I did something similar when I built my GH.

Pressure treated 4 x 4's in 3 feet of concrete on top of a foot of gravel at
the corners and every 4 feet in between. Pressure treated 5/4 x 6's
(decking) on the interior AND exterior of the frame, with the interstitial
space filled with expanding foam for insulation. Then I put the 4 x 4's on
the top.

My GH is on a slope, so I added several truckloads of fill to level the
floor, covered that with fine gravel. (Right front is 1 foot above grade,
back left is 5 feet above it!

Attached the GH frame to the 4 x 4's with lag bolts - has withstood a minor
earthquake and hurricane-force winds...

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!


"Dan" wrote in message
...
I have a question for the experts here. Having never built a greenhouse,
your input is quite welcomed!

Living in the Austin, Texas area, I'm considering building a hobby GH.
Since everyone I've asked has said to build it at least twice as large as
I
think I need, it will be 16x20 feet in size.

My question involves the footer. What I'm thinking of at this point is to
have post holes drilled around the perimeter at every 4' at about 18" or
2'
depth. Then slam some rebar down in there, along with 6" diameter or so
steel pipe which will extend 2' above ground level. Will fill the holes
and
pipe with concrete for a good base, and lay 4X4's across the top of the
piping ( or maybe 2x6 with 4x4 on top) to function as the base for the
walls. Wall frames to be bolted to this base

Does this sound reasonable? Will place concrete blocks between the pipes
to
fill-in the space, with a stone facing on the exterior.

Does this sound like it will be strong enough to support the GH, as well
as
keep the GH anchored to the ground during windy periods? It will be
sheltered on three sides by my home and sizable trees to reduce wind
issues.
The exposed side will be the south.

Your advice is appreciated! :-)

Dan...