Question
I'm planing on building a retaining wall 30' away from my new house the soil is sandy no draining issues.   do i need to back fill it with rock or just on the bottom of the wall?


thank you in advance.

Answer
It depends on a couple of factors, such as the total length of your 3 ft.wall (20 feet versus 200 feet long!!), if you provide "weep holes" at the base (I usually omit a vertical mortar joint between the base coarse bricks/concrete masonry units about every 6 to 8 feet), if the area above the wall is sloped or flat, and how the foundation is tied to the brickwork. If the wall is under three feet (36") I usually don't backfill it completely with drain rocks.   I do try and provide a path of escape for any water that gets behind the wall...and sandy soil is pretty darn porous stuff.

Imagine a wave of solid water hitting the back of your wall.  Would it withstand the pressure? Water weighs almost 9 lbs. per gallon.  A square foot of water is 7-1/2 gallons.  Even a simple 3 ft. x 20 ft. wall has to hold back over 3 tons of weight.

Factor all that in, then no I don't think you need to fill it to the top with rock, but please do add some.