Step 1 : Excavation
We broke ground on May 21, 2003. With the permission of our local building codes department and using the experience of our concrete expert, we decided to build our greenhouse on a frost protected shallow foundation. This style of construction allowed us to construct our foundation at minimal cost, yet ensure that it would survive the cold winters of New Hampshire. Visiting a local greenhouse owner also allowed us to see the benefits of building our greenhouse into the ground. The floor will be approximately 35" below ground, allowing us to add height inside the greenhouse but have only a short wall visible above ground. Building below ground should also reduce the costs of heating and cooling the greenhouse. Here you can see how much larger this will be than the Sunglo we now grow in.
The forms were carefully created to size and the ground was leveled to allow a large concrete footing around the perimeter with a minimum of 4 inches in the middle. A very small pitch was added from the middle to the sides so that the finished concrete will have an incline toward the outside walls. Along the sidewalls we planned to create inclined trenches to catch the water and run it down into the drains. The drains are set to be 1 inch below the surface of the concrete, which should allow plenty of depth for the small trench drains along each sidewall. Here you can see the drains that are connected to the 55-gallon drum in the center. We cut the bottom off the drum, drilled many large holes in the side and filled it with crushed gravel to just below the drainpipes. Our sandy soil should allow for excellent drainage out of the buried drum.