The Samuel Roberts Noble Foundation, Inc.

Permanent Raised Bed Gardening: Corrugated Sheet Metal Beds - Bed Assembly

Bed Assembly


Using a permanent marker, designate the corners of one end of each bed by marking the appropriate perimeter stake line. Using the example of 40-inch beds on 5-foot centers, mark the string at zero, 40, 60, 100, 120, 160, 180, 220 inches and so on along the length of the string, depending on the number of beds to be constructed. Mark off the corners on the other end of the bed using the same procedure.

Next, install the bed border stakes. Place one edge of a carpenter's square against the outside edge (away from the plot) of the perimeter line, making sure the apex is on the first ink mark. Position a 5/8-inch by 36-inch-long sucker rod stake at the end of the adjacent arm of the square on the corner that is in line with the ink mark. Drive the stake into the ground to a depth of 18 inches. Repeat the process until all of the stakes on both ends of the beds are in place.

Because the perimeter stake lines are under tension, they will have a tendency to stretch causing them to sag over time changing the location of the ink marks. To ensure accuracy, don't delay installing the stakes. If you can't finish the job in one day, disconnect the lines and reconnect them when you start again, making sure the previously installed stakes match their corresponding ink marks.

Designate the exact location of the first border by stringing a line between the border stakes at each end of the bed. Adjust the elevation of the line so it just touches the perimeter lines. If the line does not line up with the ink marks on the perimeter line, make needed adjustments to the stakes. Repeat this process when locating each additional border.

Starting at one end of the bed (perimeter line), measure along the border string line and make a mark at 10 1/2-feet and another at 20 1/2-feet using a permanent marker. These marks designate the location of the 2-inch by 4-inch board unions that form the bed frame.

Set concrete blocks directly under the marks on the string and at both ends 6 inches inside the perimeter lines.

Next, position the drilled 2-inch by 4-inch boards on the concrete blocks. The ends of the boards should join over the blocks. The 10 1/2 and the 9 1/2-foot-long boards should be oriented such that the ends with holes drilled 3 inches from the end are next to the perimeter lines. The 10-foot-long board should be in the middle.

Connect the boards using 2-inch by 4-inch saddles and joint hanger nails.

With the 2-inch by 4-inch frame section turned on edge, use wood shims to raise the elevation of the frame. Adjust the elevation so the top of the frame is even with the string line. Because the string line represents the outside surface of the bed, be sure to position the outer surface of the frame inside the string (towards the bed interior).

Next, drop a 5/8-inch by 36-inch sucker rod stake into each hole, and with the help of a sledgehammer, drive the stakes flush with the top of the boards.

To lock the frame in place, use 1 5/8-inch wood screws to fasten 1-inch by 2-inch wood lath to the top of the wood frame. Space the screws one foot apart.

You can now remove the string line and the concrete blocks and shims from beneath the frame section.

Move to the other side of the bed and repeat process. Remember to place the 2-inch by 4-inch boards in the same sequence and orientation as the previous group and locate them on the inside of the line towards the bed interior.

Once you've completed construction of the side frame sections, install the sheet metal lining.

Start by using a chalk line to mark a line on the inner surfaces of both frame sections 1 3/4-inches below the top of the frame. Use a carpenter's square to mark a vertical line on the inner surface of both frame sections 1 1/2-inches from each end.

You will need two 12-foot long pieces and one 9-foot piece of sheet metal for each side. It doesn't matter in what sequence you install the pieces. The pieces are purposely oversized so they will overlap each other. Plan on overlapping the pieces about 20 inches.

Align the top of the sheets with the chalk mark and remember to recess the sheet metal 1 1/2-inches from each end of the side frame sections. Be sure to orient the sheets with the top edge sloping towards the frame. This will eliminate any gap between the metal and the frame, making it more difficult to cut your hands on the metal liner when working in the beds.

Attach the sheet metal to the frame using 1-inch self-piercing metal-to-wood screws. Space the screws 1 foot apart and 3/4 inches from the top edge of the metal.

Before constructing the bed ends, install a piece of angled flashing at all four corners. Insert one arm of the flashing between the frame and the liner, making sure the center fold of the flashing rests against the end of the liner. The bottom edge of the flashing should align with the bottom edge of the liner.

Secure the flashing to the liner using metal-to-wood screws (or sheet metal screws). To prevent injury, be sure to remove protruding screw tips.

Complete the frame by installing the end sections. Attach a 2-inch by 4-inch by 37-inch-long drilled board to each bed end using 3-inch wood screws. Before fastening, make sure the upper and outer surfaces of the boards are flush with the upper and end surfaces of the 2-inch by 4-inch boards in each side frame section.

Drop 5/8-inch by 36-inch-long sucker rod stakes into each hole and drive the stakes flush with the top of the boards.

Lock the end frame sections in place using pieces of lath and wood screws.

Finish construction by installing a 3-foot-long piece of sheet metal to the inside surface of each end frame section. Be sure the top of each piece is level with the top of the metal sheets on the sides of the bed before fastening with metal-to-wood screws.

Last but not least, secure the metal liner at each end of the bed to the flashing on each corner using metal-to-wood screws. Don't forget to clip off the protruding screw tips.

You have now completed a corrugated sheet metal bed. Construct additional beds using the previously described procedures.

It is now time to fill the beds.

ink marks
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