A homemade greenhouse can be constructed of cheap, local materials that you might not initially consider using, but with a little ingenuity, you can probably make something nice for very little cost – something consistent with your interest in making your money go farther, and defraying the cost of what you might normally buy at the grocery store. You might even be better prepared and considerably more self-sufficient as a result. What could be wrong with that? Nothing at all from my perspective.
I decided that my “build your own” greenhouse would be made from scratch. I used transmission class power poles that were readily available to me which meant I could build a nice greenhouse and save lots of money on materials. It also meant that the structure could be both long (up to 50 feet) and very strong. Build a homemade greenhouse with power poles? Yep, power poles and metal tubing and a little lumber.
The idea for this greenhouse was to construct a super raised bed for easy harvesting of vegetables, and then build a greenhouse over the top of it. It was a good idea on paper, and it also turned out very well in practice. This example shows that a homemade greenhouse can also be a well-made greenhouse.
The area I chose for my homemade greenhouse was a weedy spot south of substantial spruce trees that provide protection from high winds. This spot also has great southern exposure. The photo shows what the raised bed looked like soon after construction began.
The internal sides of the raised beds were constructed out of three power poles, stacked on top of one another and placed along a sunken walkway. The photo shows only two power poles because the third one is completely buried underground as a foundation. The external sides of the beds were made simply by placing another power pole on a pile of soil approximately equal to the level of the top poles along the walkway. Tin was used to line the inside portion of the beds to prevent the treated power poles from touching the soil. The same type of soil barrier was installed at the ends of the beds.
You can imagine that this homemade greenhouse was a bit tricky to work on. The raised beds made for a natural pit to fall into as we installed the metal tubing overhead. Below is a picture of the raised bed greenhouse after all vents and fans were installed and the poly glazing material was attached.
With our high winds, hail and risk of heavy spring snows, I’m very cautious, so I overbuild my homemade greenhouse structures and use woven poly for the covering.
The raised beds were constructed first. The main materials were transmission class power poles. Inside the beds, the poles were lined with corrugated metal to prevent soil from touching the preservative treatment of the poles. The sides of the poles adjacent to the walkway were lined with a 22 mil woven ripstop white poly. This keeps the dirty power poles away from the user, and reflects lots of light to make for a brighter interior.
The photo shows the white poly and corrugated metal that covers the power poles, the angle bracing on the walls, the joists, and the diagonal bracing that provides support between the roof purlins on one side of the structure and the power pole foundation on the opposite side.
Orientation of the beds is east to west, thus the resulting structure has a wonderful southern exposure, most useful for allowing winter sun to penetrate and warm up my cold-hardy crops. Tucked back up against a nice line of tall spruce trees, the entire structure is protected from winds from the northwest that can be very strong during the winter months.
In order to build a homemade greenhouse like this, heavy equipment is required to create the foundation. I used a skid steer and a backhoe. The skid steer dug the trench for the walkway, and the backhoe was used to maneuver the power poles into position.
This is dangerous work since the power poles weigh about 1,000 pounds each. You can’t let one of these things plop down on you unless you want to be included as a permanent fixture in your own homemade greenhouse.
The upper structure of this greenhouse is primarily steel tubing, with wooden framed ends. The steel tubing makes the building strong, lightweight and easy to construct. It also reduces shadowing that would occur if wood framing was used exclusively. Since the materials and fasteners are common, you save money by not needing specialty steel tubing from an out-of-town source.
The photo shows the trellises attached to the joists and diagonal bracing. Also, the wooden framed end section is shown. The steel tubing is of an exterior grade, so it should last a lifetime without any concern about mildew or rotting that you would have when using lumber. It comes with an external plastic coating in addition to the galvanized treatment.
This homemade greenhouse project also uses lumber painted white to reflect light and heat, and to help seal it to minimize effects of the elements. Here in southeast Wyoming, our climate is dry, so we don’t usually have trouble with anything rotting or rusting. It’s UV deterioration that we’re most concerned about because we have 72% sunny days during the year. We’re also at roughly a 6,700 foot elevation…thinner air and much closer to the sun than most other folks.
Metal tubing used for the walls, rafters, joists, bracing and top plates consists mainly of chain link fencing top rail on 2-foot centers.
Chain link end clamps and some electrical conduit (EMT) elbows are also used. Fasteners are large spikes, machine screws and carriage bolts. Since we have high winds here, most everything has a nylon locking nut, a double nut and is glued to prevent nuts from backing off on the threads. I realize this is overkill, but when I go to sleep at night and the winds are beating the crap out of my homemade greenhouse, I sleep well because I know that I built it super strong…it’ll be there when I wake up in the morning.
This greenhouse has rafters that are metal tubing instead of lumber. The rafters tie into a set of roof purlins, one on each side of the building. Due to the rigidity of the roof, there is no ridge piece.
Five diagonal braces run perpendicular to the building. They start at the sole plate (power pole base) and end at the purlin on the opposite side that ties the rafters together. If the wind or snow is going to provide a roof load, it will be transferred directly to the foundation. This makes it especially robust, and I don’t worry at all about snow loads.
Ceiling joists cross between the 5 pairs of diagonal braces and are tied into the diagonal bracing. Angled wall bracing runs the full length of the building on both sides and eliminates the need for purlins on the 5 foot high walls. All this bracing makes for an exceedingly strong structure, no matter how stress is applied to it.
The photo shows how the joists and diagonal bracing are tied together to make very strong support for the walls and roof. This photo also shows the purlins that are tied to the rafters, and the EMT 90 degree conduit that forms the ridge by connecting the ends of two rafters at the peak.
Wooden framed ends are used for several reasons. First, the wooden frames at the ends allow vents and fans to be easily framed and attached. The aluminum frames of the vents and fans can be screwed into the wood to hold them in place. This would be difficult if the framed ends were made of steel tubing.
Second, the wooden framed ends allow the UV protected ripstop woven poly covering to be attached easily with staples. Again, if steel tubing was used, it would be much more difficult to get the poly covering stretched and fastened in place.
Lastly, wooden ends allow for easy construction of gussets to keep the ends from shifting. Gussets are made from pieces of plywood that bridge corners and the peak. Gussets provide shear strength and can be used as a substitute for cross bracing. Without gussets, the ends of the greenhouse would tend to shift. If you’re viewing the greenhouse from an end, gussets prevent it from shifting left and right because they’re installed perpendicular to the walls running lengthwise.
As one might expect, with a homemade greenhouse comes homemade doors. If the ends of the greenhouse were to shift due to a lack of gussets, the door frame would go out of square, thus preventing proper operation of the door.
The UV protected poly covering is stapled onto the wooden framing, and in selected areas it is screwed into the metal framing. In either case, white plastic lath is used to help hold the ripstop poly in place.
The overall design is like a simple peaked roof on a single car garage. It sheds snow easily and catches lots of light from the sun. The drawback of the design is that the power poles take up quite a bit of room inside the structure – about 3 square feet per linear foot of the raised beds. This is the price you pay for having heavy no-cost materials that won’t sag or deform. It’s also the cost of the sunken walkway that allows you to simply reach out and get your harvest without bending over.
The overall dimensions of this homemade greenhouse are about 12 feet by 36 feet, with each of the two planting beds measuring roughly 3 feet by 36 feet, with a 3 foot by 36 foot long walkway running down the middle. The telephone pole walls that run the length of the walkway consume about 3 feet of width.
Heating the greenhouse will be inexpensive. The walkway is filled with about 18 inches of moist sand. I say moist sand because the structure is located directly over a portion of my leach field, so the soil stays moist from the constant evaporation. Beneath the 18 inches of sand is a single 200 foot circuit of three quarter inch Pex piping. This piping will be plumbed into a steel tank with a pump. The pump will circulate about 20 gallons of water through three flat plate solar collectors and then into the underground piping. This will make the sand-filled walkway act as a thermal battery to collect heat during the day and slowly release it to the greenhouse throughout the night.
A waste oil heater will also be connected to the water circuit so the solar panels can be bypassed and the water heated directly. The heater will be housed in its own “doghouse” outside and adjacent to the greenhouse. This will allow for occasional supplemental heating without the need for a heater taking up precious space inside.
If you are going to build a homemade greenhouse like this, and you don’t have power poles, you can skip the sunken walkway and just make the walls taller, say 8 to 10 feet. It should work just fine as long as you make the walls tall enough to get the diagonal bracing well overhead and out of your main walkway down the middle of the structure. If you make the walls taller, you might want to add a purlin on each side wall, and shorter cross bracing with a sharper angle. Ideally, the cross bracing might bridge across the last 3 or 4 upright pieces of tubing at each end, with the upper ends of the cross bracing meeting up with the framed ends of the building.
If you add purlins to the walls, they will not allow the cross bracing to lay flat against the walls. This is why my structure uses tubing that acts as a combination purlin and angle brace. With a little bending of the angle brace tubing, you can probably weave it around the inside of the purlin as it passes from the top plate at the wooden end framing down to the foundation, and then tie it into the purlin and wall tubing pieces with fasteners.
In the absence of power poles, a concrete foundation would work well, or make the sole plate out of horizontal steel tubing and use end clamps to connect the walls to it. Then, anchor the sole plate to the soil with earth anchors.
The photo shows how end clamps are used to tie together the top plate, wall tubing, rafters and the joists. Note the double nutting on each threaded connection. This makes the homemade greenhouse quite vibration proof.
If you have power poles and don’t want the sunken walkway, you can simply bury the power poles level with grade and start from there. I would wrap the power poles in poly before burying them to keep the preservative treatment from touching the soil.
In hindsight, the following are things that I would do differently with this homemade greenhouse and the reasons why.
The foundation is all “no cost” material for this greenhouse. The rest of the structure is readily available at the hardware store and salvage yard. Indeed, this is a homemade greenhouse for those who have a mindset slanted in favor of do-it-yourself projects and frugality.
Clair Schwan is an avid vegetable gardener who considers his gardens to be important assets. To him, vegetables in the garden are a bit like money in the bank. It’s all part of his self-reliant lifestyle. See his adventures in gardening at Frugal-Living-Freedom.com.