Question
Ken,
I am located in Monmouth County NJ 08527.  Laast year we moved in to an "active' adult retirement community which was 3 years old.  We have individual homes/lawns that are maintained through our maintenance fee.  The lawns are fertilized twice a year and we have underground sprinkler systems.  Since moving in, I have learned that the problem began with the builder.  They came in and removed all the topsoil and then sold it.  After completing the homes, (which were now surrounded with rocky sand, they put down sod.  In many instances, it died immediately and required replacement.  Lots of watering is required, and I guess the roots have a problem getting through the sand/stone. There are frequeet brown spots. I don't expect miracles, but without tearing up the existing lawn, is there anything that can be done?  

Answer
You have a few options depending on the level of costs/care you wish to perform.

water sandy soils frequently, such as every 2 days during hot summer months, but otherwise every 3-4 days in spring and fall. Fertilize with extra potash if possible (espoma makes 5 lb bags of sulfate of potash 0-0-50 available at good garden centers). Spread 2 lbs per 1000 sq feet lawn area twice per year.
Potash leaches easily on sandy soil which is reason I recommend it.

Mow your lawn tall, and mow frequently. avoid mowing too close.

If you wish to improve soil, the best way is to rent a sod cutter and cut the lawn into lanes of sod and then cut these into sections (1 sq foot pieces) and put aside while you mix in a 2-3" layer of topsoil. Replace sod pieces so that the edges butt right up against each other, but stagger the seams so they are not right on top of each other (think of the arrangement of bricks in a wall). Water well for the first 7-10 days after replacement.

Brown spots are typically from draught and mowing too low. Raising mower height to 2.5-3.5" (minimum) and watering more frequently than normal should provide an acceptable result. You can then add more topsoil if this is not enough.