The Practical Blog › Single Post

Prairie Sky Farm High Tunnel Build 2015: The Photos

Welcome to Part Two: The Photos, from the high tunnel build workshop at Prairie Sky Farm (Part 1 is the video blog posted on Oct. 6). While doing recon for part names I had forgotten, I came across this high tunnel guide from Illinois that I think is worth a look, especially for selecting and squaring the site, which is not covered in this blog post.

Be warned, this is a long blog post, and mostly photos. Descriptions of each photo are below the photo. The post is divided into five sections: 1. Ground Posts and Bows; 2. Base, Hip, Purlins and Braces; 3. Endwalls; 4. Plastic; 5. Roll-Ups and Doors.

1: Ground Posts, Bows and Tools

10 Hanson tunnel 2015 parts 2

Bow parts, trellis, and flashing stacked from delivery.

9 Hanson tunnel 2015 parts 1

Bow pieces, baseboard, trellis, flashing, and purlins waiting to be assembled.

11 Hanson tunnel 2015 parts 3

High tunnel hardware laid out for easy searching.

1 Hanson tunnel 2015 (213) tools 1

Some necessary tools: extention cords, nut drivers, wrenches, scissors, tin snips, (sunscreen!), 100′ tape measure, locking wrench, wire stripper, snip and electric tape (for installing blower), pipe wrench, hammers, rubber mallet, tape measure, drill bits, vice grips, socket sets, chisel, screwdrivers, pens and markers. (aluminum tape included in the high tunnel kit).

2 Hanson tunnel 2015 (214) tools2

More 100′ tape measures (to set up the site you’ll want at least two), cordless drills and impact drivers, ear protection, 5-6 baseballs or tennis balls. We set up serveral impact drivers to drive in tek screws – hundreds of them. The drills were used to tighten down nuts on lag bolts. According to Montri, the number of cordless drills and drivers is usually the limiting factor for high tunnel builds.

5 Hanson tunnel 2015 (217) tools 5

Impact socket set (notice the 5/16″ is out somewhere in use).

3 Hanson tunnel 2015 (215) tools 3

Sawzall for cutting purlins, flashing, and a few other pieces of steel. We also used a jig saw and angle grinder to cut the poly.

4 Hanson tunnel 2015 (216) tools 4

several long levels, string, flags, and a rogue bit set.

6 Hanson tunnel 2015 (218) tools 6

Post levels

7 Hanson tunnel 2015 site prep

After the site was leveled and the corners squared, corner posts were put in and all other ground posts were laid out around the edges, with a measuring tape running along both sides.

8 Hanson tunnel 2015 workshop prep site

Ground posts were then pounded in (finished with a skid steer – see the video). Be sure to use the plug/cap when pounding in ground posts or the openings at the top can be bent. Baseboards and hip boards were laid out along the sides, purlins were laid out down the interior. The first endwall bow was dropped on (just to make sure we measured right). This is where we began Day 1 of the workshop.

12 Hanson tunnel 2015 connect bows

To assemble the bows, we set up a station on a flat surface; screwing together the joints when akimbo makes for a crooked house. The distance between the wooden stakes holding the ends is 1″ shorter than the width of the tunnel; this provides supportive tension when dropped onto the ground posts. This bow isn’t quite set – the end of the bow should be flush with the stake.

13 Hanson tunnel 2015 connect bows 2

We added an additional set of stakes where the cord (bottom of the truss) runs across the bow. These stakes had a string running between them which guided the placement of the cord.

14 Hanson tunnel 2015 connect bows 3

Here is a completed bow. The parts of the truss and cord and sorted and laid out on each side of the bow to make work more efficient. This high tunnel used a W-truss. #12 Tek screws were driven through each piece connection, including through the brace bands that hold the trellis. All screws driven in so that the heads would not poke out the top and rip the plastic.

18 Hanson high tunnel 2015 assembling bows4

The proper order of bow assembly is first to put the brace bands on the bows in their approximate locations (after building the first bow, we measured and marked the rest). Next, Tek screw the pieces of the bow together. The cord is the first part of the truss to go on. Last, the supporting truss pieces are assembled.

19 Hanson high tunnel 2015 assembing bows3

Bow assembly moves quickly with 4-5 people.

15 Hanson tunnel 2015 (34) building bows

Jeremy and Josh fit two truss pieces into a single brace band along the cord. The brace bands are closed with a carriage bolt and nut, being careful to keep them level with the rest of the bow. Thankfully these nuts can be loosened and adjusted (which was needed a few times!).

16 Hanson high tunnel 2015 assembling bows2

Zac drives a Tek screw into the brace band of the truss.

20 Hanson high tunnel 2015 bows up (2)

From the staging area across the driveway, the bows are carried one at a time to be placed into the ground posts. If you damaged the tops of your ground posts when pounding them in… now is when you might find out.

21 Hanson high tunnel 2015 carrying bows up

Ladders on both sides and a person at the top are set up.

22 Hanson high tunnel 2015 bows up3

The group walks the truss up.

23 Hanson high tunnel 2015 bows up best

One side sets their bow end down over the ground post. Then the other side goes, shaking it until it drops down. Don’t stand on the outside of the ground posts – if the bow slips off, the tension of the bow may cause it to spring out. Also, watch your fingers! A clip of the bow setting is in the video blog. You can also see the purlins set out along the inside of the tunnel, ready for the next step.

25 Hanson high tunnel 2015 endwall bows no truss2

The last bows on each side should not have any trusses. These bows will have the steel endwall frame attached, then the poly siding.

26 Hanson high tunnel 2015 tek screws bow to ground

After all the bows are set into the ground posts, drive tek screws in to affix the connection. Remember to keep the screw heads on the inside of the structure so they don’t rip the plastic.

2. Base, Hip, Purlins and Braces

1 Hanson high tunnel 2015 perlins baseboard out

Baseboards, hipboards and purlins were laid out along the inside and outside of the high tunnel for quick access.

1 Hanson tunnel 2015 (27) string level

We knew the posts were all dropped to the same depth, but we wanted to see if the house would set up level (if the ground was perfectly level). The helps when getting the baseboards on – you might need to dig out a little on one side, or build up a gap. We were a little bit off, so had to scrape out about an inch in some places.

1 Hanson tunnel 2015 (32) string level wrap

We ran a string level from corner post to corner post, wrapping the string and securing it with a Tek screw, as shown here (to keep the string from sagging).

2 Hanson high tunnel 2015 leveling baseboard

Jeremy, Adam, and Chris checking the level and driving a Tek screw through the baseboard (also called a hat purlin, because of the profile shape), onto the ground post. Between Adam and Chris some soil had to be dug away to keep the base level.

3 Hanson high tunnel 2015 leveling baseboard 2

Sarah and Jeff check the level of the baseboard after digging some soil out.

4 Hanson tunnel 2015 (40) baseboard conx

A Tek screw connecting two baseboard pieces where they overlap at a ground post. Tek screws are driven into the top and bottom lips.

4 Hanson tunnel 2015 (155) eye bolts in baseboard

an eye-bolt juts out of the baseboard. These are threaded with the anti-billow string (that will go on after the plastic).

4 Hanson tunnel 2015 (160) eye bolt ratchets

Josh using a wrench and a socket on each side to affix the eye bolts.

5 Hanson tunnel 2015 baseboard end

This piece fits inside the baseboard (hat purlin), acting as a cover to keep debris out. We didn’t get it seated quite straight (sorry, Sara).

6 Hanson tunnel 2015 base board end inside

The hat purlin end cover from the inside, showing where the Tek screw was driven through.

7 Hanson tunnel 2015 (29) multi level

Adam shows the post level to the crew and discusses the string level as we prepare to finish the baseboard and hip boards.

9 Hanson high tunnel 2015 hip conx

The hip boards took several people’s hands to hold, drive, and check the level.

7 Hanson tunnel 2015 (46) hip conx to end post outside

At the corner post, the hip board was secured with two brace bands and carriage bolts. Check out the video showing how they held the bolt until it was sucked into the channel by the nut’s pressure on the band. This view is on the outside of the tunnel.

8 Hanson tunnel 2015 (45) hip conx to end post inside

The corner post at the hip board on the inside.

11 Hanson tunnel 2015 (41) hip conx

Ok, stay with me, here, or go watch the video. To connect two pieces of the hip board (aluminum double plastic attachment channel), you need to use a pre-drilled steel plate (for carriage bolts with the braces), and then drive through two Tek screws.

To begin, put the heads of the carriage bolts in the single channel on the inside of the hip board.

12 Hanson tunnel 2015 (43) hip conx inside plate

Looking at the finished product from the inside.
The steel plate has been pre-drilled to let the carriage bolts pass through. Once the bolt heads are in the channel, fit the steel plate over the bolt (it only covers the side of the ground post where the pieces connect), then add the washer, nut, and tighten down on each side. Lastly, drive Tek screws through the hip board into the steel plate, and drive a Tek screw through the brace band into the ground post.

13 Hanson tunnel 2015 (44) hip conx inside alt

The other side of the ground post (still on the inside). The steel plate doesn’t reach this bolt, but this nut should be tightened along with the bolt in the previous picture.

11 Hanson tunnel 2015 (42) hip conx 2

The finished outside of the hip board. Notice the Tek screws are inside the channel where they won’t rip the plastic (The plastic will lock into this channel with wiggle wire). Also, the join point for the two pieces is slightly offset from the post-center.

14 Hanson high tunnel 2015 the right size kolbe

You can also find an appropriately-sized person if you are short on levels.

7 Hanson tunnel 2015 (50) wind bracing

Some extra wind bracing in the first two segments of the tunnel (the corner post is on the left).

16 Hanson high tunnel 2015 perlins

While on the ground, the bows were marked to show where the purlins should attach. The purlins were also measured and marked for where the bows should cross the purlins. Often, crew needed a rubber mallet to knock the bows into the proper position. Without doing this, the top can appear “lumpy”.

15 Hanson high tunnel 2015 perlins cover

Dan tells Jeremy and Bob if their marks are properly lined up.

17Hanson tunnel 2015 (54) perlins screw

Jeremy drives a Tek screw in where the purlin pieces meet. Here you can see the Sharpie mark on the purlin; the mark on the bow isn’t visible, but should be between the two stirrup braces (fixed with carriage bolts).

18 Hanson tunnel 2015 (56) perlin end measure

The purlin end was a little tricky. And end piece needs to go on, meaning the last piece before the end needs to be measured and cut to fit the tunnel. Adam likes to measure for this piece.

19 Hanson high tunnel 2015 measuring last perlin

Chris and Jeff would hold up the end piece and mark where to trim off the pulin. They measured a few times before making the cut.

20 Hanson tunnel 2015 (58) perlin end

The finished purlin end connecting to the bow. You can see the short purlin end piece connected to the bow with two steel braces and carriage bolts (heads to the outside, to protect the plastic).

21Hanson high tunnel 2015 bows up perlins on

A view of the high tunnel with the purlins on – in the center and half-way down each side of the bow.

22 Hanson high tunnel 2015 (216) center truss

One last center purlin was put on across the cord. It isn’t much for structure, but is nice for hanging things. It is secured by a few stirrup braces.

24 Hanson tunnel 2015 (82) cross perlin detail 2

Cross braces were added to the first two segments from each corner, starting just above the shoulder of the bow and running diagonally to the next bow.

25 Hanson tunnel 2015 (77) cross perlin

From the second bow, another purlin is started above where the first connects, and run diagonally to the third bow.

23 Hanson tunnel 2015 (81) cross perlin detail

Close up of the cross brace connection to the first bow.

Hanson tunnel 2015 (84)

Zac and Jeff finish connecting the top of the cross brace to the third bow.

26 Hanson tunnel 2015 (153) rollups set out

(Pretend the plastic isn’t there yet.) We laid out the roll-up bars and screwed together using steel connection bars and Tek screws.

27 Hanson tunnel 2015 (154) rollup conx

The finished roll-up bar with an unused connection piece. We marked the center of each connection piece, fit it into one side and drove the screw. Then connected the next roll-up bar segment and screwed them together.

3. Endwalls

1 Hanson high tunnel 2015 assembling endwall

The endwalls were laid out on the ground to check the pieces prior to assembly. We found that one of the pieces (like the one Josh is holding) was incorrect for our design; it had connection points sticking out into the doorway. After checking our conclusion several times, we decided to trim off the extra bits with an angle grinder, which worked perfectly.

2 Hanson high tunnel 2015 (211) assembling endwall

The endwalls were then assembled on the ground at each end, with the top of the end wall nearest the high tunnel so it could be lifted and walked forward (see video). Here, Daniel and Bob push the pieces together while Zach drives Tek screws to the joins.

3 Hanson high tunnel 2015 (206) checking doorway

Michael and Adam measure the doorway to ensure the wall is assembled properly before standing it up.

4 Hanson tunnel 2015 (62) end wall frame up

The group stands up the endwall and slides it side-to-side until centered and in proper position. See video.

5 Hanson tunnel 2015 (74) leveling end wall

The endwall was a bit taller than the tunnel, so we dug down about an inch under the endwall.

6 Hanson tunnel 2015 (65) hangers in vent

The vent hangers (held with pliers) fit inside the window frame and are affixed with Tek screws.

7 Hanson tunnel 2015 (67) vent up
The vent was raised using the bucket on a front-end loader (see video). It is attached on top with brace bands. The level of the endwall was checked prior to putting in the vent, and then the level of the vent was checked. After this photo the vent had to be pulled out to remove the small stoppers (next to Adam’s shoe) on the bottom right and left corners of the vent; then it sat flush on the endwall.
9 Hanson high tunnel 2015 (209) peeling taping poly

Josh and Jeremy peel the protective film off the polycarbonate and tape the bottom edge with a breathable vent tape. Adam marked the inside face of each panel – one side is UV-treated and must face out.

10 Hanson tunnel 2015 (83) poly on endwall

After setting out the poly panels to decide where to place them for best fit, they were put in one-by-one, starting on the outside.

15 Hanson tunnel 2015 (90) endwall gap

The panels were wiggled and pushed down into a single-h channel at the bottom of the endwall, and also pushed into a single-h channel on the sides. The single-h channel (aluminum) was Tek screwed to the steel endwall frame. (also notice the gap at a low spot – this will be built up and filled with dirt).

14 Hanson tunnel 2015 (85) poly on endwall 2

We needed a person on each side to push the panel down into the single-h channel.

11 Hanson tunnel 2015 (95) cutting poly

A few oddly-shaped sections toward the middle of the endwall needed pieces cut to fit. After trimming the panel out of the doorway (see video) Adam and Jeff use a jigsaw to cut the scrap piece to fit an odd space next to the vent.

12 Hanson tunnel 2015 (89) poly puzzle2

The trimmed (previously scrap) piece of poly fills the gap between two panels. Aluminum double-H channel is used to join two pieces of poly. The double-H channel is Tek screwed to the frame.

13 Hanson tunnel 2015 (87) poly puzzle

Poly is on the endwall, untrimmed (except the doorway has been trimmed).

16 Hanson tunnel 2015 (91) endwall conx

Detail of the endwall showing the single-h channel holding the poly panel on the left, and the poly screwed to the endwall frame with a long Tek screw and washer with a rubber gasket.

17 Hanson tunnel 2015 (92) endwall conx2

More detail of the endwall assembly. The poly was secured to the frame about every 2 feet.

18 Hanson tunnel 2015 (183) endwall poly screws to frame

Close up of the longer Tek screw, washer and rubber gasket used.

19 Hanson tunnel 2015 (127) day 2 begin

At the beginning of Day 2 of the build, the poly was on the endwalls, but untrimmed.

19 Hanson tunnel 2015 (132) foil tape over poly

After the poly was trimmed using an angle grinder (see video), aluminum tape was put over the top of the poly.

20 Hanson tunnel 2015 (147) foil over endwall poly

Aluminum tape covers the top of the endwall poly, staying inside of the bow.

21 Hanson tunnel 2015 (151) endwall flashing fold

L-flashing covers the endwall, starting from just under the shoulder. At the bend of the endwalls, the L-flashing is snipped (see video) and folded under to promote water running off the outside. Here, the plastic attachment channel (U-channel, wiggle-wire channel), is Tek screwed over the L-flashing.

22 Hanson tunnel 2015 (161) endwall flashing

Adam, Chris and Daniel work on the L-flashing.

24 Hanson tunnel 2015 (139) start endwall wiggle channel

Josh puts a Tek screw through the U-channel on the endwall.

25 Hanson high tunnel 2015 (244) wiggle channel over flashing

Zach, Jeff and Josh work on L-flashing and U-channel on the other endwall.

27 Hanson tunnel 2015 (167) wiggle channel over flashing

Daniel and Chris finish the L-flashing and U-channel.

26 Hanson tunnel 2015 (173) wiggle channel over flashing endwall detail

Notice the Tek screw in the U-channel holds both the channel and the L-flashing; the L-flashing is also Tek screwed on the front.

26 Hanson tunnel 2015 (156) flashing fold wiggle channel detail

Front Tek screw on the L-flashing where the flashing was snipped and folded under.

4. Plastic

1 Hanson tunnel 2015 (130) unrolling plastic

Adam and Jeremy unroll the plastic (order long) along the side of the high tunnel.

1 Hanson tunnel 2015 (140) measuring plastic to cut

Adam uses a straight-edge to mark his cut line. Measurements are marked on the plastic. We left a few feet on both ends… better to trim than to be short! See the video blog for Adam’s discussion of IR plastic.

2 Hanson tunnel 2015 (134) ropes over frame

Ropes were thrown over the high tunnel (see video). These will be used to pull the plastic over.

3 Hanson tunnel 2015 (142) plastic ready to pull

The rope is held to the plastic by wrapping around a tennis ball placed underneath (see video). At this stage we needed all hands on deck, but there is a brief video of the plastic being pulled over. People stood on each side of the tunnel; one side pulled the ropes, the other side stood next to the tunnel with the plastic going over them, helping to unfold.

Because this high tunnel has a double layer of plastic, the blower was quickly installed after the first layer was on. Adam cut the second length of plastic, the ropes were thrown over again, and the tennis balls tied on again. The second piece of plastic was pulled over.

4 Hanson high tunnel 2015 (260) holding plastic

After both sheets of plastic was pulled over, we stood on the plastic to hold it down (it was too windy!) while Adam and Chris checked that the plastic was even and squared with the house.

5 Hanson high tunnel 2015 (280) tightening plastic with wiggle

We stood like this (or sat or laid down on the plastic) until wiggle wire was worked down to our place along the hipboard. Here, I am about the be freed from by Daniel and Michael. The wiggle wire started on one side and we stretched the plastic taut as we moved along.

6 Hanson high tunnel 2015 (262) holding plastic 2

Chris checks the squareness of the plastic from above while Zach holds the end on.

7 Hanson high tunnel 2015 (277) pulling plastic tight protecting edge

Sara adjusts the cardboard that temporarily protects the plastic from the shoulder of the high tunnel as it is pulled taut.

8 Hanson high tunnel 2015 (273) wiggle wire hip knuth nelson

Jeff and Josh work the wiggle wire into the top of the double-U channel of the hipboard (see video).

10 Hanson tunnel 2015 (177) uncul plastic under endwall wiggle

The plastic held to the end wall U-channel by wiggle wire.

11 Hanson tunnel 2015 (179) uncut plastic end and hip wiggle

The untrimmed plastic held on with wiggle wire at the hip board and ends.

9 Hanson high tunnel 2015 (307) wiggle into rollers

Jeff and Josh working wiggle wire into the roll-up bar (hip boards and endwalls were done first).

12 Hanson tunnel 2015 (184) cutting plastic

Adam and Jeff trimming the plastic after it is fixed to the roll-up bar.

5. Roll-Ups and Doors

7 Hanson tunnel 2015 (189) roller detail

Unfortunately I missed the part where they assembled the side-roll-up crank. Hopefully it’s well-explained in the manual… looks like it’s a few Tek screws holding the pieces together. Note that the side is rolled to the inside, so water can run off the edge cleanly, keeping the plastic dry.

1 Hanson tunnel 2015 (192) tenion string start

Here, Daniel and Michael are running the anti-billow rope off the spool, through the bottom eye, then a hook straight above, then beginning to alternate down the line.

2 Hanson tunnel 2015 (196) tension string at base

Eye bolt on the baseboard set at an angle.

3 Hanson tunnel 2015 (194) tension string at hip

Hook on the bottom of the hipboard Tek screwed after the plastic is on.

4 Hanson tunnel 2015 (203) tension string at hip with wiggle

Another view of the anti-billow rope hook on the hipboard.

6 Hanson high tunnel 2015 (335) tension string

We helped feed the rope through (see video). Hipboard hooks were at each ground post; baseboard eye bolts were half-way between the ground posts. At the far end, Adam tied the rope off, then we tightened the rope back and tied off the near end (we didn’t use a ratchet, just tightened by pulling).

8 Hanson tunnel 2015 (182) inflation blower

The blower (crudely wired, for now) inflates the space between the two layers of plastic. The is mounted inside the high tunnel in the corner, on the cross brace just above the hipboard.

9 Hanson tunnel 2015 (172) door hinge 2

Hinges for the door were affixed with three Tek screws per hinge.

10 Hanson tunnel 2015 (171) door hinge

Sometimes driving the Tek screws is harder work than you expect.

11 Hanson high tunnel 2015 (338) setting the door

Installing the doors seemed the most tedious part of the process (it is also at the end…). If you weren’t level throughout the rest of the build, you’re in trouble now. We were fastidious with the level, and it payed off. Here, Sara and I are following Bob’s directions for micro-adjustments before he Tek screws the hinges to the endwall frame.

12 Hanson tunnel 2015 (197) leveling door

We used shims to hold the door level while driving the rest of the Tek screws. Adam shows Chris how to assemble the latch.

13 Hanson tunnel 2015 (207) flashing on door

Jeff and Chris install aluminum backing on the inside of the high tunnel at places where the door opens. This prevents the doors from swinging the wrong way against the hinges and from excessive draftiness (see videos).

14 Hanson tunnel 2015 (210) nearly completed

Bob closes the doors – a perfect fit.

15 Hanson tunnel 2015 (205) inside with doors on

A view from inside the completed tunnel.

16 Hanson tunnel 2015 (61) lunch

We did take a couple breaks… ok, only for lunch really. This spread includes dried beef from Story City Locker, bread from Daily Bread, melon homegrown from Slim’s Country Market, apples from Wills Family Orchard, veggies from Lacewing Acres and Kirsch Gardens, and other items from Wheatsfield Coop.

17 Hanson tunnel 2015 (101) PFI sign

Thanks again to the great PFI members and hosts, and Adam Montri, for making this build a fun (if sweltering) weekend!