Saturday, January 23, 2010

This web site is my attempt to show how to build a simple greenhouse simply and affordably. The pictures in this blog are from several greenhouses in Western North Carolina. The design was put together by my dad, John Wilson of Black Mountain, NC. I'm not sure which aspects were his and which he borrowed from others. Thanks to Arthur Morgan School and Calvin Allen for their greenhouses where I took photos as well as my own.

The basics:

Put rebar pieces in the ground in two rows 10 ft. apart. The rebar should be 2 ft. apart in the rows. I dug holes in the ground about a foot deep and then put in the rebars and poured concrete around them. These pieces of rebar stuck out of the ground approximately 16 inches. Some who build these greenhouses do not pour concrete but just pound rebar pieces in the ground. You must make your own choice on the best path for you.

One thing to consider regarding the concrete footers for the rebar is that greenhouses in windy locations can be picked up by the wind and turned over making a mess of your work if they are not secured properly to the ground. If you are in a windy location I suggest using concrete at every 3rd or 4th piece of rebar and after the PVC is installed drill a hole through the PVC and rebar and put a small bolt or nail through the hole to keep your greenhouse from being blown away.

I decided to build my greenhouse 22 ft. long. You can make it larger or smaller depending on the space available and the size of greenhouse plastic you can find.

After the rebars are in place the construction will take about 2 - 4 hours with 2 - 4 people if you have basic construction skills. The rebar work was done a week or two before the greenhouse raising parties.

You will need 20 ft. pieces of 1 inch PVC piping for the main frame of the greenhouse. Installing them is the easiest part...let the kids help with this.

The next thing to do is install the horizontal lumber that holds the greenhouse together. You will need pieces of pressure treated 1x3 lumber. If your greenhouse is 20 feet long you will need 60 feet of these boards. So that is 3 ft. of 1x3 lumber for every foot of length of your greenhouse. Get an extra board or two for splicing boards. You will also need 3 metal u-bracket pieces for every piece of PVC pipe for attaching the 1x3 lumber pieces to the PVC pipes.

Attach the lumber approximately 24 inches from the ground on each side of the greenhouse and another at the top.

Then you need to build a wall at each end of the greenhouse. I went to a used building supply store and bought a window (approximately 2 ft. high by 3 ft wide) and a 36 inch storm door. I framed one end for each of these with pressure treated 2 x 4's. Some people prefer a door at both ends of their greenhouse.

After the wood is all installed it's time put on the plastic! Greenhouse plastic comes in different lengths and widths. It's different than the usual clear plastic that you can buy at a building supply. You will need the plastic at least 24 ft. wide and as long as your greenhouse plus at least 12 ft. I've found that it's difficult to find the exact right length and so I have to buy a length twice as long as I need. This is ok since the plastic lasts about 6 years on a greenhouse and you will have replacement plastic ready in your basement if you remember where you put the box!

Cut your plastic to the correct length and have some friends help you place it over the greenhouse. You will now need 1/4 inch pressure treated firring strips to secure the plastic to the horizontal boards 2 ft. from the ground. Secure one side then have help pulling the plastic tight before securing it to the other side.

Then you need to secure the plastic to the ends with firring strips.

You will have 2 – 3 feet of plastic hanging below the wooden 1 x 3 boards on each side of your greenhouse. These need to be taped to another 1 inch PVC pipe. You will need to use a special greenhouse tape that is available from the place you buy the greenhouse plastic. Tape the end of the plastic to the PVC pipe. It can be rolled up to allow ventilation in the spring, summer and fall and allowed to un-roll in the winter to keep the greenhouse toasty. Little pieces of string and screws will allow you to hold the pipe with rolled up plastic in the “up” position and this can be easily undone to allow the pipe to unroll when it’s cold.

Install the window on one end in the opening with hinges and the storm door on the other end.

To make beds I used 1 x 10 locust boards. I made two 4 ft. wide beds along each side with a 2 ft. path down the middle. It is not a good idea to use pressure treated wood since it’s treated with chemicals that may leach into the dirt.

Plant the beds with good things to eat and enjoy having a longer growing season in your own yard!

List of materials for my 20 ft. long greenhouse:

22 pieces of rebar 24 inches long
6 bags sacrete (more or less)
13 pieces of 1" PVC 20 ft. long
33 U-shaped brackets
70 ft. 1 x 3 pressure treated boards
70 ft. 1/4 inch thick firring strips
4 - 2 x 4 x 14 (pressure treated)
2 - 2 x 4 x 10 (pressure treated)
2 - 2 x 4 x 12 (pressure treated)
used window
used storm door
Greenhouse plastic 24 ft. x 40 ft.
1 roll greenhouse tape
100 ft. 1 x 10 locust boards
misc. screws and nails

The cost of the the materials for the last greenhouse I helped build which was 40 ft. long was $583.00