To assemble the arch frame of the greenhouse, we choose, based on considerations of ensuring the necessary bearing capacity and minimizing costs, round PVC pipes with a diameter of 15 mm. Both arches themselves and a longitudinal element will be made of them, which will connect the arches to each other and create a strength structure sufficient in rigidity and strength, designed to withstand maximum snow load and wind pressure.
For a greenhouse measuring 1220 × 2440 mm, three arches are enough. If your region has snowy winters and strong winds, you can add another arch to give the frame of your greenhouse additional strength and rigidity. The ends of the arches can be fixed both outside the wooden base and inside. For definiteness, we choose the last option.
Pipe length determination
To determine the length of the arched blanks in the form of a semicircle or so for a greenhouse 1220 mm wide, we use the mathematical relationship between the circumference (C) and diameter (D), which in our case is equal to the width of the greenhouse, i.e. 1220 mm.
C = πD = 3.14 × 1220 = 3831 mm.
Then the length of the pipes (L) from which we are going to make arches will be equal to half the length of the circumference calculated by us:
L = C / 2 = 3831/2 = 1916 mm.
If you want to make the greenhouse a little higher, then the obtained length of the pipe billet from which the arches will be made is enough to slightly increase, for example, to a size of 2150 mm. Then the cross section of the greenhouse instead of a semicircle will have the shape of a semicircle elongated upward, i.e., half-circle. Cut 3 or 4 blanks with a length of 2150 mm.
To choose the length of the longitudinal element that will connect the arches along the top, we lay a three-meter pipe on the base parallel to the long side. We abut the end of the pipe across the base cross from the inside. After that, at its other end, make a mark at a distance of 25 mm from the other inner edge of the crosspiece to the larger side and cut off the excess with a hacksaw. These additional 25 mm will be needed for reliable connection of the longitudinal element with the arches.
To fix the arches, we drive in the four internal corners of the base and in those places where intermediate arches will be installed, pieces of reinforcement with a diameter of 12 mm and a length of 500 mm, leaving a 150 mm pin above the ground.
Next, we alternately fix one end of the arch blank on the pin, bend the pipe and put the other end on the mating pin.
Before fixing the longitudinal element of the frame of the greenhouse to the arches below, put on its ends plastic plugs that will protect the plastic film from breaking when it is stretched to the finished frame.
Then, with the help of metal U-shaped clamps of a suitable size, we fasten the intersection of the longitudinal element with arches. Given the elasticity of the plastic pipes, it is enough to tighten the clamp nuts by hand, but you can also tighten them slightly with a wrench.
Now you can pull the plastic film over the assembled frame so that a film strip remains on all sides.
What is this for, we will tell a bit later.To increase the reliability of the shelter for plants, a plastic film in several places can be fixed to the arches using pieces of a rubber tube 75-80 mm long and cut along the length on one side. So that the tubes do not fly off under the gusts of wind, they can be fixed using suitable clamps.
The remaining strip of plastic film around the perimeter of the base is collected and pressed with various weights (pieces of reinforcement, bricks, stones, etc.).
This will further strengthen our structure, especially when snow falls, which will further press down the film and, in addition, give the greenhouse and the land adjacent to it a neat appearance.