Talk with your appliance rep about which ones are stackable. Most have a small bracket that attaches to the backside to hold the top and bottom units together (so the dryer on top does not slide off!).

As for space, you don't need much, but find a way to get to the water shut-off in case you have a hose rupture, or if you are gone for an extended period of time. In the drawing, it looks as if there is a cabinet above the washer/dryer stack? You could have a plumber route lines through there with quarter-turn shut offs.

Also in the drawing, it looks like a step or platform below? This will make it difficult to pull the units out. Dryer hoses need to be cleaned periodically - if it is hard, you may find that you clean it less.

I like the design - just find a way to make it easy to get behind. Hooking up dryer vents, washer hoses, and even plugging the units in can be difficult in a confined area. Best of luck with your project - Robert

Most front load machines are designed to be stacked. Not sure what the relevance of the exterior rending is, but nice simple design.

Thanks for the advice! One more question: Does the dryer always stack on top of the washer?

Yes. The washer is heavier due to the weight of the water, so it goes on the bottom