Retaining walls and seat walls

A retaining wall holds back soil. Saturated soil weighs far more than dry soil and behaves like a fluid pressing against the back of the wall. That hydrostatic pressure is what pushes walls out of plumb, opens joints, and eventually rotates the whole face forward.

You will not see any of the components that prevent it. They are all behind the wall, and they are the first things a cheap bid removes.

What goes in behind the face

1. Compacted leveling pad. Crushed aggregate, compacted, level. Everything above inherits errors made here.
2. Buried base course. At minimum the bottom course sits below finished grade. This is what stops the wall sliding forward at the toe.
3. Clean angular drainage stone, full height. Not rounded pea gravel and not just a scoop at the bottom. It gives water a path down instead of a place to build pressure.
4. Perforated drain tile that goes somewhere. A pipe terminating inside the backfill is decoration. It must daylight to a real outlet.
5. Geogrid where height demands it — layers extending back into the retained soil, tying wall and soil mass into one structure.
6. Compacted backfill in lifts, and a cap course set with adhesive.

The height threshold worth knowing

Above roughly four feet — and lower if a driveway, pool, slope or structure loads the top — a retaining wall becomes an engineered structure. In much of Michigan that means a permit and stamped drawings from a licensed engineer.

We will tell you when your wall crosses that line and we will not quietly build a five-foot wall as though it were a garden edge. If a contractor quotes a tall wall with no mention of engineering or permits, that omission is the most important thing in the quote.

Terracing is usually the better answer

Two shorter walls stepped back from each other frequently cost less than one tall wall, avoid the engineering threshold, drain better and look better. The catch is that they need real horizontal separation — stack them too close and the upper wall surcharges the lower one, which is worse than the single tall wall you were avoiding.

Where the grade allows it, we propose terracing before we propose height. On the sloped lots near Stony Creek in Shelby Township and the rolling ground in Bruce Township, this comes up constantly.

Seat walls are a different product

A seat wall retains almost nothing. It defines a space and gives people somewhere to sit, which means the governing dimensions are ergonomic rather than structural: roughly 18 inches high and 12 to 16 inches deep on the cap. Priced at $90 to $150 per linear foot, they are one of the highest-value additions to a patio because they add permanent seating without consuming floor area the way furniture does.

What a retaining wall will not do

It will not fix a drainage problem originating uphill. If water sheets down a slope toward your foundation now, a wall in its path will pond water behind it and make things worse. Surface drainage gets solved first, then the wall.

It will not stabilize a slope that is actively sliding. That is a geotechnical problem needing an engineer, not a landscaper with a plate compactor.