Tuesday, December 18, 2012

Cold Frame/Mini Greenhouse/Potting Bench post 3

I added another descriptor to the name of this thing.  Now that the floor of the box is finished it looks like it will make a good outdoor potting bench. 

The stained pieces were dry on Monday and ready for assembly.  Just as in the trial assembly the front and back frames were built (or rebuilt) first, then the two frames fastened together by crosspieces.  The front 2 x 2 leg was replaced with a 2 x 4 leg.   Everything was squared and braced, and lastly a diagonal piece that makes the front roof was held in what looked like a good angle and marked.  Both diagonal pieces were cut identically, the back legs were cut to go underneath the diagonals, and the diagonals were fastened to the legs. 
At the end of the day the basic frame was together.   The bottom of the greenhouse is held by a temporary frame to hold the legs at the correct distance.  Later I will build a shelf unit near the bottom that will not only hold pots but provide the structural support that the temporary support frame does now .

I took my time putting the greenhouse back together.  I’d like to be able to make more of these units and sell them if they perform as I hope and if I can make them at reasonable cost.  That’s why I’m sweating the details on this prototype.  The lid and sides will be covered with the twinwall polycarbonate lites used in greenhouses.  This material is much lighter than glass, is very tough and has a higher R-value than a single sheet of acrylic or glass.  
This weekend I came up with the design for the sides.  It’s so simple that it took a week before the answer came to me.  Here’s the detail of how this works: 

The bottom of the side lite goes outside the 2 x 2 crosspiece, and inside the 2 x 2 diagonal (the crosspiece is flush with the inside of the legs, the diagonal is flush with the outside, leaving a small gap for the lites).  I meant to cut a groove in the back 2 x 4 leg that the lite would fit into but forgot, so I’ll have to tack a stop onto that leg to hold the lite in place.  Once the side lites are attached the side 1 x 8’s will be attached to the 2 x 4 legs.  (Yes there will be a gap between the 1 x 8 and the side lite).
2 x 2’s were fastened to the front and back 1 x 8's to support the floor of the greenhouse.  This floor will have to support a lot of weight - containers, seed flats, and maybe bricks for thermal mass - so I kept the 2 x 2’s high on the 1 x 8 to use it’s depth for load-bearing (think of the 1 x 8 as a sort of floor joist).   The 2 x 2 supports have grooves on the side that is attached to the 1 x 8 to allow water to drain out.  I installed the carsiding floor today and left a small gap at each end to let water drain.
I wanted to use red cedar for everything but after I recovered from sticker shock I realized that wasn’t going to happen.  Cedar carsiding is about 4 times the cost of pine, so I went with the pine and used cedar for the framing and the rough sawn pieces like the 1 x 8.  With several coats of stain and if there’s no standing water the pine carsiding should hold up for a while.  Cedar is not only durable but light as well as strong, but the expense is a deal breaker. 
Here’s the greenhouse with the floor installed.  I also installed some short diagonal braces at each corner to rigidify the structure. I’m really liking the look of the carsiding.  Tomorrow I’ll put on the back siding and maybe build the lid. 

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