10.7.2014 to 10.26.2013 How I Built a PVC Hoop House

There are many ways to build a hoop house, but none that I could find that fit my particular situation and design concerns. So my hoop house is an amalgamation of instructions I found on several websites plus the fluff and nonsense that goes on in my head. (See the bottom of this post for references.)  Mine will be 12′ x 34′ because that’s the space I have for it inside my fenced garden.
In my last post on this subject, I mentioned site preparation. Part of that process is staking out the corners and getting them square. So far that’s been the hardest part of the construction. But when you really need square corners, remember, Pythagoras was right. I figure I spent a good three hours on this little chore. My site is squared enough, but not level. I don’t have the equipment necessary for leveling. Just a slight slope down to the southwest – not enough to justify retaining walls – I hope.
Constructing the End Walls
With the footprint squared and roped off, it was time to begin working on the end walls. I don’t have a nice level concrete floor, so I laid a 12 foot 2×4 on the ground and attached a painted PVC arch to the ends with strap iron. Then I added the 2×4 framing for the door and ventilation windows. On the north wall, I have a full size door and two low ventilation windows. On the south wall, I will have one ventilation window as high as I can get it, with a short door beneath it.

October 1st.  The north end wall all framed up.  Notice the lack of symmetry.  That's from the flexing of the PVC and me not noticing.  The south wall turned out much better.  Once installed however, this lack of symmetry didn't make a bit of difference.

October 1st. The north end wall all framed up. Notice the lack of symmetry. That’s from the flexing of the PVC and me not noticing. The south wall turned out much better. Once installed however, this lack of symmetry didn’t make a bit of difference.

I’m not going to give dimensions on the cuts I made as I was sort of making it up as I go and learning in the process. PVC bends easily and secures to the baseboard with a couple pieces of strap iron. But being highly flexible, getting that arch centered on the baseboard took some doing. I found the arch laying down on the ground wasn’t the same arch once the end wall was placed upright on its ground stakes. All the wood pieces are screwed together. Using nails in outdoor wooden construction is just stupid as nails work themselves out in a season or two.

The end walls are heavy and are best moved by two people unless you happen to have a young man around who just wants to show off. October 3,

The end walls are heavy and are best moved by two people unless you happen to have a young man around who just wants to show off. October 3,  (Image blurred intentionally.  He’s camera shy.)

Then with some help from my husband and two cranky sons, we moved the end walls into the garden. They were heavy, but not so heavy that a 20 year old seething with testosterone can’t move one on his own. We placed them roughly where they were supposed to be, pounded in some t-posts and zip-tied the end walls to the t-posts. We didn’t do a great job. It was getting dark. But the manly men did the requisite schlepping and that was important. (Thank you, guys.)

6 foot t-posts support the end wall from being pulled inward from the weight of accumulating snow or pushed inward by the wind. Fastened to the end wall with zip ties.  October 4.

6 foot t-posts support the end wall from being pulled inward from the weight of accumulating snow or pushed inward by the wind. Fastened to the end wall with zip ties. October 4.

The Ground Stakes and the Arches
With the end walls assembled and roughed in place, I pounded in my ground stakes. Not a fun job and I learned I definitely wasn’t meant for swing sledge hammers or working on railroads. (That job suuuuucked!)

The ground bars.  Mine didn't go in perfectly vertical.  Nor did they go in the ground in a straight line, even though I was using a string to guide their placement.  It's not a critical error, but it definitely affected the over all aesthetics of the finished hoop house.  October 4.

The ground bars. Mine didn’t go in perfectly vertical. Nor did they go in the ground in a straight line, even though I was using a string to guide their placement. It’s not a critical error, but it definitely affected the over all aesthetics of the finished hoop house. October 4.

I slipped the arches on the ground stakes and discovered the hoops on the end walls were much higher than the rest of the hoops. I spent a whole day excavating the area under the end walls and resetting them at lower level. (I think I hurt myself pulling up those t-posts which weren’t set the right way the first time. Nothing that some ibuprofen and a couple of rest days on a heating pad couldn’t fix though.)

Here you can see how much higher the end walls are compared to the hoops.  I dug out the dirt underneath the end walls and reset them at a lower level.  This, plus attaching the purlin helped even out the structure. October 6.

Here you can see how much higher the end walls are compared to the hoops. I dug out the dirt underneath the end walls and reset them at a lower level. This, plus attaching the purlin helped even out the structure. October 6.

Anchoring the hoops
I did splurge a bit on those ground stakes. They are 2 foot long steel rods with holes punched through them every couple of inches. I could have used rebar but couldn’t figure out a way to tie the PVC to rebar. I could have used larger diameter PVC sleeves and connected the hoop to the sleeve with a bolt. But how do you pound PVC into the ground without shattering it. What I was trying to do at this point was to anchor the arches so the wind can’t lift them out of the ground. My solution was to thread my PVC arches onto those rods and then drill a hole through the PVC, line it up with one of the holes on the rebar, shove a nail through and presto – the hoop house doesn’t fly when a heavy wind gets under the plastic. It was a good plan. But getting all those little holes lined up was nearly impossible. Only the west side of each arch is secured thusly. I cracked two of the pipes badly enough that I had to replace them. But, the nails hold the PVC down securely and should give plenty of resistance should the wind try to lift the structure vertically. At least on one side.
The Center Purlin or Ridgeline
Next, I installed the PVC ridge line. It’s also known as a purlin and it is critical to hoop house construction. Without it, the plastic covering sags between each arch and rain and snow will accumulate there quickly. Water in any form is heavy and puddles of water on the top of a hoop house will pull it down.

The ridge pole or center purlin installed.  My hoop house looks a little lumpy at this point.  October 8.

The ridge pole or center purlin installed. My hoop house looks a little lumpy at this point. October 8.

Most of the instructions I had read affixed the purlin with either bolts drilled through the two crossing pieces of PVC or with special metal brackets made just for the job called cross connectors. I used zip ties. They will get taped over before I put on the plastic film. Seems to be working just fine and zip ties are so much cheaper than bolts or cross connectors.
One last note on construction thus far: all my PVC connections are strictly dry fitted. I did not prime and glue the joints. Time will tell if this ends up being a major engineering flaw.
Game Called on Account of Weather
Now we are having a whale of a nor’easter. Since I am at a point where I require power tools, construction is halted for the time being.
A Week Later
Nothing but murk for the last week. Rain, drizzle, mist, fog. Those were our choices. Cooler and damp. Mold. Allergies. Not much got done for a week. But the damp abated for a couple of days and I got back to work by putting on the baseboards. I got cheap at the lumber yard and bought 1×6’s for the base boards.  If I ever build another hoop house, I will definitely use 2×6’s.  The 1 bys just have too much flex.

Here you can  sort of see how I attached the PVC to the baseboard - with strap iron (aka hanging tape) The side rail is laying on the ground waiting to be installed and in the foreground, the broken PVC pipe.  When the PVC is flexed into a bow shape that puts tension on it and it becomes very prone to cracking and breaking when you try to drill holes in it.  Doesn't matter how slow you go with the drill.  October 16.

Here you can sort of see how I attached the PVC to the baseboard – with strap iron (aka hanging tape) The side rail is laying on the ground waiting to be installed and in the foreground, the broken PVC pipe. When the PVC is flexed into a bow shape that puts tension on it and it becomes very prone to cracking and breaking when you try to drill holes in it. Doesn’t matter how slow you go with the drill. October 16.

My parents came up for a visit and my neighbors showed up too. They all helped me put on the side rails. The side rails are 1×4’s attached to the hoops with bolts 3 feet off the ground. As it turns out, PVC does not like being drilled, especially when it is under tension. I broke two of the arches trying to drill through them. Snapped right in two. At this point, dry fitting the two pieces of each arch is making me look like a genius. Lucky for me, a last minute alteration in plans left me with extra lengths of PVC.

Here you can see the base board and the side rail.  Notice how the side rail seems to sag in places.  That's because of those imperfectly installed ground bars. October 18.

Here you can see the base board and the side rail. Notice how the side rail seems to sag in places. That’s because of those imperfectly installed ground bars. October 18.

But . . . the replacement PVC wasn’t painted. So I spent the next morning painting the two broken during side rail installation plus the two I broke trying to anchor them to the ground bars. While the paint was drying, I taped. I went over every surface in the structure that would come in contact with the plastic covering. Anything rough got taped over.

The U-Channels
There are a couple of ways to attach plastic to a hoop structure. One of the most ingenious ways is a U-channel (also known as poly latch) and wiggle wire (also known as steel spring). The channel is metal and comes in 6 or 8 foot lengths. It can be bolted onto baseboards, side rails and end walls. It took a corded drill to drill the holes through the aluminum. The cordless drill didn’t have enough torque. I used machine screws to secure the channel to the side rails. It took about an hour per side.
The Plastic Goes on
Happily the wind has been very calm for quite a stretch and on Friday, October 19, it was quite calm – perfect weather for playing with large sheets of plastic.  I cut two 7’ lengths of plastic for the end walls. I attached the film to the end walls with a combination of lath at the bottom and sides of the frame and duct tape around top of the arch. Having an air compressor with a nail gun makes this job go fairly quickly.

Still air and good friends makes covering the hoop house quick work.  It really helps if they can read your mind, but isn't absolutely required.  October 18.

Still air and good friends makes covering the hoop house quick work. It really helps if they can read your mind, but isn’t absolutely required. October 19.

Happily, reinforcements arrived as I was finishing up the first end wall. Working together, we did the other end wall and the four corners of the hoop house below the side rail. (See picture.) I don’t know that this is strictly necessary, but it seemed like a nice design feature that will help limit cold air seepage when the lower side walls are in the down position.
The main cover glided over the structure very easily and then we had to figure out how to work the U-channel and wiggle wire. Wouldn’t you know? You wiggle it! This stuff is brilliant, but it takes three people to install it. One person holds the plastic tight. The second person wiggles the wire into the channel securing the plastic. The third person holds the loose end of the wire so the first person doesn’t get his eye put out. Having a fourth person to untangle the lengths of wiggle wire is great, because wiggle wire really likes to copulate.

The U-channel and the wiggle wire smugly holding the greenhouse plastic firmly in place.

The U-channel and the wiggle wire smugly holding the greenhouse plastic firmly in place.  October 20.

We didn’t quite finish the all the finer point of locking down the plastic. It got dark. I ran out of lath. The air compressor went temporarily on strike demanding a shorter and better quality extension cord. So we had dinner, a bottle of wine and I got to celebrate the fact I now have something that looks an awful lot like it should, except that it has no doors.

Another Weather Delay
The air compressor said it would go back to work. I have more lath, but we’re in the murk yet again. More waiting for a smidge of a dry spot so I can safely use power tools and electricity outside.
The Finer Points of a Roll-Up Side Wall
Eventually, I got back out there and taped the long side, bottom edges of the plastic to ½ inch electrical conduit. Add a couple of 90° joints and theoretically I had a roll-up side wall. Except, of course, it didn’t roll evenly and the ends sort of bunched and flapped around when the side wall was in the down position, making an unacceptable influx of air. But all the problems went away when we added about 250’ of paracord.

Here you can see the side wall in the down position and being held snugly against the baseboard by the paracord which is zigzagged over the top of the hoop house.The paracord at Tractor Supply came in 100 foot lengths in either orange or black.

Here you can see the side wall in the down position and being held snugly against the baseboard by the paracord which is zigzagged over the top of the hoop house.The paracord at Tractor Supply came in 100 foot lengths in either orange or black. October 20.

To install the paracord, I installed eye bolts on the baseboard at every other arch and in all four corners. Then I wove it back and forth over top the structure like half a shoe lace. I then added a shorter piece of paracord over each end wall. (This is a two person job as no matter how careful you are at unwinding paracord, it’s going to tangle into an unbelievable knot. Additionally, two people make it easy to toss the cord back and forth over the hoop house and to keep tension on it as you thread it through your eye bolts.)

Despite great care, this sort of mess happened with all three skeins of paracord.  It really wants to bunch back on itself and has to be held under slight tension to relieve the tangle.

Despite great care, this sort of mess happened with all three skeins of paracord. It really wants to bunch back on itself and has to be held under slight tension to relieve the tangle. October 20.

The paracord serves three purposes. First, since it is laced over the top of the hoop house, it acts as an anti-billowing device for the plastic covering when the house is open on a breezy day. Second, it holds the side wall snug up to the arches which makes the seal much better when the side wall is down and makes rolling up effortless. And finally, the short pieces of paracord over each end wall, keep the ends of the side wall from getting all frumpy and allowing air in when the hoop house is closed up.

Two 90 degree fittings on the 1/2 inch roll up bar makes raising and lowering the sides insanely easy.

Two 90 degree fittings on the 1/2 inch roll up bar makes raising and lowering the sides insanely easy. October 20.

My husband rigged up a simple loop of paracord and an eye hook screwed into the end wall as a means of keeping the side-wall in the up position. Works like a dream.
A Door!
With a hard freeze coming, the pressure was on to get the last of the summer veg out of the garden. That’s occupied most of my time for the last two weeks. Peppers, sweet potatoes, louffa gourds, tomatoes, and basil. Lots and lots of basil. My neighbor wanted basil and I was glad to share. Besides I wanted to pick her brain on how to attach a door. She ended up hanging around and helped me install a door. The woman is a genius. Or maybe, she just has more experience.

The door!  The plastic is held on with lath on the inside edges.  Additional lath on the front of the door nailed into the two cross pieces to minimize billowing. October 22.

The door! The plastic is held on with lath on the inside edges. Additional lath on the front of the door nailed into the two cross pieces to minimize billowing. October 22.

The door is necessarily smaller than the opening to enable it to swing freely and allow for expansion when it gets wet. But that makes for some very large gaps around the edges. She solved this problem simply by adding furring strips around the door frame, set back from the outer edge just far enough to allow for the depth of the door. It’s a beautiful thing having a door!
I had purchased door handles similar to ones you’d see on a screen door or storm door, but these ended up being too small for my door which is made from ripped in half 2×4’s. So my neighbor jury-rigged a piece of wood on a screw. The wood is padded with plastic trimmings and taped smooth with duct tape. It works beautifully, but I do have this fear of having a door handle that only works from the outside. We have a similar set up in the white room where I start my seeds. My husband locked me in there one night. (Not intentionally, he swears.) The white room is in the barn where there is no cell signal to speak of. Can’t call out. I could only send text messages. I ended up texting my daughter at college and had her call the house phone until she finally got one of my boys to answer. Eventually, my son came down and let me out. I was nearly out of battery power on the cell phone by the time I got rescued.
The only way out of the white room is the door. Technically speaking, if someone were to shut me in the hoop house, I could lift the side wall curtain and crawl out that way, or, if I was really desperate, I could cut through the plastic on the door, so I guess I am okay with my little pivot latch. Besides, cell phones work in the hoop house.
The First Plants go in and the lessons begin
With so much work to do to bring in the summer veg before the frost, I didn’t get to spend much time in the hoop house. Before I got the door, it was fun to walk by the hoop house and thump the plastic and listen to the “rain” inside. So much condensation. My glasses fog up when I first enter the house, but they adjust fairly quickly. Working inside means getting dripped on and getting warm. I will have to install a coat hook.

The first plants go in the hoop house.  It's October 23rd and it's taken over a month to get to this happy day.

The first plants go in the hoop house. It’s October 23rd and it’s taken over a month to get to this happy day.

I planted three flats of lettuce. In our current weather pattern (overnight lows in the 30’s and day time highs near 60), I am finding the house has to be opened up fairly early in the morning, usually by 9 am. It heats up to over 80° very quickly if the sun is shining. So far, I haven’t had any wind issues, but when the winds are gusty, I only raise the side wall on the lee side. The beds also dry out much more quickly than beds outside the hoop house. On October 25, we had our first freeze of the season. The day before, I moved two tomato plants into the hoop house. They were late season starts I had been growing in buckets. The lettuce was unfazed by the 32° low, but the tomatoes were absolutely done in. So much to learn . . .
I haven’t done the math yet, so I don’t have exact figures, but this 12×34 hoop house cost around $800. Half of that cost was for the greenhouse plastic and I half the 100’ roll left over, so I guess you could say this is a $600 hoop house.

Even though I still have more doors and windows to install plus the 2×4 snow braces for the arches, I will end this overly long post here. But if you want to continue, I’ve got footnotes for you.
References and Design Requirements:
This link is where I started, suckered in by the author’s claim of building a greenhouse for $50. Well, turns out the guy had a lot of materials “on hand,” and he admits it would have cost him $150 if he had to buy the materials. Still, that’s a real bargain. I include this link here because a) he’s got some good basic construction ideas, especially on the end walls and b) he includes pictures of what happens when these sorts of structures collapse due to rain or snow loads. (You may have to flip through several links to get all the information as he did his write up in several different posts.)
http://doorgarden.com/10/50-dollar-hoop-house-green-house
This link takes you to a PDF of pictures documenting the construction of a high tunnel, presumably in Alaska. It’s very light on written instruction, but the pictures detail features that are not covered in most other how-to sites I found. It includes how to install roll up sides.
http://dnr.alaska.gov/ag/Grants/BrianOlsonHighTunnels2008.pdf
This link takes you to a nice PDF on high tunnel construction. There are no construction pictures, just diagrams, good written instructions and materials lists, although, I have to warn you, I based my materials lists on this and ended up with way too much lumber. The end wall design on this site was slightly different from most others that I looked at in that the base plate for the end wall was laid broadside to the ground and extended outside the footprint of the hoop house by a foot on each side, if that makes sense. (See page 7 of the PDF) I ended up using a different design for my end walls – well actually I just sort of made it up as I went as cutting angles is a gift I don’t seem to have.
https://extension.usu.edu/files/publications/publication/GH_High_Tunnels_2008-01pr.pdf

Johnny’s seeds also has an informative file on erecting a hoop house, but they use chain link top rail for their hoops, bent to perfection on a pipe bender they sell. Their hoop houses look much sturdier than mine with all that metal, but Johnny’s hoop houses suffer from a major problem – access. Their hoop houses don’t come with end walls per se and getting inside the hoop house involves crawling under gather plastic. Still, it’s a good place to start.

My Requirements

After perusing these and many other sites, I decided the following:

  1. The hoop house must have roll up sides and a means of ventilation on the end walls. This will hopefully make a one season structure into a three season structure – four if I use shade cloth.
  2. To save on costs, I will construct my hoop house out of 1” electrical conduit on three foot centers. It comes in 10 foot lengths and two together will span 12 feet with a little more than 6 feet of head clearance at the top of the arc. It may not be a comfortable space for my 6’4” husband, but this is my workspace and I’m 5’7”. I’ll manage.
  3. To add structural stability against rain, snow and wind loads, I will bolster end walls with t-posts and diagonal braces connected to the baseboard. The center purlin will be braced at intervals with vertical 2×4’s. I will add side walls about 3 feet off the ground to further stabilize the structure and to give me a place to firmly affix the plastic covering.
  4. I will use 6 mil greenhouse film. It’s not the high dollar anti-condensation stuff, but it is UV stabilized and comes with a 4 year warranty. 6 mil plastic from the major box stores won’t last a year, is very fragile and difficult to work with and doesn’t come in widths wide enough for my purposes. I have enough film to put two layers on, if I want to upgrade at a future date by adding an inflation fan.
  5. If the hoop house survives the winter without collapsing under a heavy snow, then I plan to put screening on the lower side walls and the ventilation windows. Maybe I can actually grow squash next summer, if I am able to exclude those darn squash bugs, stink bugs and vine borers!
  6. I will rely on my existing irrigation system and hand watering until I can afford an upgrade.

I shared this post at The Backyard Farming Connection, Wildcrafting Wednesdays #111


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10.7.2014 to 10.26.2013 How I Built a PVC Hoop House — 1 Comment

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