How to Backfill a Patio on a Slope

Stake the corners of the site with garden stakes and tie one long string around them to make a clear outline. Tie another string around the bottom of the stake on the highest point of the hill and pull the string so it runs level over the lowest stake. Use measuring tape to measure the distance between the lowest and highest points to see how high the support walls will need to be. The raised side of the patio should be no higher than 3 feet to ensure stability.

Dig out the grass within the string outline with a shovel. Dig out 6 inches of topsoil from the site and continue digging the high side until the bottom is within 3 feet of the lowest area of the site. Tamp the sloped soil site with a manual tamper.

Pour 3 inches of 3/4-inch gravel over the sub-base and tamp it.

Construct retaining walls around the lowest side of the site and the two perpendicular sides. Line the inner perimeter with flat blocks or stones. Use the largest, flattest stones for the first course. Begin at the lowest side and dry stack the walls one course at a time or spread a 1/2-inch thick layer of mortar between the layers and sides of each stone. Extend the side walls deeper into the slope with each course. Fill in any gaps with small and medium stones and continue stacking until the walls reach the same height as the highest end of the subsoil.

Backfill the expanse between the retaining walls and slope it with 3/4-inch gravel. Add 3-inch thick layers at a time and tamp the rocks between each new layer. The remaining expanse from the gravel base to the top of the retaining walls should be deep enough for a 1-inch bed of sand plus the height of the pavers, flagstones or other paving materials.

Pour coarse bedding sand on the gravel until the bed measures 1 inch thick and spread it smooth.

Lay the paving materials flush against each other over the sand bed in your chosen pattern. Sweep masonry sand over top and push it down into the joints with a broom.