Does anyone know if there is such things as a "code" for the height between the wall cabinet and the counter top. I have heard both, that there is and that there isn't.
In most areas there is not a code regarding height of a wall cabinet above counter. The standard is about 18". But the wall cabinet could actually sit on the counter if you wanted it too and you didnt need the counter space.
The exception is the height of a wall cabinet over a range or cooktop. Generally it is 18" to nonflammable material over electric, 24" over gas (say metal range hoods) and 30" to flammable materials.
I don't know what you intend to do regarding backsplash height (that's the distance b/w the finished counter and the bottom of the upper cabinet and light rail), but here's what I usually tell people when they're considering the height for their backsplash.
The standard is 18"...regardless of the reasons why, it's still the standard..
How this affects your kitchen....
Refrigerator and other tall cabinet heights...Because wall cabinets are meant to be mounted at a standard height, cabinet manufacturers take this into account when designing tall cabinets. Tall cabinets are designed to be the same height as the installed wall cabinets so the tops all line up. When you change the height a wall cabinet is installed at, it affects cabinet top alignments.
With the refrigerator you can usually mount the upper cabinet a little lower OR order a shorter upper cabinet, but be sure you don't make the alcove any shorter than 72" tall b/c newer refrigerators are 70" to 72" tall (and seem to get taller each year!)
With other tall cabinets like oven cabinets and pantry cabinets, they're a standard height and designed so they're the same height as the wall cabinets when those wall cabinets are installed 18" above a 36" high counter. If you have custom cabinets, this may not be an issue b/c your cabinetmaker can adjust the cabinet heights. But, if you are using stock or even some semi-custom cabinets, you cannot change the height. You can often get taller cabinets for use w/36" or 42" tall wall cabinets, but not shorter for 30" mounted lower. But, even those that are taller are also adjusted based on standard wall cabinet heights + an 18" backsplash height.
Keep in mind that if you're using an appliance on your counter, you must be sure you have room under the base cabinets to move that appliance around easily. Don't, for example, tell yourself you're only going to use it in front of your upper cabinets so you don't need to worry about its fit. In reality, you will be moving things around on your counter while you work and most likely your appliance will be moved under the cabinets at some point. You don't want to tear your light rail off or damage it (or the cabinets).
Also remember that "standard" upper cabinets are 12" deep + 1" for the door...so they stick out 13" over your counter...leaving you only 12" or so of workspace in front of the upper cabinets...not much room to work in by itself! (If you have deeper upper cabinets...say 15", there's even less counter frontage in front of your upper cabinets...3" less, so 9".)
Another consideration is vertical work...