The purpose of these instructions is to assist the hobbyist in constructing a 16' x 24' greenhouse to house and maintain their collection. It was written and designed for the individual with limited carpentry skills. However, anything or everything in these instructions can be changed or modified to fill your needs. Basic knowledge such as, how to determine if a corner is square, and how to use a level is essential! Electrical writing, plumbing, and laying a permanent foundation are not within the scope of these instructions. The reason I use these dimensions (16' x 24') for this greenhouse, is that it is very easy to build structures such as these, using 8' squares. The main items (2" x 4"s, fiber glass sheets, plywood, and lattice panels) used in this construction are readily available in 8' lengths, and there is little or no waste. Additionally, it is extremely easy to enlarge or decrease the structure design based on your needs. Also, based on your needs, determine beforehand if you want electricity, telephone, gas, or water within this greenhouse, and plan accordingly. Some items will be color coded for ease in locating. Depending upon the size of your monitor, it will probably be easier if you print out copies of the drawings, rather than try to read them off of the screen.
It is essential that the site where you have decided to build your greenhouse is as level as possible. In addition to that, I usually have an inexpensive gravel fill brought in to elevate my site by as much as 8 inches. Locally we use a produce called 'Dirty Birdseye', which costs approximately $6.00 a ton, plus hauling. This elevating the site really helps in the winter, when everything else is under an inch or two of water.
1. For squaring your site, you will need to run a string-line as shown in Drawing-1 .The easiest way to do this is to set out 8 stakes. The distance between stakes '1' & '2' and '5' & '6' is approximately 20', and the distance between stakes '3' & '4' and '7' & '8' is approximately 28', (this is indicated by the arrows outside of the rectangle). The reason each line is approximately 4' longer than the dimensions of the greenhouse, is to allow you working space when digging the post holes, and setting up the supporting posts. You will notice that the rectangle formed by the lines is exactly 16' x 24'. Once you have set out the lines, and squared all of your corners, you should never remove any stake until all of the posts are securely in the ground.
Note: I like to use the 8 stake method, because this allows you to move the strings, without disturbing the stakes and messing up your measurements, when digging the post holes. The other method is 4 stakes, one in each corner, however, they must be moved when you are ready to dig your post holes, and there goes your measurements!
1. It is essential to set the four 10' corner posts first. Measurements are from the outside of each end post, and not the center of the post. The distance between posts '1' & '9' and '4' & '12' is exactly 16', and '1' & '4' and '9' & '12' is exactly 24'. See Drawing-2
2. Set the two remaining front 10’ posts, ('2' & '3') in the ground, at 8’ intervals. Measurements are from the outside of the end posts, to the center of each of these posts. Repeat the process for the back two posts, '10' & '11'.
3. Set the two end-center 12’ posts, ('5' & '8') in the ground, exactly 8' from each end post. Measurements are from the outside of the end posts, to the center of each of these posts. When these two posts are set, string a line between them to assist in setting the remaining two (2) 12’ posts, ('6' & '7') in the center of the building.
Note: All of my posts are set two feet in the ground, into concrete. All post holes are 2' deep and 12" in diameter. After setting each post in concrete, and before the concrete starts hardening, use a level and make sure the posts are plumb! Allow concrete to set for 24 hours before nailing into the posts.
1. We will do the upper most 2" x 4"s first. See Drawing-3. This will also allow us to make any minor adjustments if any post is slightly out of plumb. The six uppermost 2" x 4"s [red] going North to South, and the four 2" x 4"s [red] in the very center, can be attached with either galvanized nails, screws or lag bolts. If you decide on galvanized screws or lag bolts, pre-drill your holes for ease of installation, and counter-sink your lag bolts.
2. Next, we will construct the front of the greenhouse. See Drawing-4. Note that the 2" x 4" bracing is not the same in all areas. I use a single 2" x 4" x 4' for bracing the center of the lattice, two pieces of 2" x 4" x 2' for bracing the fiber glass sheets, and three pieces of 2" x 4" x 2' for bracing the exterior plywood. I use different bracing because of the difference in weights and wind resistance. If you feel it is necessary to add additional bracing for your area, do so at this time. Please note that the three pieces of 2" x 4" x 8's on the bottom [green], are pressure treated! Also, when installing the fiber glass sheets, it is best to use wiggle molding as a backing, and aluminum nails with rubber washers. (I did not include these on your lists of materials!) Added Drawing-4a.
3. We'll now start on the back of the greenhouse. The only difference between the back of the greenhouse and the front, is the door opening. The materials are the same, just in different amounts. See Drawing-5 .
4. We'll now do the sides of the greenhouse. See Drawing-6. Again there is little difference from doing the back of the greenhouse.
5. Now we come to the roof. See Drawing-7. Here is where you have to decide if you want to cover the roof with fiber glass sheets, or 6 mil UVR greenhouse film. The life expectancy of 6 mil UVR greenhouse film is 3 to 5 years. It is inexpensive and easy to install, however, on a single poly roof (single layer) the slightest cut will render it useless, particularly in a wind storm. [In 12 years, this has never happened to me, but you must consider that factor.] If you are in a high wind area, or experience hail storms, I would recommend a double poly roof. Important - for your roof rafters, you must buy 2" x 4" x 10', however, if you are using fiber glass sheets, you must cut 6" off of each rafter, making them 9 1/2' long. This is to compensate for the thickness of the 4" x 4" posts, and the 2" x 4"s on both ends of each rafter. If you are using poly for the roof covering, then you must cut 12" off of each rafter, making them 9' long. This is because poly comes in 20' wide rolls, and it would not be wide enough to overlap the roof for attaching purposes. If you decide on a fiber glass roof, you must consider the side-end portions of the roof, where they form triangles. [Shown as the light colored yellow area on the drawing]. You can still cover this portion with small pieces of poly, or cut the fiber glass sheets to fit these areas. When installing the roof rafters it is best to use joist hangers and tie down hangers. These will tremendously increase the strength of your roof during a wind storm! I would not even consider building a greenhouse without using these. Check with your local hardware or lumber store for these items. You will need one joist hanger and one tie down hanger for each roof rafter. When cutting the braces for between the roof rafters, do not cut too many ahead of time. The old carpenter's adage, "Measure twice, cut once", really applies here. There is nothing worse than cutting 20 pieces of bracing, and finding they are all 1/2" too short!
1. The reason I use fiber glass sheets on the upper portion of all of the walls, is for light transmission. I use the 4' x 8' lattice panels both for light transmission, ventilation in the summer, and they help break up the sun's rays. The exterior plywood on the bottom portion is for strength, and to help keep small animals out. I have had small animals scratch their way through a poly covered wall.
2. In the winter, I cover all sides of the greenhouse with inexpensive 'cheap' plastic covering. This is a temporary covering, which I remove and throw away in the spring, and I don't want to waste money on it.
3. With this greenhouse, you can make any modification necessary for the area where you live. I put my first one up approximately 12 years, and it is still standing, a little wood borer damage, but functioning perfectly.
4. If you have questions regarding availability of materials, choice of materials, carpentry techniques, or any of the thousand or more questions that can arise when building something, please ask advice from your local lumberyard or hardware store personel. I will be unable to respond to individual inquiries. However, if you find a technical flaw in the drawings or instructions, please contact me. I have counted and re-counted, read and re-read everything here, however, mistakes are possible, so please read everything with an Eagle's eye.
