Pit Garden Supplies -- Supplies, Materials, and building techniques used on this project.

Pit Garden Supplies

This article originally appeared on our sister site A Prepping Homestead:

We’re getting close to breaking ground on our planned pit greenhouse, and so it’s time to get a list of Pit Garden Supplies together to ensure we don’t get held up by ordering snafus. We’ve decided to build this to last, so it’s not just a hole in the ground with a transparent roof like a typical walipini.  We’re going to be building a full foundation, framing in a solid roof, building stairs, a raised platform over the cold sink, poly roofing, a set of stairs, doors, the list goes on and on.   Here’s what I’m planning from the start (I will update with items that we ended up needing after the project is finished):

Foundation  — We’re planning on using a system similar to what this guy demonstrates on YouTube  (I picked this one because I like his accent 😉  FYI, this is not the same wall I would build as a foundation for a house.  We want it to be strong and resist caving in, but there will be very little load on it.  Areas I’m cutting corners to reduce cost are using 6x8x16 blocks instead of 8x8x16 due to the larger blocks being 70% more expensive, and not building as deep or as wide a footer as one would for a house as minor settling isn’t going to be a big deal for this structure.  I’m also planning on not reinforcing the footer with rebar.

  • Footer — We first need to create a concrete footer for a level start to our block wall.   I’m planning a footer that is 10″ wide and 6″ deep.   Our pit is going to be 16′ by 24′ so the pad will be roughly 80 linear ft.  Tossing this into a calculator, it tells me we need 65 60lb bags.
  • Gravel channel around bottom inside of wall (6″ deep by 6″ wide)  and for cold sink which will be a little wider.  I’ve calculated about 1 cubic yard which is about 1.25 tons, or in my case, a couple of loads in the truck bed.  (I’m no scientist!)
  • Cinder Blocks — As mentioned I’m going to use 6x8x16 blocks.    We are going to be building roughly 560 square feet of wall.  Honestly less because of the door and varying heights, but that will be more than enough and I’m happy to have some extra block laying around.  That calculates to about 630 blocks.
  • Mortar Mix — We need enough to join the blocks and I’m planning to fill 24″ O.C. to reinforce with the rebar.  This site says that’s roughly 2.3 cubic yards.  It takes about 60 60lbs bags to make a cubic yard, so 140 bags to be safe.
  • Metal Lath on the row below the top, place the top row and fill. Put J bolts into mortar to then attach wood cap.
  • Mason Line, Joining Tool, Racker, and Brush if you don’t have them
  • Rebar, vertically every 4 ft horizontally and I’ve heard everything from every other or every 4 rows for horizontal so I’m planning every third.  My math makes that 240ft for the horizontal, and 140ft for the vertical.  So 280ft.  Plus the wire ties.
  • We will also use sheets of foam insulation to put around the foundation before back filling.

Framing — There isn’t much to do, but we need to frame in for the roof, side the slight angle of the framing, and frame a door.

  • Exterior door — Try to find used, or purchase pre-hung exterior steel door
  • Framing for the roof need only be 2×4 as Polycarbonate is very light weight.  I have a lot of scrap laying around, but will need to purchase some as well.  This handy guide demonstrates framing span recommendations for different snow loads on the different types of Polycarbonate roofing.  I plan on double wall 8mm panels, and given our moderate snow load in town, and the fact that our width evenly divides by 32″ 9 times I was planning 32″ spans.  But as you’ll see in a later section you really need 24″ spacing in order to ensure the seams of the polycarbonate roofing land on studs.   This means 10 16′ 2×4’s, 24′ of 2×6 for the king post which I have, and say 10-15 10′ 2×4’s for miscellaneous framing.
  • Some metal siding for the framing above the block walls, luckily we have this as well laying around the homestead.
  • There will be more for the platform above the cold sink.  One thought I’ve had is to use Trex materials as this is going to be a moist environment.   I’ll have to compare costs and will update this when I have a decision.

Entrance — Not just a door, but we need a staircase down into the pit as well.

  • I plan on building a gravel lined ramp down into the pit.  (note, need more gravel!)
  • Then building a standard staircase, couple of 2×12’s, and a bunch of 2×10’s to build the stairs.  I will probably wing this with lumber on hand and run to the store to get what I don’t have.
  • I’m hoping to find a basement bulkhead door for cheap used….  Otherwise I may craft something myself out of random wood we have laying around.

Roof — I’ve discussed the framing above, but we need roofing material

  • The front facing roof on our pit greenhouse is going to be made up of Polycarbonate panels.   Our primary roof will be 14’x24′, and the front near vertical section will be roughly 2’x24′. This site sells 4’x16′ sections of which 6 would cut up and work for our dimensions.  There are many other sites though so I may find a less expensive option and switch.
  • We will also need joining material such as this and end caps

Incidentals — Too much to list here, luckily much of this will be in the random parts bins…

  • Caulk
  • Screws, I personally like the star drive
  • knobs, handles, pull things

I think this is a pretty good start.  At least everything I should be sourcing ahead of time is on this list.  There’ll certainly be much more that needs grabbing as the need arises, but luckily, right now, there’s multiple hardware stores within 10 minute drives of us….  Now it’s time for digging!

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Andrew Blessing

Pit Greenhouse Design
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