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Low Tunnel Construction: How to Build a Mini Hoop House

3/1/2013 12:32:32 PM

Tags: winter gardening, low tunnel, hoop house, season extension, Doug S.

If you’re interested in having fresh spinach, lettuce, chard, or any other cold-hardy crop on hand late into winter or early in spring, you should build a low tunnel or two (also called a mini hoop house). These easy to build, easy to use, and relatively inexpensive structures can extend your growing season by several weeks, if not months depending on your region. Plus, they can be built in only about an hour.

If you build just one low tunnel, it will cost you about $58.00 in materials. However, you’ll be left with an extra piece of plastic sized perfectly to make a second low tunnel, which would only run you about $53.00 extra. If that sounds too costly for your tastes, you could always substitute the 1”x2”x10’s in my materials list with some cheaper wood or scrap wood you might have on hand, and that could save you about $27.00 dollars per low tunnel. Also, if you own your own electric hand grinder, you could purchase the rebar in longer lengths and cut them to size, which would save you about 42 percent, or $5.00 per low tunnel.

Mini Hoop House 

Here are step-by-step instructions of how to build a low tunnel. The end product will measure roughly 9’4”L x 3’W x 20”H, which I should note is one hoop shorter in length than the version seen in my photos (I made my first low tunnel a little too long, which left my remaining piece of plastic a bit undersized. That’s not a problem, per se, except that one would end up with two different sized low tunnels if you made two.)

Tools You’ll Need: 

Screw gun
Drill bit for predrilling screw holes
Handsaw
Staple gunBox knife
Hammer or sledge hammer
Tape measure
Pencil or marker

Materials You’ll Need for Each 9’4”L x 3’W x 20”H Low Tunnel:   

1/2"x10' PVC pipe (4)

3/8" x 1' steel rebar piece (16) — You can find these precut at big-box home improvement stores. If you have your own electric hand grinder and want to save money, buy longer lengths and cut your own to size. Before doing so, see my note in the second paragraph above, and also my note in Step 1.

Short wood stake (2)

1"x2"x10’ hemlock or white pine board (4)

3.5 mil plastic sheeting (10' x 25'; one roll) — I don’t recommend going any thinner than 3.5 mil in thickness if you want it to be sturdy.

Inexpensive spring clamp (2)

Wood screw, 1 inch (22)

Wood screw, 1 1/2 inch (8)

Wood staple, 3/8 inch (small box)

Step 1 

Decide where you want your mini hoop house to go. You’ll want to make sure it gets plenty of sun, and orient it so that its ends aren’t facing any prevailing winds (the plastic sheeting will be folded and clamped shut on the ends, so you’ll need to minimize the possibility of wind getting under them).

Once you’ve picked a good spot, mark out two parallel lines 3 feet apart from each other and about 9’4” long (the two long ends of your low tunnel will follow these two lines). Now, on each of these two lines, drive a piece of rebar with your hammer halfway into the ground every 16 inches. When done, you’ll have two rows of rebar with 8 pieces spaced 2 feet apart — a total of 16 pieces.

Note: If your rebar pieces are easily moved once driven in the ground, your soil is loose and you need longer pieces of rebar; perhaps 2 foot lengths instead of 1 foot lengths would be better. If you’re saving money by cutting your own rebar to size, be sure to test one out before going to town with your hand grinder!

Step 2 

With your handsaw, cut each of the 10-foot PVC pipes in half. You’ll end up with eight pieces 5 feet long each. These will be your hoops. Now, take a piece of the cut pipe and place one end over a piece of rebar sticking out of the ground. Make sure the rebar goes into the pipe freely and your pipe goes all the way to the ground without the rebar moving (if the rebar moves, see my footnote in Step 1). Now, gently bend the pipe toward the piece of rebar directly opposite and place the remaining end of the pipe over it. Because of the tension this puts on the pipe, you should be careful. This also might take a little extra muscle. You should now have a hoop. Repeat this for all remaining pieces of pipe. Once done, your low tunnel frame will be complete.

Low Tunnel Construction 

Step 3 

At the base of your low tunnel frame on the front side, measure out about an inch from the front edge and about a foot inward from each of the outermost hoops. Drive a wood stake securely into the ground in these two spots, allowing them to lean back slightly. These two stakes will serve to retain the wood rod and plastic roll on the front side whenever your top is closed.

Step 4 

Lay a 1”x2”x10’ board on a flat surface. Open and unfold the roll of plastic sheeting. With your box knife and the board as a straight edge, cut a piece of plastic 12 1/2 feet long by 10 feet wide (this will give you two pieces 10 feet by 12 1/2 feet each if you’re using a 10’x25’ roll). Take the side that is 12 1/2 feet long, align its edge along the outside edge of face (the 2-inch side) of the board, and allow the plastic to overhang each end of the board by an equal distance (about 19 to 20 inches per side). Staple the plastic liberally along the entire length of the board making sure that each staple seats well and doesn’t stick up.

Now, take another 1”x2”x10 and marry it to the one you just stapled the plastic onto. The plastic should now be sandwiched by the two boards. Screw the two 1”x2”x10’s together with 1 inch wood screws using one about every foot or so. Be sure to sink the screws below the surface slightly. The second board will serve as a batten to help secure the plastic if any staples were to rip through it.

Repeat this process on the opposite side of the plastic so that your plastic is now framed with 1”x2”x10’s on the two opposite sides that measure 12 1/2 feet. These board assemblies will be called the “wood rods.” The plastic will stick out beyond the end of each wood rod by about 15 inches or so, which is needed so you can fold in and clamp the ends in Step 7.

Step 5 

Place the plastic over the low tunnel frame so that a wood rod is located on each of the long sides of the frame. On the back side of the low tunnel frame (NOT the side you want to have access to for harvesting, watering or weeding), allow the wood rod to rest on the ground. Align the wood rod so that both ends are flush with the outermost hoops, and also so it rests snugly against the face of all hoops. If the ends aren’t flush, reposition one of the outermost hoops. If the face of the hoops don’t rest snugly against the wood rod, reposition them, too (however, an inch or less is probably OK since the wood screws will pull everything together). Remove any slack and wrinkles from the plastic.

Step 6 

Now, on the outermost hoop, predrill a hole in the wood rod and continue the hole through to the PVC pipe. Place a 2” wood screw in the hole and secure the wood rod to the hoop snugly. Repeat this process for each remaining hoop. Be sure to predrill each hole and then screw each hole immediately so alignment can be maintained (in other words, don’t predrill all holes and then place all the screws after that as they will never line up).

Note: If you don’t predrill, you risk splitting the PVC pipe.

Step 7 

Now that the backside of the wood rod and plastic are secured against each hoop with screws, move to the front side of the low tunnel and begin to roll the wood rod there over the plastic. Roll it tightly to eliminate any extra plastic or needless slack. Once the plastic is at its desired tightness, gently place the plastic roll/wood rod on the ground between the front side of the low tunnel frame and the stakes you drove in Step 3.

With the plastic top in place and the low tunnel closed, move to the ends and fold in both ends of the plastic similar to how you would wrap the ends of a gift with wrapping paper. Once folded, place one spring clamp over the folds on each end to hold them in place. This should secure the ends and make them wind resistant. But remember, whenever you want to roll back your top, the clamps must first come off.

Covered Low Tunnel 

Of course, this is how I built my low tunnel, and you’re free to deviate from the recipe (so to speak) as you wish. Maybe you’ve got some old building materials laying around that could easily substitute for my materials list, or maybe you want your mini hoop house to be a little bit wider or taller. Whatever the case may be, the fundamentals of building a mini hoop house are the same, and these instructions should give you a good starting point to build a good quality version that will last for many seasons to come. Just be sure not to leave the plastic sheeting and hoops out in the sun after you’re done using the structure for the season as they will dry out, crack, and otherwise degrade. Good luck and happy growing!


Doug S. is a backyard gardener and DIY enthusiast. He’s also the owner and operator of Assistimate Estimating Services, an online company that provides estimates for all kinds of building projects and damage repairs. 



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Post a comment below.

 

donna
3/9/2013 4:35:09 AM
I have got to give this a try!

Terry Jackson
3/9/2013 12:02:13 AM
texas wind loves these things

Charles Bingham
3/8/2013 5:01:33 PM
Why not just stick the PVC in the ground, the lumber will support it, if the PVC is put on the inside of frame. That is how I have been doing it on my raised beds.

Curtis Breuer
3/5/2013 5:26:23 AM
How much difference in temperature can be expected with this system? For example, if the outside temperature was 28F, would the inside be above 32F?







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