Is replacing my whole lawn with a composite deck and a retaining wall realistic?

A 14-inch drop is actualy the perfect height for a simple dry-stack block wall or a timber wall. You don't need deep concrete footings for something that short. Just dig a trench about 6 inches deep, fill it with **compacted crushed stone**, and level your first course. If you try to slope the framing instead of building a wall, you're going to end up with a weird gap under the rim joist that's a magnet for rodents and debris. To get that clean transition you want, build the wall first. Then, set your deck posts back from the wall and cantilever the joists so the composite boards hang slightly over the edge of the wall. This hides the top of the blocks or timber and gives you that integrated look. Since you have a miter saw, you can **picture-frame** the deck boards to hide the cut ends. It makes a huge difference in how professional the final result looks. One thing to watch out for is your AC unit if it's nearby. It needs airflow to breathe, and composite decking can get incredibly hot in direct sun. If the deck is going right up against it, make sure the framing is beefy enought to handle the weight if you're moving the unit, or just leave a gap. Also, check your local codes; some places require a railing if the drop is over 30 inches, but at 14 inches, you're usally in the clear. You can definitely do this with a miter saw and a drill, but you'll also want a level and a hand tamper for the base of the wall. If the base isn't level and packed down, the wall will start to lean or sag within a year. It's a lot of manual labor—digging and hauling stone—but it's not technically difficult once you get the first row of blocks perfectly flat. The hardest part is honestly just the grunt work.

The AC unit thing has me worried becuase mine is right where I want the deck. If I leave a gap for airflow, is there a way to frame it so it doesn't look like a random hole? I’m also curious about drainage. Since the yard slopes toward that new wall, do I need a pipe or somethig behind the blocks? I’m terrified of water just sitting there and rotting the joists. I'm brand new to this, so I'm trying to figure out the prep stuff before I spend money on boards.

You defintely need to toss some perforated pipe and gravel behind that wall. Wrap the pipe in filter fabric so it doesn't get choked with silt over time. If water builds up back there, it’ll eventually heave your blocks or turn your joist area into a swamp.

For the AC unit, try building a 'trap door' or a removable frame using the same decking. It keeps the look seamless but lets you pull it up for repairs. Just leave a few extra inches of clearance around the unit itself so the fan doesn't struggle. It's way cleaner than leaving a raw opening in the middle of your new boards.

Don't forget to lay down a heavy-duty weed fabric and a layer of gravel across the whole dirt area before you start framing. If you skip that, you’ll be fighting weeds growing through your deck gaps forever, and trying to spray them once the boards are down is a total pain. Also, since you only mentioned a miter saw, you’re definately going to need a circular saw too. Trying to do long rip cuts on a miter saw won't work, and you'll almost certainly have to rip that last board down to size to get it to fit flush against the house or the wall edge.