Retaining Wall Installation in the Catskills & Hudson Valley

Why retaining walls fail

Almost every failed wall fails for one of three reasons: water, frost or a poor base. Soil behind a wall that can't drain gets saturated and heavy, and it pushes. In winter that wet soil freezes and expands, and the push gets worse. If the base underneath is just the dirt that was there, or loose fill, the wall starts to lean or bulge within a few seasons.

So a lasting wall is really a drainage project. Behind the wall goes a zone of clean crushed stone, with a perforated pipe at the bottom that carries water out to daylight, and fabric to keep the surrounding soil from clogging the stone. With that in place, water drains out instead of building pressure, and there's less wet soil to heave in the cold.

How a wall goes in on a sloped lot

First the bank is excavated back far enough for the wall, the drainage stone, and on taller walls the layers of geogrid that tie the wall into the hill. Then a trench is dug for the base, filled with crushed stone, and compacted in lifts until it's dead level. The first course sits partly below grade, and it's the most important one: if it's off, every course above it is off.

The wall rises course by course, with drainage stone placed behind each one and the soil behind that backfilled and compacted as the wall goes up, not dumped in at the end. On rocky mountain lots, a wall can sometimes bear right on ledge, which makes an excellent base, and big stone dug out of the site can be good material for a boulder wall. Mortared stone and poured concrete walls are different: they're rigid, so their footings have to sit below frost depth, which is about 4 feet in most of this area.

Does a retaining wall need a permit or an engineer?

Short garden walls usually don't. Taller walls often do: many codes call for an engineered design once a wall holds back more than about 4 feet of soil, and walls with a driveway, building or steep slope above them need one sooner because of the extra load. Ask your town's building department before you settle on a height.

Even below that height, two shorter walls with a planted terrace between them are often cheaper and more stable than one tall wall, as long as they're spaced well apart. They usually look better, too.

Retaining wall installation costs and what to get ready

Height and length are the obvious cost drivers, but the ground matters just as much. Rock in the base trench, a wet seep coming out of the bank, a tight lot where material has to be carried in, and how far the drain pipe has to run to reach daylight all add time. The material makes a real difference too, from segmental block to natural stone to large boulders. Justin walks the site, looks at the slope and soil, and gives a straight price.

Before he comes out, think about what the wall is for (a flat lawn, a patio, a parking spot, holding up a driveway), where the property line is, and what will sit or drive near the top. Then avoid the classic mistakes: skipping drainage stone because the wall is "only" a few feet tall, backfilling with the clay that came out of the cut, and letting downspouts or driveway runoff pour in behind the wall. If water is the bigger issue on your lot, start with drainage and erosion control, and plan the grading above and below the wall at the same time.