I posted before but something happened to it. I believe the reason you can't find plans is because it is impractical. At 7 ft off the ground, how will you insulate the floor, make it airtight, keep it warm and yet allow run-off water to drain through? You say it is a wooden deck. Even protected wooden decks deteriorate over time and have to be replaced. How will you deter rot due to drain through and sweating? Are you willing to tear down your greenhouse every 1-15 years and replace it all? Why not remove the deck, build some steps to the ground and build the greenhouse at ground level? You will be surprised how much heat is derived from the ground under you greenhouse. I have a brick floor and a fan blowing across it picks up heat to add about 5 degrees to the inside greenhouse temp.

It can, in fact, be done. Link below, but might have to subscribe to view the pics. The floor is the tricky part.

The following are the steps or layers, from the bottom up in order:
Frame, leveling with drainage holes in mind
2" rigid foamboard
1/2" plywood (I believe that they make ACQ treated plywood) with 3 1/2 inch deck screws and construction adhesive.
Cut 4" drain holes
PVC 3" to 2" couplings for drains, installed
Seal the water by basically installing a roof on the floor. He used a product from Acrylabs. It is applied like "heavy latex paint" and into this you press a fabric. Then there are a couple more finish coats. The "paint" and fabric are cut for the drains and the cut ends are tucked into the drain holes.

Then basically you put the the GH as you would normally.

If it were me, I would replace traditional decking with something that would not rot like Trex. Then you would have good air circulation around your wooden joists and beams and you could keep them treated.

Here is a link that might be useful: GH on a deck

Some good ideas there. I'm going to research this Trex thing. I'm not sure I understand the need for a 2" drain or any drain for that matter. For any drain to work the flooring would have to be sloped toward it. This deck has been in the weather for 12 years and no rot anywhere. If a GH were on top it would be exposed to practically no water. Whats the big deal for a drain?

I guess a drain is only important if you intend to water your plants!

Two issues here, one is the moisture and the decking underneath. Regarding the decking, I'm just thinking that if you go to the trouble of putting up the GH on the deck, then one of the boards developed rot 2-5 years from now, then what a PITA it will be to replace it.

The other is moisture in the GH. All kidding aside, you WILL have to account for the water in the GH, mostly from watering, but also from misters, condensation, whatever. I wouldn't begin to try to do it without a floor drain of some kind.

danr wrote:

"This deck has been in the weather for 12 years and no rot anywhere. If a GH were on top it would be exposed to practically no water. Whats the big deal for a drain?"

It's fine now because water can evaporate and dry out. With a structure over the top, not gonna happen.

Trex-type material is very flexible, many colors, etc.

Dan

I've plans to convert a deck as well. Any luck with your plans? I'm debating wood frame vs salvaged galvanized pipe. I'm settled around the floor and creating drains to the gutters (this deck is on a second story on top of a kitchen).

My dimensions are 12X16. Koaxfrax