Rocky Creek Valley Farm EQUIP High Tunnel Program

2013 EQUIP High Tunnel Program

Progress Report & Log Back to Study Page

March 1, 2013 Initial Assessment: Materials purchased ready for assembly. The project is for a 30' x 72' high tunnel (H.T.) with 5' side walls, double layer plastic, curtain side walls and wood end walls by us. Four bids were taken; two were almost identical at roughly $5,400.00 tax included. Both were very good sturdy units. Some of the lower end units will not stand up during high winds. The other two bids were a higher quality product but the prices were approximately $6,500.00 ea, one of those was on sale. We went with the cheaper one that was in stock, a Zimmerman High Tunnel. Very good quality in my opinion.

The wood runners for the sides and wood for the end walls including two 36" storm doors and bag concrete mix for the post totaled just under $1,000.00. I will be installing two 10' x 12' rolling doors on each end on barn door track to accommodate the tractor. This added approximately $350.00.

The total erected cost of materials is projected to be almost exactly $7,000.00. All labor by us. We purchased enough irrigation materials and plastic mulch to irrigate the high tunnel for approximately $150.00. The project is now finished: Final cost and production data. The log below will just hit the highlights of the assembly process.

I assembled and erected almost the entire high tunnel by myself, I cannot recommend this. The times could be cut by 60 to 75% with just one helper. It would eliminate endless trips up and down the ladder, clamping one end so you can attach the other, on and on. Get a helper. I have 40 plus years in construction and engineering and I had problems working alone, if this is your first major project and you try to do it alone you are in trouble.

My high tunnel (H.T.) is 30'x72', your dimensions my vary from the instructions slightly. High tunnels are very forgiving in terms of dimension and alignment. However, errors compound themselves, try to be accurate. Use a string line and level on everything. A 1/4" error on the first bay times 13 post equals 3 1/4" at the other end. This is how people get themselves into situations that are not repairable. Look at completed projects and talk to people who have erected high tunnels before.

Tool List - Center punch, hammers, several 1/8" drill bits, four or more quick grip clamps, channel locks, impact driver, cordless drill, powered drill also for drilling because the speed is much higher than most cordless drills. cargo strap as long as the width of your H.T., tool belt, sockets for the impact driver to fit all of the nuts and screws, string lines, plumb bob, post lever, 2' and 4' levels, shovels, ladders, scaffolding if you can get it, circular saw, hack saw, sharpies, tape measures, squares, sawhorses, large half round file, plumbers sandpaper, WD-40.

Listing the hours for each item was an after thought and I was working alone, they are approximate as best I can remember. With a team your times should be considerably less. Get the site clear and as level as possible before starting anything. Water needs to drain away form the H.T. so a slight slope in the length of the H.T. is beneficial. You might want to consider preping the ground before erecting the HT because it is much easier to work with a tractor than a hand tiller and wheelbarrow once the walls are up.

POST - It took about 6 hrs to drill the post, cut the re-bar, dig the holes, square and level the area and set the four corner post in concrete. Inserting re-bar or a bolt in the bottom of the post ensures the post will not pull out of the concrete under heavy loads. I recommend setting all post in concrete, at minimum set the 3 post on each end to provide stability for the wind load on the end walls.

TIP - All the post can be marked at one time by lining up the ends and placing a board across at the appropriate height and spray painting along the edge. This is my ground level, 32", it provides a quick reference point for the string line.


First load of material	Post anchor method

SQUARING the H.T. - By using the 3 4 5 method of squaring. Set two corner post on one side. Set a string line between them. Measure down from one corner 40' set a stake. Measure across from the same corner post 30' to where you think the corner should be set a second stake. Now measure between the two stakes. The dimension should be 50'. If not adjust the stake at the corner until you get exactly 30' and 50' on those two sides of the triangle. My unit was 30" x 72" to the outside of the post. Set the corner post first and allow the concrete to set overnight so that the string lines can be pulled tight without effecting the polition of the corner post.


Post level, If you don't have one, go buy one, they are cheap.	Easy way to mark a uniform height on post

CENTER POST - It took approx. 8 hours to dig the 22 center post holes with a tractor post hole digger and set the post in concrete. If the post are not plumb and equally spaced in width you will have a very difficult time setting the trusses on the post. Take the time to get it right.


Post set in concrete	Jig to space post equally

TIP - Remember the post are 2 1/2" in dia. If you start measuring from the center or the side wall be consistent and don't forget the diameter. I set my corner post at 30' x 72' and deducted the pipe diameter in the first bay on each end to then obtain 6' bays for the rest of the H.T. Using a string line on the top and bottom of the post, with a post jig and a post level it is easy to get your post aligned and plumb.

TRUSS ASSEMBLY JIG - Save your self a lot of headaches and do what I tell you here. Get four sets of saw horses and three sheets of plywood. Tack the three sheets of plywood to three of the sets of sawhorses, making three table/jigs. In a level area position the two tables at each end of the truss and one at the apex. Use the other sawhorse set in the middle to hold the W truss. Level the sawhorses and plywood with blocks and shims. Use this table to assemble your trusses. If the trusses are not extremely flat when assembled they will not fit on the post and none of the bracing will line up correctly. Crooked trusses can also weaken the structure considerably under high wind loads. Additionally, if your are old like me, workig standing up is much easier than constantly getting up and down on your knees.

PIPE - You will note there are burrs inside and on the outside of the pipe where it was cut and the male ends were rolled. This will make sliding them together difficult. Use the half round file to clean the edge of the female pipe ends and the plumbers sandpaper to clean up the edge of the male ends. A spray of WD-40 and they will slide together easily.

TRUSS ASSEMBLY - Place the three top truss pieces on the assembly table. Before slipping them together slide all the brackets onto the pipe. This is much easier then trying to spread the brackets apart and then squeeze them back together. Now slip the three pieces together. Make sure they lie flat. Use the cargo strap to pull the ends together until they are the exactly the same width as your post are set apart (30' on the outside in my case). Screw the three pieces together, make sure no screws are on top or they will tear the plastic liner. The two end trusses also cannot have screws faceing the endwall plastic. Assemble the lower cross member first. Measure up the same distance from the bottom of the pipe on each side to ensure it will be level when erected. Next assemble the W truss components. Screw all the couplings in place and drill all piloet holes for cross members while the trusses are on the table, it is much easier than working from a ladder. It took about 1.5 hr per truss to assemble and drill all the holes. Drilling all the holes takes time. the screws are self drilling, but pre-drilling helps alot. NOTE: Make sure you do not put screws on top of the truss where they will tear holes in the plastic roof. All screws must go on the sides or bottom.

SETTING the TRUSSES - If you have a tractor and a boom this is a three person job. If not you will need a section of movable scaffolding and at least 4 to 6 strong people. File and sand the ends as previously described. Remember the two ends walls do not get the W truss, they will be framed in with either wood or metal studs. Set the trusses on the post, slide the sides down evenly until completely seated. Tapping on the post with a hammer will help move stubborn trusses into position. With a tractor and 3 people setting the trusses took just over 2 hrs.

BRACES - Put a tek screw in each cross brace bracket to keep them from sliding on the pipe. Install the cross braces on the end trusses. My unit had a stringer for the two end trusses. There will be no truss webbing because of the end wall. You will need to coordinate how you are going to build the end wall with this stringer. As shown I screwed mine to the back side of the end wall. My manufacture recomends two tek screws in each of the pipe slip joints, my supplier recommends three per joint. I strongly recommend three in all locations. Heavy winds can generate a lot of force, I have seen more than one HT lying flat on the ground. This took about 4 hrs.

TOP RAIL - Install 2x8 lumber along the top of the post first (hip rail). Ensure the post is plumb before attaching to the wood. Do not splice the lumber at the post. The structure will be much stronger if spliced between the post. One method is to start with a 10' piece at the end and then use 12' lumber thereafter. A 32" splice gets you three splices from a 8' board. Put screws through the clamps into the post and an additional screw into the post and truss to keep them from separating from wind uplift. The rails took the better part of a full day.

BOTTOM RAIL - Install 2x6 lumber along the bottom along the ground. Use a string line to keep it level. This took about 4 hrs.

PULLIES - The pullies just take time. Try to keep them as high on the wood stringer or the curtain wall will not crank up tight to seal the sides. This took about 6 hrs. We had a problem with birds and our free range chicken. If you also anticipate an issue put chicken wire on the opening before you start on the curtain wall and pully system. Ours is on the outside, which works, but would be nicer if I had forseen the problem in advance.

WIGGLE WIRE TRACK - Screw the wiggle wire track along the top of the 2x8 rail. Screw approximately every 12". This took less than 2 hrs.

CURTAIN WALL INSIDE CORD - Start 18" in from the end and start a 1 1/4" roofing nail every 3' for the cord to loop over. Do the same for the bottom rail starting 3' in from the end. Weave the cord on the nails and then drive the nails down tight.

CURTAIN BOTTOM - I used plastic cap roofing nails to attach the bottom of the curtain wall to the bottom wood stringer..

OUTER CORD - Install eye bolts half way between the nails holding the inner cord web. The outer cord must me loose enough to allow the curtain to fold up and drop down with out restricting it. By using eye bolts top and bottom you can adjust the slack so that the curtain drops without binding. Leave yourself several feet of slack at one end until you get it adjusted.

END WALL - I am posative I over-engineered my end walls, but they work great. It took about a day for each end, plus about another day to build all the doors.

END WALL PLASTIC - You must use the plastic stapling strips or the staples will just pull through the plastic durring the first wind. Next time I think I will use lathe and sheet rock screws.

VENT - Vents at the eaves of the end wall are important. In the spring and fall when the H.T. is closed to prevent frost bite. When the sun hits the H.T. the temperature can jump to well over 100 deg. in just a matter of minutes, killing your seedlings. The vents can be opened to let the heat out. Heat rises so venting at the top is most effecient.. Many people put a door or fan on a thermostat to automate this process.

DOORS - Spend the $75 to install at least one personnel door. We put one at each end, I also put a 12' wide by 9' high door at each end so that we could drive the tractor or a truck straight thru the H.T. I think in the long run you will be glad you put in all the doors. The extra cost is minimal. At least build the end walls with the doors framed so that in the future all you have to do is cut the plastic and hang a door. As an after thought we dicided we needed both solid doors and screen doors to keep out the deer. The outer solid doors slide and the inner screen doors hinge.

PLASTIC ROOF - Pulling the plastic roof over the trusses takes a few people. Make sure there is absoutly no wind. Use tennis balls and a soft rope to tie the edge of the plastic in about 4 places. When pullling the second plastic layer on watch not to roap burn a hole in the first layer of plastic.

PLYWOOD LINER - We are spending the money to line the ends with plywood. This not only protects the plastic from accidental puncture but gives us a place to hang some hand tools, and mount irrigation equipment and future solar controllers and temperature sensors.

TIP - Drainage - One issue people do not think about is drainage. All the water that hits the H.T. roof has to go somewhere. Make sure it can drain away. Many people have problems because the sides stay too wet to grow crops.

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Disclaimer: Read and follow manufactures instructions and follow all local buillding codes. RCV Farm is making no design calculation this information is merely to assist the user in the assembly of the high tunnel where manufactures instructions my be vague or lacking. - See full legal disclosure
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