Drainage Behind a Sandstone Retaining Wall

Yes, You Need Drainage

A 55-foot long, 4-foot tall sandstone wall without drainage will eventually fail from hydrostatic pressure. Even with a slight back-slope, water accumulates behind the wall and pushes it outward.

Simple, Effective Drainage System

1. Perforated pipe: Lay 4″ corrugated perforated drain pipe (with a fabric sock if soil is silty) along the base of the wall, behind the first course.
2. Gravel backfill: Cover the pipe with 12–18″ of clean 3/4″ washed gravel.
3. Filter fabric: Wrap the gravel in non-woven geotextile fabric to prevent soil migration.
4. Outlet: Daylight the pipe to a low point or connect to a storm drain.

Installation Depth

Place the pipe 4–5 inches below the top of the gravel layer (i.e., near the bottom of the wall footing). This keeps the water table below the wall base.

Pro Tip

Add weep holes (3/4″ PVC) through the wall face every 6–8 feet as a backup if the pipe clogs.