The early birds get the returns
PART 2: Detailed instructions for building your very own fieldhouses--only $600 to $800 for a 96-foot house--Duct tape required.

By Paul and Sandy Arnold

Posted MAY 30, 2003: In 1992 we started designing our own “fieldhouse” structures that would help us get a jump on the season and be very low-tech and simple to build and dismantle. We termed these structures "fieldhouses" because they are temporary, sit directly on our growing fields and lend themselves easily to rotations--an invaluable crop management practice for disease and insect control.

We utilize two homemade designs that have worked well for us, one with metal hoops and one with PVC plastic hoops. In the fall, two metal-hooped houses are constructed and remain up all winter, since they can withstand snow loads. In the early spring (March), one or two plastic-hooped houses are constructed. All the houses are dismantled by approximately June 1st when all danger of frost has passed.

Plastic-piped house

This design with PVC hoops is only used in the spring (and sometimes in the fall), since it is not able to withstand any snow load. Ours have gone down to the ground several times with snow and they actually do spring back up nicely, but eventually the pipes will break! Total cost of the plastic house was about $600 when we built ours years ago (no labor included).

The standard fieldhouse we build is 14 feet wide and 96 feet long. This design uses twenty-five 1-inch by 20-foot plastic schedule 40 PVC pipes for the hoops (for a 96-foot house). Two 100-foot strings with stakes attached to each end are set up parallel to each other and 14 feet apart. These are used as guides to keep the house in an approximate rectangle. 1-1/4-inch galvanized pipes approximately 2 feet long are set along the strings every 4 feet.

The pipes are then sledgehammered into the ground as close to the string as possible; if you have rocks like we do, a pipe can be moved a few inches either way up or down the string. If the pipes are being re-used, the dirt must be removed from them first by tapping them together (great kid job!). We place a 2 x 4-inch board on the pipe to prevent damage to the top of the pipe as we hammer. About 6 inches of pipe should be left above the ground. Most of the pipes we use have been obtained free from fencing companies, who, in our area, throw away pipes shorter than 3 feet. The plastic hoop ends are then placed into these metal pipes.

Next we attach 1 x 4-inch rough-cut boards along one side of the fieldhouse about 3 feet off the ground to create a vented side. It is best to choose the side that does not get the prevailing wind. Pre-drill holes on the boards every four feet, starting about 2 inches from the end and a little below the center of the board. Secure the boards to the plastic hoops wit 5/16-inch U-bolts (they come in all different sizes but we use mostly 2 x 2-1/2 x 5/16-inch, zinc-plated) with the nuts facing the outside of the fieldhouse. The U-bolts go through the pre-drilled holes.

Shorter wood scraps (15 to 18-inches long) are used to strengthen the areas where the separate boards meet. Wherever two boards butt together, place a short wood scrap behind and then place 3 screws (1-1/4 to 1-1/2 inches) on each side (6 total per joint). Depending on how far the bolts stick out beyond the boards, we either countersink the nuts or wrap two layers of duct tape over the ends of the bolts to prevent damage to the greenhouse film. We duct tape a piece of carved rigid foam insulation on both ends of the boards to protect the greenhouse film; it can be saved and used for many years.

A duct tape marvel: The ridge pole (this fieldhouse has two--only one shown) and side diagonal braces are attached by duct tape--perfect for this temporary construction.

The ridge pole is a series of 5 additional PVC pipes (each 20 feet long) which are duct taped as straight as possible to the inside of the hoops and down the center. The pipes are overlapped about 10 to 12 inches and wrapped with duct tape, especially on the cut ends that could damage the plastic. Side diagonal bracings (PVC) are attached by duct tape, 2 on each end, starting at the ridgepole at the greenhouse ends and ending at the ground level, attaching to each of the 4 hoops they cross. At both ends of the fieldhouse at the peaks, the pipe ends need many loops of duct tape to stay put. Two wrappings of duct tape are usually all that is required every other place a PVC pipe crosses another pipe. Remember, these houses are only temporary.

A trench 6 to 8-inches deep is dug along the side of the fieldhouse that does not have the vented side (and board). The trench will hold one end of your greenhouse film and should be dug very close to the outside of the metal posts. The end walls are pre-made units of 2 x 4-foot construction that utilize a 4-foot-wide x 5-foot-high door and are permanently covered with plastic (lathed on). Our doors are 4 feet wide to accommodate our harvest wheelbarrows, but can be made to any size that works best. These removable end units are screwed into four 2 x 4 x 2-foot-long stakes. The stakes are sledgehammered into the ground about 10 to 12 inches and two 3-inch sheetrock screws are used to secure each stake.

We use 3-year greenhouse film (24 feet by 100 feet) which is lathed and screwed onto the end units when the winds are totally calm (always roll the lathe/plastic under for rain drainage), then the one side is buried into the trench. It is important to pull the plastic tight in all directions before securing. If the plastic is buried too deep into the trench, it can’t be pulled up easily by hand, and if it’s buried too shallow, it pulls out with the wind. Practice makes perfect! The other side is secured to the side boards by screwing lathe strips on the top part of the boards, and the plastic can then be rolled up for venting when spring temperatures reach 60°F to 70°F.

Venting the crop: A simple string system holds the rolled plastic off the ground when more air flow is needed.

We use a simple string system to tie up the plastic every 8 feet. One end of the string is tied onto the side board through a 1/2-inch hole we drill on the lower side; then, after the plastic is lifted or rolled up, a small tied loop at the other end of the string is hooked over a screw partly inserted into the lathe strips above the drilled hole. Again, roll the plastic under before securing so rain runs off, instead of inside, the plastic rolls. If you have strong winds, the vented side plastic can be secured to the ground with cement blocks on top of boards. These are temporary structures and are not designed to withstand heavy winds, but we never have problems if both sides are secured down.

It takes us about 8 hours with 2 people to put one up and a lot less time to dismantle! We dismantle the 1 x 4-inch boards in sections, and number them as we go (leaving the short scrap wood pieces attached to one board), so they can be pieced back together the next season.

Metal-piped house

The piecing together of this design is similar to that of the plastic-piped structure. Total cost of the metal house was about $800 when we built ours years ago (no labor included).

Bending and peaking: We are low-tech with bending, but do use a pipe bender to make the peak gothic style (sheds snow better).

This design uses twenty-five 3/4-inch galvanized water pipes that are 21 feet long. These are available from any plumbing supply facility and cost about $23 each in our area. We bend the pipes ourselves into a half-circle using a jig with about twenty short pieces of 2 x 4-inch boards (about 8 to 10-feet long). The boards are each attached with 2 screws onto our hay wagon about one foot apart. The one end of the pipe is attached to the wagon with 2 boards, then one person merely “walks” the pipe around the jig until it touches the last small board. Next, using a pipe bender, we bend the peak to be gothic style, bending until an attached string shows the ends are 14 feet apart. Finally, a slight bend is put six inches from the end of each pipe, so the hoop drops into the fence pipes easily.

If this type fieldhouse is used only when there will be no snow, the pipes can be placed every 6 to 8 feet instead of every 4 feet. This type of fieldhouse is utilized all winter on our farm and it can take almost any snow load. However, we often remove the snow using a large push broom and clear along the sides if necessary with shovels or a front-end loader, mostly to get light to the plants inside faster. During the winter, the plastic on both sides is buried in the ground. All other details of construction are similar to the plastic house as described above.

Duct tape is used to bind everything together and to tape over bolts, pipe ends, etc. to protect the greenhouse film. The greenhouse film usually lasts us 6 seasons, but often as many as 9 seasons. We fold, label, and store it in a dark, cool place (rootcellar). Screws and not nails are used when needed for ease of removal and reuse of all materials, and the specified lengths can be changed depending on board widths, etc.

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