Slopes within a landscape can present inconveniences related to mobility, erosion and maintenance of vegetation or other features on the slope. Retaining walls can create multiple flat steps that are more easily managed than a steep hill. Proper wall building, which includes adequate preparation of a foundation and careful stacking of wall material, will help to ensure that the wall serves as an attractive and enduring landscape interest. Many municipalities require that walls more than a few feet tall be professionally engineered, so homeowners may elect to build multiple shorter walls rather than one tall wall.
Dry-Stacked Stone and Timber Walls
Excavate a trench at the bottom of the slope or — if there will be multiple walls — wherever the lowest wall is planned. For stacked stone or timber walls, dig a trench 5 to 7 inches deep plus 1 inch for every 8 inches of planned above-ground wall height.
Prepare the foundation. For stacked stone or timber walls, place 4 to 6 inches of gravel in the trench and tamp the gravel down while checking frequently for level and making adjustments as needed. Place an inch of bedding sand on top of the gravel and again check for level.
Place the first course of material atop the foundation material. For stacked stone walls, use the largest, heaviest stones for the base layer. Check the stones for level and make adjustments as needed. With timber walls, drill holes at the ends of each timber for the base layer and place the timbers in the trench, check for level and pound rebar through the holes to secure the timber.
Place the second course of stone or timber atop the first course. Stagger the material so that vertical joints do not align between courses. Set the material for the second course back about 3/4 inch from the face of the course below it. This slight leaning back, known as cant or batter, will give the wall added stability. With dry-stacked material, fill the spaces between larger rocks with rubble and use shims to make large rocks level and steady. When setting timber courses, drill holes in each layer every 4 feet and pound galvanized steel spikes through the timbers to secure layers to each other.
Backfill the area behind the wall as each layer is added. Place gravel in the space immediately behind the wall
Continue placing courses of material and backfilling until the desired wall height is reached.
Excavate a trench for the foundation. Masonry walls require a poured concrete footing that extends below the frost line, has a thickness equal to or greater than the width of the wall and reaches a foot behind and in front of the wall.
Make or obtain forms for the poured concrete foundation. Oil the interior of the forms and pour concrete into the form. Level the top of the poured concrete with a wooden board.
Place the first course of block, brick or stone atop the partially cured concrete foundation. Spread a layer of mortar on the first few feet of the foundation with a trowel, set the material in the mortar, adjust for level and fill in spaces between the material with mortar. Continue laying small, 3-foot or 4-foot sections along the length of the wall until the first course is laid.
Set the material for the second course atop the first course. Stagger the bricks, blocks or stones so that vertical joints do not align between courses. Again, work in short, manageable sections to prevent the mortar from drying.
Continue placing layers of material until the desired wall height is reached. Masonry walls more than a few feet high or in areas with high soil moisture or precipitation require weepholes spaced regularly throughout the wall.
Lay perforated drain pipe or drain tiles at the base of the back of the wall to facilitate drainage.
Backfill the area behind the wall. Place several inches of gravel in the space immediately behind the wall and fill in the remainder of the space with soil from the slope above.