Retaining Walls in Minneapolis, MN

Retaining walls in the Twin Cities fight two forces at once: the weight of the soil behind them and the water that soaks into that soil, freezes and pushes. Most walls that lean, bulge or crack fail for the second reason. A wall that drains, with clean stone behind it and a pipe at the base, gives that water a way out before it can freeze against the back of the blocks.

Where walls help

Many Minneapolis lots slope from the house toward the sidewalk or alley, and some neighborhoods near the river and lakes have steep yards. A low wall can turn a slope into a flat patio area, hold back a raised front yard, keep soil off a driveway, or terrace a hill into planting beds. Short walls of a few courses are common; taller walls need more planning.

The 4-foot line

In Minneapolis and Saint Paul, a retaining wall taller than 4 feet needs a building permit. Saint Paul's handout measures height from the base of the footing to the top of the wall, at any point along it, and notes that walls carrying a surcharge, such as a driveway or another structure above, can need a permit at any height. Engineered designs must be signed by an engineer licensed in Minnesota. When a design approaches that height, we either split it into two shorter terraced walls with proper spacing, or plan for engineering and a permit. Tiered walls can also trigger engineering, so we check before assuming terracing avoids it.

How a segmental wall is built

• A trench dug below grade and filled with compacted aggregate as a leveling pad
• The first course buried below the finished ground line, set perfectly level
• Clean, open-graded stone behind each course instead of the excavated soil
• A perforated drain pipe at the base, routed to daylight
• Each course set back per the block maker's specifications
• Geogrid reinforcement laid into the soil at the intervals the manufacturer calls for on taller walls
• A capstone glued on top

Choosing the block

Segmental concrete block is the standard for residential walls because it is made for this use, comes with tested installation specs and handles freeze-thaw well. Natural stone looks more traditional and costs more. Timber walls are cheaper at first but rot over time. Fixr lists segmental block walls at about $15 to $35 per square foot of wall face, natural stone at $25 to $75, and timber at $15 to $30.

Drainage for neighbors and foundations

Building a wall changes how water moves across a lot. We look at where the drain pipe will empty and at runoff toward neighboring yards and your foundation, and plan the grade above the wall so it slopes away from the top course.