The valve box can be dug up and reset at ground level. When you do this the valve will still be at the same depth in the ground. Raising the box usually allows soil to seep into the box and cover the valve. If the valve box is only an inch too deep, raising the box should not cause too much of a problem later on as long as the valve is still protected inside the box.
When you have to raise the box more than an inch, soil and other debris will most likely filter under the box and cover up the valve(s) from the sides. This can create problems with the operation of the valve(s) and will hamper any repairs that need to be done later.
Valve boxes are designed with cutouts at the bottom. These are the areas where the pipe enters and exits the box. When these cutouts are removed and the the box placed over the pipe, the valve will be properly protected and placed above the soil at the base of the box. Putting a layer of gravel in the bottom of the box helps keep soil from filter under the sides of the valve box.
Three and six inch extensions are available for valve boxes for your local box store, hardware store and irrigation supply company. This photo shows a three inch extension placed on a standard size valve box. The item on the left of the photo is a 6 inch extension for a jumbo size valve box. The lid fits into the recessed area of the extension.
Instead of raising the box, consider placing an extension on top of the box. You may need to dig up the box and set it deeper in order to do that. Be sure the valve box is parallel with the slope of the soil.
The more secure the irrigation valve(s) are ensconced inside the valve box the better. Valves that are covered with mud and other debris are problems waiting to happen.
If you don't feel comfortable correcting valve boxes that are too deep, lawn care, landscape or irrigation installation professionals can do this for you.
