How to build a tree house - concrete

OK, what does a tree house have to do with sustainability? I am considering this to be a laboratory to teach my kids, ages 6-9, about solar power and energy use. If things go well, it will also be a house heated by wood and cooled by shade and wind. I hope it is a place where they will learn about solar panels, batteries, inverters and how much energy lights and fans use.

We dug the footing piers as close to safe frost depth as possible and about 12" wide. In central Missouri this is 36" deep. I used a post hole digger (shown above).

I tried my best to dig the piers 7'-6" on center so that 6"x6"x10' support posts with 8' boards around the outside would create an 8' x 8' square. This makes for an easy deck level with no cutting of lumber later. The stakes and string are used to measure things closely, keep things square and level the footing piers. Remenber A squared + B squared = C squared? Or a rectangle that is 3' x 4' x 5' will always form a 90 degree angle. This will help keep things square.

Using a level, I verified that the string line was level all the way around. Because the ground is not level, I could measure the same distance down from the string to the top of the concrete piers and make sure that all concrete is the same height.

Where the ground was lower, I used Sonotube to elevate the footing form to the height of the holes that were flush with the ground. A plastic tub and bags of concrete were used to mix the concrete in the woods.

We mixed the concrete by adding water from our hose until it was thoroughly wet, but not runny.

One of the pier footings flush with the ground, troweled smooth and a rebar set in the center. A hole drilled in the posts will secure them to the footing later. This is 18" rebar that is 1/2" thick (9" in the concrete and 9" above ground).

All the concrete poured to the top of the forms and/or flush with the ground as measured from the level string line down to the concrete uniformly.

Another view of the concrete in relation to the Oak tree. Our tree house is stand alone from the tree, but later on we will attach the deck level to the tree.

Next step is the support frame and deck (click here).