjustable, reusable and is a custom fit every time.  Wrapping with  offers a similar method of clamping.  It might not be ideal in every way, but it is effective, tried and true, and can be used with any fiberous/twine/string/rope material available, which is often rather economical.   Again the sheathing material is conformally wrapped, so it does not require a precision structure.  It is generally a lot easier, faster and more forgiving to build something when it doesn't have to be precise (because the allowable tolerance is greater).

A lack of consistency in building materials makes them harder to use. Some of the skill needed to build a wall is built into blocks and bricks and morter.
Building a good drystacked wall is a skill worth mastering, but building a cinder block wall is a lot easier.
On my property I have stones and rubble,but little skill masonry. If I want to use those  stones, I will employ slipcasting,because my ultimate goal isn't to become a stone mason,it's to grow food.
Similarly, if I'm going to lash together wood or bamboo, I'll use zip ties or wire.
When I build with pvc, I dry fit, then I run a self tapping screw or three through the joint.
Most of the branches I have worked  with need to be predrilled, or they will break.
PVC becomes brittle when the plasticizer leaches out.
This reliably occurs in CPVC supply lines,especially those that carry hot water.
I have seen this in my work, which is why I won't install the stuff. I use PEX instead. Regular Pvc for the drains.

Mike Phillipps wrote:This is like the argument between building log homes using natural logs, versus building them from kits made of machined dowels.  If you really want everything to snap together like tinker-toys, you can probably put some sort of tool-die in a hand-drill chuck and quickly turn the end of a pole into a dowel.  This isn't necessarily strong or efficient though.  A clamping system is often preferred, even on tight-tolerance designs.  

The historic log homes  in my region feature logs hewn into rectangular solids.
I wouldn't want a log home, they seem like a waste of wood,prone to pests and neither well insulated or with enough thermal mass.
That said, I wouldn't tell someone who chose to build with logs they could achieve the same outcome with a different material.
Not that the anyone seemed  set on building with pvc,it's just one option.



Wood is no subsituite for pvc in a hoop house without a huge injection of SKILL,either by the builder, or off-site.
Building from wood poles you process yourself is great, but its not an option that is affordable for all of us in terms of time,energy,skill and money.

William,  If you're going to go on a permaculture website and quote the "be nice" policy, can you please not post comments that attack the use of non-toxic alternatives to chorinated-plastic materials?  

I already explained that wood poles are at least as available as plastic poles.  It is easy to trim them.

Access to petroleum-based chorinated-plastics shouldn't be assumed to be "given", especially on "permies.com".
Plenty of people here don't live in the city.  And plenty of people here consider wood poles to be more available than plastic poles.  Plenty of people here are anti-plastic if there is an alternative, especially the more toxic chlorinated-plastics and ones with plasticisers that can potentially leach into the soil and food.  
There's nothing wrong with folks suggesting alternative materials, especially when those materials are in many ways better.

A well known problem with a PVC hoop house is it doesn't hold up in wind and snow.  Looking at the engineering data for "modulus of elasticity", that determines strength and rigidity, we see that most woods are 4 times stiffer than PVC, and even pine is 3 times stiffer.  And this doesn't even include the fact that plastic pipe is hollow.    http://www.engineeringtoolbox.com/young-modulus-d_417.html

Many of these woods are rot-resistant, including pine, and pine is extremely common, available and inexpensive.
If the wood is unpainted/untreated, then after several years the wood will rot, probably around the time that unpainted PVC would get sun-damaged, brittle and crack and flake off itty-bitty bits of chlorine plastic.  

If the greenhouse is covered, ventilated, and drained then it should be dry enough that wood and plants will be slow to rot.  
You know, plants are also made out of wood, so the same environment that protects the plants from rot also protects a wood structure from rot.  In other words, vent it enough to keep the humidity below 70% relative-humidity.  

When plastic cracks and flakes in the sun, the only way to get rid of all those plastic bits is to shovel away all the dirt it's in.  I've seen this first hand many times, even in material that you'd expect would be UV-stabilized like in an above-ground plastic swimming pool.  Nope, there are now little bits of swimming pool everywhere all over the garden/lawn.  It's very difficult to get rid of, and any chemicals in it will be leaching out for many years.  You might as well know what you're signing up for.  Just sayin'.  

Mike Phillipps wrote:William,  If you're going to go on a permaculture website and quote the "be nice" policy, can you please not post comments that attack the use of non-toxic alternatives to chorinated-plastic materials?  

Since I haven't posted any comments attacking the use of non-toxic alternatives,I will gladly continue.
Pointing out why plastic might be the right choice for some, and offering experiences with the locating,harvesting,and processing of natural materials that differ from the statements you have made, isnt making an attack.

Mike Phillipps wrote:I already explained that wood poles are at least as available as plastic poles.  It is easy to trim them.

You have indeed asserted that this is what you believe.
I have asserted something that doesn't match your assertion.

Mike Phillipps wrote:Access to petroleum-based chorinated-plastics shouldn't be assumed to be "given", especially on "permies.com".
Plenty of people here don't live in the city.  And plenty of people here consider wood poles to be more available than plastic poles.  Plenty of people here are anti-plastic if there is an alternative, especially the more toxic chlorinated-plastics and ones with plasticisers that can potentially leach into the soil and food.  
There's nothing wrong with folks suggesting alternative materials, especially when those materials are in many ways better.

I agree.

Mike Phillipps wrote:A well known problem with a PVC hoop house is it doesn't hold up in wind and snow.  Looking at the engineering data for "modulus of elasticity", that determines strength and rigidity, we see that most woods are 4 times stiffer than PVC, and even pine is 3 times stiffer.  And this doesn't even include the fact that plastic pipe is hollow.    http://www.engineeringtoolbox.com/young-modulus-d_417.html

Pvc hoophouses suffer from wind and snowload damage in the same way that deeply mulched gardens suffer from plagues of slugs.
The vulnerability depends on the local circumstances and the execution.

Stiffer,yes. Which is why they would be hard to make hoop houses of.
Even green, they won't bend the same way.
A roundwood structure,lashed together,
will have protrusions that will snag plastic sheeting.
Glass will be hard to fit to such a frame, ridged plastic less so.
Dimensional wood ,can easily accommodate these glazings.
Fresh evergreen boughs would probably make a good hoop house. Of course hoophouses use plastic.
And me personally I don't know where to get them.

Mike Phillipps wrote:Many of these woods are rot-resistant, including pine, and pine is extremely common, available and inexpensive.
If the wood is unpainted/untreated, then after several years the wood will rot, probably around the time that unpainted PVC would get sun-damaged, brittle and crack and flake off itty-bitty bits of chlorine plastic.

I didn't know that pine was rot resistant.
Osage, locust, yes. This is good to know, as pine is indeed relatively easy to come by.

My pvc fence posts are 10 years old. No sign of disintegration. Maybe it's happening on an an unseen level.
Kiln dried dimensional lumber last long enough outdoors,out of contact with the soil,longer if kept dry.
I imagine green saplings might do as well.

Mike Phillipps wrote:
If the greenhouse is covered, ventilated, and drained then it should be dry enough that wood and plants will be slow to rot.  
You know, plants are also made out of wood, so the same environment that protects the plants from rot also protects a wood structure from rot.  In other words, vent it enough to keep the humidity below 70% relative-humidity.

Yes, plants are sometimes made of wood,in the same way that that animals are made of meat.
Yet wood rots in humidity that plant thrive in,and meat rots in places animal grow.
For my greenhouse/coop frame I've used pvc, treated and untreated wood,and natural wood branches.
I am certain the pcv will out last the rest.
I am planning on swapping out some of the PVC for wood or bamboo.
It's on a slopped roof,a place where the rigidity is needed and the flexibility of pvc is a detriment.

Mike Phillipps wrote:When plastic cracks and flakes in the sun, the only way to get rid of all those plastic bits is to shovel away all the dirt it's in.  I've seen this first hand many times, even in material that you'd expect would be UV-stabilized like in an above-ground plastic swimming pool.  Nope, there are now little bits of swimming pool everywhere all over the garden/lawn.  It's very difficult to get rid of, and any chemicals in it will be leaching out for many years.  You might as well know what you're signing up for.  Just sayin'.  

Of those  who build pvc hoop house I'm sure some of them have had this experience.
I'm also certain many of them have not.

That doesn't make sense.  First you say you need flimsy plastic to bend it into a hoop, then you say you need ridged/rigid? plastic to hold glass.  

But I'm realizing from this thread that people like the Ikea type kits that are cheap and have designs that look "perfect" in the picture with parts that all supposedly fit together perfectly.  That's what people in the city buy, even if it's made of OSB/particle board and falls apart the first time it gets wet.  

Introducing the Ikea greenhouse with some pretentious sounding European name.  :)

Ridged plastic would mate with a lashed pole building relatively easily because it could be drilled and secured where it meets the wood and cut to fit around protrusions.
I was trying to explore how one might glaze a lashed pole building.
Glass seems prohibitively difficult.
Plastic sheeting actually could be used,it would take more work than on the smooth arches of a hoop house or the flat planes of a dimensional lumber structure,but it could be done. Still easier than the other options,but it will die before any pvc would.

Flexibility is required for a hoop house. Flimsiness is a side effect of using a material that so easily bends.
The material used for the hoops has to bend into a cemicircle  without breaking.
Plastic is easy, as would be some wood boughs,if available,metal can be done with the right tool, and dimensional lumber can be bullied into staying in an arc with no small effort.

Plastic sheeting, 4 mil or better is usually used to cover a hoop house.
I was thinking how one could cover a hoop house without it.
Cloth,greased or ungreased and cellophane come to mind. Both are rather flammable, but then,so is plastic.
Gotta look into it. I bet greased cloth beats plastic for R-value,if only by a litttle.

I won't use OSB at all.
I prefer plywood, or hardboard.
Hardboard doesn't even use glue, but one side is usually painted or varnished.
It's the stuff pegboard is made of.
The North wall of my coop/ greenhouse is made of reused plywood, the North roof of interior doors.
A layer of tarps under a used carpet keeps them dry,otherwise they would collapse,their glue destroyed by moisture.
I had another weird idea, on the subject of  conduit joints.
A tennis ball could be cut and/or drilled to receive the ends of 1/2" conduit.
A self tapping screw, or "injection" of cement could keep them in place.

Back to the alternative glazings. Cloth, treated with silicone,could be water and wind proof,and still allow light to penetrate.
Window screen can be coated in such a manner.
Cloth,put in place and sprayed with waterglass might work,but I think cured waterglass might still be susceptible to wetness.
Wax of course could work.
Gelatin? Again,not resistant to wetness,I wager.
Can it be mixed with something else?
Time for a new thread

Ridged plastic would mate with a lashed pole building relatively easily because it could be drilled and secured where it meets the wood and cut to fit around protrusions.
I was trying to explore how one might glaze a lashed pole building.
Glass seems prohibitively difficult.
Plastic sheeting actually could be used,it would take more work than on the smooth arches of a hoop house or the flat planes of a dimensional lumber structure,but it could be done. Still easier than the other options,but it will die before any pvc would.

Flexibility is required for a hoop house. Flimsiness is a side effect of using a material that so easily bends.
The material used for the hoops has to bend into a cemicircle  without breaking.
Plastic is easy, as would be some wood boughs,if available,metal can be done with the right tool, and dimensional lumber can be bullied into staying in an arc with no small effort.

Plastic sheeting, 4 mil or better is usually used to cover a hoop house.
I was thinking how one could cover a hoop house without it.
Cloth,greased or ungreased and cellophane come to mind. Both are rather flammable, but then,so is plastic.
Gotta look into it. I bet greased cloth beats plastic for R-value,if only by a litttle.

I won't use OSB at all.
I prefer plywood, or hardboard.
Hardboard doesn't even use glue, but one side is usually painted or varnished.
It's the stuff pegboard is made of.
The North wall of my coop/ greenhouse is made of reused plywood, the North roof of interior doors.
A layer of tarps under a used carpet keeps them dry,otherwise they would collapse,their glue destroyed by moisture.

I had another weird idea, on the subject of  conduit joints.
A tennis ball could be cut and/or drilled to receive the ends of 1/2" conduit.
A self tapping screw, or "injection" of cement could keep them in place.

Back to the alternative glazings. Cloth, treated with silicone,could be water and wind proof,and still allow light to penetrate.
Window screen can be coated in such a manner.
Cloth,put in place and sprayed with waterglass might work,but I think cured waterglass might still be susceptible to wetness.
Wax of course could work.
Gelatin? Again,not resistant to wetness,I wager.
Can it be mixed with something else?
Time for a new thread😁

Specialty fittings and connectors---For PVC:    https://formufit.com/

For chain link fence top rails:     http://www.tarps.com/fittings2.htm

1/2" Steel-conduit     1 1/4" PVC
------------------            ------------------
$2.80                        $4.00  
less expensive         43% more expensive
UV immune              Eventually breaks down in UV
non-toxic                  Chlorinated plastic and plasticisers
18 times stiffer         95% more flimsy
Holds its shape        Will bend and sway causing other components to loosen and fail

Half-inch conduit can be bent to any curved profile marked out by screws on a wood board.  
https://www.youtube.com/watch?v=97efefttsTQ

Here a professional urban farmer shows how to build a better "poly low tunnel" using conduit.
http://www.youtube.com/watch?v=uEszLA7QNcc
The hoops are lashed together to not tip over under loads from rain, wind and snow.

Did you know that if poly film contacts PVC it can be damaged?  Read what this link says under "warranty":

http://www.greenhousemegastore.com/product/4-year-greenhouse-film/plastic-greenhouse-film

Quote:
"...Polyvinyl chloride (PVC) based materials including any type of PVC pipe, PVC wire or PVC tape, etc. may react with greenhouse polymer films and cause wear. In such cases Chlorine generated from the degradation of PVC and the residual chlorine inside PVC may attack and destroy the Hindered Amine Light Stabilizer in the greenhouse polymer film. This may cause the film to prematurely degrade and will void the warranty. If using with pvc, please use our white felt in between."  

Maybe you could wrap the PVC pipe with a scrap piece of poly instead of their expensive "felt tape" ($0.31/ft) but either way this is an extra step.  Ehh, it gives me a bad feeling.  :/  

Having built hoophouses and an attached greenhouse using pvc pipe and plastic electrical conduit, I recommend never using them for these jobs. Why? Catastrophic failure, that's why. They aren't intended to be structural elements in constructing any sort of building and they do not perform well in that role.  I used them because they were the least expensive option I found - but since they Failed, they were not so inexpensive after all.  If you live someplace that has snow - don't use the pvc pipe or the plastic electric conduit for building structures.  If you get significant winds, or heavy rains, again, I urge you not to use them.

I'm not speculating about what might work, I'm sharing my experience of something that failed, in the hope that you won't have to go through the same experience.