Step 3: The Concrete Form
I decided to build the greenhouse with a concrete footing mostly to discourage our infamous Newfoundland winds from picking it up from my yard and delivering it swiftly to the next town. In September of 2010 when Hurricane Igor hit, that's almost precisely what happened to my neighbor's patio of about 10 by 15 feet. So yeah... concrete footing it is.
The footing itself is 5 1/2 inches tall by 5 1/2 inches deep going all the way around the perimeter of the greenhouse. The outside dimensons are 10 feet 2 inches by 14 feet 2 inches and the inside dimensions are 9 feet 3 inches by 13 feet 9 inches. The framing is 2 by 4 lumber so when the bottom wall plates are placed on the concrete the is an inch of concrete exposed all the way around both inside and outside.
The form itself is constructed out of 2 by 6 lumber with some 1 by 3 strapping for braces. This should be pretty stright forward to anyone with decent DIY skills. I built the form in the driveway and then moved the whole thing into position later.
Next came the anchor bolts and rebar. I drilled holes in each piece of strapping and inserted the anchor bolt, secured temporarily by the washer and nut. Then came the rebar. I bought the rebar in 8 foot lengths so it worked out that I only had to make one cut to get it all to fit right. That cut I made rather tediously with an angle grinder. I took advantage of the hook shape of the anchor bolt to hold the rebar up off of the ground a little, so that it is suspended inside the concrete rather than underneath it. Everything was tied up nice and tight with tie wire before calling that a day.
Before pouring the concrete I made sure everything was nice and square by checking the measurements of the corners. The distance between each pair of opposite corners should be the same or it's not square...even though it may look like it.
FInally, the last picture shows the PVC sewer pipe for the greenhouse drain. It goes from the inside of the greenhouse, underneath the footing and ends right where the french drain will be running perpendicular to it.