If you want to build a greenhouse of your own to save money on produce, I applaud your intentions. A greenhouse for vegetables is a nice way to support a plan for frugal living and good health.
Unheated greenhouses can help you raise vegetables year round in most of the country, so it can substantially contribute to lowering your food bill.
You can also save money by building your own, and if that’s your goal, then the quonset hut style is the design and approach I suggest.
Our greenhouse #3 is made from chain link top rail on 2 foot centers, but with a twist, or rather a bend.
The top rail steel tubing is bent into hoops to make ribs for the greenhouse. This approach simplifies construction – a rib replaces two walls and two rafters.
Build a Greenhouse with Chain Link
This quonset hut style structure makes use of the natural strength of a semi-circle, and it is easy to brace.
It can shed snow reasonably well because of the curvature, and provides lots of usable space under the galvanized arches.
There are no vertical supports to get in the way.
For this project, I purchased a tubing bender from Lost Creek Greenhouse Systems out of Mineola, Texas. Loy and Shirley Robinson run this operation, and they are great people to deal with.
I’m certain you’ll be just as impressed as I am. They are down to earth and very responsive to your needs and interests.
If you are going to build a greenhouse like this and need a tubing bender, these are the folks to talk to.
They sell a nice product at a reasonable price.
They have written instructions and videos about how to build a greenhouse (and other projects) using their tubing benders.
They’re happy to help you with advice and suggestions to ensure your success. Tell ’em Clair sent you.
Plan the Greenhouse
Let’s talk about planning to build a greenhouse. I’m a deliberate kind of guy, so I like to plan, then work the plan. It is the best approach to success, regardless of the endeavor.
The truth is that many times along the way I modified the original plan to build a greenhouse, but let’s just pretend that everything I tell you is what I planned from the beginning.
It will simplify the explanation and make me feel much better about telling you the story.
So, let’s take a look at my build a greenhouse planning for this large quonset hut style structure:
- One of my first interests was orientation of the building to follow an east to west direction so the broadside of the structure makes good use of winter sun that is low on the horizon. As this homemade greenhouse is part of the winter gardening effort, good orientation for solar gain is important.
- Wind is a primary factor here in Wyoming, especially during the fall through spring seasons. With this building having almost no protection from trees or other structures, I had to design for resisting constant wind. Bracing and anchoring against wind is a key to success.
- Snow load is of concern mainly during the spring as our winter snows are usually dry powder. The spring will provide us an occasional heavy wet snow. I didn’t want to have to take the snow off of the structure, so I had to consider bracing the roof for snow load.
There were three key assumptions when I decided to build a greenhouse of this size and in this location. They were:
- The building must withstand sustained 100 mph winds with no stuctural damage.
- The structure must be able to carry 12 inches of wet spring snow until the sun melts it away.
- All anchoring and fastening must be convenient for periodic retightening.
Design a Greenhouse
Basic design considerations included use of 4 purlins and a ridge piece. Purlins are horizontal members that tie the ribs together to keep them spaced evenly.
The ridge piece is similar to a purlin except it is installed directly overhead, instead of on the walls.
These 5 horizontal members are necessary as the curvature runs about 30 feet, so this gives about 5 feet in between each horizontal member.
It also provides more points to tie into with other structural members.
Cross bracing on the walls is necessary to keep the building from swaying lengthwise on the foundation from east to west.
Some people use cables and strapping for cross bracing, but these only give strength when pulled – very much like a rope.
I wanted much more rigidity, so I used steel tubing – it gives strength whether pulled or pushed.
Build a greenhouse with a large arch like this and you better have diagonal bracing to keep the curvature in shape against wind and snow loads.
Diagonal bracing also helps distribute snow loads lower on the building and it strengthens the shell.
Proper anchoring of the sides is especially important for high wind areas like Wyoming.
I opted for a staked anchoring system for each rib and an outside overall building anchoring system that pulls the structure down onto its staked foundation.
The main anchoring system for the building employs large turnbuckles and “dead men” buried deep in the soil.
This approach to anchoring offers adequate support for initial construction, and good long term push and pull resistance from both sides.
Although unconventional, I thought it necessary and wise in light of the high wind success criteria of the plan.
Bracing each end will involve 2 rigid steel tube tie-ins between the upper door frame (the center of each end) and the upper purlin.
This will help keep the door frame and ends from bowing in or out from high winds. Any pressure on the door frame will be transferred to the purlin which in turn will push the building along its length.
Since there are 3 sets of cross braces on each side of the building, there is no way the purlins are going to budge.
Go here for a basic view of the cross section of the structure.
This diagram shows a typical view of the end of the structure and how it is configured.
Here is an overhead view of the end of the greenhouse structure and how it is tied into the upper purlins.
Build a Greenhouse
When you build a greenhouse of a rounded or quonset hut design, the ribs can be assembled as a separate activity.
This allows much of the building to be prefabricated.
The ribs are attached to concrete form stakes driven into the ground about 2 feet deep. Four side purlins and a ridge piece are used to hold the ribs together.
Diagonal bracing every fourth rib is used to tie the center ridge piece to the lower purlins on each side.
Ceiling joists tie the upper purlins on either side of the arch with the diagonal bracing.
When you build a greenhouse this way, the joists and diagonal bracing can be tied together to form sets of triangular shapes adjacent to the shell that make the structure very strong.
This strength helps resist our regular high winds and will distribute snow loads from the ridge to points lower on the structure.
The picture below shows that the joists connect the upper purlins together, and the diagonal bracing runs from the ridge piece down to the lower purlins (not shown).
The joists and the diagonal braces are tied together to make 5 triangular shaped sections that create a strong shell across the upper portion of the ribs.
Cross bracing on the sides of the ribs was tricky because the walls are not straight up and down. Instead they are curved to form the roof as well as the walls.
To create side bracing, sections of pipe were bent by hand in a gentle arch, then woven between the rafters and lower purlin until the bottom of the cross brace pipe meets with the bottom of a rib, and the top end of the cross brace pipe meets with a rib almost as high as the upper purlin.
There are 6 pairs of “V” shaped cross braces, 3 pairs on each side, with one set at each end, and one set in the middle.
The cross bracing achieves an excellent angle to resist end-to-end movement, and it ties in 7 ribs and the lower purlin.
Reaching fairly high into the arch, the cross bracing adds more strength to upper portions of the building that will be hit hardest by wind.
The photo to the left shows the angle bracing at one corner of the greenhouse.
Notice that is is secured to a foundation stake at the bottom and attached high on the third rib on either side of the center.
Wherever the cross bracing interfaced with a rib or purlin, an attachment was made with a machine screw, washer and nylon locking nut.
In addition, the cross bracing is woven beneath the ribs and over the purlin, so it is locked in there tight.
Fasteners for this project include chain link fence end clamps, machine screws with nylon locking nuts, carriage bolts with a nut and lock washer, and self-tapping sheet metal screws.
All nuts face inward so they can be checked for tightness over the years and retightened if needs be.
In other words, the nuts can be reached for tightening without the need to disturb the poly cover of the building.
Ribs are doubled at the ends and middle to accomodate composite 1 by 8 boards that will be used to fasten the UV protected poly covering.
Composite 2 by 6 boards are run along the sides at the bottom for the same reason.
A type of “C” channel fastener, called “poly fastener”, will be mounted to the composite boards.
The channel has an insert that is used to “capture” the poly covering inside the “C” channel, much like “wiggle wire”.
The double rib in the center of the building covered with the 1 by 8 composite material will be used to staple the poly covering in place using plastic lath on the outside of the poly cover.
In this way, we only need to stretch the poly covering halfway across the structure (from the middle to the end) and then secure.
Otherwise, we’d have to stretch the covering all the way from one end of the structure to the other, more than 62 feet before securing.
Stretching only half way should allow for a tighter fit and should be much easier to do.
Note: You must use UV protected poly. You can’t use the plastic sheeting that comes in rolls from the hardware store.
It won’t last more than a year or so before it crumbles away. The greenhouse film is more expensive, but it will last much longer.
When you build a greenhouse, you want it to last – that means the poly covering too. Get one that is UV protected.
The woven poly, cinch strap, poly fastener and installation tool were all purchased through Northern Greenhouse Sales where Bob and Margaret Davis are the proprietors.
They’re nice people to deal with and they’ve been in business for almost 30 years. They specialize in strong, UV protected woven poly greenhouse covers and also carry pond liners and poly for other outdoor projects.
Give ’em a shout and tell ’em Clair Schwan sent you.
Tools typically used to build a greenhouse of this type include:
- Tubing bender.
- Chop saw, portable band saw or hack saw.
- Air rachet for tightening carraige bolts, end clamps and machine screws.
- Portable and corded drills with nut drivers and screw driver bits.
- Various size drill bits and lots of ’em.
- Hand rachets and screwdrivers for finish tightening.
- Hand levels, string and laser level.
- Rubber mallets, claw hammers and sledge hammers.
- Ladders and scaffolding.
- Hand,ear and eye protection.
Power tools aren’t necessary, but they make everything much easier to accomplish. Your most important tool is a friend to help hold things in place and pass you tools and fasteners.
The photo to the left shows me and a friend assembling the structure.
When you build a greenhouse with 20 foot purlins and ribs with a 30 foot arch that are 12 feet high, it’s best to have help.
One last word on construction, when you build a greenhouse of any style, the more perfect you conduct each step, the more perfect the end result will be.
The most important parts to get perfect are the ribs and the foundation.
The ribs should be assembled on a flat surface so there is no wave in the rib.
The foundation has to be level and evenly spaced so the ribs are placed with consistent spacing.
When you build a greenhouse, the word “perfect” means “well made”. We want to build a greenhouse in a well made manner, but it isn’t necessarily a problem if you have some minor imperfections as the plants growing inside don’t care.
They won’t care if your purlins aren’t exactly level or your ribs are spaced a little unevenly.
The key point to remember is that your construction won’t get more precise as you build a greenhouse, it will get less precise.
The reason is that you aren’t going to disassemble the thing and start over if you find a minor imperfection, so the minor imperfections just build ontop of one another as you go, resulting in an ever less perfect structure.
Therefore, when you build a greenhouse it is important to start out as exact as you can and keep to that standard (without driving yourself crazy).
A little imperfection is just fine. It won’t hurt a thing. Remember, you’re building a greenhouse – you’re not building a Swiss watch with jewel movements.
Heat and Insulate a Greenhouse
The underground heating system for this greenhouse is similar to the other two.
The system has 2 circuits of 240 feet of 1 inch Pex piping, with one circuit on the south side, and one circuit on the north side.
Each circuit is directly under the planting bed, and operate independent of each other. Each will have its own insulated 55 gallon drum buried deep underground and plumbed into 5 flat plate solar water heating panels.
The piping beneath the beds is about 24 inches deep, so it should have lots of soil mass to heat up for energy storage.
Each circuit represents a thermal battery of about 930 cubic feet.
Piping for the underground heating is plenty deep enough that garden tools won’t come anywhere close to it.
The storage drums and pumps will be located sufficiently deep so that the system drains back when shut off.
This will concentrate the heated water in the insulated barrel deep in a pit to help keep the pump from freezing, even during the coldest of weather.
When you build a greenhouse, you might want to build a waste oil heater for it like I am doing.
Each circuit for greenhouse #3 will be connected to a surface level waste oil heater that will be housed in its own “dog house” near the structure.
The waste oil heater will allow supplemental heating for limited periods, or when I want to get a “push start” for the solar system. All waste oil heaters and heat exchangers will be homemade, so the cost will be scrap materials, electricity for shop tools, and my time.
Rigid closed cell foam insulation surrounds the planting beds of this greenhouse to a depth of 2 feet. This will help hold in energy from the hot water system and soil warmed by the sunlight. Otherwise, the colder surrounding soil will rob energy away from the planting beds.
As you probably figured, trenching for the pipes and insulation must be done first, and well marked so you know where the building has to be set in place. If you don’t mark the location of piping and insulation underground, then you might drive a foundation stake into one of them, or you might place the foundation stake so close to one of your trenches, that you don’t have enough undisturbed soil to hold it in place with the strength you desire.
The trenching part is a lot of work, but like the rest of the structure, it is a one time investment that should pay dividends each year for many years to come.
So, build a greenhouse as best you can one stage at a time and you’ll be happy with the results for many years to come.
Current Status and What’s Ahead
Greenhouse #3 is in the final construction stages now, and will be finished soon.
It is the largest of the three greenhouse structures, measuring 20 by 62 feet.
What remains to be completed are the ends, side supports, vents and fans, and the underground pumping and storage system.
The doorways, doors and foundation of the ends will be made from wood. Chain link fence top rail tubing provides the rest of the structure.
Like wood, the steel tubing has good compression and tensile strength, but it also offers rot resistance and eliminates the need to paint.
Another significant part of the project that is underway are the vents.
Both ends will incorporate a half-moon shaped vent at the top that will hinge at the bottom and open outward to let warm air escape out the sides.
Inlet air will come from numerous dormer style vents on both sides below the lower purlin.
In addition, 3 ceiling vents at the ridge line will allow for a good chimney like effect to draw out the warm air.
The middle vent will incorporate a fan to create draw. This will help remove heat when it is just too hot in the middle of a warm sunny summer day.
Lessons Learned while you Build a Greenhouse
Anyone who gets to build a greenhouse of their own design should be smarter than when they started, right? I am, so let me share with you my insights:
- First, when you build a greenhouse of this size, you are starting to stretch the capability of chain link fencing top rail for windy areas like Wyoming. I’m not an engineer, so I have no technical basis for saying so, but I would limit a 20 foot wide structure like this to about 30 feet in length if you are expecting high winds.This limited structure will provide more rigidity for the amount of “sail” you might have in the wind, largely because it places the rigid ends of the building much closer together. It also allows for more concentrated cross and diagonal bracing of the structure.
To stay consistent with my own recommendations, I’m going to build a greenhouse with an “end” in the middle. This will put a very rigid wall within 30 feet of each end, but it won’t have any covering associated with it – just a large doorway and supports radiating out to the rib and purlins.
- Second, regardless of the dimensions, get the heaviest gauge top rail you can find. It costs about 10 cents more per foot, but provides a more rigid building material. When you tighten a bolt on 18 gauge versus 17 gauge, you can tell the difference. Get the 17 gauge if you can. You have to look at the pipe labeling because home improvement stores probably don’t even know the wall thicknesses they stock, and different stores (or even the same store) can have different thicknesses in stock.
- Third, use a foundation appropriate for your soil and wind loads. I selected concrete foundation stakes because you can bolt through them and through the bottom of each end of the ribs. Knowing that I needed supplemental bracing for our high winds, the form stakes were adequate as initial alignment and anchoring points for the structure during construction.When the poly covering is installed, the supplemental turnbuckle bracing will be put in place immediately to serve as the primary way the building is pulled down onto its foundation, and the main way the building is kept from being pushed by the wind.
- That’s why I build a greenhouse structure first, and then only when I know it is rock solid do I install the poly covering.
For buildings constructed in more moderate wind conditions, I would suggest 1 inch galvanized piping from a salvage yard pounded in 3 to 4 feet deep. An anchor for both ends of each rib is warranted, as it adds rigidity and lasting strength to the structure.
An alternative is a traditional earth anchor that is screwed into the ground about 3 feet deep.
- If connected to a rail or bottom framing board, a handful of anchors on each side would nicely tie down a greenhouse. More tie down strength is better, because any area of the country can experience high winds on occasion.
My consultation with Loy Robinson before building this greenhouse convinced me that the last thing I want to do when I build a greenhouse is to let all my hard work and investment above ground be destroyed by high winds because I didn’t anchor it well enough below ground.
If your plan for frugal living includes a greenhouse to grow your own vegetables, then you’ll want to tie it down well so your investment doesn’t blow away.
- Frugal living is about doing things inexpensively, and it’s also about protecting your investments.
Good fortune to those that choose to build a greenhouse and take more control of the quality and variety of their food supply.