Planning to start on a 25′ X 50′ deck for a greenhouse area. Thinking of doing 2X12 rim joists, with 6X6 posts on 10′ centers, with 2X10 joists on 16″ centers, and 5/4 decking. All ACQ. Posts set in-ground on concrete.
The question is, would it be a good idea to beef up under where the GH will sit? The structure will be very light. 3″ square tube with polycarbonate covering. It’ll be 12’X40′.
Any loading tables would be appreciated.
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Then the green house is sitting on the deck?
Sounds like you have plenty of support except where you might have things like barrells of water or compost or potting soil but mostly ok.
Why not save deck money and build over a gravel bed setting the GH down within the deck. Your floor would be kind of a thermal sink in winter. You'd save a bunch on that area of the deck. Just dig the same as you would a footing at the perimeter tamp in more gravel then set either 6" x 8" PT beams or railroad ties around under the exterior walls.
I did this for my small GH and after 2 years all is still fine.
This is kind of a unique situation. I'm in Central Texas where it gets really hot. We only have about 10 days of sub-freezing weather and frosts per winter. The rest of the time it's 40's-50's. DW grows a lot of bouganvillas and hibiscus and needs a large area to propagate and store the large plants, without much pruning, during November-March. This structure must be usable duriing the summer also, so we build them under deciduous trees like Post Oaks and Water Elms. Bare in the winter allows solar transmission, shade in the summer with the leaves and 50% shade cloth.
I have a 10'X14' GH presently, but it is too small. The area we want to build on has the required trees but is sloped and poorly drained. We would have to deck around the GH anyway to make the area 100% usable. This deck would have a 12'X40 GH with the middle 10' on both sides having 5' sliding doors for cross ventilation. An exhaust fan in either end and removeable panels on the remaining areas would make it tolerable duriing the summer. It also needs to be 12' or less wide so I can clean the polycarbonate with a powerwasher w/o climbing on the structure.
I've already designed it with a pad, and may still do it that way. This seems to be more space-effecient and usable at this time.
It's not the greenhouse, it's the stuff in it. Soil is heavy, especially when wet.
You've got to figure out what your worst-case load is -- how much soil will you be supporting? And figure it for after more stuff gets stuffed in here and there, not the original neatly organized plan. Plus bags of fertilizer, etc, stuck in the corners and under the benches.