Hi George, to be honest attic grows are difficult, in terms of load, water up, water down, adequate hight for a uniform grow with lighting, space to move around, work flow, etc etc.
I’ve read the previous pages since posting re F&D best for SOG as I didn’t have the specific run down on your situation, and will throw this into the mix for consideration since you have a drain sorted. It’s what a mate of mine did when challenged with a similar scenario to you. I’ll try and explain what he did.
Build a low profile frame on the floor to have a very slight slope to which you mount corrugated roof sheet, at the lower end (water catchment and drain end) mount roof guttering on the end to collect the run off, slope, and plumb it into your drain. You’d want it so you have just enough length ways access to plants, i.e rows, however the catchment gutter as a single length., it will be low enough that you’d be able to step over it anyway.
That’s the “table” and run off sorted.
He used a single res, pump, solenoid, timer, piping and netafim system to feed fabric pots with coco that sat on the sheeting. You may consider 2x res’s. Think he had two stakes per pot, and one pot per sq foot, 5 gal pots. He manifolded his plants to keep them low, and flipped not long after the base manifold was finished. I.e vertical facing plants about 6” high, effectively had a hybrid SOG.
Just another way to consider, and it’s simple. He got outstanding yields and was an easy clean down between runs.
I’d also consider
@Renfro idea of rockwool slabs.
I’d throw the idea of a single huge F&D table in your situation, it’s fought with complexity and issues. You’d be looking at something like 2 or more large boat bilge pumps and float switches in a catchment pan/s under the table/s to pump back into the res/s. Just a recipe for disaster in my mind. Just as an example, I run a 200ltr res under each 4x4ft table.
Best of luck with it all
Cheers
Ozy
