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Mar 11, 2018 2:33 PM CST
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For anyone with greenhouse construction knowledge, PLEASE give me your opinions:

A little background... We have been planning a greenhouse for about 2.5 months now. I went through all sorts of research and finalized (we thought) on a Connely 18 x 24 aluminum framed commercial type greenhouse. Original quote was 6 grand for the kit which was based on what their website stated as standard engineering. Well when I started reading, the quote was not to the published specs, and so I had them give me a quote for the wind and snow load that was stated on their website. Turns out that added about 2 grand to the kit and shipping was now over 2 grand as well making the price over 10 grand and we have not even started with site prep, foundation etc. Finished greenhouse would have been in the 15 grand range easy.

So back to the drawing boards as this is supposed to be a back yard fun greenhouse, not a bank breaking commercial operation. I am not convinced that any of the Chineese knockoff type greenhouses are worth the money and or will hold up with the larger size we are looking for. So lot's more research and we decided to build a hoop style greenhouse to conserve on the finances but still something very nice and built to withstand Central Oregon weather including winds and snow.

I bought a pipe bender for making all the hoops and any and all bracing that will need to be bent to match the curve of the house. The hoops will be 3 pieces of 1 3/8 inch 17 ga galvanized pipe secured together with screws and clamps.

The structure: 20 x 28 foot high tunnel hoop house. The specifics:

12x12 concrete footings with anchor tie bolts every 2 feet. 2 PT 2x6's bolted to the concrete for the sill. 1 3/8 galvanized hoops spaced every 2 feet and secured to the sill on both sides with a 6 inch galvanized sleeve srewed into the sill with 4 large screws. Hoops will have a truss pattern in the middle top for extra strength.

7 runs of purlins clamped at every intersection of the hoops, with cross bracing in all directions. 7 anchor eye bolts in the middle of the walls and end s for 3/8 inch steel aircraft cable to tie in a cross brace fashion to the concrete. End walls will be framed with wood 2x4's, held securely to the end hoops with special clamps and the base screwed into the sill plate.

Added strength will be provided by 3 concrete piers in the middle with 4x4 posts and 2x8 ridge under the hoops from end to end in the middle to support weight if the snow does not melt or fall off in the winter.

Covering will be a double layer 6 mil UV protected thermal anti-condensate poly with 3 pressure fans secured to the sill all the way around with the wiggle wire system.

Cooling and fresh air provided in a 2 stage system, first stage is a 12" exhaust fan located on the north peak end wall with two motorized 24" intake louver vents on the north wall as well. Second stage ties into the same motorized intake vents with a 24" fan on the south end wall peak. When both fans are running it will move about 5,200 cfm which replaces all the air in the greenhouse in less than 60 seconds.

Main door will be a full split glass storm door with half to be opened when needed for extra air intake.

We will make 12" raised beds filled with potting soil and in between the beds will be 6 inches of washed gravel for the walkways. Gravel to provide a moisture cooling effect in the summer when sprayed with water. Plant water to be proved in the rear by our irrigation water pond, endless supply.

My big question is will a 12" x 12" concrete footing big enough for this structure.

Sound like it might work in a windy and snowy environment??? Any and all input greatly appreciated!!!
Mar 13, 2018 1:11 AM CST
Name: Jim
Northeast Pennsylvania (Zone 6b)
Gardens feed my body, soul & spirit
Greenhouse Vegetable Grower Fruit Growers Seed Starter Canning and food preservation Region: Pennsylvania
Hi @coshotgun and welcome to the NGA forum! You are going to love having a greenhouse!

Variables to consider whenever building a greenhouse foundation are winter frost depth and soil compaction. Other considerations on the structure itself are maximum wind and snow loads. I did a bit of reading, and it seems you have a pretty wild climate in Central OR, right? You might want to consult with a building engineer in your region for advice specific to your particular situation.

My PA Food Forest Thread at NGA
“The one who plants trees, knowing that he will never sit in their shade, has at least started to understand the meaning of life.” (Rabindranath Tagore)
Last edited by MoonShadows Mar 13, 2018 1:13 AM Icon for preview
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