How should I handle the sloped dirt and drainage under a new elevated deck?

Trench that pipe first, without question. If you put down fabric and gravel before fixing the drainage, you'll just end up tearing half of it back up later when that line inevitably clogs or water undermines the new stone bed. Plus, hauling trench dirt across freshly spread rock is a massive headache. Swap that black corrugated pipe for solid 4-inch PVC if you can swing it. Corrugated tubing holds standing water in the ridges, traps debris, and collapses easily under foot traffic. Dig the trench deep enugh to keep at least a quarter-inch drop per foot, route the pipe well clear of your stair footings and the edge of the patio, and dump the water out to daylight into the yard with a pop-up emitter or a grated outlet. Once that line is buried and tamped down, pick up every single scrap cutoff and piece of construction debris out of the dirt. Leaving scrap lumber—even pressure-treated—sitting on damp ground against the foundation is just asking for termites and mold. After the debris is cleared, rough-grade the soil so surface water clearly slopes away from the posts and the house. Only after the water management is fully locked in shold you pin down a heavy **non-woven geotextile fabric** and spread two to three inches of clean crushed stone, like #57 gravel. Skip the cheap woven weed plastic; it tears easily and traps standing moisture on top. Doing the drainage first will keep those stair footings completly solid thru the winter and save you from having to rebuild the slope in six months.

Are you guys planning to turn that high space underneath into a dry patio once the dirt is sorted? Seeing all that clearance has me so excited because I've been obsessively researching under-deck ceiling systems! Like those corrugated vinyl troughs that catch the rain dripping thru the deck boards so you can put couches and lights down there. Has anyone here actualy installed one of those kits, or do they just end up clogged with leaves and spiders?

Whatever you do with that slope, make sure your husband doesn’t bury the bottom of those posts. Back in the day we’d see folks build a beautiful cedar or hemlock deck, mound up the dirt to make the slope look even, and five years later the posts rotted right off at the base becuase the concrete collars were under two inches of wet mud. Before everyone got hooked on buried pipe and plastic, we just cut a simple earthen swale along the high side with a spade and mattock to kick surface wash around the structure. A little manual contouring now beats fixing sunken piers down the road.

Quick update — trenching that pipe first was definitely the right call, and we started digging it out this morning. But after the warning about not burying the posts, we're stuck on how to grade around them safely. How much clearance should we leave between the top of the concrete collars and the gravel so the wood stays totally dry?