How a retaining wall works
A retaining wall holds back soil that would otherwise slide downhill. What you see is the face of the wall, but most of the work is hidden:
- Base: a trench dug below the ground and filled with packed gravel so the wall sits on firm, level footing.
- Wall units: concrete blocks, cut or natural stone, or timbers, set slightly leaning back into the hill.
- Drainage: clean gravel and a perforated pipe behind the wall so rain water can escape instead of pushing on it.
- Reinforcement: taller walls often need grid fabric layered into the soil behind them, or a poured concrete design from an engineer.
Building on Pittsburgh hillsides
Western Pennsylvania has a lot of clay soil, steep ground and freeze-thaw winters. Wet clay gets heavy, and water that freezes behind a wall pushes on it every winter. That is why drainage and a solid base matter more here than almost anything else. A good contractor will look at where water comes from, how steep the slope is and whether anything heavy, like a driveway or a garage, sits above the wall.
See retaining wall cost in Pittsburgh for what affects the price, and when you need a retaining wall if you are not sure yet.
Permits and choosing a contractor
Short garden walls often need no permit, but taller walls, or walls holding up a driveway, a structure or a neighbor's property, usually do and may need engineered drawings. In the City of Pittsburgh that runs through the Department of Permits, Licenses, and Inspections (PLI). Outside the city, your township or borough handles it. Read retaining wall permits in Pittsburgh for a plain-English overview.
Before you hire anyone, check that they are registered as a home improvement contractor with the Pennsylvania Attorney General, ask for proof of insurance, and get a written estimate that spells out the wall material, height, length, drainage and cleanup.