A few of you have asked about my hand built greenhouses. I have four decent sized greenhouses around the 30ft x 50 ft size. I keep them short on purpose because I run all these with no equipment, like fans, or anything. I built my first greenhouse in 1989 and every few years I had to build another one. Each time I learned how to make it better and I have attached a picture of part of my best one, which is 40x60x12. Each of these are made out of lumber. I put shade cloth on top of the frame, and then tack "5 year poly" on top of the shade cloth. This poly is 6 mil and has UV inhibitors. They say it is good for 4 years, but I have got 6 years out of one batch.
Before I explain how I build these, let me mention, all of these went through 3 good sized hurricanes in a 3 week period several years ago, where all three eyes of these storms were 12 miles or closer to my location. Worst was 125 mph sustained wind. The plastic was shredded, and each greenhouse had 2 or 3 minor boards that needed replacing, but they did great. The fancy metal greenhouse kits are said to last 15 years and two of these have been in for 25 years and I've only had to replace a single board here and there over all these years. Also, if anyone had one of these things during a bad storm, if any of the metal frame gets bent, which they do, it is an expensive fix.
Instead of worrying about this big looking greenhouse I want to start with the basic square and work up from there. This is all pressure treated wood. Take four 4x4s and bury them at least 2 feet into the ground, no need to concrete them in, they aren't as flexible during a storm and can snap. Let's make this square 12 feet x 12. Two of them should be 6 to 8 feet above ground (I like 8 way better for head room and extra room for the heat that builds towards the top) and the other two should be around two feet taller than the others. This way you have a slope for the water to run off. Nail 2x6s on all four sides, framing the top. You now have a 12x12 greenhouse that will withstand a hurricane for $70. For tacking the plastic down, I run 1x4s at the bottom. You could use 2x4s if you want, but the cheaper boards in this application seem to work alright.
Let's say you want to make it larger some day. You can go either direction, but let's say you want to make a gable end look, all you need is two more shorter 4x4s and three more 2x6s, and for $32 more dollars, you have a 12ft x 24ft greenhouse. Now if you want to double that someday, with four more 4x4s and six 2x6s, you have doubled that space.
On the one in the picture I built this one all at the same time so I didn't use as many 2x6s. It is 40 feet wide, so 4 squares wide (10 feet that way) and 60 feet long ( five 12 foot boards) In this case I cross braced the top in two ways. The short way has 2x4s going down, being nailed to the posts. The long way needed 2x6s because the pressure of tightening the plastic bends 2x4s the long way. Instead of toe nailing the 2x6s, I hung them with metal truss brackets. Hopefully that explains everything you see in the picture.
The shade cloth stays on all the time. The plastic on the top stays on during the year and lasts about 5 years. The plastic on the sides and ends I either drop down, or strap up after winter is over which means, with 8 foot sides, no real intense heat is generated in the lower 8 feet of the greenhouse. The heat rises and vents out the gable ends.
To close up these greenhouses during a freeze event one square on each end is plastic that is not attached, except for the top. The sheet of plastic is attached at the top and the bottom has a 1x4 tacked to the plastic. I use that board, which is fairly light, to roll the plastic up and I use the nylon strapping tape to strap it up when it needs to be up. When it needs to come down, roll down the plastic and I tack the plastic down with the staple hammer to the 4x4s. The next morning, after the temps go above freezing, I pull the staples on the side 4x4s and roll the plastic back up until the next time.
This works very well for me in Florida. I do have a few to several freeze events each year, but I rarerly have a freeze where it stays below freezing all day. Tom
