PVC Hoophouse Construction (updated 3/11/12)
We’ve been talking about a greenhouse since we bought our house. We both would love one, but we still have a number of projects higher up the list than a greenhouse (the barn roof, bathroom remodel, refinishing wood floors, the intermittently leaking chimney, etc.). Still, the idea of extending the growing season is just too good to pass up, and our small raised bed pvc hoops have been so great we decided to try a pvc hoophouse (HH) made from conduit. We purchased the materials and got started earlier this month, and Tuesday began construction in earnest. Here’s the process. (Click to enlarge all photos.)
We have serious groundhog issues, so the HH would need to be within the garden fence. We decided to increase the fenced area slightly on the eastern side of the garden, and sited the HH in the northeast corner of the garden, against the north side fence, to the east of the raised beds, running in a N-S direction. In this photo, the north end is at the top.
Our site had previously been worked as a garden bed, and last winter held the hen’s snow dome, so it is level (mostly), and a well drained as any spot in the garden. We held off planting there knowing the HH would be sited there, but finally had to break down and plant our second crop of tomatoes, started especially for the HH, before we’d built it. We only damaged one (plants are along the staked line on the right).
Next, we used large deck screws to construct the2″X’6′ base. Prior to putting the base together, we had measured the location of each rib and screwed conduit clamps in place for holding the hoops in position. The finished size of the base is 8′x16′. On the (southern) door entrance end, we put the 2″x6″ with the 6″ side to the ground to make a sill and provide a nice base for the end wall frame. Note the tomatoes on the right, contrasting with the cardboard under the base on the right in the photo (as weed prevention). This is not the ideal orientation, but it fit the available space. If we build another, it will be oriented so the long side is on the south.
Once the base was completed, it was time to set up the hoops. Because we occasionally get heavy wet snow or big storms with over 16″ of snow, we decided to place the hoops fairly close together. The hoops are relatively inexpensive components compared to the cost of constructing a new HH should this one collapse under snow. We originally planned for 7 ribs, but ended up with 8 ribs at approximately 21″ intervals. We still need to pick up 4 additional pieces of conduit to complete the rib installation.
We wanted the final height to be between 6 1/2′ and 7′ in height, so we set it up and determined we needed to remove 1′ from each conduit –in essence the HH is now constructed from 2-9′ pieces of conduit attached in the center. If we had been able to make the HH a little wider, we would not have needed to trim the conduit, but we just didn’t have the space. If this experiment proves wildly successful, we will probably make space in the future for a wider and probably longer HH.
Once we were certain we liked the height, we tightened the screws holding the conduit in place, making sure the conduit was level with the bottom edge of the baseboard.
We found 16′ lengths of 1″x3″ at the lumber store, so we decided to use that for purlins. We attached the side purlins 36″ from the bottom of the baseboard, using 2 self-drilling screws for each rib to minimize torquing. Be sure to pre-drill holes at the ends of the 1″x3″ to prevent splitting. We installed both side purlins and called it a day. We’ll attach the center purlin next, and add the final 2 hoops. Note the tight spacing between the new hoop house and the raised bed with shade cloth on the left. I need to get cardboard for weed control down on that side, too.
End wall construction
We used lumber we had on hand, remnants from past projects. We ripped some 2″x4″s and 2″x6″s down to 2″x2″s to construct the frame, making the lumber we had work. First, we attached the three upright pieces to the hoophouse sill at about 4 feet from the ground. We used self-tapping coated decking screws for the construction, in case we should need to deconstruct the hoophouse. (Note the white floating row cover hanging from the hoops –we used it to cover our tomatoes when we had a frost warning earlier this week.)
To the uprights, we attached the horizontal piece, and attached a final upright between the horizontal piece and the center purlin. Lastly, we cut 2 pieces to run diagonally from the top upright to the sidewall edges of the horizontal piece.
We used a screen door from our shed which was in rough shape and needed work; instead, we used this door for the hoophouse, simply cutting off the part of the door that needed repair as the door was too large. We rarely use that door, so this was an easy and cheap solution.
We will probably add a horizontal piece between the door frame and the sidewall vertical to strengthen this wall, which will get a workout from the door being used.
We started to cover the end walls with plastic, using some left over from past projects. I had planned to use greenhouse plastic, but as we had this on hand we used it –and I’m glad we did as we will do things slightly differently next time.
The plastic cover
I picked up the plastic for the hoophouse from Greenhouse Supply in Brewer, ME. They kindly sold me at a discount a 50′x20′ piece of Super UVA Clear 6mil cover off a damaged roll. This piece is large enough that we could use half and reserve half for a replacement or second hoophouse. I highly recommend looking into this option, it saved us a bundle.
Earlier in the day Dan had laid the plastic, which was folded, out in the sun to warm up. Friends Karen and Bill came by just in time to helped lift the plastic on. We unfolded one half, measuring to be sure, and carefully cut the whole piece in half using a utility knife with a sharp new blade. Then, the four of us each took a corner and lifted it over the hoophouse frame from the side. Having extra help made it easier to avoid tearing the plastic on our welded wire fence. After making sure we had it evenly placed, we placed straw bales over the excess plastic on the sides to hold it in place temporarily.
Within a few minutes it was noticeably warmer in the hoophouse than the outside air temperature, and within 60 minutes it was 82°F, while the outside temperature was about 66°F (although it felt warmer in the sun).
Note the difference in clarity between the plastic on the end wall and the greenhouse plastic. The end wall plastic is ordinary plastic purchased from the local hardware store. The blue sky over the tomato plants is seen through the new greenhouse cover.
On a future weekend, we need to tack the plastic to the side purlins and the ends, and fix the sides so that we can roll them up when we need ventilation.
Tacking on the plastic cover
We began with the south end wall,
which has the entry door. We carefully pulled the plastic over the end hoops taut and tacked it to the end wall framing using our air-compressor staple gun, pinching the plastic under strips of plaster lathe we saved from an earlier home renovation project. The trick here was to gently pleat the plastic — fold edges on the top to avoid water collection– and hold it in place as we stapled. The lathe will help protect the plastic –without it the plastic cover would be more likely to tear at the staples.
There is not enough plastic to cover the entire end from the roof down, (and that would have had too much gathered plastic) so we trimmed off the extra plastic then used those pieces to cover the door and the larger sections of end wall. The extra pieces of plastic will be saved for repairs or smaller secondary row covers inside the larger hoophouse.
Adding Vents to the End Walls
I had read somewhere about someone creating vents with foam insulation glued to the plastic cover. It sounded like a good idea, but finding an adhesive that would work on both foam and plastic proved nigh on impossible. So, Dan, clever lad that he is, suggested wood framing, stapling the plastic to it, cutting the vents, and inserting foam to close the vents. We created the frames using leftover pieces from framing in the end walls. If this proves to be successful,
someday I’d like to make endwalls from clear polycarbonate. But first, the hoophouse will have to prove its worth.
On the north end wall, right. Note the thermometer sensor attached to the framing on the left.
On the south end wall, left. Once the chooks have moved to their spring and summer home, we can also open the door for venting. We will also create roll-up sides one the ground has thawed and we can free up the plastic sides.
We tacked the plastic to the vent frame from the outside using old plaster lathe.
We added fiberglass screen for reinforcement and bird prevention. We happened to have some in stock, left over from covering our rain barrels.
Using a very sharp utility knife, I carefully cut slits in the plastic. Later, we can cut larger openings, but for now, cutting that expensive plastic was scary! (Although I do have on hand greenhouse repair tape
after damaging the plastic earlier this winter. Sigh)
Trimming the foam insulation to fit. Because we made do with available lumber, the frames are not perfectly square, but making do is an essential part of the cost-value ratio.
In the colder months, we’ll seal any air leaks around the edges, but with warmer temps on the way, no need to worry about that right now. We will still need to add some sort of handle to facilitate removal of the panel when it is inserted snugly, but for all practical purposes, I can cross that project off the list.
Repurposed window end walls
Today (11/01/09), we closed in the open north end of the hoophouse with some aluminum-frame storm windows which became available when we replaced some of the aging windows in our house.
Wow, I LOVE the visibility we have with the glass, and the frames added some rigidity to the structure as well. Where the windows didn’t cover, we recovered with inexpensive plastic sheeting from the hardware store which we also use with good results for small raised bed hoophouses in the garden.
To install, we simply added framing made from a 2′x4′ ripped in half to make a 1′x3′. We then used galvanized self-tapping screws to attach the window frames to the hoophouse framing. The final step was adding the plastic to the uncovered area, and tacking down the plastic with lathe salvaged from a house project. This makes me wish I had a few more windows to replace! I may have to start perusing Uncle Henry’s for some used aluminum windows. It makes the hoophouse a lot brighter, I hope the plants like it as much as I do.We still have not buried the plastic on the sides of the hoophouse. We left it unburied thinking we might want to roll up the sides for venting this summer, but it never really got hot enough to need it. For now, we have covered the plastic with scraps of plywood scrounged from the town’s waster transfer station, where it was destined to be ground up into incinerator chow. I think this is a much better use.
Adding wiggle wire to secure the plastic cover
This weekend, Dan and I added wiggle wire to the hoophouse to fix the roll-up sides into place for the winter. It is such a simple idea, yet the perfect method for fastening the plastic cover -absolute genius. Whoever invented this deserves every penny of patent royalties they get.
I purchased the wiggle wire from Griffins Greenhouse & Nursery Supply in Gray, ME. The base was actually much heavier gauge than I expected. It was quite a job to cut it to length with a hacksaw and drill holes for screws through it. This is good, as I hope I will be re-using it for years to come. The wire is some kind of spring-tensioned steel I imagine, fairly light in gauge. I suspect this might be something I will need to replace, but time will tell.
The first step was to determine how to attach the wiggle wire base. If you look at the hoophouse construction page, you will see the single biggest mistake we made when constructing the hoophouse –we attached the hoops to the outside of the wooden base frame. We realized it was a mistake later, when we put the plastic on, but I don’t think we really understood how challenging this would prove until now, when installing the wiggle wire. The wiggle wire needs a straight plane for attachment. We decided to simply attach a length of 1″x3″ strapping on the outside of the hoops, supporting it with blocking made from more strapping.
Once this was completed, we measured and then cut the base to length. Dan cut each piece of the heavy aluminum with a hacksaw, then filed the cut ends to reduce the likelihood of the plastic tearing on the sharp ends. While Dan cut, I drilled holes for the screws. Next, we screwed the base to the hoophouse frame with galvanized flat-headed screws. This part went pretty quickly, and soon we were ready to fasten the poly down.
This part was actually more complex than it would appear to be, perhaps because of our flawed design. We added additional framing to the sides of the hoophouse last spring when we made the roll-up sides. In retrospect, we should have made the vertical framing pieces flush with the outside of the base frame, but we did not. This meant that when securing the poly with the wiggle wire, it is slightly contorted. It works, and in a perfect world it would not look like this, but, as I frequently try to remind myself, perfect is the enemy of good, and the hoophouse works.
The impact of this was most apparent when attempting to fasten the cover. I first fastened the side shown above, then the long bottom edge. When I went to attach the entry end side, the plastic was to taught to allow me to push it into the base track. I needed to remove the wire from the bottom edge, and then I was able to fasten the side down. The final step was to fasten the bottom edge. As I inserted the wiggle wire, which is indeed accomplished by wiggling the wire into the base channel, up, then down, I tried to pull the poly as taut as possible without tearing.
When I removed the wiggle wire from the bottom edge, I did notice some tearing in the plastic. I’m not sure whether this is a standard result of inserting the wiggle wire, or because of the age of my poly or the fact that the bottom of the plastic has abraded over the years. I did not even attempt to repair these small tears, I can only hope the covering will be firmly enough in place to reduce friction wear and that it will last another couple of seasons. I did patch with repair tape one other larger hole that was just above the base framing on the side wall.
One thing I noticed, which in retrospect doesn’t surprise me, is the wiggle wire expands in length as when inserted. This is no doubt due to the pressure on the beds from the channel, but it caught me by surprise and on the side verticals, I cut the wire too long and had to trim it at the end. I’m sure the wire could readily be cut with a hacksaw, but we have some nice bolt cutters which worked great. Heavy wire cutters just didn’t cut it in this instance.
It is a great to have this project completed, and I feel much less intimidated by the idea of constructing a larger hoophouse at some future point now that I’ve used the wiggle wire. And believe me, a larger hoophouse is in my future.