How to build a (hula)hoop house for the garden

As I mentioned in a previous post, I want to build a hoop house for the garden using hula hoops for the rounded supports.  I finally started work on it last night.

First, I cut the hula hoop in half with a hacksaw.  I identified where the join was located (where the single tube was joined to make a circle) and dropped a line from that location and made a mark on the hula hoop where the line intersected the circle.  I did this to be sure I'd segment the hoop into two equal halves.  Then I cut the hoop at the join mark and the line intersection mark with a hacksaw to make two equal arcs.

Once that was done, I measure the distance between the two ends of each arc and found that mine was approximately 36" from end to end.  To make a square box (which is what I'm doing), I'm going to have the hoop arcs span from one corner to the opposing corner.  The hoop arc represents the hypotenuse (the long diagonal piece for the non-engineers) of a right triangle (meaning there's a 90 degree angle opposite the hypotenuse and separating two equal length sides).  To calculate the distance the sides need to be requires the use of some trigonometry.

In a right triangle, sides X and Y in the picture the same are the same length.  So once you calculate the length of X, you automatically know what Y is.  We know that the hypotenuse is 36" as represented by the measurement of the hula hoop arc from above.  To calculate X we use the formula below.

sin (angle) = Opposite side / Hypotenuse

Plugging in what we know, we have the following:

sin (45 degrees) = X / 36"

36" x sin (45 degrees) = X

36" x .707 = X

25.45" = X

To track down the sin of 45 degrees, you can either use a scientific handheld calculator, the scientific function of the calculator built into your computer operating system, or if you happen to know the square root of two, divide that by two.  I used my computer calculator because I've long since forgotten my sin angle stuff from schooling.

So now we know the length of the sides.  As such, I cut two sides of my lumber to 25.5" long (because it's close enough).  For the other two sides, I made them 3" longer.  The reason for that is that you need the inside of your box to have the dimensions as we calculated.  2x4s, 2x6s, 2x8's (and so on) are the dimensions of the lumber before they have been planed, the actual thickness is 1.5".  We are having two sides to you need the wood to be 3" longer.  Now we have all four sides cut.

Now, put the long sides oppose to one another and the short sides opposite to one another to make a square.  Then drill pilot holes (so your wood doesn't split) a little smaller in diameter than your wood screw.  Once that's done, install your wood screws.  I recommend either 2.5" or 3" long wood screws to give plenty of thread engagement with the wood you're screwing into.  You will now have a square frame.

Now that that is done, you can install some conduit brackets to clamp the hoop pieces in place.  The size brackets depends on the diameter of your hoop arcs.  Mine is 3/4" across, but since it's a half-circle piece, the conduit brackets need to be for 1/2" conduit.  I test fit everything and it looks like it'll work nicely.

Once you install the conduit brackets, you're all set to install it in the garden.

Over top you cover it with either a greenhouse fabric or you can use plastic (ideally, UV light resistant to keep it from breaking down).  Just bear in mind that the thicker the plastic, the less light is let in to help the plants grow.  The benefit to thicker plastic is that it helps retain more heat if you're concerned about really cold winters.

I just covered mine with the greenhouse fabric since I think the bulk of the really nasty weather is over for Maryland.