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 second "build your own" greenhouse would be made from scratch, and I used transmission class power poles that were readily available to me. This 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. Let’s take a look to see just how it can be done.
The idea for this second 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 high spruce trees that provide protection from high winds. This spot also has great southern exposure. The photo below 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 above 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.
If you look closely on the right side of the photo above, you'll see tin. This 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. The photo below shows the tin after it was installed on the inside of the beds.
The photo below also shows how the project looked after much of the metal tubing was put in place and the wooden ends were constructed.
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.
By the way, when you need a clear cover for your homemade greenhouse, take a look at THOR Tarp. They specialize in custom made greenhouse covers, shade cloth and a wide range of tarps for various applications. And, they've been in business for over 12 years.
With lots of different materials and options to choose from, I'm sure they can help with your greenhouse project (and many other kinds of projects.)
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. Northern Greenhouse Sales provided both the clear woven poly for the external cover and the super heavy duty white woven poly used to cover the telephone pole foundation on either side of the sunken walkway.
Bob and Margaret Davis are the proprietors at Northern Greenhouse Sales, and they're nice folks to deal with. In business for almost 30 years, they specialize in strong, UV protected woven greenhouse covers and also carry pond liners and poly for haystack covers and other outdoor projects. Tell 'em Clair Schwan sent you.
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 above 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, as is the case with my first homemade greenhouse, 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.
Caution: this is dangerous work since the power poles weigh about 1,000 pounds each, and I used nine of them. 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 above shows the trellises attached to the joists and diagonal bracing. Also, the wooden framed end section is shown. And, you'll notice that our winter squash plants have just been set into the soil beneath the fabric mulch.
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. I should note that 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, and we're 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 out here on the prairie, 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 with peace of mind because I know that I built it super strong...it'll be there when I wake up in the morning.
This homemade greenhouse has rafters just like the wooden ones in greenhouse #1, except they 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.
We wondered if this design would make for a good home for squash plants. Well, take a look at the picture below and compare with the picture above, and decide for yourself. It's clear that the environment is conducive to growing squash as these two "brutes" went unnoticed in the thick growth that our homemade greenhouse encourages.
Also, notice how the winter squash has taken to the trellises and grown up and over the sunken walkway (from left to right in the photograph) to reach the south side where we grow the summer squash. I guess they're just not satisfied with their 3 foot by 36 foot bed. They want more room to stretch out. Fine with us, the overhead fruits make harvesting from this homemade greenhouse just that much easier.
After our first season, the winter squash yield was about 175 to 200 pounds from 12 plants. The summer squash yield was about 275 to 300 pounds from 12 plants. We're set for squash this winter thanks to homemade greenhouse #2, now fondly referred to as The Squash House.
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 my second homemade greenhouse 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 below 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 in this homemade greenhouse 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, and 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's screwed into the metal framing. In either case, white plastic lath is used to help hold the ripstop poly in place.
The overall design of this homemade greenhouse is like a simple peaked roof on a single car garage. It sheds snow easily and catches lots of light from the sun. That's what make it a hot place that squash love.
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.
Let me offer a note about heating this homemade greenhouse. 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. (Not to worry, I have an alternative location for the leach field should it fail some day and need to be replaced.)
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 homemade 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 homemade 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.
Note: 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 above 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 homemade greenhouse, and 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, and of course, lots of squash.