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Tom Uhll's greenhouse

"I am handy but not a great carpenter..."

Somewhere in the world, it's always just the right time to start building a greenhouse. Tom has generously taken time to document the construction of his greenhouse. It's inexpensive, and you can build one, too!

When I saw the greenhouse project built by North Carolina State University on Sherry's Greenhouse web page, I decided that--being affordable and quite simple--this would be the greenhouse of our choice. I am handy but not a great carpenter, and this looked like something I could easily do.

North Carolina Cooperative Extension Service - "A Small Backyard Greenhouse"
NOTE: This is a pdf file. If you don't already have Adobe's Acrobat Reader which is necessary to download this file, you can get it free of charge at

One of my biggest decisions was the location of the greenhouse so that it would have a southern exposure and a safe distance from trees, etc. I chose a spot on the southern side of my existing barn. I also wanted to attach it to the barn so that I could vent into the workshop and take advantage of the free heat the greenhouse would provide. My problem, as you will see from the photos, is that the barn is a quonset with an addition on the back. I had to build the frame away from the curve of the quonset and centered to the workshop door.

My next problem was the fact that the ground ran uphill away from the barn. I built the frame at eye level, because if I made it perfectly level the barn end would have been built up 3 feet, and I could not dig into the hill because of the problem with run off from the hill. I was lucky that I had a pile of fill next to the barn, and my neighbor was kind enough to use his back hoe to fill in the frame for me.

I started--as I said--by centering the end of the greenhouse to the workshop door and out 2 feet (see Photo 1). I used pressure-treated 2X6's (this being the most expensive part of the project) for the frame, which measures 12 feet by 14 feet. I dug down about two feet in each corner and buried a pressure-treated 4X4 and attached the 2X6's to them to hold the framework during heavy wind.

Once the frame was built I started building the PVC [polyvinyl chloride plumbing pipe] framework. I had trouble finding the PVC crosses and finally got them from Home Depot. I also could not get schedule 80 here in the Northeast, so I went with the schedule 40 hoping that it will be strong enough to hold the heavy snows we get here. I figured with a 2X4 support in the center and a little heat during a storm, the schedule 40 should work just fine. The bill for PVC pipe, crosses, tees, glue and cleaner along with the electrical conduit and clamps was $36.

The assembly of the PVC framework is very simple and only takes a few minutes to complete. The most important part is working on something flat so that the tee's and crosses are all lying in the same direction. Once these are glued you cannot change them.

I started by cutting one of the pipes into 22 1/2 inch lengths. I glued a tee to the first one, then a cross, and then another 22 1/2 inch section--continuing in that order until the final tee was ready to be glued on. At that point, insert a piece of electrical conduit 12 feet long into the center and slide it in as far as you can, then glue on the end tee. That completes the assembly of the PVC center section.

I placed the completed PVC center section along the 14' side on top of the 2X6' and marked the location of each rib down the side of the 2X6's for the EMT (Electrical Metallic Tubing) straps or clamps (see Photo 2). I then loosely screwed in two EMT straps--one near the top of the frame and one near the bottom at the marks. Do not place these too close to the edge so that they do not split the wood. These have to be loose so as to slip in the PVC ribs when that is built.

Now you glue on the 10' PVC pipes to make the ribs. You need a lot of space to work with this now. Once the ribs are installed and the glue has dried sufficiently, the rib framework can be installed onto the frame (Photo 3). It takes at least two people to do this.

Starting with both people at one end, lift the end ribs and start to bow the frame. Lift and slide the pipe down into the two EMT clamps that were previously installed. You will see why it was important to leave these loose. Do not tighten yet. Work your way down the frame doing the same with each rib. When all the ribs are in place, start tightening the EMT clamps--making sure that the bottom end of the ribs are all lined up with the bottom of the 2X6. (Photo 4)

The next step is to build the end walls. I used treated 2X4's for this as there is a lot of moisture in the greenhouse. I wanted them to last a long time as I found this to be the most difficult part of the project, and I did not want to rebuild this again. The angles are great and are hard to get together to be solid (remember I said I was not a great carpenter). I built the wall on the floor of the greenhouse after getting all the measurements. When building the end walls, you need to decide at which end you will be placing the door and build the door frame at this time. I chose to place a door on both ends. One so that I could open into my workshop, and the other to exit out to my herb garden or to bring in supplies without having to go through the whole barn.

As you can see from
Photo 5, I used a storm window as my outside door. I will attach an automatic vent to this window so that if the temperature gets too warm in the greenhouse the window will open. If you use this method be sure to notice which direction the wind comes from and have it open in the opposite direction.

I then used small pieces of thin plywood as braces for the corners where the angles meet. Before I stood the wall up, I atttached a thin strap of sheet metal to the frame. When I stood the frame up, I bent the metal over the end rib and screwed it into the wood frame on the other side. This holds it in place so that you can shift it around to level it and nail in the bottoms. Repeat the process for the other end. If it is built right, both ends should be identical.

Now the ends are on, and all the screws are tightened and holding the ribs (make sure there are no screws left loose, as you will tear the plastic during installation when it hits a screw if it is out). I bought a roll of 6 mil plastic (24'XlOO') for $75 at my local feed store. I priced plastic made for greenhouses 20'X25', and it would have cost anywhere from$60 to over $100. Greenhouse plastic is guaranteed for 3 years, but for what I got I can cover the greenhouse 4 times. If I were to remove the plastic each year in the off season (an awful lot of work) and replace it in the fall, well then this will last for a long time and I feel it was a better investment.

As my roll was 24 feet wide, I cut a piece 24'X25' and laid it out along one side of the frame. I marked the center edge of each side of the plastic along the 25' edge. This will be important to be sure you are not short on the ends. Now again it takes at least two people to work this on--starting with one person at each end and lifting the plastic up and over the frame. Line up the marks on the edge of the plastic with the center of the 2X6 frame. You cannot just staple the plastic to the wood as the staples would tear the plastic as you pulled it tight. I used the nylon webbing that goes around shipping crates (available for free from almost any store). I started stapling the nylon webbing from the center out to the ends;then I moved to the opposite side and repeated the process--having my wife pull the plastic down and tight as I stapled along.

Once the sides are stapled, start at one side of the end--pulling and folding under all the excess. It will be wrinkled in places, but one nice thing about using the nylon webbing is that it can be pulled loose and restapled. I tried to be sure that the nylon was close to the edge of the plastic so that wind could not have anything to catch on. Otherwise, it will get under there and start working the plastic loose.

When the ends were stapled, I then went around the whole greenhouse and put in more staples, tapping them in with a hammer to be sure they would not pull loose. After all is secure, you can cut off the excess plastic from around the outside edge and the pieces that were folded inside the green house. Do not cut the plastic too close if you want to remove the plastic at any time and then reinstall it, as you will not have enough to pull on if cut too close.

The greenhouse is basically complete at this point. I wanted to be sure of the strength of the 40 weight PVC, so I ran a 16' two by four under the PVC at the top and rested it on the top of the door frame. I attached one end to my barn as added support, and it also serves as a ridge for the little roof between the greenhouse and the barn.

As I said in the beginning, I wanted to attach the greenhouse to my work shop and use the excess heat from the greenhouse. I nailed two 2X4's to each side of the door of the greenhouse and two to each side of the door to the workshop. I then had access to some left over pieces of exterior plywood and cut these to fit. I put hinges on one piece and had it open in so that I can go out to the vegetable garden through this door with plants, etc. I used a scrap piece of plastic to cover this extension and duct taped it to the end of the greenhouse and stapled it under the roof edge. [Notice in the photo above how the greenhouse is attached to the workshop.]

This nearly completes the greenhouse. The only thing left to do is the work benches, heating and lighting. I built a bench on old 55 gallon oil drums. The drums are not only for support but also will be filled with water that will heat up during the day and release heat at night and hopefully cut down on the amount of heat needed to keep the greenhouse warm. I will use a small electric heater with a kerosene backup in case of electrical outage. All of this will be experimental the first year, and I am sure I will be making numerous changes to the greenhouse.

Tom's greenhouse is based on the one in the website of the North Carolina Cooperative Extension Service - "A Small Backyard Greenhouse"
NOTE: This is a pdf file. If you don't already have Adobe's Acrobat Reader which is necessary to download this file, you can get it free of charge at . Go to that site also to see a line drawing of construction details. Tom did a few things differently, but it's more or less the same.

Tom Uhll's bill of materials, a shopping list of the items you will need for your greenhouse project, is on a separate page so that you may print it without graphics.

Update: Tom's greenhouse weathers big storm!

Hi Sherry.
Just wanted to let you know that we got 18 inches of real wet snow yesterday [this was in December] and the greenhouse took all the weight with just a 2X4 support in the center. We were only supposed to get a few inches so I paid no attention to it and did not put heat in the greenhouse. When I woke and saw all the snow and how heavy it was I got worried. Looks like I did a good job. I don't know how well it would have survived without the extra 2X4 running the length under the ribs and the support in the center but I don't have to worry anymore. -- Tom

Update: Tom's BIG problem!

Hi Sherry,
I have a problem. I have already outgrown my greenhouse. I have gone crazy and have close to 2 thousand seedlings started already. I am going to have to build more shelves and probably when the plants get bigger I will be taking the shelves out and spreading it all out on the floor. Thats OK because it will be warmer by then.

I am having a ball. I call the greenhouse my clubhouse as I spend a lot of time out there. On cold nasty days I sit in there enjoying the warmth and watching the birds out of the window. I am expecting to get the new gas heater tomorrow and will let you know how that works out.

I already have an outlet for lots of my herb plants. Co-workers and farm stands, plus I am putting a sign at the end of my road and will let people come and help themselves on the honor system. My area is a good area and I don't expect much to be stolen. I also will give plants to my family and friends. See ya.



Deer ate crop - Tom dismantled greenhouse

Sherry, I would appreciate it if you took my email address off the page with my plans. I no longer use the greenhouse and have actually taken it down and apart. It did not work out for me. It cost too much to heat here in the NE, and I have a terrible problem with deer. My whole crop that was started in the greenhouse this year was eaten by deer within 2 days of planting it in the garden. My neighbor has a fence over 8 feet high and the other day I went by and saw a deer standing in her gardening having a feist. We are so discouraged and nothing works short of shooting them all. You are welcome to keep the plans and use them as you wish, but I would appreciate not getting all the emails asking questions anymore. It is amazing how many I do get. It is several a week. Good luck with your site.

Tom Uhll

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