Greenhouse Walls Iron Work


Greenhouse forms viewed from the north.

The new greenhouse we’re building is a large open three sided shed which will be dividable into different configurations for housing animals during the winter while still giving them free access to the out doors as well as providing plant growing space.


Greenhouse forms viewed from the east.

A couple of weeks ago we poured the footers for the walls. We’ve been working on getting the form for the walls up. Yesterday and the day before I coverd the raising of the outer wall forms and the concrete flume. Next comes the iron work, the rebar that provides tensile strength in the walls.

Concrete has excellent compressive strength, typically 3,000 psi. That’s 432,000 pounds or 216 tons per square foot. A square foot is about the space my feet take up – I weight 180 lbs. Concrete has a lot of compressive strength. While congrete does well under pressure it is weak under tension. Steel on the other hand has excellent tensile strength. Combine the two in either Reinforced Concrete (RC) like we’re doing here or Ferro-Cement (FC) like we did on the barrel vault style roof of our cottage and you have a very strong structure. Without the steel the concrete may fracture, shear and crumble.


Greenhouse forms viewed from the south.

The greenhouse is set into the bank of the hill in order to give it a lower wind profile and protect its back from the cold of winter. This is much like the early dens we built for our pigs that have served us for years.


Tying Rebar

The rebar, or reinforcing bar, comes in 20′ long sections that are 1/2″ in diameter. This is refered to as #4 rebar. Each number represents 1/8th of an inch in diameter. #4 is what is readily available around here and works well for many applications. We also used rebar to build the hoops of our chicken coop.


Twisted Tight

The photo above shows how to tie rebar. Wires are used to connect the bars securely together until the concrete sets around the steel. The tool in my hand twists the wires tightly. Careful not to over twist or you’ll break the wires.


Finished Perfect Rebar Ties

A trick is to pull firmly and twist slowly as you spin the wires together. It is important to get a tight tie. You’ll notice I do two ties, in opposing directions to get a secure connection between the pieces of rebar.


Splicing two long sections of rebar overlapped 18″ (36x diameter).

The premade rebar ties are more expensive than plain wire but well worth the 2¢ each cost. The tool is only about $5 and does a far better job than a pair of pliers or stick. If you’re going to be tying much rebar, get the ties and tool.


Footer Rebar Stub Tied to Next Vertical Upright.


Spinner Tool, Homemade Tie, Nippers.

If you run out of ties, as I did right at the end, you can make your own. A jig is the best way to do it.


Homemade tie #2

You can also simply twist a piece of wire onto the rebar…


Tightening Homemade Tie #2

…and then tighten it. It works although it is not as fast as the ‘real’ thing.

I’ve mentioned on other projects about bending rebar and people have often asked how. It’s really very easy. Rebar is soft iron and bends very readily, especially if you have a long length.

To make hoops for a hoop house simply place one end of the rebar section in a hole in the base of the structure. Then grab the other end and bend it down to the opposite side’s hole. The rebar will take on the new shape. See this article I write a long time ago for some visuals.


How to Bend Rebar #1

For shorter bends the rebar can be quite hard to manipulate. What you need is leverage. A section of steel pipe works perfectly. Put the end of the rebar into the pipe, slightly shorter than you want to bend, and then place your foot over the rebar on the ground at about the place you want bent.


Bending Rebar #2

Pull upward on the pipe handle.


Bending Rebar #3

Pull past the angle that you want as the rebar will spring back a little bit.


Bending Rebar #4

Relax back to the desired angle.


Bent Rebar

Voila! Perfectly bent rebar. Using this technique you can even bend sections that are just a few inches long on one side. With two pipes you can get very small angles.


Long view of finished steelwork.


Wide Angle View of Greenhouse Forms.

Next we need to put up the inner forms for pouring the walls. The weather’s been holding nicely and work is progressing quickly.

Outdoors: 50°F/26°F Sunny
Farm House: 65°F/53°F
Tiny Cottage: 65°F/55°F