How to frame greenhouse...corners

I'm using old windows to build a greenhouse. The plan is to build a short wall and have the windows sit on top. There will be posts for each corner and 1 on each side of the door, sunk in the ground.

The wooden frame around each window is 5 inches wide, so when they join at the corner there is this space. I have several ideas on what lumber to use for the corners and how to do it, but it's not experience behind those ideas, just what looks like it will work.

Since the window frames are 5" wide, I figured I'd use 2x6 for the support posts and the stem wall. The roof is going to be polycarbonate, so there really isn't much weight to support.

Any thoughts or suggestions?

This is an example of the short wall with windows on top.




The greenhouse I'm building will be a shed roof style, like this one.



These are the windows and door for the front. Stem wall under the side windows. Top 3 windows will be transom and hinge open for ventilation.



This is what the corner looks like when the windows come together, and where I'm trying to figure out how to locate the corner post and frame the opening.



Rough diagram of the front.

 

Why not use a 6x6" in the corner?

 

I thought I replied but just realized I didn't. I'm using redwood for the ground contact lumber, including the corner posts which will be buried. Other lumber not exposed to the ground or weather with be less than. I'd also like to have continuous corner posts, which would be 12ft. I can do that with 2x6 and 2x4, but not realistic for a redwood 6x6. A 6x6x8 is around $75. Very cost prohibitive. I also realize I don't have to have that 12ft run and can break it up where the transom window section starts.

I'm still prepping the ground and digging holes, so plans are still changeable. I may scrap the shed roof and go with a gable style, then I won't have that very tall front.

 

You're going to need more than the four corner post to support that structure so maybe In not following you. Here’s a tutorial to embedding posts on the ground but you can google more or buy a diy book to ensure proper support for a building like that.
https://www.lowes.com/n/how-to/build-a-deck-post-holes-and-framing

 

In addition to the 4 corners, there will be a 2x6 on either side of the door. Between the corners will be a short wall (pony/knee/cripple - not sure proper name) that the windows will sit on. That wall will be framed with studs like a normal wall. Look at the first picture in my original post for an example of this.

I'm going to set the posts in compacted 3/4 washed crushed rock. I've read extensively about setting posts and decided I don't want to use concrete as it seems to facilitate rot from water. With redwood and rock, I can expect 20+ years.

What has surprised me is that in researching building a greenhouse with recycled windows, nearly 100% of the time they don't use buried posts, rather they set ground contact boards on a gravel base and build on that. I've seen some use rebar or all-thread and stake them through those boards into the ground. That seems crazy to me so I decided to bury the posts.

 

I guess you can sister 3 2x6's for a 6x6?

 

What are the long short walls going to sit on/be supported by?
Any posts set on dirt around them (including if set on a gravel base but still surrounded by dirt above the gravel) will rot far faster than a post on a gravel bed with poured concrete around to ground level (or a little higher). Best method is to wrap post in sheet metal at the ground level interface on a concrete embed.

 

I'm digging a trench between the post holes, a few inches deep. The holes will be lined with weed barrier before the rocks are compacted in to stop them from migrating into the soil. The trench and floor of the greenhouse will also be lined with barrier and have rock on it. The wall will sit on this trench. The floor in the greenhouse will have 6 inches of the 3/4 crushed rock. The rock will also be on the ground, exterior to the wall, for a few inches out.

 

I used 4x4

 

This is the way to do it.

Forget using the corner posts as the structure and use the floor as a foundation instead. It'll save a ton of headaches. You won't have to worry about pulling those corner posts when the eventually heave, rot, shift or whatever.

 

Are those telephone poles? Looks nice. Is this a greenhouse? I wonder about the wood subfloor and water...

There will be water involved so I need a floor that can get wet and drain. I have an unused sprinkler line I'm going to plumb into the GH. May have some misters for humidity (tropical plants), watering plants will overflow, a sink that will drain into catchment for watering, etc.

A lot of the examples I've seen just lay 2x6s on the ground and build on that. It strikes me as unstable and could imagine settling issues. I just wanted to take it 1 step further with the posts. Being as I live in California and it seems like we'll never get a decent rain again, rot is probably unlikely! A few screen shots of the "foundations" I've seen;